The atmospheric oxidation of α-pinene and β-pinene (C10H16), emitted in appreciable quantities from forested regions (~85 Tg y–1), contributes significantly to the global burden of secondary organic aerosol (SOA), a substantial component (15–80% by mass) of atmospheric fine particulate matter (PM2.5), which exerts large but uncertain effects on climate as well as adverse impacts on air quality and human health. Deciphering the molecular composition, and in turn formation and aging mechanisms, of α-pinene and β-pinene SOA is essential to reducing uncertainty in assessment of their environmental and health impacts. However, molecular characterization of α-pinene and β-pinene SOA is significantly hindered by their chemical complexity. In this work, we constrain the formation, abundance, and evolution of molecular products in SOA derived from ozonolysis and photooxidation of α-pinene and β-pinene using a combination of laboratory experiments, liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS), and organic synthesis. Through detailed MS/MS analysis, coupled with 13C isotopic labeling and OH scavenging, we identify a suite of dimeric compounds (C15–19H24–32O5–11) formed from synergistic O3 + OH oxidation of β-pinene (i.e., accretion of O3- and OH-derived products/intermediates). Informed by these structural analyses, together with 18O isotopic labeling and H/D exchange, we synthesize the first authentic standards of several major dimer esters identified in SOA from ozonolysis of α-pinene and β-pinene and elucidate their formation mechanism from targeted environmental chamber experiments. Additionally, we synthesize a series of pinene-derived carboxylic acid and dimer ester homologues and find that the ESI efficiencies of the dimer esters are 19–36 times higher than that of commercial cis-pinonic acid, a common quantification surrogate. Finally, we investigate the aqueous (photo)chemistry (kinetics, products, and mechanisms) of the carboxylic acid and dimer ester homologues at cloudwater-relevant concentrations as a function of pH.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/893j-7x60, author = {Kong, Weimeng (Stephanie)}, title = {Nanometer-sized Aerosol Particles in the Atmosphere: Measurement, Analysis, and Impact}, school = {California Institute of Technology}, year = {2021}, doi = {10.7907/893j-7x60}, url = {https://resolver.caltech.edu/CaltechTHESIS:09272020-215437294}, abstract = {New particle formation (NPF) from gaseous precursor vapors is frequently observed in the ambient environment and contributes to a major source of global cloud condensation nuclei (CCN). The survival and CCN activation of newly formed particles are highly dependent on particle growth below 10 nm. Characterizing and understanding nanoparticle early growth will therefore help to quantify the impact of NPF on cloud reflectivity and global energy budget. In this work, I first present a recently developed instrument, the Caltech nano-Scanning Electrical Mobility Spectrometer (nSEMS), which consists of a charge conditioner, a novel differential mobility analyzer (DMA), and a two-stage condensation particle counter (CPC). This new design, coupled with a data inversion method that combines empirical calibration and COMSOL simulation, can help to measure nanoparticle size distributions from 1.5 nm to 25 nm more accurately. This instrument was employed in the experiments conducted in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN) to better understand NPF, particle growth and survival. Multiple experimental parameters were varied to study the influence of different highly oxygenated molecules (HOMs) and inorganic trace gases, such as ammonia and nitrogen oxides on particle early growth. Experiment results have suggested a novel mechanism that may help to explain nanoparticle formation and growth in highly polluted urban environments or in the cold free troposphere. In as little as a few minutes, freshly nucleated particles as small as 2 nanometers in diameter can grow very rapidly due to simultaneous condensation of nitric acid and ammonia. This can help them to survive through the so-called “valley of death” where they would otherwise be lost to larger particles, and instead allow them to grow to sizes where they are less vulnerable to loss and can continue on to sizes where they influence local air quality or climate. Further, the laboratory results of nanoparticle growth were incorporated into the Global Model of Aerosol Processes (GLOMAP) model to study the impact of this extremely rapid growth on the global CCN budget. Having realized the importance of conducting well-controlled chamber experiments and of using chamber experimental data, we established an online data infrastructure, the Index of Chamber Atmospheric Research in the United States (ICARUS), for storing, sharing, and using chamber data. A combined effort of the described works contributes to better measuring the size distribution of nanoparticles and to understanding their impact on global climate.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, } @phdthesis{10.7907/yvj9-fv16, author = {Charan, Sophia Mohini}, title = {Secondary Organic Aerosol Formation from Volatile Chemical Products: Understanding Aerosol Yields and Dynamics}, school = {California Institute of Technology}, year = {2021}, doi = {10.7907/yvj9-fv16}, url = {https://resolver.caltech.edu/CaltechTHESIS:05312021-044610797}, abstract = {Particulate matter impacts public health and climate. A major component of small particulate matter, called secondary organic aerosol (SOA), is formed from the condensation of the oxidation products of organic compounds emitted into the atmosphere in the gas phase. Recent analysis suggests that volatile chemical products are responsible for a large fraction of the particulate matter formed from petroleum sources: perhaps more than motor vehicles. This is especially the case in urban areas, which have significant air pollution burdens.
Understanding exactly which precursors are responsible for this large SOA formation and under which conditions is difficult: for each compound, different chemical pathways dominate and even similar molecules can form vastly varied amounts of aerosol. Even if one could study every compound, extrapolating data to the atmosphere is non-trivial. SOA formation is principally understood through laboratory chamber studies, but these studies require a rigorous, quantitative grasp of chamber phenomena to meaningfully interpret the results.
In this dissertation, computational simulations of environmental chambers illuminate the physico-chemical processes that occur within a chamber and the manner in which these processes interact, in order to help extrapolate data to real-world conditions. In particular, the contribution of particle charge to the rate of particle-wall deposition within environmental chambers is investigated.
With this understanding, the amount of aerosol formed per precursor emitted, called the secondary organic aerosol yield, is investigated for benzyl alcohol and decamethylcylopentasiloxane (D5). At atmospherically relevant concentrations, benzyl alcohol and D5 have disparate SOA mass yields: as much as 100% for benzyl alcohol and ~1% for D5. Both of these findings differ from what was previously modeled and measured, indicating the importance of performing experiments on the compounds of interest and evaluating the oxidation products under atmospherically relevant conditions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/adpa-0947, author = {Rooney, Brigitte Lee}, title = {Modeling the Impact of Biomass Combustion on Atmospheric Aerosol}, school = {California Institute of Technology}, year = {2020}, doi = {10.7907/adpa-0947}, url = {https://resolver.caltech.edu/CaltechTHESIS:06012020-155204817}, abstract = {Biomass burning is a significant source of atmospheric particulate matter less than 2.5 micrometers in diameter (PM2.5) and encompasses a variety of activities, fuels, and emissions profiles. A significant portion of the world population relies on solid biofuels for cooking and other household activities. Residential use of solid biofuels can have negative impacts on human health, particularly in southeast Asia, and contribute to ambient air quality. In addition, wildfires are of increasing concern as climate changes and human activity expands further into the wildland-urban interface. Understanding the contributions of biomass combustion to air quality is critical for creating mitigation strategies.
In this work, the impact of biomass burning on air quality is examined using numerical and observational methods. The Community Multiscale Air Quality modeling system (CMAQ) and the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) are used to study two biomass burning scenarios: the combustion of solid biofuels for cooking in rural India and the November 2018 Camp Fire in northern California. Model simulations are combined with surface and satellite observational data to evaluate their performance as well as their applicability to health and economic impact assessment studies. Additionally, discrepancies in methods used in laboratory experiments and field studies of cookstove emissions are investigated. Contributions of cookstove and wildfire emissions to PM2.5 are estimated, and climate and health co-benefits of residential solid biofuel use is assessed. This thesis strives to expand the current understanding of sources of PM2.5 and provide a base for future computational studies of biomass burning impacts on air quality, climate, and human health.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/783S-K686, author = {Huang, Yuanlong}, title = {Development of Methods to Study Secondary Organic Aerosol}, school = {California Institute of Technology}, year = {2019}, doi = {10.7907/783S-K686}, url = {https://resolver.caltech.edu/CaltechTHESIS:05232019-231457899}, abstract = {Secondary organic aerosol (SOA) in the atmosphere contributes significantly to air pollution and has profound impacts on regional and global climate change, as well as human health. SOA, as opposed to directly emitted particles, refers to those particles formed from oxidation of gas-phase compounds followed by nucleation and/or gas-particle partitioning, as well as those modified by gas-phase oxidants (e.g., O3, OH radical, and NO3 radical) through heterogeneous reactions within their lifetime in the atmosphere. Investigations of SOA formation in the laboratory have been carried out in batch reactors (e.g., environmental smog chambers) and continuous flow reactors (e.g., oxidation flow reactors). Compared with the real atmosphere, the reactors in the laboratory have boundaries and defined residence times under different operation conditions. To better constrain the experimental results and derive reliable parameters for aerosol models (e.g., yields of volatile organic compounds), a full understanding of the role of the reactors on the gas-phase components and suspended particles is needed.
In this thesis research, a number of studies were carried out to understand the role of the reactor itself on the behavior of SOA-forming systems. This includes the effect of the Teflon-walled Caltech Environmental Chamber on vapor molecules and characterization of the newly-built Caltech PhotoOxidation Flow Tube reactor (CPOT) for atmospheric chemistry studies.
Vapor-wall interactions in Teflon-walled environmental chambers have been studied; however, conflicting results existed in the literature concerning the basic timescales of vapor-wall loss in environmental chambers. The competition between vapor-particle and vapor-wall interactions determines the fate of vapor molecules in the reactor. A unified theory and empirical equations have been developed in this thesis to explain the observed vapor-wall interaction timescales. About 100 compounds have been studied to verify this theory. In characterizing the flow reactor performance, computational fluid dynamics (CFD) simulations have been combined with residence time distribution (RTD) experiments, revealing, among others, the importance of the inlet design of the reactor and the effect of temperature gradients on radial mixing in the reactor. An axial-dispersed plug flow reactor (AD-PFR) model framework was developed as a basis on which to simulate photochemistry occurring in the CPOT. An analytical solution for the cumulative RTD, which uses data during the transition period to a steady state, can be applied to diagnose the dispersion condition inside the flow rector.
Since SOA formation involves interactions among gas-phase molecules, particle surfaces, and particle bulk phases, a state-of-the-art experimental technique (field-induced droplet ionization mass spectrometry, FIDI-MS) and a comprehensive model coupling gas-surface-aqueous multiphase transport and chemical reactions have been applied to investigate the gas-phase OH-initiated oxidation of pinonic acid (PA) at the air-water interface. The interfacial oxidation mechanism has been found to differ from that of homogeneous reactions, and the kinetics depend on both OH diffusion from gas-phase to the interface and aqueous-phase reaction of pinonic acid + OH. The model calculation shows that, under typical ambient OH levels, PA is oxidized exclusively at the air-water interface of droplets with a diameter of 5 µm, demonstrating the critical importance of air-water interfacial chemistry in determining the fate of surface-active species.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/Z9T72FF1, author = {Mui, Wilton}, title = {Development and Applications of Opposed Migration Aerosol Classifiers (OMACs)}, school = {California Institute of Technology}, year = {2017}, doi = {10.7907/Z9T72FF1}, url = {https://resolver.caltech.edu/CaltechTHESIS:09062016-204048228}, abstract = {Particle electrical mobility classification has made important contributions in atmospheric and climate science, public health and welfare policy, and nanotechnology. The measurement of the particle size distribution is integral to characterization of the sub-micrometer aerosol particle population. The differential mobility analyzer (DMA) has been the primary instrument for such measurements. Aerosol particles are transmitted through the DMA on the condition that their migration time across an electrode separation distance is approximately equal to the advective transport time from the inlet to the outlet; these two travel times are induced by an electric field between the electrodes and an orthogonal particle-free carrier gas flow. However, scientific interest has increasingly shifted toward both the nanometer-scale particle size distribution and the miniaturization of instruments. The classical DMA suffers from severe resolution degradation and diffusional losses of nanometer-scale particles, as well as being ill-suited for lightweight, low-power applications. It is relatively recently that miniaturization of DMAs for portable applications has appeared in the scientific literature. Additionally, an abundance of efforts on DMA design have yielded instruments that can probe the nanometer-scale particle size regime, though their use is restricted to the laboratory as they require powerful pumps and operate at near-turbulent flow conditions.
The opposed migration aerosol classifier (OMAC) is a novel concept for particle electrical mobility classification introduced about a decade ago. In contrast to the DMA, the OMAC transmits particles on the condition that their migration velocity in an electric field is approximately equal to the advective transport velocity by a particle-free flow; the migration velocity is induced by an electric field between two porous electrodes, through which a particle-free cross-flow moves in an anti-parallel direction to the electric field. Because of this flow field arrangement, the length scale over which diffusion must act to affect resolution is the entire electrode separation distance in the OMAC, whereas in the DMA it is smaller by about a factor of the sample-to-carrier gas flow rate ratio. As a result, resolution degradation due to diffusion occurs at a lower operating voltage in the OMAC compared to the DMA. Not only does this suggest a larger dynamic range for the OMAC, but also the capability to classify nanometer-scale particles with greater resolution and lower operating voltages and flow rates.
Motivated by the theoretical advantages of an OMAC compared to a DMA, this thesis details the design and characterization of OMAC classifiers to verify the performance of realized OMACs. The capabilities of prototype radial geometry OMACs were first investigated. They demonstrated sub-20 nm particle diameter classification at high resolution using modest flow rates, making them amenable to non-laboratory applications. Additionally, the delayed resolution degradation of OMACs was validated by the maintenance of resolution at operating voltages below those at which a DMA would have experienced severely degraded resolution.
Various applications were then carried out to validate the use of OMACs in both nanometer-scale and sub-micrometer particle size regimes. The first OMAC application was in the field of biomolecule analysis, in which the radial OMAC was operated as an ion mobility spectrometer coupled to a mass spectrometer to resolve conformations of sub-2 nm biomolecules. The resolving power of the radial OMAC was high enough to differentiate peptide stereoisomers and populations of thermally-induced biomolecule conformations.
In the aerosol measurement field, aerosol particle size distributions are typically obtained by passing the sample through an ionization source to impart charges on the sample particles, before mobility separation and detection. The detected signal must be inverted, using detector efficiencies, classifier transfer functions, and charge distributions, to obtain the true particle size distribution. While detector efficiencies and classifier transfer functions are typically well-quantified for the specific instruments used in the measurement, the charge distribution is almost never calculated for the specific measurement conditions. This is due both to the computational expense of, as well as the present impracticability of obtaining all the information needed for carrying out such calculations. Aerosol scientists typically use one parameterization of the charge distribution, regardless of the measurement conditions. Thus, the charge distribution represents the greatest source of bias in particle size distribution measurements. Having demonstrated high resolution of sub-2 nm ions, the radial OMAC was then used to obtain mobility distributions of gas ions formed in a bipolar aerosol charger. These ion mobility distributions were then used to quantify the particle size distribution bias due to the use of the common charge distribution parameterization.
In atmospheric nucleation field, the radial OMAC was deployed as part of an airborne particle detection payload over a large cattle feedlot. Again, the radial OMAC demonstrated the ability to obtain nanometer-scale particle size distributions, that, when paired with a concurrently-deployed DMA, allowed for the measurement of ambient particle size distributions over the entire sub-micrometer size range. A spatially-dense set of such particle size distributions allowed for the calculation of particle growth rates from a clear nucleation event from cattle feedlot emissions.
Finally, OMACs were evaluated for their performance at low-flow rate operation to obtain sub-micron particle size distribution for deployment as portable exposure monitors, distributed network area monitors, and unmanned aerial vehicle instrumentation. The radial OMAC showed high fidelity to a reference instrument in reported ambient particle size distributions for nearly 48 hours of unattended operation. A planar geometry OMAC prototype was designed and characterized as well, indicating design and construction issues that caused deviations from ideal behavior. The planer OMAC qualitatively agreed with a reference instrument in reported ambient particle size distributions for about 12 hours of unattended operation. Both radial and planar OMACs were more compact, lower in weight, and less demanding in power consumption than a classical DMA, showing high potential for further miniaturized instrumentation development.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Flagan, Richard C.}, } @phdthesis{10.7907/Z92805K8, author = {Schwantes, Rebecca Helen}, title = {Identifying Isoprene and Toluene Gas-Phase Oxidation Products to Better Constrain Ozone and Secondary Organic Aerosol Formation in the Atmosphere}, school = {California Institute of Technology}, year = {2017}, doi = {10.7907/Z92805K8}, url = {https://resolver.caltech.edu/CaltechTHESIS:11022016-133509841}, abstract = {Anthropogenic pollutants such as NOx interact with volatile organic compounds (VOCs) such as isoprene and toluene to produce ozone (O3) and oxidized low volatility compounds that are responsible for forming secondary organic aerosol (SOA). Understanding the processes that form O3 and SOA from VOCs is important for understanding climate interactions and air quality. Both O3 and SOA are harmful air pollutants. O3 directly contributes to warming while the influence of aerosols is far more complicated, but ultimately leads to regional cooling. Understanding the chemistry that produces O3 and SOA will help better predict how future regulations will influence climate and air quality. A series of experiments using the Caltech chamber facility were designed and performed to better understand the influence of isoprene and toluene gas-phase oxidation products on O3 and SOA formation.
First, in order to conduct experiments, the new Caltech chamber facility was characterized. Second, to understand the oxidation products from isoprene in the presence of anthropogenic pollutants such as NOx, a chemical ionization mass spectrometer (CIMS) was used to identify the gas-phase products from the oxidation of isoprene by the nitrate radical (NO3). First-generation nitrates were identified to be predominantly δ-nitrates while first-generation nitrates formed from OH oxidation of isoprene in the presence of NO are predominantly β-nitrates. This has important consequences for NOx recycling and O3 generation because these β- and δ-nitrates react with O3 and OH at different rates and form different products. Photooxidation products from nitrooxy hydroperoxide, a product from isoprene + NO3 oxidation (in the presence of hydroperoxy radical-HO2), were identified to be predominantly propanone nitrate and nitrooxy hydroxy epoxide. Nitrooxy hydroxy epoxide undergoes reactive uptake to seed aerosol similar to isoprene dihydroxy epoxide, suggesting it may be important for SOA formation.
Lastly, first- and later-generation photooxoidation products from cresol and benzaldehyde oxidation were identified. Cresol and benzaldehyde are products from toluene OH oxidation. Low volatility ring-retaining products produced from cresol oxidation were detected in the gas phase by the CIMS and in the particle phase using offline direct analysis in real time mass spectrometry (DART-MS). Products detected included polyols such as dihydroxy, trihydroxy, tetrahydroxy, and pentahydroxy toluenes and benzoquinones such as hydroxy, dihydroxy, and trihydroxy methyl benzoquinones. These results suggest that even though the cresol pathway only contributes ∼20% to gas-phase toluene oxidation, products from the cresol channel potentially generate a significant fraction ( ∼20-40%) of toluene SOA.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/Z9930R6T, author = {Bates, Kelvin Hamilton}, title = {Isoprene Oxidation Mechanisms and Secondary Organic Aerosol Formation Under HO2-Dominated Conditions}, school = {California Institute of Technology}, year = {2017}, doi = {10.7907/Z9930R6T}, url = {https://resolver.caltech.edu/CaltechTHESIS:05312017-144547085}, abstract = {Isoprene, a volatile hydrocarbon emitted by plants, represents the single most abundant source of non-methane organic carbon to the atmosphere. After its rapid oxidation by OH radicals in the troposphere, isoprene may follow any of a number of complex reaction mechanisms to form more highly functionalized products, depending in large part on the relative abundance of reactive radicals such as HO2 and NO; some of these products can be sufficiently water-soluble, non-volatile, and/or reactive to partition into atmospheric particles and contribute to the creation of secondary organic aerosol (SOA). In this work, I explore the gas-phase oxidation mechanisms and SOA formation potential of second- and later-generation products formed in the HO2-dominated reaction cascade, which predominates in remote regions and is estimated to account for over >40% of isoprene oxidation. Pure standards of significant isoprene products, such as isoprene epoxydiols (IEPOX) and C4 dihydroxycarbonyl compounds, are synthesized, and the rates and product yields of their gas-phase reactions with OH are measured by CF3O- chemical ionization mass spectrometry in environmental chamber experiments. Results are compared to field observations from the Southern Oxidant and Aerosol Study in the Southeastern United States, where significant concentrations of these compounds were detected, and are integrated into a global chemical transport model to investigate their effects throughout the atmosphere. Further, the results from these and other gas-phase kinetic and product studies are incorporated into an explicit isoprene oxidation mechanism, designed to simulate the effects of isoprene chemistry on oxidant concentrations and to produce accurate representations of products known to be involved in condensed phase processes, including IEPOX. Finally, additional chamber experiments with synthetic IEPOX and inorganic seed aerosol are performed to derive particle uptake coefficients and examine the effects of particle pH, liquid water content, and chemical composition on IEPOX-SOA formation, using aerosol mass spectrometry and differential mobility analysis. The gas- and particle-phase reaction rates and product yields reported herein, along with the explicit model, provide important constraints on the fate of isoprene-derived carbon in the atmosphere and on the influence the HO2-dominated isoprene oxidation pathway exerts on SOA and oxidant budgets.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, } @phdthesis{10.7907/Z9959FH7, author = {Coggon, Matthew Mitchell}, title = {Field and Laboratory Studies of Atmospheric Organic Aerosol}, school = {California Institute of Technology}, year = {2016}, doi = {10.7907/Z9959FH7}, url = {https://resolver.caltech.edu/CaltechTHESIS:09222015-114148959}, abstract = {This thesis is the culmination of field and laboratory studies aimed at assessing processes that affect the composition and distribution of atmospheric organic aerosol. An emphasis is placed on measurements conducted using compact and high-resolution Aerodyne Aerosol Mass Spectrometers (AMS). The first three chapters summarize results from aircraft campaigns designed to evaluate anthropogenic and biogenic impacts on marine aerosol and clouds off the coast of California. Subsequent chapters describe laboratory studies intended to evaluate gas and particle-phase mechanisms of organic aerosol oxidation.
The 2013 Nucleation in California Experiment (NiCE) was a campaign designed to study environments impacted by nucleated and/or freshly formed aerosol particles. Terrestrial biogenic aerosol with > 85% organic mass was observed to reside in the free troposphere above marine stratocumulus. This biogenic organic aerosol (BOA) originated from the Northwestern United States and was transported to the marine atmosphere during periodic cloud-clearing events. Spectra recorded by a cloud condensation nuclei counter demonstrated that BOA is CCN active. BOA enhancements at latitudes north of San Francisco, CA coincided with enhanced cloud water concentrations of organic species such as acetate and formate.
Airborne measurements conducted during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) were aimed at evaluating the contribution of ship emissions to the properties of marine aerosol and clouds off the coast of central California. In one study, analysis of organic aerosol mass spectra during periods of enhanced shipping activity yielded unique tracers indicative of cloud-processed ship emissions (m/z 42 and 99). The variation of their organic fraction (f42 and f99) was found to coincide with periods of heavy (f42 > 0.15; f99 > 0.04), moderate (0.05 < f42 < 0.15; 0.01 < f99 < 0.04), and negligible (f42 < 0.05; f99 < 0.01) ship influence. Application of these conditions to all measurements conducted during E-PEACE demonstrated that a large fraction of cloud droplet (72%) and dry aerosol mass (12%) sampled in the California coastal study region was heavily or moderately influenced by ship emissions. Another study investigated the chemical and physical evolution of a controlled organic plume emitted from the R/V Point Sur. Under sunny conditions, nucleated particles composed of oxidized organic compounds contributed nearly an order of magnitude more cloud condensation nuclei (CCN) than less oxidized particles formed under cloudy conditions. The processing time necessary for particles to become CCN active was short ( < 1 hr) compared to the time needed for particles to become hygroscopic at sub-saturated humidity ( > 4 hr).
Laboratory chamber experiments were also conducted to evaluate particle-phase processes influencing aerosol phase and composition. In one study, ammonium sulfate seed was coated with a layer of secondary organic aerosol (SOA) from toluene oxidation followed by a layer of SOA from α-pinene oxidation. The system exhibited different evaporative properties than ammonium sulfate seed initially coated with α-pinene SOA followed by a layer of toluene SOA. This behavior is consistent with a shell-and-core model and suggests limited mixing among different SOA types. Another study investigated the reactive uptake of isoprene epoxy diols (IEPOX) onto non-acidified aerosol. It was demonstrated that particle acidity has limited influence on organic aerosol formation onto ammonium sulfate seed, and that the chemical system is limited by the availability of nucleophiles such as sulfate.
Flow tube experiments were conducted to examine the role of iron in the reactive uptake and chemical oxidation of glycolaldehyde. Aerosol particles doped with iron and hydrogen peroxide were mixed with gas-phase glycolaldehyde and photochemically aged in a custom-built flow reactor. Compared to particles free of iron, iron-doped aerosols significantly enhanced the oxygen to carbon (O/C) ratio of accumulated organic mass. The primary oxidation mechanism is suggested to be a combination of Fenton and photo-Fenton reactions which enhance particle-phase OH radical concentrations.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/Z9FX77DG, author = {McVay, Renee Catherine}, title = {Modeling the Effect of Vapor Wall Deposition on the Formation of Secondary Organic Aerosol in Chamber Studies}, school = {California Institute of Technology}, year = {2016}, doi = {10.7907/Z9FX77DG}, url = {https://resolver.caltech.edu/CaltechTHESIS:05172016-133615016}, abstract = {Laboratory chamber experiments are used to investigate formation of secondary organic aerosol (SOA) from biogenic and anthropogenic precursors under a variety of environmental conditions. Simulations of these experiments test our understanding of the prevailing chemistry of SOA formation as well as the dynamic processes occurring in the chamber itself. One dynamic process occurring in the chamber that was only recently recognized is the deposition of vapor species to the Teflon walls of the chamber. Low-volatility products formed from the oxidation of volatile organic compounds (VOCs) deposit on the walls rather than forming SOA, decreasing the amount of SOA formed (quantified as the SOA yield: mass of SOA formed per mass of VOC reacted). In this work, several modeling studies are presented that address the effect of vapor wall deposition on SOA formation in chambers.A coupled vapor-particle dynamics model is used to examine the competition among the rates of gas-phase oxidation to low volatility products, wall deposition of these products, and mass transfer to the particle phase. The relative time scales of these rates control the amount of SOA formed by affecting the influence of vapor wall deposition. Simulations show that an effect on SOA yield of changing the vapor-particle mass transfer rate is only observed when SOA formation is kinetically limited. For systems with kinetically limited SOA formation, increasing the rate of vapor-particle mass transfer by increasing the concentration of seed particles is an effective way to minimize the effect of vapor wall deposition.
This coupled vapor-particle dynamics model is then applied to α-pinene ozonolysis SOA experiments. Experiments show that the SOA yield is affected when changing the oxidation rate but not when changing the rate of gas-particle mass transfer by changing the concentration of seed particles. Model simulations show that the absence of an effect of changing the seed particle concentration is consistent with SOA formation being governed by quasi-equilibrium growth, in which gas-particle equilibrium is established much faster than the rate of change of the gas-phase concentration. The observed effect of oxidation rate on SOA yield arises due to the presence of vapor wall deposition: gas-phase oxidation products are produced more quickly and condense preferentially onto seed particles before being lost to the walls. Therefore, for α-pinene ozonolysis, increasing the oxidation rate is the most effective way to mitigate the influence of vapor wall deposition.
Finally, the detailed model GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere) is used to simulate α-pinene photooxidation SOA experiments. Unexpectedly, α-pinene OH oxidation experiments show no effect when changing either the oxidation rate or the vapor-particle mass transfer rate, whereas GECKO-A predicts that changing the oxidation rate should drastically affect the SOA yield. Sensitivity studies show that the assumed magnitude of the vapor wall deposition rate can greatly affect conclusions drawn from comparisons between simulations and experiments. If vapor wall loss in the Caltech chamber is of order 10-5 s-1, GECKO-A greatly overpredicts SOA during high UV experiments, likely due to an overprediction of second-generation products. However, if instead vapor wall loss in the Caltech chamber is of order 10-3 s-1, GECKO-A greatly underpredicts SOA during low UV experiments, possibly due to missing autoxidation pathways in the α-pinene mechanism.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/Z9QZ27WP, author = {Zhang, Xuan}, title = {Investigation of Fundamental Processes Governing Secondary Organic Aerosol Formation in Laboratory Chambers}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z9QZ27WP}, url = {https://resolver.caltech.edu/CaltechTHESIS:05282015-214235298}, abstract = {Our understanding of the processes and mechanisms by which secondary organic aerosol (SOA) is formed is derived from laboratory chamber studies. In the atmosphere, SOA formation is primarily driven by progressive photooxidation of SOA precursors, coupled with their gas-particle partitioning. In the chamber environment, SOA-forming vapors undergo multiple chemical and physical processes that involve production and removal via gas-phase reactions; partitioning onto suspended particles vs. particles deposited on the chamber wall; and direct deposition on the chamber wall. The main focus of this dissertation is to characterize the interactions of organic vapors with suspended particles and the chamber wall and explore how these intertwined processes in laboratory chambers govern SOA formation and evolution.
A Functional Group Oxidation Model (FGOM) that represents SOA formation and evolution in terms of the competition between functionalization and fragmentation, the extent of oxygen atom addition, and the change of volatility, is developed. The FGOM contains a set of parameters that are to be determined by fitting of the model to laboratory chamber data. The sensitivity of the model prediction to variation of the adjustable parameters allows one to assess the relative importance of various pathways involved in SOA formation.
A critical aspect of the environmental chamber is the presence of the wall, which can induce deposition of SOA-forming vapors and promote heterogeneous reactions. An experimental protocol and model framework are first developed to constrain the vapor-wall interactions. By optimal fitting the model predictions to the observed wall-induced decay profiles of 25 oxidized organic compounds, the dominant parameter governing the extent of wall deposition of a compound is identified, i.e., wall accommodation coefficient. By correlating this parameter with the molecular properties of a compound via its volatility, the wall-induced deposition rate of an organic compound can be predicted based on its carbon and oxygen numbers in the molecule.
Heterogeneous transformation of δ-hydroxycarbonyl, a major first-generation product from long-chain alkane photochemistry, is observed on the surface of particles and walls. The uniqueness of this reaction scheme is the production of substituted dihydrofuran, which is highly reactive towards ozone, OH, and NO3, thereby opening a reaction pathway that is not usually accessible to alkanes. A spectrum of highly-oxygenated products with carboxylic acid, ester, and ether functional groups is produced from the substituted dihydrofuran chemistry, thereby affecting the average oxidation state of the alkane-derived SOA.
The vapor wall loss correction is applied to several chamber-derived SOA systems generated from both anthropogenic and biogenic sources. Experimental and modeling approaches are employed to constrain the partitioning behavior of SOA-forming vapors onto suspended particles vs. chamber walls. It is demonstrated that deposition of SOA-forming vapors to the chamber wall during photooxidation experiments can lead to substantial and systematic underestimation of SOA. Therefore, it is likely that a lack of proper accounting for vapor wall losses that suppress chamber-derived SOA yields contribute substantially to the underprediction of ambient SOA concentrations in atmospheric models.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/Z93F4MJR, author = {Schilling, Katherine Ann}, title = {Secondary Organic Aerosol Composition Studies Using Mass Spectrometry}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z93F4MJR}, url = {https://resolver.caltech.edu/CaltechTHESIS:05222015-145550415}, abstract = {Trace volatile organic compounds emitted by biogenic and anthropogenic sources into the atmosphere can undergo extensive photooxidation to form species with lower volatility. By equilibrium partitioning or reactive uptake, these compounds can nucleate into new aerosol particles or deposit onto already-existing particles to form secondary organic aerosol (SOA). SOA and other atmospheric particulate matter have measurable effects on global climate and public health, making understanding SOA formation a needed field of scientific inquiry. SOA formation can be done in a laboratory setting, using an environmental chamber; under these controlled conditions it is possible to generate SOA from a single parent compound and study the chemical composition of the gas and particle phases. By studying the SOA composition, it is possible to gain understanding of the chemical reactions that occur in the gas phase and particle phase, and identify potential heterogeneous processes that occur at the surface of SOA particles. In this thesis, mass spectrometric methods are used to identify qualitatively and qualitatively the chemical components of SOA derived from the photooxidation of important anthropogenic volatile organic compounds that are associated with gasoline and diesel fuels and industrial activity (C12 alkanes, toluene, and o-, m-, and p-cresols). The conditions under which SOA was generated in each system were varied to explore the effect of NOx and inorganic seed composition on SOA chemical composition. The structure of the parent alkane was varied to investigate the effect on the functionalization and fragmentation of the resulting oxidation products. Relative humidity was varied in the alkane system as well to measure the effect of increased particle-phase water on condensed-phase reactions. In all systems, oligomeric species, resulting potentially from particle-phase and heterogeneous processes, were identified. Imines produced by reactions between (NH4)2SO4 seed and carbonyl compounds were identified in all systems. Multigenerational photochemistry producing low- and extremely low-volatility organic compounds (LVOC and ELVOC) was reflected strongly in the particle-phase composition as well.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/4J4Q-HP22, author = {Ensberg, Joseph James}, title = {Studies of Ambient Organic and Inorganic Aerosol in Southern California}, school = {California Institute of Technology}, year = {2014}, doi = {10.7907/4J4Q-HP22}, url = {https://resolver.caltech.edu/CaltechTHESIS:03192014-130444619}, abstract = {
The negative impacts of ambient aerosol particles, or particulate matter (PM), on human health and climate are well recognized. However, owing to the complexity of aerosol particle formation and chemical evolution, emissions control strategies remain difficult to develop in a cost effective manner. In this work, three studies are presented to address several key issues currently stymieing California’s efforts to continue improving its air quality.
Gas-phase organic mass (GPOM) and CO emission factors are used in conjunction with measured enhancements in oxygenated organic aerosol (OOA) relative to CO to quantify the significant lack of closure between expected and observed organic aerosol concentrations attributable to fossil-fuel emissions. Two possible conclusions emerge from the analysis to yield consistency with the ambient organic data: (1) vehicular emissions are not a dominant source of anthropogenic fossil SOA in the Los Angeles Basin, or (2) the ambient SOA mass yields used to determine the SOA formation potential of vehicular emissions are substantially higher than those derived from laboratory chamber studies. Additional laboratory chamber studies confirm that, owing to vapor-phase wall loss, the SOA mass yields currently used in virtually all 3D chemical transport models are biased low by as much as a factor of 4. Furthermore, predictions from the Statistical Oxidation Model suggest that this bias could be as high as a factor of 8 if the influence of the chamber walls could be removed entirely.
Once vapor-phase wall loss has been accounted for in a new suite of laboratory chamber experiments, the SOA parameterizations within atmospheric chemical transport models should also be updated. To address the numerical challenges of implementing the next generation of SOA models in atmospheric chemical transport models, a novel mathematical framework, termed the Moment Method, is designed and presented. Assessment of the Moment Method strengths and weaknesses provide valuable insight that can guide future development of SOA modules for atmospheric CTMs.
Finally, regional inorganic aerosol formation and evolution is investigated via detailed comparison of predictions from the Community Multiscale Air Quality (CMAQ version 4.7.1) model against a suite of airborne and ground-based meteorological measurements, gas- and aerosol-phase inorganic measurements, and black carbon (BC) measurements over Southern California during the CalNex field campaign in May/June 2010. Results suggests that continuing to target sulfur emissions with the hopes of reducing ambient PM concentrations may not the most effective strategy for Southern California. Instead, targeting dairy emissions is likely to be an effective strategy for substantially reducing ammonium nitrate concentrations in the eastern part of the Los Angeles Basin.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/9SGJ-TT23, author = {Chen, Yi-Chun}, title = {Aerosol-Cloud-Precipitation Interactions in Marine Stratocumulus Clouds}, school = {California Institute of Technology}, year = {2013}, doi = {10.7907/9SGJ-TT23}, url = {https://resolver.caltech.edu/CaltechTHESIS:06102013-101017079}, abstract = {
Marine stratocumulus clouds are generally optically thick and shallow, exerting a net cooling influence on climate. Changes in atmospheric aerosol levels alter cloud microphysics (e.g., droplet size) and cloud macrophysics (e.g., liquid water path, cloud thickness), thereby affecting cloud albedo and Earth’s radiative balance. To understand the aerosol-cloud-precipitation interactions and to explore the dynamical effects, three-dimensional large-eddy simulations (LES) with detailed bin-resolved microphysics are performed to explore the diurnal variation of marine stratocumulus clouds under different aerosol levels and environmental conditions. It is shown that the marine stratocumulus cloud albedo is sensitive to aerosol perturbation under clean background conditions, and to environmental conditions such as large-scale divergence rate and free tropospheric humidity.
Based on the in-situ Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) during Jul. and Aug. 2011, and A-Train satellite observation of 589 individual ship tracks during Jun. 2006-Dec. 2009, an analysis of cloud albedo responses in ship tracks is presented. It is found that the albedo response in ship tracks depends on the mesoscale cloud structure, the free tropospheric humidity, and cloud top height. Under closed cell structure (i.e., cloud cells ringed by a perimeter of clear air), with sufficiently dry air above cloud tops and/or higher cloud top heights, the cloud albedo can become lower in ship tracks. Based on the satellite data, nearly 25% of ship tracks exhibited a decreased albedo. The cloud macrophysical responses are crucial in determining both the strength and the sign of the cloud albedo response to aerosols.
To understand the aerosol indirect effects on global marine warm clouds, multisensory satellite observations, including CloudSat, MODIS, CALIPSO, AMSR-E, ECMWF, CERES, and NCEP, have been applied to study the sensitivity of cloud properties to aerosol levels and to large scale environmental conditions. With an estimate of anthropogenic aerosol fraction, the global aerosol indirect radiative forcing has been assessed.
As the coupling among aerosol, cloud, precipitation, and meteorological conditions in the marine boundary layer is complex, the integration of LES modeling, in-situ aircraft measurements, and global multisensory satellite data analyses improves our understanding of this complex system.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/BPKE-M777, author = {Yee, Lindsay Diana}, title = {Chemistry of Secondary Organic Aerosol Formation}, school = {California Institute of Technology}, year = {2013}, doi = {10.7907/BPKE-M777}, url = {https://resolver.caltech.edu/CaltechTHESIS:03162013-090820386}, abstract = {
The photooxidation of volatile organic compounds (VOCs) in the atmosphere can lead to the formation of secondary organic aerosol (SOA), a major component of fine particulate matter. Improvements to air quality require insight into the many reactive intermediates that lead to SOA formation, of which only a small fraction have been measured at the molecular level. This thesis describes the chemistry of secondary organic aerosol (SOA) formation from several atmospherically relevant hydrocarbon precursors. Photooxidation experiments of methoxyphenol and phenolic compounds and C12 alkanes were conducted in the Caltech Environmental Chamber. These experiments include the first photooxidation studies of these precursors run under sufficiently low NOx levels, such that RO2 + HO2 chemistry dominates, an important chemical regime in the atmosphere. Using online Chemical Ionization Mass Spectrometery (CIMS), key gas-phase intermediates that lead to SOA formation in these systems were identified. With complementary particle-phase analyses, chemical mechanisms elucidating the SOA formation from these compounds are proposed.
Three methoxyphenol species (phenol, guaiacol, and syringol) were studied to model potential photooxidation schemes of biomass burning intermediates. SOA yields (ratio of mass of SOA formed to mass of primary organic reacted) exceeding 25% are observed. Aerosol growth is rapid and linear with the organic conversion, consistent with the formation of essentially non-volatile products. Gas and aerosol-phase oxidation products from the guaiacol system show that the chemical mechanism consists of highly oxidized aromatic species in the particle phase. Syringol SOA yields are lower than that of phenol and guaiacol, likely due to unique chemistry dependent on methoxy group position.
The photooxidation of several C12 alkanes of varying structure n-dodecane, 2-methylundecane, cyclododecane, and hexylcyclohexane) were run under extended OH exposure to investigate the effect of molecular structure on SOA yields and photochemical aging. Peroxyhemiacetal formation from the reactions of several multifunctional hydroperoxides and aldehyde intermediates was found to be central to organic growth in all systems, and SOA yields increased with cyclic character of the starting hydrocarbon. All of these studies provide direction for future experiments and modeling in order to lessen outstanding discrepancies between predicted and measured SOA.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/WZXD-KX70, author = {Loza, Christine Lauren}, title = {Investigations of Secondary Organic Aerosol Formation in Laboratory Chambers}, school = {California Institute of Technology}, year = {2013}, doi = {10.7907/WZXD-KX70}, url = {https://resolver.caltech.edu/CaltechTHESIS:05312013-115629933}, abstract = {Secondary organic aerosol (SOA) is produced in the atmosphere by oxidation of volatile organic compounds. Laboratory chambers are used understand the formation mechanisms and evolution of SOA formed under controlled conditions. This thesis presents studies of SOA formed from anthropogenic and biogenic precursors and discusses the effects of chamber walls on suspended vapors and particles.
During a chamber experiment, suspended vapors and particles can interact with the chamber walls. Particle wall loss is relatively well-understood, but vapor wall losses have received little study. Vapor wall loss of 2,3-epoxy-1,4-butanediol (BEPOX) and glyoxal was identified, quantified, and found to depend on chamber age and relative humidity.
Particles reside in the atmosphere for a week or more and can evolve chemically during that time period, a process termed aging. Simulating aging in laboratory chambers has proven to be challenging. A protocol was developed to extend the duration of a chamber experiment to 36 h of oxidation and was used to evaluate aging of SOA produced from m-xylene. Total SOA mass concentration increased and then decreased with increasing photooxidation suggesting a transition from functionalization to fragmentation chemistry driven by photochemical processes. SOA oxidation, measured as the bulk particle elemental oxygen-to-carbon ratio and fraction of organic mass at m/z 44, increased continuously starting after 5 h of photooxidation.
The physical state and chemical composition of an organic aerosol affect the mixing of aerosol components and its interactions with condensing species. A laboratory chamber protocol was developed to evaluate the mixing of SOA produced sequentially from two different sources by heating the chamber to induce particle evaporation. Using this protocol, SOA produced from toluene was found to be less volatile than that produced from a-pinene. When the two types of SOA were formed sequentially, the evaporation behavior most closely represented that of SOA from the second parent hydrocarbon, suggesting that the structure of the mixed SOA particles resembles a core of SOA from the first precursor coated by a layer of SOA from the second precursor, indicative of limiting mixing.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/J69H-EK18, author = {Craven, Jill Suzanne}, title = {Studies of Ambient and Chamber Aerosol Composition Using the Aerosol Mass Spectrometer}, school = {California Institute of Technology}, year = {2013}, doi = {10.7907/J69H-EK18}, url = {https://resolver.caltech.edu/CaltechTHESIS:04112013-190107672}, abstract = {This thesis presents composition measurements for atmospherically relevant inorganic and organic aerosol from laboratory and ambient measurements using the Aerodyne aerosol mass spectrometer. Studies include the oxidation of dodecane in the Caltech environmental chambers, and several aircraft- and ground-based field studies, which include the quantification of wildfire emissions off the coast of California, and Los Angeles urban emissions.
The oxidation of dodecane by OH under low NO conditions and the formation of secondary organic aerosol (SOA) was explored using a gas-phase chemical model, gas-phase CIMS measurements, and high molecular weight ion traces from particle- phase HR-TOF-AMS mass spectra. The combination of these measurements support the hypothesis that particle-phase chemistry leading to peroxyhemiacetal formation is important. Positive matrix factorization (PMF) was applied to the AMS mass spectra which revealed three factors representing a combination of gas-particle partitioning, chemical conversion in the aerosol, and wall deposition.
Airborne measurements of biomass burning emissions from a chaparral fire on the central Californian coast were carried out in November 2009. Physical and chemical changes were reported for smoke ages 0 – 4 h old. CO2 normalized ammonium, nitrate, and sulfate increased, whereas the normalized OA decreased sharply in the first 1.5 - 2 h, and then slowly increased for the remaining 2 h (net decrease in normalized OA). Comparison to wildfire samples from the Yucatan revealed that factors such as relative humidity, incident UV radiation, age of smoke, and concentration of emissions are important for wildfire evolution.
Ground-based aerosol composition is reported for Pasadena, CA during the summer of 2009. The OA component, which dominated the submicron aerosol mass, was deconvolved into hydrocarbon-like organic aerosol (HOA), semi-volatile oxidized organic aerosol (SVOOA), and low-volatility oxidized organic aerosol (LVOOA). The HOA/OA was only 0.08–0.23, indicating that most of Pasadena OA in the summer months is dominated by oxidized OA resulting from transported emissions that have undergone photochemistry and/or moisture-influenced processing, as apposed to only primary organic aerosol emissions. Airborne measurements and model predictions of aerosol composition are reported for the 2010 CalNex field campaign.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/YZY9-EW06, author = {Metcalf, Andrew Richard}, title = {Atmospheric Black Carbon: Measurements in the Los Angeles Atmosphere and Aging by Condensation of Organic Aerosol}, school = {California Institute of Technology}, year = {2012}, doi = {10.7907/YZY9-EW06}, url = {https://resolver.caltech.edu/CaltechTHESIS:05242012-112013951}, abstract = {Aerosol particles in the atmosphere scatter and absorb solar radiation; an interaction that yields the largest uncertainty in models of future climate change. While most aerosols scatter light and, therefore, cool the environment, absorbing aerosol warms the environment. In particular, black carbon (BC) aerosol, the largest component of absorbing aerosol, may exhibit the second-largest forcing on climate behind greenhouse gases. In addition, the mixing state of BC aerosol, or the degree to which a BC core is coated with a scattering substance, may significantly increase the absorbing potential of BC. This thesis presents results from field and laboratory studies of BC aerosol, its mixing state in the atmosphere, and how it ages in the presence of condensing secondary organic aerosol.
A major field study, CalNex 2010, was conducted in Southern California to study air quality and climate change issues. Measurements of BC aerosol in and around the Los Angeles (LA) Basin reveal the evolution of BC aerosol from a thinly coated state near sources in the eastern LA Basin to a more thickly coated state in the outflow regions of the Basin. While the majority of BC aerosol emitted in the LA Basin remains near the surface, some BC aerosol is transported to the free troposphere through sea-breeze and mountain-flow coupling. BC aerosol above the inversion layer tends to be thickly coated, indicating that it is more aged than the BC measured near the surface.
To understand how the mixing state of BC evolves with secondary formation of species in the atmosphere, carefully controlled environmental chamber experiments were conducted. Two types of secondary organic aerosol (SOA) precursors, alpha-pinene and naphthalene, were reacted in the chamber to condense secondary products onto BC seed aerosol. The rate of growth and magnitude of absorption enhancement due to the secondary coating on BC was measured, revealing that growth of coatings is diffusion-limited. Particle composition measurements reveal that condensed SOA onto BC seed particles is nearly identical to nucleated SOA from the same parent hydrocarbon. Measurements of coating thickness and optical properties provide insight to single-particle SOA growth and volatility.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/HH11-8N22, author = {Lebo, Zachary John}, title = {Computational Modeling Studies of Fundamental Aerosol-Cloud Interactions}, school = {California Institute of Technology}, year = {2012}, doi = {10.7907/HH11-8N22}, url = {https://resolver.caltech.edu/CaltechTHESIS:03292012-204204319}, abstract = {Basic questions regarding the interaction between changes in human activity and the atmosphere remain unanswered. Among these, the link between aerosol particles and cloud formation and development, especially in an altered climate, is a large point of uncertainty in recent climate projections. This should come as no surprise given the uncertainty in model parameters required to predict droplet activation, even in the most detailed models used for climate predictions. Here, a detailed spectral mixed-phase microphysics scheme and a state-of-the-art continuous two-dimensional (2-D) aerosol-droplet microphysics scheme have been developed and coupled to the Weather Research and Forecasting (WRF) model to more closely analyze the effects of aerosol perturbations on single clouds or cloud systems with the hope of ultimately improving numerical parameterizations used by microphysics schemes in general circulation models (GCMs).
The continuous 2-D aerosol-droplet model is developed to explicitly treat the entire spectrum of aerosol, haze droplets, cloud droplets, and drizzle drops while allowing the solute mass spectrum to evolve within the droplets. In other words, the aerosol mass is conserved and regeneration of aerosol particles upon droplet evaporation is physically accurate without any a priori assumptions. The model is tested by performing simulations of marine stratocumulus and the results are compared with those from the aforementioned bin and bulk models. It is shown that microphysical processing of aerosols alone results in a large shift in the aerosol spectrum toward larger particles (via collision-coalescence of droplets). This could have potentially large effects on the activation of regenerated particles. Future studies with the model will address the need for better parameterizations of the aerosol regeneration process.
The spectral mixed-phase microphysics scheme is used in conjunction with a two-moment bulk microphysics model to study the effect of aerosol perturbations on deep convective clouds. The bin model shows that with an increase in aerosol number concentration comes an invigoration and a decrease in precipitation. On the other hand, the bulk model suggests that the storm ought to weaken and precipitation will increase in a more polluted environment. The invigoration predicted by the bin model is a result of the suppression of the collision-coalescence process that permits more droplets to be lofted above the freezing level, hence increasing the bulk freezing rate aloft. The additional freezing and subsequent deposition acts to increase the latent heating and thus increase buoyancy. However, the cloud particles in the polluted cases are now smaller and more numerous and consequently have a shorter evaporation/sublimation timescale and a longer sedimentation time-scale. The ultimate result is for precipitation to decrease in conjunction with a moistening of the mid- to upper-troposphere. The difference in the sign of the aerosol effect between the two models is thought to be related to the saturation adjustment scheme used in the bulk model and is addressed by including an explicit treatment of condensation and activation within the bulk model, similar to the algorithm utilized in the bin model. The results of the inter-model comparison demonstrate the significance of the saturation adjustment assumption on the sign and magnitude of the aerosol effect on deep convective clouds.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/CGKH-EW24, author = {Chan, Man Nin}, title = {Mass Spectrometric Analysis of Organic Aerosol Composition: Laboratory and Ambient}, school = {California Institute of Technology}, year = {2012}, doi = {10.7907/CGKH-EW24}, url = {https://resolver.caltech.edu/CaltechTHESIS:12152011-220323752}, abstract = {Organic compounds contribute a significant mass fraction of ambient aerosol and play a role in determining the physiochemical properties of ambient aerosol. A significant fraction of organic aerosol is secondary organic aerosol (SOA), which is produced when the volatile organic compounds (VOCs) originated from various anthropogenic and biogenic sources react with atmospheric oxidants such as ozone, hydroxyl radicals, and nitrate radicals to form lower volatility organic compounds, which subsequently partition into the particle phase. Understanding the composition of ambient aerosol is crucial for identifying their sources and formation mechanisms and predicting their properties and effects on various ambient processes. This thesis focuses on investigating the composition of laboratory–generated SOA formed from the oxidation of biogenic VOCs of atmospheric importance (isoprene and β–caryophyllene) and ambient aerosol collected in the field campaigns using advanced mass spectrometric techniques. By comparing the mass spectrometric data collected for the both laboratory–generated SOA and ambient aerosol, we propose reaction pathways and new chemical tracers for these biogenic VOCs, which enhance our knowledge of the composition, sources, and formation pathways of SOA in the atmosphere. With a better knowledge of the SOA composition, a product–specific model is proposed to predict the composition and aerosol mass yields (mass of SOA formed per mass of hydrocarbon reacted) of laboratory–generated α–pinene SOA.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/WCT5-RM26, author = {Pye, Havala Olson Taylor}, title = {Investigations of Global Chemistry-Climate Interactions and Organic Aerosol Using Atmospheric Modeling}, school = {California Institute of Technology}, year = {2011}, doi = {10.7907/WCT5-RM26}, url = {https://resolver.caltech.edu/CaltechTHESIS:08172010-150049831}, abstract = {Aerosol, or particulate matter (PM), is an important component of the atmosphere responsible for negative health impacts, environmental degradation, reductions in visibility, and climate change. In this work, the global chemical transport model, GEOS-Chem, is used as a tool to examine chemistry-climate interactions and organic aerosols.
GEOS-Chem is used to simulate present-day (year 2000) and future (year 2050) sulfate, nitrate, and ammonium aerosols and investigate the potential effects of changes in climate and emissions on global budgets and U.S. air quality. Changes in a number of meteorological parameters, such as temperature and precipitation, are potentially important for aerosols and could lead to increases or decreases in PM concentrations. Although projected changes in sulfate and nitrate precursor emissions favor lower PM concentrations over the U.S., projected increases in ammonia emissions could result in higher nitrate concentrations.
The organic aerosol simulation in GEOS-Chem is updated to include aerosol from primary semivolatile organic compounds (SVOCS), intermediate volatility compounds (IVOCs), NOx dependent terpene aerosol, and aerosol from isoprene + NO3 reaction. SVOCs are identified as the largest global source of organic aerosol even though their atmospheric transformation is highly uncertain and emissions are probably underestimated. As a result of significant nighttime terpene emissions, fast reaction of monoterpenes with the nitrate radical, and high aerosol yields from NO3 oxidation, biogenic hydrocarbons reacting with the nitrate radical are expected to be a major contributor to surface level aerosol concentrations in anthropogenically influenced areas such as the United States. Globally, 69 to 88 Tg/yr of aerosol is predicted to be produced annually, approximately 22 to 24 Tg/yr of which is from biogenic hydrocarbons.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/GZY7-P532, author = {Hersey, Scott Patrick}, title = {Studies of Aerosol Composition and Hygroscopicity}, school = {California Institute of Technology}, year = {2011}, doi = {10.7907/GZY7-P532}, url = {https://resolver.caltech.edu/CaltechTHESIS:05262011-104023732}, abstract = {Atmospheric aerosols have significant impacts on human health, regional visibility, and the radiative energy balance of Earth, but there remain many uncertainties about their sources and evolution in the atmosphere, as well as the details and magnitude of their impact on climate. This thesis introduces a novel instrument for measuring aerosol hygroscopicity, an important factor in the overall climate impact of aerosols, and presents results from several field campaigns and laboratory experiments aimed at characterizing the chemical composition and hygroscopicity of atmospheric particles.
Aerosol water uptake determines particle size, which thereby determines an aerosol’s scattering properties and radiative forcing. The Differential Sizing and Hygroscopicity Spectrometer Probe (DASH-SP) was designed to make rapid measurements of hygroscopicity on timescales short enough for aircraft deployment. Combined with an iterative data processing algorithm, the DASH-SP is demonstrated to accurately measure particle size, growth, and ``effective" refractive index for particles from 135 nm to over 1 μm on timescales as short as a few seconds.
The DASH-SP was deployed off the coast of Central California to measure aerosol water uptake in a marine atmosphere impacted by aged anthropogenic emissions. Composition data from an Aerosol Mass Spectrometer (AMS) indicates that organics are uniformly highly oxidized (O:C ratio = 0.92 ± 0.33), and aerosol growth data from the DASH-SP indicates that in such a highly-oxidized environment, growth factor GF = Dp,wet/Dp,dry) can be accurately predicted as a simple function of relative humidity (RH) and organic volume fraction.
A major ground-based sampling study was carried out in Pasadena, CA, a receptor site for transported Los Angeles pollution, and was dubbed the Pasadena Aerosol Characterization Observatory (PACO). Results indicate that organics dominate transported Los Angeles aerosols, and that they are overwhelmingly oxidized in nature. Aerosol species tend to reside in distinct size modes, with inorganics typically found in larger, accumulation-mode aerosol, while semivolatile secondary organic aerosol (SV-OOA) products appear to reside predominantly in a fine mode. Hygroscopicity was found to be a strong function of organic mass fraction (OMF).
The end of PACO sampling coincided with a major forest fire in Los Angeles County. The impact of this fire on the sampling site is explored by comparing water soluble organic carbon (WSOC) and organic mass-to-charge (m/z) markers from the AMS. In the absence of fire influence, WSOC concentrations are primarily driven by concurrent photochemistry and sea breeze transport from source-rich areas. Fire periods are characterized by significant primary production of WSOC and overnight/early morning transport of fire emissions to the sampling site.
Finally, DASH-SP results from the May 2010 CalNex field experiment indicate that aerosol hygroscopicity is determined primarily by the mass fraction of organics and nitrate in the aerosol. Overall hygroscopicity is very similar to that measured during PACO, though organics appear to be less hygroscopic during CalNex - likely because PACO represented transported, aged aerosol, while CalNex flights covered the entirety of the LA basin, including more source-rich areas.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/2FKC-Y116, author = {Chhabra, Puneet Singh}, title = {Studies of Chamber Organic Aerosol using an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer}, school = {California Institute of Technology}, year = {2011}, doi = {10.7907/2FKC-Y116}, url = {https://resolver.caltech.edu/CaltechTHESIS:05182011-094338191}, abstract = {Secondary organic aerosol (SOA) contributes a substantial fraction to total ambient particulate mass. SOA is a complex mixture of different organic species formed via many gas- and particle-phase reaction pathways. The Aerodyne aerosol mass spectrometer (AMS) has become a standard tool in measuring the bulk chemical composition of SOA in realtime. In addition to acquiring mass spectra of SOA, the high-resolution time-of-flight AMS, or HR-ToF-AMS, can distinguish and quantify ions with the same nominal mass but different elemental compositions. This thesis presents results from several studies in which the HR-ToF-AMS is used to chemically characterize SOA generated in chamber experiments.
Glyoxal is a common oxidation product of both biogenic and anthropogenic volatile organic compounds (VOCs) and is known to partition into wet inorganic aerosol. Chamber studies of glyoxal uptake onto ammonium sulfate aerosol are conducted to better understand the mechanisms controlling glyoxal uptake onto ambient aerosol. Organic growth due to glyoxal uptake was found to be reversible under dark conditions. HR-ToF-AMS spectra provide evidence for glyoxal dimers and trimers existing in the particle phase. HR-ToF-AMS spectra indicate the irreversible formation of carbon-nitrogen compounds in the aerosol. Organosulfates are not detected under dark conditions; however, active photochemistry was found to occur within aerosol during irradiated experiments. Carboxylic acids and organic esters are identified within the aerosol. An organosulfate, which had been previously assigned as glyoxal sulfate in ambient samples and chamber studies of isoprene oxidation, is observed only in the irradiated experiments. Comparison with a laboratory-synthesized standard and chemical considerations strongly suggest that this organosulfate is glycolic acid sulfate, an isomer of the previously proposed glyoxal sulfate.
Developments in HR-ToF-AMS data analysis have allowed for the measurement of the elemental composition of SOA. Additional graphical representations of AMS spectra and elemental composition have been developed to explain the oxidative and aging processes of SOA. It has been shown previously that oxygenated organic aerosol (OOA) components from ambient and laboratory data fall within a triangular region in the f44 vs. f43 space, where f44 and f43 are the ratios of the organic signal at m/z 44 and 43 to the total organic signal, respectively; we refer to this model as the “triangle plot.” Alternatively, the Van Krevelen diagram has been used to plot the elemental composition of SOA and describe the evolution of functional groups in SOA. The variability of SOA formed in chamber experiments from twelve different precursors in both “triangle plot” and Van Krevelen domains are investigated. Spectral and elemental data from the high-resolution Aerodyne aerosol mass spectrometer are compared to offline species identification analysis and FTIR filter analysis to better understand the changes in functional and elemental composition inherent in SOA formation and aging. SOA formed under high- and low-NOx conditions occupy similar areas in the “triangle plot” and Van Krevelen diagram, and SOA generated from already-oxidized precursors starts higher on the “triangle plot.” The most oxidized SOA come from the photooxidation of methoxyphenol precursors which yielded SOA O/C ratios near unity. ∝-pinene ozonolysis and naphthalene photooxidation SOA systems have had the highest degree of mass closure in previous chemical characterization studies and also show the best agreement between AMS elemental composition measurements and elemental composition of identified species. In general the elemental composition of chamber SOA follows a slope shallower than -1 on the Van Krevelen diagram. From the spectra of SOA studied, the triangular region originally constructed with ambient OOA components with chamber aerosol can be reproduced. Ambient data in the middle of the triangle represent the ensemble average of many different SOA precursors, ages, and oxidative processes.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, } @phdthesis{10.7907/PVWD-HZ44, author = {Surratt, Jason Douglas}, title = {Analysis of the Chemical Composition of Atmospheric Organic Aerosols by Mass Spectrometry}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/PVWD-HZ44}, url = {https://resolver.caltech.edu/CaltechTHESIS:03122010-020001934}, abstract = {Although secondary organic aerosol (SOA) makes up a substantial fraction of the organic mass observed in tropospheric fine particulate matter, there remain significant uncertainties in the true impact of atmospheric aerosols on climate and health due to the lack of full knowledge of the sources, composition, and mechanisms of formation of SOA. This thesis demonstrates how the detailed chemical characterization of both laboratory-generated and ambient organic aerosol using advanced mass spectrometric techniques has been critical to the discovery of previously unidentified sources (i.e., role heterogeneous chemistry) of SOA.
The focal point of this thesis is given to the detailed chemical characterization of isoprene SOA formed under both high- and low-NOx conditions. Until recently, the formation of SOA from isoprene, the most abundant non-methane hydrocarbon emitted into the troposphere, was considered insignificant owing to the volatility of its oxidation products. In conjunction with the chemical characterization of gas-phase oxidation products, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX) and methacryloylperoxynitrate (MPAN), that are formed during isoprene oxidation under low- and high-NOx conditions, respectively. Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to enhance low-NOx SOA formation. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NOx SOA. More specifically, the further oxidation of MPAN leads to SOA by particle-phase esterification reactions. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants could be a substantial source of “missing urban SOA” not included in current SOA models.
Increased aerosol acidity is found to result in the formation of organosulfates, which was a previously unrecognized source of SOA. By comparing the tandem mass spectrometric and accurate mass measurements collected for both the laboratory generated and ambient aerosol, previously uncharacterized ambient organic aerosol components are found to be organosulfates of isoprene, α pinene, β pinene, and limonene-like monoterpenes, demonstrating the ubiquity of organosulfate formation in ambient SOA. We estimate that the organosulfate contribution to the total organic mass fraction in certain locations could be substantial (upwards of 30%).
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/61XH-D105, author = {Chan, Arthur Wing Hong}, title = {Chamber Studies and Modeling of Secondary Organic Aerosol Formation}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/61XH-D105}, url = {https://resolver.caltech.edu/CaltechTHESIS:05182010-161102525}, abstract = {
Secondary organic aerosol (SOA), formed from atmospheric oxidation of gas-phase hydrocarbons, comprise a large fraction of ambient particulate matter. Significant uncertainties exist in identifying the sources and mechanisms responsible for SOA formation, making it difficult to understand its impact on global climate and local air quality. Laboratory chambers have been a valuable tool to study underlying chemical mechanisms of SOA formation and to quantify SOA formation from select hydrocarbons in a controlled environment. However, a good understanding of the chemical processes involved is required to be able to extrapolate data acquired from smog chamber studies. This thesis presents results from experimental investigation of SOA formation from atmospherically important compounds, and model simulations of kinetic mechanisms involved in SOA formation.
The distinguishing mechanism of SOA formation is the partitioning of semivolatile hydrocarbon oxidation products between the gas and aerosol phases. While SOA formation is typically described in terms of partitioning only, the rate of formation and ultimate yield of SOA can also depend on the kinetics of both gas- and aerosol-phase processes. Here a general equilibrium/kinetic model of SOA formation is presented to provide a framework for evaluating the extent to which the controlling mechanisms of SOA formation can be inferred from laboratory chamber data. Current atmospheric models systematically underpredict SOA formation, suggesting that in current models, 1) signicant SOA precursors could be missing and 2) SOA forming processes could be misrepresented. Aerosol formation from oxidation of 2-methyl-3-buten-2-ol (MBO) and polycyclic aromatic hydrocarbons (PAHs), two important classes of compounds previously assumed to be an insignicant SOA source, is studied. Upon photooxidation, MBO produces glyoxal (an important SOA intermediate), but the yields are too low to be atmospherically important. Photooxidation of napthalene and other 2-ring PAHs leads to substantial amounts of aerosol, and can account for a large fraction of SOA formed from oxidation of diesel exhaust and other primary emissions.
Isoprene is a signicant source of atmospheric organic aerosol; however, the oxidation pathways that lead to SOA have remained elusive. Under remote low-NOx conditions, epoxydiols are formed from gas-phase photooxidation of isoprene, and are found to undergo reactive uptake to lead to low-volatility compounds, such as C5-methyltetrols and organosulfates observed in ambient particulate matter. Under urban high-NOx conditions, methacrolein, an important C4 aldehyde formed from isoprene oxidation, is found to form SOA via reaction with NO2 to form peroxy methacryloyl nitrate, which subsequently forms low-volatility oligoester products. As a result of radical chemistry of aldehydes, SOA formation from isoprene depends critically on the NO2/NO ratio, and the implications on ambient aerosol formation are discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/6B9K-AT89, author = {Murphy, Shane Michael}, title = {Analysis of the Chemical Composition of Atmospheric and Chamber Generated Aerosol Using Mass Spectrometry}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/6B9K-AT89}, url = {https://resolver.caltech.edu/CaltechETD:etd-05292009-113717}, abstract = {This thesis presents results demonstrating the use of particulate composition measurements to determine the mechanisms of aerosol formation in both chamber and field studies. Aerosol composition measurements are also used to theoretically estimate the water-uptake behavior and ability to nucleate cloud droplets of atmospheric aerosol; these estimates are compared with in-situ airborne measurements. Common to all studies presented is the use of online aerosol mass spectrometry, a technique with high time resolution and minimal artifacts.
Chemical mechanisms involved in particle formation from the photooxidation of isoprene were explored in chamber studies using both online and offline mass spectrometry. The yield of aerosol and the nature of oliogmers formed was found to depend on the NOx concentration. Peroxides were found to be important under low-NOx conditions while under high-NOx conditions the majority of the particulate mass was found to derive from reaction products of methacrolein.
Particle formation from photooxidation of aliphatic amines was shown to be a feasible route of secondary organic aerosol formation in the atmosphere. Chamber studies at low relative humidity demonstrated that particle formation is primarily the result of acid-base reactions between amines and nitric or sulfuric acid, though diverse oxidized organic compounds are also formed. Thermodynamic calculations show that certain amines can compete with ammonia to form aminium salts at atmospherically relevant concentrations. An airborne field study near a major bovine source in the San Joaquin Valley, CA gave evidence of particulate amine formation in the atmosphere.
The composition of particulate emissions from ships was studied during a joint shipboard and airborne field project in the Eastern Pacific. Particulate emissions were found to contain significantly higher levels of organic material than accounted for in current inventories. Observed hydrophobic organic material is concentrated in smaller particles and acts to suppress hygroscopic growth and activity of ship-exhaust particles as cloud condensation nuclei.
Ongoing research involves quantifying the impact of reactions within cloud droplets on the organic composition of aerosols. A recently completed field campaign investigated the role of particle chemistry in determining if aerosols can act as ice crystal nuclei.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/0ZWE-9K94, author = {Chen, Wei-Ting}, title = {I. Global Simulations of Interactions between Aerosols and Future Climate and II. Sensitivity of Multiangle Imaging to the Optical and Microphysical Properties of Biomass Burning Aerosols}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/0ZWE-9K94}, url = {https://resolver.caltech.edu/CaltechETD:etd-12182008-174607}, abstract = {To understand the interaction between aerosols and climate, equilibrium simulations with a general circulation model are carried out in Part I to study the effects of future climate change on aerosol distributions, as well as the climate responses to future aerosol changes. The predicted warmer climate induced by carbon dioxide modifies the climate-sensitive emissions, alters the thermodynamic partitioning, and enhances wet removal of the aerosols. The direct radiative perturbations of aerosols, and the modification of clouds by aerosols can potentially change the temperature distribution, the hydrological cycle, and the atmospheric circulation; the pattern of climatic impacts from aerosols are differentiated from those of anthropogenic greenhouse gases. In Part II, the aerosol retrieval algorithm of the remote sensing instrument, the Multi-angle Imaging SpectroRadiometer (MISR), is assessed for the retrieval of biomass burning aerosols. By comparisons with coincident ground measurements and theoretical sensitivity tests, specific refinements to particle and mixture properties assumed in the algorithm for biomass burning aerosols are proposed. Representative case studies confirm the theoretical results and underline the key role of surface characterization in the remote sensing of aerosols.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/FMCM-4Q81, author = {Sorooshian, Armin}, title = {Aerosol Composition and Hygroscopicity Studies: Instrument Development/Characterization, Ambient and Laboratory Measurements, and Modeling}, school = {California Institute of Technology}, year = {2008}, doi = {10.7907/FMCM-4Q81}, url = {https://resolver.caltech.edu/CaltechETD:etd-05072008-174726}, abstract = {
Aerosols influence climate by altering the global energy balance via scattering and absorbing solar radiation (direct effects), and by their effect on the reflectance of clouds and occurrence of precipitation (indirect effects). Aerosols also influence biogeochemical cycles, lead to diminished environmental visibility, and harm human health. This thesis focuses on advancing knowledge of critical properties, specifically composition and hygroscopicity, which govern the role of aerosols in climatic and environmental change. The methods used in this work include a combination of instrument development/characterization, ambient and laboratory measurements, and modeling.
An instrument was developed to quantify the water-soluble composition of aerosols. The particle-into-liquid sampler (PILS) grows ambient particles into droplets that grow sufficiently large to be collected by inertial impaction. After being collected in vials, the liquid sample can be analyzed with a variety of analytical methods including ion chromatography. Results from characterization tests are presented, which summarize instrument accuracy, precision, size and time resolution, and uncertainties. An instrument model was developed to simulate operation of the PILS; the model considers plumbing transmission efficiencies, droplet growth, mixing effects, and volatilization losses. Model predictions and measurements are compared and are shown to exhibit good agreement.
A second instrument, termed the differential aerosol sizing and hygroscopicity spectrometer probe (DASH-SP), was developed to quantify aerosol hygroscopic growth and refractive index. This technique employs size classification of dry aerosol particles, equilibrates the classified particles to multiple relative humidities, and then measures the sizes of the grown particles using optical particle counters. Similar to the PILS, results from an extensive set of characterization test are presented. DASH-SP measurements of growth factor for various inorganic and organic acid salts are reported and compared to thermodynamic predictions.
Airborne aerosol measurements from four separate field campaigns are presented. The main topics of investigation from the ambient experiments include the following: (1) in-cloud production of secondary organic aerosol; (2) a characterization of the sources and character of water-soluble aerosol composition during the 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS); and (3) a comprehensive airborne characterization of aerosol from a massive bovine source.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/3M7R-9620, author = {Tong, Chinghang}, title = {Thermodynamic Modeling of Organic Aerosol}, school = {California Institute of Technology}, year = {2008}, doi = {10.7907/3M7R-9620}, url = {https://resolver.caltech.edu/CaltechETD:etd-09172007-160334}, abstract = {
Modeling atmospheric aerosols containing a large organic fraction with unknown chemical composition and properties has been a constant challenge. The dissertation focuses on the theoretical treatment of the thermodynamic equilibrium of atmospheric aerosol involving organic species.
We present a vapor pressure estimation method, based on quantum chemistry methods, to predict the liquid vapor pressure, enthalpies of vaporization, and heats of sublimation of atmospheric organic compounds. Predictions are compared to literature data, and the overall accuracy is considered satisfactory given the simplicity of the equations. Quantum mechanical methods were also used to investigate the thermodynamic feasibility of various acid-catalyzed aerosol-phase heterogeneous chemical reactions. A stepwise procedure is presented to determine physical properties such as heats of formation, standard entropies, Gibbs free energies of formation, and solvation energies from quantum mechanics, for various short-chain aldehydes and ketones. Equilibrium constants of hydration reactions and aldol condensation are then reported; predictions are in qualitatively agreement with previous studies. We have shown that quantum methods can serve as useful tools for first approximation, especially for species with no available data, in determining the thermodynamic properties of multifunctional oxygenates.
We also present an atmospheric aerosol phase equilibrium model to determine the aerosol phase equilibrium of aqueous systems. Phase diagrams for a number of organic/water systems characteristic of both primary and secondary organic aerosols are computed. Effects of organics on the deliquescence behavior of electrolytes are also shown in the inorganic/organic/water phase diagrams.
Finally, we evaluate the performance of four recent activity coefficient models developed for inorganic-organic-water mixtures typical of atmospheric aerosols. Based on the comparison on water activities, it is found that models that include ion-organic mixture parameters (referred to as coupled models) do not necessarily produce more accurate predictions than those models that utilizes additive approaches (referred to as decoupled models). Since the chemical composition and physical properties of the organic fraction is largely unknown, the additive approaches of the decoupled models are more feasible than the coupled model.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/XFEN-5Q08, author = {Ng, Nga Lee}, title = {Chamber Studies of Secondary Organic Aerosol Formation}, school = {California Institute of Technology}, year = {2007}, doi = {10.7907/XFEN-5Q08}, url = {https://resolver.caltech.edu/CaltechETD:etd-05242007-210716}, abstract = {
Atmospheric oxidation of volatile organic compounds leads to the formation of secondary organic aerosol (SOA). Laboratory chambers provide a controlled environment for investigating aerosol formation and evolution. This thesis presents results on aerosol formation from a wide range of parent organic compounds under a variety of experimental conditions.
The effect of particle-phase acidity on aerosol formation is explored in a series of alkene ozonolysis experiments. Oligomeric species are detected regardless of the particle-phase acidity, indicating the ubiquitous existence of particle-phase reactions. As acidity increases, larger oligomers are formed more abundantly and aerosol yields also increase. Volatile organic compounds generally not considered to be SOA precursors, including isoprene and glyoxal, have been shown to lead to aerosol formation. Uptake of glyoxal into particles is evidence that small molecules can potentially produce aerosol via reactive absorption. Although there is strong evidence that heterogeneous reactions play an important role in SOA formation, the detailed mechanisms remain poorly understood. In a comprehensive study on aerosol formation from biogenic hydrocarbons, it is found that data on aerosol growth as a function of the amount of hydrocarbon reacted provide important insights into the general aerosol formation mechanisms by identifying rate-determining steps and whether SOA is formed from first- or second-generation products.
The mechanism of aerosol formation by isoprene is specifically investigated over a range of NOx concentrations. Aerosol yields are found to decrease substantially with increasing NOx. The same NOx dependence is observed for monoterpenes ([alpha]-pinene), as well as aromatic hydrocarbons (m-xylene, toluene, and benzene). It is suggested that peroxy radical chemistry plays the central role in the observed NOx dependence. The NOx dependence for larger compounds is, however, different from that of isoprene, monoterpenes, and aromatics. For sesquiterpenes such as longifolene and aromadendrene, aerosol yields increase with increasing NOx concentration. The reversal of the NOx dependence of SOA formation for the sesquiterpenes appears to be the result of formation of relatively nonvolatile organic nitrates, and/or the isomerization of large alkoxy radicals that leads to less volatile products.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/5647-T777, author = {Henze, Daven Ker}, title = {Forward and Inverse Analysis of Chemical Transport Models}, school = {California Institute of Technology}, year = {2007}, doi = {10.7907/5647-T777}, url = {https://resolver.caltech.edu/CaltechETD:etd-05312007-133239}, abstract = {Assessing the discrepancy between modeled and observed distributions of aerosols is a persistent problem on many scales. Tools for analyzing the evolution of aerosol size distributions using the adjoint method are presented in idealized box model calculations. The ability to recover information about aerosol growth rates and initial size distributions is assessed given a range of simulated observations of evolving systems. While such tools alone could facilitate analysis of chamber measurements, improving estimates of aerosol sources on regional and global scales requires explicit consideration of many additional chemical and physical processes that govern secondary formation of atmospheric aerosols from emissions of gas-phase precursors. The adjoint of the global chemical transport model GEOS-Chem is derived, affording detailed analysis of the relationship between gas-phase aerosol precursor emissions (SOx, NOx, and NH3) and the subsequent distributions of sulfate - ammonium - nitrate aerosol. Assimilation of surface measurements of sulfate and nitrate aerosol is shown to provide valuable constraints on emissions of ammonia. Adjoint sensitivities are used to propose strategies for air quality control, suggesting, for example, that reduction of SOx emissions in the summer and NH3 emissions in the winter would most effectively reduce non-attainment of aerosol air quality standards. The ability of this model to estimate global distributions of carbonaceous aerosol is also addressed. Based on new yield data from environmental chamber studies, mechanisms for incorporating the dependence of secondary organic aerosol (SOA) formation on NOx concentrations are developed for use in global models. When NOx levels are appropriately accounted for, it is demonstrated that sources such as isoprene and aromatics, previously neglected as sources of aerosol in global models, significantly contribute to predicted SOA burdens downwind of polluted areas (owing to benzene and toluene) and in the free troposphere (owing to isoprene).}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/KQ8A-2Q95, author = {Varutbangkul, Varuntida}, title = {Ambient and Laboratory Studies of Aerosol Size Distributions and Hygroscopicity}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/KQ8A-2Q95}, url = {https://resolver.caltech.edu/CaltechETD:etd-05242006-175333}, abstract = {The optical properties, health effects, atmospheric lifetime, and climate impact of ambient aerosols are influenced directly by their size distribution, chemical composition, and phase. The aerosol hygroscopicity, which is also a function of composition, governs the size and phase changes of these particles when subjected to varying ambient relative humidities (RH). This thesis presents results from a wide variety of studies involving laboratory and ambient measurements of aerosol size distributions and water uptake properties in the subsaturated regime. Time evolutions of particle size and hygroscopic growth were investigated for various secondary organic aerosol (SOA) systems generated in a smog chamber from ozonolysis of cycloalkenes and photooxidation of biogenic terpenes. SOA yields were measured at various initial parent hydrocarbon concentrations and correlated with the structure of the parent compound. The amount of water uptake of the aerosol at a reference RH was found to inversely correlate with the SOA yield. The hygroscopicity of many atmospherically relevant pure organic species was also studied using an unconventional particle generation scheme employing a nonaqueous solution. Experimental results were compared with predictions from an equilibrium thermodynamic model. In these works, organic aerosols are shown to exhibit complex hygroscopic growth, dependent on the particle chemistry, phase, and surrounding RH. Implications of the experimental techniques used on the observation of particle growth, deliquescence, and efflorescence are discussed. A number of other studies incorporating aircraft-based measurements of aerosol size distributions and hygroscopicity with other ambient measurements into various cloud microphysics models are also presented.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/FEP1-P208, author = {Rissman, Tracey Alayne}, title = {Theory, Field Measurements, and Laboratory Experiments Concerning the Cloud Condensation Nucleus Properties of Organic and/or Insoluble Aerosol Components}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/FEP1-P208}, url = {https://resolver.caltech.edu/CaltechETD:etd-05262006-115411}, abstract = {Predicting how the future climate of Earth will change as a result of increasing human emissions is one of the greatest problems facing science today. The earth’s climate is the result of a delicate balance between incoming and outgoing radiation. Anthropogenic emissions of aerosol particles into the atmosphere have the potential to affect the earth’s climate in significant ways through both direct and indirect effects on the earth’s radiative balance. One of the largest uncertainties in aerosol radiative forcing is associated with the relationship between atmospheric aerosols and cloud formation, properties, and lifetime. Clouds form by water condensing on small particles (aerosols) in the air (referred to as cloud condensation nuclei, or CCN), and how the increasing levels of atmospheric particles will affect Earth’s clouds and its hydrologic cycle represents one of the key problems in the science of climate. Through theoretical, field, and laboratory investigations, the results presented here reinforce the importance of atmospheric aerosol chemical composition in determining the ability of an aerosol particle to act as a CCN. A study that incorporates surface tension and limited solubility effects, especially of organic compounds, in parameterizations of cloud droplet activation indicate that these chemical effects can rival those of the meteorological environment. An inverse CCN/aerosol closure study of field measurements indicates that assumptions of simple chemistry and mixing state in the interpretation and analysis of field cloud condensation nuclei (CCN) measurements may not necessarily be sufficient and/or realistic, depending heavily on the location of the field study. Properties of organic compounds, such as functional groups, extent of dissociation, and solubility were found to influence the CCN activity of the compounds in laboratory experiments with pure organic aerosols. However, the importance of careful planning of laboratory experiments, in consideration of the properties of the organic compounds, was reinforced and results were carefully interpreted to avoid experimental bias in the conclusions.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/d2ff-ad43, author = {Chung, Serena Hsin-Yi}, title = {Global Distribution, Radiative Forcing, and Climate Impact of Carbonaceous Aerosols}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/d2ff-ad43}, url = {https://resolver.caltech.edu/CaltechETD:etd-02012005-131605}, abstract = {This thesis is motivated by the need to better understand and quantify the climate effects of carbonaceous aerosols, i.e., black carbon (BC) and organic carbon (OC). Global three-dimensional distribution of carbonaceous aerosols is simulated online in a general circulation model (GCM). The carbonaceous aerosol model includes primary BC, primary OC, five groups of biogenic volatile organic compounds (BVOCs), and fourteen semi-volatile products of BVOC oxidation by O3, OH, and NO3, which condense to form secondary organic aerosols (SOAs) based on an equilibrium partitioning model. Human activities since the preindustrial period are predicted to have increased global burdens of BC and OC by an order of magnitude and almost tripled the SOA production rate. Based on an older emission inventory for BC, the direct radiative forcing of increased atmospheric BC burden is estimated to warm the atmosphere by 0.51 to 0.8 W m-2, depending on how BC is mixed with other tropospheric aerosols. For OC, the estimated anthropogenic direct radiative forcing at top of the atmosphere (TOA) is -0.1 to -0.2 W m-2, depending on the water-uptake property of OC. When BC, OC and sulfate are combined, the estimated direct radiative forcing at TOA is -0.39 to -0.78 W m-2. Using an updated emission inventory, direct radiative forcing of anthropogenic BC at TOA is estimated to be +0.33 and +0.6 W m-2, for BC mixed externally and internally with present-day level of sulfate, respectively. Using a GCM coupled to a mixed-layer ocean model, these estimated forcings for BC are predicted to warm surface air temperature by 0.2 to 0.37 K. The temperature increase is the largest over northern high latitutdes during winter and early spring. Even though the predicted global-averaged warming due to BC is less than that of greenhouse gases, significant regional differences do exist, such as substantial warming in central and eastern Russia predicted for BC. In addition to temperature increase, direct radiative forcing of anthropogenic BC is also predicted to lead to a change in the hydrological cycle by shifting the intertropical convergence zone northward.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/H3BE-W731, author = {Lu, Miao-Ling}, title = {Large-Eddy Simulations of Marine Cumulus and Stratocumulus and Study of Humidity Halos and Aerosol Indirect Radiative Effects}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/H3BE-W731}, url = {https://resolver.caltech.edu/CaltechETD:etd-03172005-152448}, abstract = {The first part of the thesis focuses on understanding the characteristics of the cloud humidity halos, the significant enhancements in humidity around cumulus clouds, and their radiative impacts. The simulated cloud and halo properties were compared with the measurement data from the aircraft campaign – “Cloud Halo” conducted in Hawaii, 2001. The cloud halo spatial distribution, the relationship with the vertical wind shear, and the temporal variation with cloud lifetime are explored by the 3D numerical simulations. Results suggest that halos are formed as a result of evaporation of cloudy air or detrainment of high humidity by the turbulent mixing in the cloud lateral boundary regions, or simply due to cloud dissipation. Humidity halos absorb the incoming sunlight, warm the atmosphere, and cool the surface. The 3D radiative transfer model results show that the SW column absorption (surface - 3.4 km) enhanced by the halo is 1.32 W m-2 averaged over the cloud mature and dissipating stages, a 1.3% change in the absence of the halo, for the cloud of the Cloud Halo experiment.
The second part of the thesis is to understand the first and second aerosol indirect effects by conducting 98 3D LES simulations of the marine stratocumulus clouds - under various conditions of nighttime and daytime, SST (sea surface temperature), aerosol number concentration, and large-scale subsidence rate. Based on the statistical analysis, the cloud optical depth is found to be positively correlated with the cloud liquid water path, which is mainly regulated by large-scale subsidence and SST. The regression analysis shows that the second aerosol indirect effect is more pronounced in clean than polluted clouds and that it increases (reduces) the cloud optical depth for the same relative change in aerosol number concentration than considering the Twomey (first indirect) effect alone. Introducing a small amount of giant sea salt aerosols into the simulation lowers the number of cloud droplets activated and initiates precipitation for non-drizzling clouds. It also results in a reduction of cloud optical depth by 3% - 77% for heavily drizzling cases.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/1YNP-QQ95, author = {Bahreini, Roya}, title = {Studies with the Aerosol Mass Spectrometer}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/1YNP-QQ95}, url = {https://resolver.caltech.edu/CaltechETD:etd-05032005-180939}, abstract = {Fast time-response of the Aerodyne Aerosol Mass Spectrometer (AMS) makes it a well-suited instrument for ambient field measurements. On the other hand, laboratory chamber experiments provide the opportunity to study a specific system in a more controlled environment. The goal of this thesis is to provide a summary of laboratory and field measurements using the AMS.
During laboratory chamber photooxidation experiments of diiodomethane (CH2I2), particle nucleation was observed at CH2I2 concentrations down to 15 ppt, which is comparable to the total gas-phase iodine species measured at coastal areas. Iodine oxides and oxyacids were observed in the aerosol mass spectra obtained by the AMS, consistent with the known gas-phase chemistry.
Airborne measurements by the AMS during the ACE-Asia field study revealed that the non-refractory submicron aerosols in the pollution layers of the boundary layer up to 3700 m were mainly composed of sulfate, ammonium, and organics. These pollution plumes originated primarily from urban and industrial areas of China and Korea.
The laboratory chamber experiments of oxidation of cycloalkenes, terpenes, and m-xylene provided the opportunity to study the Secondary Organic Aerosol (SOA) forming potential, i.e., yield, and determine SOA effective density and chemical composition. Evidence of acid-catalyzed heterogeneous chemistry in the ozonolysis of a-pinene was observed since the total AMS organic mass during the experiments with acidic seed particles had a greater contribution of higher molecular weight fragments. The mixtures of SOA compounds produced from similar precursors studied resulted in broadly similar AMS mass spectra. Thus, fragmentation patterns observed for biogenic vs. anthropogenic SOA can be potentially useful in determining the sources of ambient SOA.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/TGKK-QB38, author = {VanReken, Timothy Mark}, title = {Understanding the Relationship between Aerosols and Clouds: Field Investigations and Instrument Development}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/TGKK-QB38}, url = {https://resolver.caltech.edu/CaltechETD:etd-11142003-134303}, abstract = {The research presented in this thesis is part of the ongoing effort to better understand the role of atmospheric aerosols in the development of clouds. Cloud condensation nuclei (CCN) are the subset of the aerosol population that can activate and grow into cloud droplets under suitable atmospheric conditions. The supersaturation at which a given CCN will activate is dependent on the particle’s size and composition, but the details of the relationship are not completely understood. CCN observations from the CRYSTAL-FACE (Cirrus Regional Study of Tropical Anvils and Cirrus Layers- Florida Area Cirrus Experiment) field campaign are presented in Chapter 2. These measurements are compared to predictions based on measured aerosol size distributions with an assumed chemical composition to determine whether activation theory is sufficient to describe what is observed. The analysis indicates that, in cases like those included in the study, CCN concentrations can be accurately predicted from the size distribution even in the absence of detailed chemical compositional data.
A case study is described in Chapter 3 to demonstrate the potential importance of anthropogenic aerosols in the development of clouds. During a CRYSTAL-FACE flight, an aerosol plume was encountered in the boundary layer near the base of a large mixed-phase convective cloud. Evidence suggests that an oil-burning power plant south of Miami was the likely source of the plume. The convective cloud was probed at higher altitudes, and a spatial gradient was observed in the ice particle concentrations. The evidence linking the plume in the boundary layer to the upper-level trends is inconclusive, but worthy of further study.
The measurement of CCN in the atmosphere is difficult, and improved instrumentation would significantly improve our ability to obtain the detailed information necessary to understand the relationship between aerosols and clouds. The concept for an improved CCN spectrometer is outlined in Chapter 4; this new design would expand the resolvable range of supersaturations for which data can be obtained. The dependence of the instrument’s performance on various design parameters is evaluated, and a configuration is proposed that would be a significant improvement over currently available instrumentation.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/ZA39-HJ32, author = {Bhave, Prakash Viththal}, title = {Air Pollution at the Single-Particle Level: Integrating Atmospheric Measurements with Mathematical Models}, school = {California Institute of Technology}, year = {2003}, doi = {10.7907/ZA39-HJ32}, url = {https://resolver.caltech.edu/CaltechETD:etd-05252003-091827}, abstract = {Particulate air pollution is of growing concern in the United States and around the world. Elevated concentrations of aerosols (solid particles and liquid droplets suspended in air) are correlated with increased cases of lung cancer, cardiopulmonary disorders, and human mortality. A detailed understanding of the size, chemical composition, and concentration of atmospheric particles is needed to assess their effects on human health, as well as on regional visibility and global climate. One can acquire such knowledge through direct measurements, or by utilizing mathematical air quality models. New and innovative instruments allow us to measure the size and composition of individual particles, rather than to infer aerosol chemical properties from bulk particulate matter samples. Concurrently, air quality models have been developed to numerically simulate the emissions of discrete particles, and their transport and chemical evolution in the atmosphere. This thesis focuses on how to integrate and compare measurements taken by state-of-the-science single-particle instruments with the air pollutant properties calculated using state-of-the-science mathematical models. A 1996 field experiment conducted in the Los Angeles air basin serves as the case study for this thesis research.
Comparisons of model calculations against single-particle observations identify specific areas where model improvements are needed, and also identify important areas for future instrumental development. These comparisons contribute to our understanding of atmospheric pollution at the single-particle level, and ultimately, may provide tremendous value to policy makers who are seeking least-cost solutions to urban and regional air quality problems. After presenting initial comparisons of single-particle measurements and model results, efforts to quantify and categorize the single-particle chemical composition data are described. The quantitatively reconstructed single-particle measurements are compared with mathematical model calculations of the atmospheric aerosol mixing characteristics. Finally, an example is presented of how the model and measurement combination enhance our ability to reduce particulate pollution in the air we breathe.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Cass, Glen Rowan}, } @phdthesis{10.7907/GNFA-V973, author = {Wang, Jian}, title = {Instrument Development and Characterization of Atmospheric Aerosol Physical Properties Through Airborne Measurement}, school = {California Institute of Technology}, year = {2003}, doi = {10.7907/GNFA-V973}, url = {https://resolver.caltech.edu/CaltechETD:etd-06092005-132829}, abstract = {Atmospheric aerosol has significant impact on climate. It influences radiative transfer by scattering and absorbing sunlight and by changing the microphysical structure, lifetime, and amount of the clouds. Due to its short lifetime, the spatial and temporal distributions of tropospheric aerosol are highly inhomogeneous. Aircraft have proven to be an effective platform in characterizing the atmospheric aerosol. To maximize the potential and to reduce the artifacts associated with aircraft sampling, both improvements in existing instruments and developments of new instruments are required.
To increase the speed of submicron aerosol size distribution measurements, a mixing condensation nucleus counter (MCNC) has been developed. By carefully designing the mixing chamber and condenser, the response time of the MCNC was significantly reduced. Our experiments demonstrate that a differential mobility analyzer (DMA) coupled with the developed MCNC can measure complete aerosol size distributions in as little as 2 seconds.
The effects of bends and elbows on the diffusional losses of particle in nanometer range were studied. The results show that the effect of bends and elbows on particle diffusion loss is significant, and for Reynolds number smaller than 250, the enhancement of diffusion losses due to bends and elbows is sensitive to both the relative orientations of the bends and elbows and the lengths of straight tubing between them. Because of this sensitivity, direct calibration or simulation is required to assess nanoparticle penetration efficiencies for any flow system containing bends or elbows at low Reynolds number. When the Reynolds number exceeds 250, the enhancement is insensitive to the actual flow configurations. Experimental results are presented, which can be used for design of aerosol flow systems at Reynolds number larger than 250.
To minimize the airborne sampling bias, an advanced differential mobility analyzer (DMA) system for measuring submicron aerosol size distribution at ambient relative humidity, with special attention to implementation on aircraft, has been developed. The system includes an active RH controller, a cylindrical differential mobility analyzer (CDMA), and a condensation nucleus counter. A cascade controller consisting of two PID modules maintains the RH inside the CDMA at ambient RH by actively adding or removing water vapor from the air stream. The flows are controlled with feedback PID controllers, which compensate for the variation of pressure as the aircraft changes altitude. This system was integrated into the CIRPAS Twin Otter aircraft and used to measure ambient size distributions during the Aerosol Characterization Experiment-Asia (ACE-Asia), carried out from March to May, 2001, in Japan.
During the ACE-Asia experiment, the above DMA system, together with an aerodynamic particle sizer (APS), was used to characterize aerosol size distributions in East Asia during 19 flights on board of CIRPAS Twin Otter aircraft. Besides providing the aerosol size characteristics, the data were combined with chemical composition and aerosol mixing state measurements to predict the vertical profile of aerosol extinction, which was compared with those derived from simultaneous direct measurements of aerosol optical depth by the NASA 14-channel sunphotometer. Agreement between the predicted and derived aerosol extinction varies for different scenarios, but the discrepancies were generally within the calculated uncertainties.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/S02W-0573, author = {Nenes, Athanasios}, title = {Toward an Understanding of the Indirect Climatic Effect of Aerosols}, school = {California Institute of Technology}, year = {2003}, doi = {10.7907/S02W-0573}, url = {https://resolver.caltech.edu/CaltechETD:etd-06022003-074653}, abstract = {This thesis is motivated by the need to improve our understanding of the aerosol indirect effect. The activation of aerosol into cloud droplets has been extensively studied, using a comprehensive numerical cloud droplet activation model. Using this model, the effect of water vapor mass transfer limitations on the cloud droplet activation process was first studied; it was found that mass transfer limitations are important for activation under polluted conditions. The potential effect of (currently unresolved) “chemical effects” on cloud droplet number (e.g., the presence soluble gases and surface active species) was also assessed. It was seen that small changes in aerosol and gas-phase composition can have a strong effect on cloud droplet number, and should be included in future estimates of the aerosol indirect effect.
A comprehensive aerosol activation parameterization was developed for use in a first-principle assessment of the aerosol indirect effect. This new parameterization introduces the concept of “population splitting,” in which the droplets are separated into two populations, each with its own growth characteristics. The effect of water vapor mass transfer limitations is explicitly introduced. The parameterization allows for treatment of chemical effects. The new parameterization shows excellent and robust agreement with a detailed numerical parcel model.
Previously unidentified mechanisms of aerosol-cloud interactions were also explored. Aerosol, when it contains black carbon, can absorb light and heat the droplet enough to affect its activation behavior. This can affect cloud properties in numerous and counterintuitive ways; black carbon heating can dissipate clouds, but may also increase cloud lifetime (and lead to a climatic cooling) by decreasing the probability of drizzle formation.
Finally, the performance of instruments used for measuring the concentration of cloud condensation nuclei (CCN) was assessed. Each design exhibits different limitations and sources of uncertainty, but all show decreased ability to measure CCN of low critical supersaturation (<0.1%). The performance of the instrumentation can be very sensitive to the operating conditions. Therefore, an in-depth theoretical understanding of the instrumentation is necessary; otherwise, CCN measurements may be subject to considerable uncertainty.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/E2SZ-YX06, author = {Liao, Hong}, title = {Interactions between Tropospheric Chemistry and Aerosols in a Unified GCM Simulation}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/E2SZ-YX06}, url = {https://resolver.caltech.edu/CaltechTHESIS:05032011-083245119}, abstract = {Anthropogenic changes in the atmospheric abundances of tropospheric ozone and aerosols make significant contributions to climate change. In turn, climate change affects the abundances of ozone and aerosols, resulting in complicated feedbacks. To move toward understanding interactions and feedbacks among tropospheric chemistry, aerosol formation, and climate change, a unified tropospheric chemistry-aerosol model is developed within the Goddard Institute for Space Studies general circulation model. The model includes a detailed simulation of tropospheric ozone-NO_x-hydrocarbon chemistry and a thermodynamic representation of sulfate/nitrate/ammonium aerosols. Two-way coupling between aerosols and chemistry provides consistent chemical fields for aerosol dynamics and aerosol mass for heterogeneous processes and calculations of gas-phase photolysis rates. Although the current version of the unified model does not include prognostic treatments of black carbon, organic carbon, and mineral dust aerosols, we include effects of these particles on photolysis and heterogeneous processes by using three-dimensional off-line fields. The unified model is applied to examine interactions between tropospheric chemistry and aerosols. This dissertation is the first step in the development of a fully-coupled climate/chemistry/aerosol model.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/10CM-8W55, author = {Adams, Peter Jonathan}, title = {Representing Tropospheric Aerosols and Their Climatic Effects in Global Models}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/10CM-8W55}, url = {https://resolver.caltech.edu/CaltechTHESIS:10122010-125450691}, abstract = {In order to better understand and quantify the direct and indirect effect of aerosols on climate, an earlier general circulation model (GCM) simulation of tropospheric sulfate has been extended by incorporating aerosol thermodynamics and microphysics. The thermodynamic simulation allows the prediction of nitrate, ammonium, and aerosol water concentrations. It is estimated that nitrate contributes as much to total aerosol mass as sulfate on regional scales in parts of Europe and North America. The direct radiative forcing associated with the sulfate-nitrate-ammonium-water mixture is estimated to be —1.14 W M^(-2) for the present day. Based on a future emissions scenario, this could increase to as much as —2.13 W^(-2) by the year 2100, an increase that results from increased nitrate concentrations. Although currently a minor contributor to aerosol direct radiative forcing, nitrate is predicted to exceed sulfate in its contribution by the end of the century for this emissions scenario. It is also found that direct radiative forcing estimates are highly sensitive to aerosol behavior at relative humidity above 90%, highlighting the shortcomings of global models in their treatment of aerosol water uptake under partly cloudy conditions. The microphysical simulation allows the prediction of tropospheric aerosol number concentrations and size distributions, key parameters in determining the indirect effect of aerosols on clouds. A two-moment sectional algorithm is used to simulate the microphysical processes of condensation/evaporation and coagulation. It has been tested by performing a simulation of sulfate microphysics. Predicted aerosol number concentrations generally agree with observations to within 25%. The microphysical simulation also reproduces key features of the tropospheric aerosol such as increasing number concentrations with altitude and land-sea contrasts in cloud condensation nuclei concentrations. It is found that there are important uncertainties in the source rates of new particles to the atmosphere, whether from in situ nucleation or emissions of particulates, that can significantly impact predicted aerosol number and cloud condensation nuclei concentrations.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/22w2-vk68, author = {Cocker, David Rea}, title = {Chamber investigations of secondary organic aerosol formation}, school = {California Institute of Technology}, year = {2001}, doi = {10.7907/22w2-vk68}, url = {https://resolver.caltech.edu/CaltechETD:etd-01232007-072920}, abstract = {Hydrocarbons in the atmosphere undergo oxidation that can lead to the formation of semi-volatile products. These products undergo gas-to-particle conversion to form secondary organic aerosol (SOA). Reaction chambers provide a controlled environment which gas-to-particle conversion is investigated. First, an extensive investigation into the aerosol forming potential of 14 biogenic hydrocarbons is reported. Traditionally, chamber experiments have been performed at relative humidity levels such that the aerosol investigated is water-free. However, atmospheric conditions are typically such that ambient aerosol contains water. A new facility to improve measurement of SOA formation under humid conditions is described. A comprehensive study on how the presence of water affects gas-to-particle partitioning in the alpha-pinene ozonolysis and m-xylene and mesitylene photooxidation systems is reported. The diurnal trends in the hygroscopic nature of Pasadena, CA, aerosol is reported for late summer, 1999. Presented are additional investigations into the identification of products resulting from ozonolysis of alpha-pinene, beta-pinene, sabinene, Delta^3-carene, and cyclohexene. A field campaign to identify similar monoterpene oxidation products in a forest environment is presented. Finally, an estimate of the global aerosol burden from biogenic hydrocarbons is provided.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/2F9Q-1772, author = {Griffin, Robert John}, title = {Experimental and computational studies of secondary organic aerosol formation}, school = {California Institute of Technology}, year = {2000}, doi = {10.7907/2F9Q-1772}, url = {https://resolver.caltech.edu/CaltechETD:etd-12222006-125228}, abstract = {Organic species are important constituents of tropospheric particulate matter in remote, rural, and urban areas. Such aerosol can be primary (emitted in the particle phase as solids or liquids) or secondary (formed in situ as condensable vapors) in nature. Secondary organic aerosol (SOA) is formed when products resulting from the gas-phase oxidation of a parent organic species partition to the particle phase. This partitioning can occur via condensation onto existing inorganic aerosol (heterogeneous-heteromolecular nucleation), absorption into an existing organic aerosol, dissolution to the aerosol aqueous phase, or homogeneous-heteromolecular nucleation.
SOA yield is defined as the amount of SOA formed per the amount of a parent organic species that is oxidized. This yield depends functionally on stoichiometric and partitioning coefficients for each of the oxidation products formed and the total amount of organic aerosol mass available to act as absorptive media. Appropriate yield parameters are developed for a series of parent organics using smog chamber experiments. The effects of parent organic structure and the oxidizing species on SOA yield are also examined during the smog chamber experiments. Such yield parameters are used to model SOA formation from the oxidation of biogenic organic species on a global and annual scale. Yield parameters can also be used to define a new concept, the incremental aerosol reactivity for parent organic species, which is a convenient way of ranking parent organics in terms of their SOA-forming potentials.
Efforts to improve the simulation of SOA formation in the California Institute of Technology three-dimensional air quality model are also described. The Caltech Atmospheric Chemistry Mechanism was designed to predict concentrations of the highly functionalized secondary organic oxidation products capable of leading to SOA. A module that treats formation of SOA thermodynamically is used to predict the distribution of these products between the gas- and aerosol-phases. The new mechanism and thermodynamic module will used to simulate a smog episode that occurred in 1993 in the South Coast Air Basin of California.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/RY6B-CY09, author = {Chuang, Patrick Yung-Shie}, title = {Experimental and theoretical studies of cloud condensation nuclei}, school = {California Institute of Technology}, year = {1999}, doi = {10.7907/RY6B-CY09}, url = {https://resolver.caltech.edu/CaltechETD:etd-02082008-164553}, abstract = {Cloud condensation nuclei (CCN), the subset of atmospheric aerosol that nucleate cloud droplet formation, are a key component in cloud formation, and are an important factor in controlling climatically-relevant cloud properties such as cloud albedo, cloud lifetime, and precipitation rate.
A CCN instrument that satisfies the constraints for small aircraft operation — minimum weight, volume, and power consumption, good robustness, and high frequency measurement — was constructed. The measurement technique was based on that of Hudson (1989) because it reportedly offered the ability to make measurements of CCN at all supersaturations simultaneously at high frequency and with good counting statistics. Modelling studies, and laboratory and field measurements, subsequently showed that this technique exhibits poor sensitivity. The CCN instrument was also studied in fixed supersaturation mode, where it is able to accurately measure CCN concentration at a fixed supersaturation, whose value ranges from 0.1 and 2%.
The CCN instrument was flown during the 2nd Aerosol Characterization Experiment (ACE-2). The data were reported at a fixed supersaturation of 0.1%. Intercomparison of these measurements with those on two other aircraft shows good agreement. A sublinear relationship between measured CCN concentration and that predicted from aerosol size distribution and chemical composition measurements, Nmeas ~ N0.72pred. In-situ measurements of below-cloud CCN concentration and cloud droplet number concentration are compared. The results are in agreement with model predictions and with previous studies. Cloud droplet concentration is predicted to depend on the CCN spectrum and updraft velocity.
Cloud droplet activation has often been assumed to be reasonably described by an equilibrium model. The error in calculated cloud droplet number concentration due to the influence of condensational growth kinetics was shown to be significant for some conditions. Such errors are estimated to lead to overestimates of indirect radiative climate forcing on the order of Wm-2. Accurate interpretation of measured CCN concentration may require consideration of activation kinetics associated with CCN instruments.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/jwwk-0n13, author = {Kusaka, Isamu}, title = {Molecular theory of vapor phase nucleation}, school = {California Institute of Technology}, year = {1998}, doi = {10.7907/jwwk-0n13}, url = {https://resolver.caltech.edu/CaltechETD:etd-01242008-085938}, abstract = {
An attempt has been made to establish the foundation of molecular level theory of vapor phase nucleation. We have focused on evaluating the reversible work of cluster formation and followed two major trends in this direction, namely, statistical mechanical density functional theory and molecular level simulation. We applied density functional theory to heterogeneous nucleation onto an ion. Our prime interest is to predict a sign preference of nucleation rate, which has been experimentally observed yet remained inexplicable in the classical framework. The theory indicates that asymmetry in ion-molecule interaction is directly responsible for the sign preference. The predicted sign dependence decreases as the supersaturation is increased. Our results from density functional theory agree well with the existing experimental observations. Molecular simulation offers an alternative to molecular level approach. A long-standing issue of fundamental importance in cluster simulation is the precise definition of a cluster. Thus far, all attempts of defining a cluster had introduced ad hoc criteria to determine unambiguously whether a given molecule in the system belongs to vapor or to a cluster for any instantaneous configuration of molecules. From a careful examination of the context in which a cluster should be introduced into nucleation theory, we conclude that such a criterion is unnecessary. Then, we present a new approach to cluster simulation which is free of any arbitrariness involved in the definition of a cluster. Instead, it preferentially and automatically generates the physical clusters, defined as the density fluctuations that lead to nucleation, and determines their equilibrium distribution in a single simulation. The latter feature permits one to completely bypass the computationally demanding free energy evaluation that is necessary in a conventional simulation. The method is applied first to water using the SPC/E model. We then turn to H2SO4/H2O binary system to obtain a large section of the reversible work surface. The resulting surface is markedly different from that in classical theory and indicates that the rate limiting step of stable particle formation in this system is the binary collision of the sulfuric acid hydrates.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Wang, Zhen-Gang}, } @phdthesis{10.7907/R5WB-VW19, author = {Odum, Jay Russell}, title = {Secondary Organic Aerosol Formation and Gas/Aerosol Partitioning}, school = {California Institute of Technology}, year = {1998}, doi = {10.7907/R5WB-VW19}, url = {https://resolver.caltech.edu/CaltechETD:etd-01252008-155400}, abstract = {An intensive smog chamber study has revealed that secondary organic aerosol (SOA) formation follows Raoult’s Law type gas/aerosol absorption thermodynamics. SOA formation was shown to occur via the gas/aerosol partitioning of semi-volatile, oxidation products rather than through the condensation of saturated, non-volatile products. The major consequence of this finding is that SOA yields are not constant, but rather are a function of the organic aerosol mass concentration. The theory has been used to successfully describe the aerosol formation potential of seventeen individual aromatic species, eight biogenic compounds, two different simple hydrocarbon precursor mixtures, and twelve different blends of whole gasoline vapor, in hundreds of smog chamber experiments. These results have been included in a 3-dimensional size- and chemically-resolved atmospheric chemical-transport model and used to simulate SOA formation in the South Coast Air Basin. The inherent dependence of SOA concentrations on primary organic aerosol (POA) concentrations, places strict constraints on organic and elemental carbon aerosol emissions inventories.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/y634-fw03, author = {Bowman, Frank Morales}, title = {Ozone and secondary organic aerosol formation from organic precursors}, school = {California Institute of Technology}, year = {1997}, doi = {10.7907/y634-fw03}, url = {https://resolver.caltech.edu/CaltechETD:etd-01092008-152853}, abstract = {A technique was developed to determine the amount of ozone and other secondary pollutants generated by individual organic components of atmospheric VOC/NO[subscript x] mixtures. This technique was used to investigate the chemical interactions associated with incremental reactivity calculations. It was shown that the incremental reactivity of an individual organic species is a result of changes in the ozone generated by each of the organics present. Incremental reactivities, therefore, are dependent on the nature of the VOC/NO[subscript x] mixture. Aldehydes, alkenes and reactive aromatics were found to have the highest incremental reactivities due to their behavior as radical sources, thereby increasing the rate of reaction of all available organics. Ozone and secondary aerosol formation within the South Coast Air Basin of California during the Southern California Air Quality Study (SCAQS) air pollution episode of August 27-28, 1987 were also analyzed and again the same species were shown to be the most productive compounds in the organic mixture. Less productive compounds, such as CO and alkanes, were also found to be major contributors to ozone concentrations due to their relative abundance. Eight reformulated fuel components were investigated to determine their ozone-forming potential. Most of the fuel oxygenates were found to have relatively low incremental reactivities due to their slow reaction rates and to the formation of relatively unreactive formate and acetate products.
Secondary organic aerosol formation was studied in the Caltech outdoor smog chamber and a model was developed to describe the gas-particle absorptive partitioning of semi-volatile organics. Particle deposition, nucleation and vapor transport to aerosol particles, chamber walls and deposited particles are accounted for by the model. Simulations of a pair of m-xylene/NOX experiments were performed to investigate the nature of aerosol growth. Characteristic transport times indicate that gas-particle equilibrium will typically be established quite rapidly. Additional delays in aerosol formation were shown to result when the condensing semi-volatile products are second-generation, rather than first-generation, products of a parent hydrocarbon. Within a smog chamber, partitioning to chamber walls and deposited particles are shown to be negligible due to unfavorable equilibrium and transport conditions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/0jjb-5n70, author = {Meng, Zhaoyue}, title = {Thermodynamic and dynamic modeling of atmospheric aerosols}, school = {California Institute of Technology}, year = {1997}, doi = {10.7907/0jjb-5n70}, url = {https://resolver.caltech.edu/CaltechETD:etd-01162008-085509}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document. This dissertation investigates thermodynamic and dynamic modeling of urban and regional atmospheric aerosols. A rigorous and efficient aerosol thermodynamic model, SCAPE2, is developed. The model considers the inorganic aerosol system of sulfate, nitrate, ammonium, chloride, sodium, potassium, calcium, magnesium, carbonate, and water. SCAPE2 can be used to predict either the equilibrium gas/aerosol partition of volatile inorganic species or the particle surface vapor concentrations if applied to the aerosol phase only. It has also the option of predicting the equilibrium or metastable aerosol water content. A three-dimensional, size- and chemically-resolved aerosol dynamic model is developed by incorporating the aerosol thermodynamic model, SCAPE2, into an urban airshed model (CIT model). The model includes advection, turbulent diffusion, condensation/evaporation, nucleation, emissions, and dry deposition. Gas-to-particle conversion is represented by dynamic mass transfer between the gas and aerosol phases. The model employs an absorption approach in dynamically modeling production of secondary organic aerosols. A calculation method for dry deposition of aerosol particles is proposed. The aerosol model is applied to simulate gas and aerosol behavior in the 27-29 August episode in the 1987 Southern California Air Quality Study (SCAQS). Simulation results are compared systematically against SCAQS measurements, and general good agreement is observed. The assumption that volatile inorganic species such as […] are at instantaneous, local equilibrium is examined and it is found that, in many instances, gas/aerosol mass transfer limits the rate of gas-to-particle conversion.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/khpq-7188, author = {Forstner, Hali J. L.}, title = {Aerosol formation from atmospheric hydrocarbon photooxidation}, school = {California Institute of Technology}, year = {1996}, doi = {10.7907/khpq-7188}, url = {https://resolver.caltech.edu/CaltechETD:etd-12182007-114559}, abstract = {Outdoor smog chamber experiments have been performed to determine the secondary organic aerosol (SOA) formation potential of various C7, C8, and C9 aromatics in sunlight-irradiated hydrocarbon- NO[subscript x] mixtures. Measured aerosol yields from toluene,m-xylene, p -xylene, ethylbenzene, m -ethyltoluene, p-ethyltoluene, and 1 ,2,4-trimethylbenzene were found to correlate with organic mass concentration according to semi-volatile gas/particle partitioning theory. Aerosol yields of the C9 aromatics were greater than those of the C8 aromatics, with m-ethyltoluene resulting in the greatest yields. Toluene and ethylbenzene demonstrated some aerosol-forming potential, but the other aromatics produced significantly more SOA.
Filter samples were also collected during the experiments to determine the molecular composition of the SOA from these aromatics Gas-phase mechanisms leading to these products have been proposed. Unsaturated anhydrides (2,5-furandione, 3-methyl-2,5-furandione, 3-ethyl-2,5-furandione) are predominant components of aerosol from all the aromatics, an observation that is consistent with gas-phase aromatic mechanisms involving ring-fragmentation. Saturated anhydrides were also detected in significant quantities, which could result from the hydrogenation of furandiones in sunlight in the particle phase. A new organic aerosol extraction procedure utilizing supercritical CO2 extraction is outlined.
Outdoor smog chamber experiments were also performed to characterize aerosol from 1-octene and 1-decene photooxidation. The dominant aerosol species were heptanal, heptanoic acid, and dihydro-5-propyl-2(3H)-furanone from 1-octene, and nonanal, nonanoic acid, and dihydro-5-pentyl-2(3H)-furanone from 1-decene. Gas-phase oxidation mechanisms of 1-octene and 1-decene with OH and O3 account for the aerosol products.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/4811-nz89, author = {Andino, Jean Marie}, title = {Experimental and theoretical studies of reactions important in photochemical smog : aromatics and alkanes}, school = {California Institute of Technology}, year = {1996}, doi = {10.7907/4811-nz89}, url = {https://resolver.caltech.edu/CaltechETD:etd-01032007-154253}, abstract = {The development of effective ozone control strategies requires the use of atmospheric models. There is general agreement within the scientific community that several aspects of the chemistry within these models has yet to be fully elucidated, and is influential in their predictions. The work in this thesis is aimed at trying to determine some of the unknown aspects of the mechanisms of important atmospheric species. Specifically, the gas-phase reactions of two large alkanes, 2,2,4-trimethylpentane and 2,2,5-trimethylhexane are investigated. These two alkanes are present in urban air, and are potential aerosol precursors. The chemistry of several aromatic hydrocarbons are also studied using both theoretical and experimental techniques. The effects of NO2 on the photooxidation of toluene, m-xylene, and p-xylene are examined, and mechanisms of each of these organics are thouroughly evaluated through closely coordinated laboratory work and computer modeling. In addition, product studies of the photooxidation of 1,2,4-trimethylbenzene and m-ethyltoluene are conducted. These studies provide the first identification of ring-retained products from 1,2,4-trimethylbenzene, and ring-retained and fragmented products from m-ethyltoluene.
A new indoor experimental reactor was designed to investigate gas-phase reaction kinetics and mechanisms. This new system has served to launch the atmospheric chemistry program at Caltech into a wide variety of new research topics.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/k1ap-np35, author = {Dabdub, Donald}, title = {Mathematical modeling of air pollution dynamics by parallel computation}, school = {California Institute of Technology}, year = {1996}, doi = {10.7907/k1ap-np35}, url = {https://resolver.caltech.edu/CaltechETD:etd-12132007-083330}, abstract = {The use of massively parallel computers provides an avenue to overcome the computational requirements in the study of atmospheric chemical dynamics. General considerations on parallel implementation of air quality models are outlined including domain decomposition strategies, algorithm evaluation and design, portability, modularity, and buffering techniques used in I/O operations. Results are given for the implementation of the CIT urban air pollution model on distributed memory multiple instruction / multiple data (MIMD) machines ranging from a cluster of workstations to a 512 node Intel Paragon. The central challenge in developing a parallel air pollution model is the implementation of the chemistry and transport operators used in the solution of the atmospheric reaction-diffusion equation. The chemistry operator is generally the most computationally intensive step in atmospheric air quality models. A new method based on Richardson extrapolation to solve the chemical kinetics is presented. The transport operator is the most challenging to solve numerically. Because of its hyperbolic nature non-physical oscillations and/or negative concentrations appear near steep gradient regions of the solution. Six algorithms for solving the advection equation are compared to determine their suitability for use in parallel photochemical air quality models. Four algorithms for filtering the numerical noise produced when solving the advection equation are also compared. A speed-up factor of 94.9 has been measured when the I/O, transport, and chemistry portions of the model are performed in parallel. This work provides the computational infrastructure required to incorporate new physico-chemical phenomena in the next generation of urban- or regional-scale air quality models. Finally, the SARMAP model is used to model the San Joaquin Valley of California. SARMAP is the updated version of RADM. It can be considered a state-of-the- art regional air pollution model. Like the CIT model, SARMAP incorporates the following atmospheric phenomena: gas-phase chemistry, advection and diffusion. In addition, SARMAP incorporates aqueous-phase chemistry and transport through cumulus clouds. Sensitivity studies performed show a significant dependence of ozone model predictions on boundary conditions.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/ZRQC-R241, author = {Russell, Lynn M.}, title = {The physics and chemistry of marine aerosols}, school = {California Institute of Technology}, year = {1996}, doi = {10.7907/ZRQC-R241}, url = {https://resolver.caltech.edu/CaltechETD:etd-12202007-134328}, abstract = {Understanding the physics and chemistry of the marine atmosphere requires both predicting the evolution of its gas and aerosol phases and making observations that reflect the processes in that evolution. This work presents a model of the most fundamental physical and chemical processes important in the marine atmosphere, and discusses the current uncertainties in our theoretical understanding of those processes. Backing up these predictions with observations requires improved instrumentation for field measurements of aerosol. One important advance in this instrumentation is described for accelerating the speed of size distribution measurements. Observations of aerosols in the marine boundary layer during the Atlantic Stratocumulus Transition Experiment (ASTEX) provide an illustration of the impact of cloud processing in marine stratus. More advanced measurements aboard aircraft were enabled by redesigning the design of the system for separating particles by differential mobility and counting them by condensational growth. With this instrumentation, observations made during the Monterey Area Ship Tracks (MAST) Experiment have illustrated the role of aerosol emissions of ships in forming tracks in clouds. High-resolution gas chromatography and mass spectrometry was used with samples extracted by supercritical fluid extraction in order to identify the role of combustion organics in forming ship tracks. The results illustrate the need both for more sophisticated models incorporating organic species in cloud activation and for more extensive boundary layer observations.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/5M1F-WC03, author = {Wyslouzil, Barbara Ellen}, title = {Aspects of homogeneous nucleation}, school = {California Institute of Technology}, year = {1992}, doi = {10.7907/5M1F-WC03}, url = {https://resolver.caltech.edu/CaltechETD:etd-08172007-132240}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document. Experimental investigations of vapor phase binary nucleation were carried out for both the methanesulfonic acid-water and the sulfuric acid-water systems. A rapid mixing device produced acid-water aerosols under isothermal conditions and at relative acidities (Ra), 0.04 < Ra < 0.65, relative humidities (Rh), 0.01 < Rh < 0.65, and temperatures, T = 20, 25 and 30°C. The number concentration of the aerosol at the exit of the nucleation and growth tube is extremely sensitive to the binary nucleation rate. Thus at low particle concentrations, when condensation did not significantly change the saturation levels the binary nucleation rates were estimated from the number concentration data as a function of Ra, Rh and temperature. Particle size distributions were also measured and found to vary with the amount of acid and water present. An integral model considering both nucleation and growth simulated the experimental system and predicted the total number of particles, the total mass in the aerosol phase, and the mass average diameter at the exit of the nucleation and growth tube. The simulations reproduced the experimental results quite well for the methansulfonic acid-water binary, if the nucleation rate was adjusted by a temperature dependent correction factor which ranged from […] to […]. Further analysis showed that the ratio of experimental to theoretical nucleation rates for both acid-water systems was a strong function of the predicted number of acid molecules in the critical nucleus. Classical homogeneous nucleation theory was extended to nonisothermal conditions by simultaneously solving cluster mass and energy balances. In vapor phase nucleation, the steady state nucleation rate was lower than the corresponding isothermal rate and this discrepancy increased as the pressure of the background gas decreased. After the initial temperature transients decayed, subcritical clusters were found to have temperatures elevated with respect to that of the background gas.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/2xd8-8y76, author = {Shi, Frank Guojun}, title = {Kinetics of Nucleation and Crystallization}, school = {California Institute of Technology}, year = {1992}, doi = {10.7907/2xd8-8y76}, url = {https://resolver.caltech.edu/CaltechETD:etd-08142007-132348}, abstract = {A link between nucleation models and experimental kinetic measurements has been established as a result of the present studies of the general transient kinetics of nucleation in the barrier region and beyond. Based on the new results on the transient kinetics of nucleation, a theoretical basis for measuring directly the nucleation energy barrier and its temperature dependency is developed, an approach for determining the interfacial atomic transfer mechanism in the nucleation process is presented and some new experimental strategies for conducting nucleation and crystallization kinetic measurements are outlined. A new mathematical approach developed for solving the nucleation kinetic equation in the barrier region and beyond is described. The results are also presented for the nucleation kinetics in some spatially inhomogeneous systems where there are mechanisms for subcritical clusters loss from the system. In addition, a chemical-nucleation model developed for the cluster formation in a chemically reacting system is outlined.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/SE1X-K706, author = {Kim, Yong Pyo}, title = {Simulation of multicomponent aerosol dynamics}, school = {California Institute of Technology}, year = {1992}, doi = {10.7907/SE1X-K706}, url = {https://resolver.caltech.edu/CaltechETD:etd-08062007-150332}, abstract = {Chemical composition and, therefore, several physical properties, such as refractive index or density, of an aerosol system may be distributed in one particle size. The effect of these particles of the same size but different properties, so-called mixed particles, on aerosol dynamics can be important. Several aspects of the number-property distribution; effect on aerosol dynamics and importance, definition, state of the art of the measurement technique, available data, and numerical schemes are discussed and further research directions are discussed. The moving sectional method is extended to simulate multicomponent aerosol dynamics resulting from condensation/evaporation processes. This method uses a Lagrangian approach in which section boundaries and component masses in a section vary according to the characteristics of condensation/evaporation rates while conserving number concentration in a section throughout the simulation. Simulation of model problems for which new analytical solutions have been obtained shows excellent agreement with the analytical solutions. Limitations and applicability of the sectional method are discussed. A technique for direct numerical solution of the multicomponent aerosol general dynamic equation is developed and tested. The method obtains the aerosol size-composition distribution without the need to make any a priori assumptions about the nature of the distribution. Numerical solutions are compared with analytical solutions for model problems of pure condensation/evaporation, pure coagulation, and simultaneous condensation and coagulation. The advantages, applicability, and the limitations of the approach are discussed. An analysis of the tandem differential mobility analyzer (TDMA) is proposed in which the conditioner between the two DMAs is simulated by the multicomponent aerosol general dynamic equation (GDE). The use of the TDMA to separate an externally mixed aerosol is illustrated by simulating the data of Liu et al. (1978). Numerical issues in grid-based photochemical air quality models are reviewed. Numerical schemes for advection and chemical kinetics in gas-phase and for dynamics in aerosol-phase are compared. Finally, a numerical code is developed based on direct numerical solution of the multicomponent aerosol general dynamic equation.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/7q3j-q875, author = {Chan, Chak Keung}, title = {Studies of Levitated Single Droplets}, school = {California Institute of Technology}, year = {1992}, doi = {10.7907/7q3j-q875}, url = {https://resolver.caltech.edu/CaltechETD:etd-07232007-131610}, abstract = {The electrodynamic balance is a very unique and versatile device to study single particles. In-situ measurements of particles in a well characterized and controlled environment are possible. Supersaturated solutions can also be studied. In this research, its applications in studying light scattering, water activities and evaporation kinetics of single droplets are demonstrated. In particular, we studied the elastic and Raman scattering of an evaporating NaNO3 droplet. Different types of size dependent optical resonance structures were identified. The strongest Raman signal received was due to internal resonance of the excitation beam, giving similar enhancements to all Raman emissions. The intensity ratio of Raman nitrate to Raman water peaks can be used as a probe to semi-quantitatively characterize the droplet compositions. Water activities of mixed NH4NO3/(NH4)2SO4 aqueous solutions were also studied using the Spherical Void Electrodynamic Levitator. The compositional water activity data were used to evaluate the performance of three commonly used mixed electrolyte models: the Zdanovskii-Strokes-Robinson model, the Kusik and Meissner model, and the Pitzer model. They all predict droplet concentrations in mass fractions to a few percents error within the range where water activity data of single electrolytes are available. Evaporation of a few ceramic precursor solution droplets were investigated. While some precursor solutions crystallized, some others formed gels. Gel formation hindered further evaporation of water and the droplets exhibited a sharp decrease in evaporation rates. An approach to study rapid evaporation of droplets in the time scales of a few seconds was also demonstrated.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Flagan, Richard C.}, } @phdthesis{10.7907/G2RC-S602, author = {Huang, David Da-Teh}, title = {Aerosol coagulation and nucleation}, school = {California Institute of Technology}, year = {1991}, doi = {10.7907/G2RC-S602}, url = {https://resolver.caltech.edu/CaltechETD:etd-06222005-162441}, abstract = {For aerosol Brownian coagulation in the transition regime of Knudsen number in the presence of an interparticle potential, the Fokker-Planck equation is solved by using the Grad’s 13-moment method. The mass and energy accommodation coefficients that are used to describe the results of collisional processes are appropriately defined and interfaced with the Fokker-Planck moment equations. Analytical and numerical solutions of the number and energy flux profiles for the potential-free, power-law potential, van der Waals potential, and Coulombic potential situations are obtained. The results are in good agreement with those predicted by the flux-matching method of Fuchs. The present fundamental approach, therefore, provides theoretical support of the coagulation coefficient expression obtained by the empirical flux-matching method.
For coagulation between ultrafine particles, we solved the BGK equation for large but finite Knudsen number situations by taking into account the van der Waals potential and/or the Coulombic/image potential. We present closed form best-fit equations for data calculated from the theory. The conditions where either Coulombic, image, or van der Waals forces predominate are determined.
A new expression of the image potential between a charged particle and an uncharged particle is obtained. We calculate the coagulation rate between the particles and are able to determine the enhancement of coagulation rate due to the interparticle potential in all size regimes.
An aerosol coagulation process is applied to the formation of aerosol particles in the semiconductor thin film preparation. In the CVD reactor, we consider simultaneous aerosol coagulation, diffusion, and generation of aerosol monomers by chemical reaction. The mass and number concentration of monomers and particles are computed as functions of temperature, pressure, input vapor concentration, and position in the reactor. The thin film growth rate can be subsequently evaluated. It is found that under certain circumstances, aerosol particle generation may significantly suppress the film growth due to monomers.
The formulation of the homogeneous nucleation free energy change of aerosol clusters is reexamined. It is shown that the inclusion of the cluster translational and rotational motion in the cluster formation free energy change is appropriate. The classical and statistical thermodynamics are shown to be consistent.
The cell model of liquids of statistical mechanics is employed to reevaluate the free energy change of cluster formation in aerosol nucleation. We provide a new molecular level theory that is applicable in the larger cluster size range where liquid-like properties begin to emerge and a cluster surface is present. The microcluster surface tension can be appropriately defined. The cluster rotational contribution to the free energy change, though it must be accounted for, is shown to be insignificant for liquid-like clusters.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/npvk-7c22, author = {Wang, Shih-Chen}, title = {Aerosol formation and growth in atmospheric organic/NOx systems}, school = {California Institute of Technology}, year = {1991}, doi = {10.7907/npvk-7c22}, url = {https://resolver.caltech.edu/CaltechETD:etd-01112007-152148}, abstract = {Secondary atmospheric aerosols are formed by gas-to-particle conversion of condensible vapors produced by reactions of primary species such as organics, NOx, SO2, and NH3. The rates and mechanisms leading to organic aerosol formation are the least well understood aspect of secondary atmospheric aerosols. Gas-phase measurements of organics, NOx, O3, and measurements of particle formation and growth have been made in smog chamber experiments to determine the total aerosol yields of the photochemical oxidation of various organics. Measurements of size distribution dynamics reveal the competition between nucleation and condensation, allowing estimation of the physical properties of the aerosol formed and the likelihood that a particular organic forms aerosol in the atmosphere. A new scanning electrical mobility spectrometer (SEMS) was developed to monitor aerosol size distribution dynamics. The measurement of particle size distributions using electrical mobility has been significantly accelerated using a new mode of operating mobility instruments. Rather than changing the electric field in discrete steps to select particles in a given mobility range, the electric field is scanned continuously. The particles are classified in a time-varying electric field, but for an exponential ramp in the field strength, there remains a one-to-one correspondence between the time a particle enters the classifier and the time it leaves. By this method, complete scans of mobility with as many as 100 mobility measurements have been made in 30 seconds using a differential mobility classifier with a condensation nuclei counter as a detector. Outdoor smog chamber experiments have been performed to determine the aerosol forming potential of selected C7- and C8- hydrocarbons in sunlight-irradiated hydrocarbon NOx mixtures. Measured aerosol size distributions were used to determine the rates of gas-to-particle conversion and to study the effects of the addition of SO2 and/or NH3 on aerosol formation and growth. The average aerosol yields by mass for the hydrocarbons studied were: methylcyclohexane 9.2% 1-octene 4.2% toluene 18.6% n-octane <0.001% Addition of SO2 to the organic/NOx systems led to an early nucleation burst and subsequent rapid growth of the newly formed aerosols. In the presence of NH3, the gas-to-particle conversion rate of the organic/NOx system was enhanced perhaps due to the formation of NH4NO3 or the reaction of NH3 with carboxylic acids. Sustained particle formation was observed when both SO2 and NH3 were present, presumably a result of (NH4)2SO4 formation. We have estimated the complexity of the 1-octene aerosol and identified 5-propyl furanone as a major component of the aerosol. Aerosol dynamics that were observed in the outdoor smog chamber experiments are simulated by numerical solution of the aerosol general dynamic equation. The vapor source generation rate was estimated directly from the experimental measurements assuming a single surrogate condensing species for each hydrocarbon studied. Sensitivity analysis of the simulated aerosol dynamics to various input parameters revealed that the physical properties of the condensing vapor are important in determining the interplay between nucleation and condensation while the vapor source generation rate is the only factor that determines the eventual total amount of vapor converted to aerosol. The simulations suggest that over 99% of the mass of condensible vapor is converted to aerosol by condensation even when a significant burst of nucleation occurs.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Flagan, Richard C. and Seinfeld, John H.}, } @phdthesis{10.7907/3cyt-0315, author = {Paulson, Suzanne Elizabeth}, title = {Contributions of biogenic and anthropogenic hydrocarbons to photochemical smog formation}, school = {California Institute of Technology}, year = {1991}, doi = {10.7907/3cyt-0315}, url = {https://resolver.caltech.edu/CaltechETD:etd-07172007-150535}, abstract = {Photochemical oxidation of biogenic (Isoprene) and anthropogenic (1-octene) hydrocarbons are examined. Experiments studied the individual daylight reactions of both isoprene and 1-octene, including those of OH, O3, and O([superscript 3]P). Results from both the smog chamber experiments and computer kinetic modeling were then used to develop photochemical oxidation mechanisms for each hydrocarbon. Aerosols formed by isoprene and another biogenic, beta-pinene, are characterized.
The OH reaction with isoprene is studied. Methyl nitrite photolysis experiments were carried out in an outdoor smog chamber in an attempt to identify as completely as possible OH-isoprene product spectrum. Emphasis was placed on identification and quantification of oxygenated products. The design of a Tenax-based cryo-trap thermal desorber used to trap, concentrate, and dry chamber samples for identification on a GC/MS is described. Analysis of the products revealed that O([superscript 3]P) can form in reaction systems designed to study OH reactions that include high concentrations of NO, and consequently NO2, hence this reaction is also examined. The yields of methacrolein and methyl vinyl ketone are determined as 25±3 and 35.5±4%, respectively, with an additional 5.1±3% as 3-methyl furan, totaling 66±3%. These results, combined with those of previous studies-allow 80% of isoprene’s products to be explicitly identified, and the general structure of the remaining products to be ascertained. The O([superscript 3]P) reaction produces 84±8% epoxides, and 8±3% species which result in production of HO2, and subsequently OH. A heretofore unidentified product of the O([superscript 3]P) reaction, 2,2 methyl butenal, is identified. The rate constant of the NO2-isoprene reaction is measured.
A series of experiments have been carried out to study the ozone-isoprene reaction in a smog chamber using externally produced O3, added to the hydrocarbon in the dark. A chemical tracer, methyl cyclohexane, was added to probe the OH formation in the system. O([superscript 3]P) formation was also examined using the known distribution of products that are unique to the O([superscript 3]P)-isoprene reaction (part 1). The results provide clear evidence that both OH and O([superscript 3]P) are produced from the O3-isoprene reaction directly in large quantities; about 0.68±0.15 and 0.45±0.15 per O3 -isoprene reaction, respectively. These additional radicals severely complicate the analysis of the O3 reaction, hence computer kinetic modeling was necessary to ascertain the products of the O3 reaction itself. The product spectrum, which differs dramatically from that published previously, is: 67±9% methacrolein, 26±6% methyl vinyl ketone, and 7±3% propene, accounting for 100±10% of the reacted isoprene. Applicability of these results to the gas-phase O3 reaction with other unsaturated hydrocarbons is briefly discussed.
The photooxidation chemistry of 1-octene is examined in detail. Formation of OH from the O3 reaction was examined with the use of a tracer/absorber, methyl cyclohexane. The O3 - 1-octene reaction is found to produce, apparently directly, significant quantities of OH, 0.55+0.2 on a per molecule reacted 1-octene basis. Almost 100% of the reacted 1-octene could be accounted for as 80±10% heptanal, 11±6% thermally stabilized Criegee biradical, and about 1% hexane. The OH - 1-octene reaction was found to produce only 15±5% heptanal. The remainder is assumed to result in the formation of alkyl nitrates (32%), and isomerization and eventual formation of multisubstituted products (52%). A separate experiment examining the O([superscript 3]P)-1-octene reaction, showed that 1-octyl oxide accounted for about 80% of the reacted 1-octene. A photochemical model was developed for 1-octene oxidation, and is compared with smog chamber results from NO/NO2-octene experiments. The most crucial factor in the performance of the model is the quantity of assumed alkyl nitrate formation.
A mechanism for the oxidation of isoprene is developed and includes the recent developments on each of isoprene’s atmospherically important reactions: O3, OH, O([superscript 3]P), and NO3. The mechanism is tested against chamber data that includes a range of mixtures of these reactions. While it performs reasonably well under conditions where the OH and O([superscript 3]P) reactions dominate, it tends to over predict O3 formation, as well as the speed of development of O3 under conditions where the O3 and NO3 reactions are important. The NO3 reaction is the most uncertain aspect of the isoprene mechanism, and may be responsible for a large part of this discrepancy. The discrepancy may also arise from the difficulty in extrapolating the results of O3 experimental results, necessarily carried out in the absence of NOx, to conditions that include significant concentrations of NOx.
An extensive set of outdoor smog chamber experiments was carried out to study aerosol formation by two representative biogenic hydrocarbons: isoprene and beta-pinene. The hydrocarbons, at concentrations ranging from a few ppb to a few ppm, were photooxidized in the presence of NOx. Isoprene was found to produce negligible aerosol at ambient conditions, whereas beta-pinene aerosol carbon yields were as high as 8%, depending strongly on the hydrocarbon to NOx ratio. Aerosol samples subjected to infrared absorption spectroscopy revealed that the dominant aerosol products for both isoprene and beta-pinene are organic nitrates, organic acids, as well as other carbonyls and hydroxy compounds. GCMS of the neutral fraction of the beta-pinene aerosol revealed nopinone and several other compounds with molecular weights ranging from 138-200 amu, indicating mainly mono- and dioxygenated products. The average vapor pressure of the 13-pinene aerosol was estimated to be 37 ± 24 ppt at 31 C. Scanning electron micrographs showed that the particles consist of both liquid droplets and agglomerates of small (40-60 nm) solid particles.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/EYF6-3M05, author = {Wexler, Anthony Stein}, title = {Inorganic Components of Atmospheric Aerosols}, school = {California Institute of Technology}, year = {1991}, doi = {10.7907/EYF6-3M05}, url = {https://resolver.caltech.edu/CaltechETD:etd-07172007-083859}, abstract = {The inorganic components comprise 15% to 50% of the mass of atmospheric aerosols and, these along with the relative humidity, control the aerosol water content. For about the past 10 years the mass of the inorganic components of atmospheric aerosol was predicted assuming thermodynamic equilibrium between the volatile aerosol-phase inorganic species, NH4NO3 and NH4Cl, and their gas-phase counterparts, NH3, HNO3, and HCl. In this thesis I examine this assumption and prove that 1) the time scales for equilibration between the gas and aerosol phases are often too long for equilibrium to hold, and 2) even when equilibrium holds, transport considerations often govern the size distribution of these aerosol components.
Water can comprise a significant portion of atmospheric aerosols under conditions of high relative humidity, whereas under conditions of sufficiently low relative humidity atmospheric aerosols tend to be dry. The deliquescence point is the relative humidity where the aerosol goes from a solid dry phase to an aqueous or mixed solid-aqueous phase. Previous to this thesis little had been known about the temperature and composition dependence of the deliquescence point. In this thesis I first derive an expression for the temperature dependence of the deliquescence point and then prove that in multicomponent solutions the deliquescence point is lower than in the deliquescence point of the individual single component solutions.
These theories of the transport, thermodynamic, and deliquescent properties of atmospheric aerosols are integrated into an aerosol inorganics model, AIM. The equilibrium predictions of AIM compare well to fundamental thermodynamic measurements. Comparison of the prediction of AIM to those of other aerosol equilibrium models show substantial disagreement in the predicted water content at lower relative humidities. The difference is due to the improved treatment of the deliquescence properties of mixed solute aerosols that is contained in AIM.
In the summer and fall of 1987 the California Air Resources Board conducted the Southern California Air Quality Study, SCAQS. During this study the atmospheric aerosols were measured at nine sites in the Los Angeles air basin. The measurements determined the size and composition distributions of the components of the aerosol and the concentrations of their gas phase counterparts during a series of intensive study periods. The comparison of these SCAQS measurements to the predictions of AIM have so much scatter that a departure from equilibrium, that can be attributed to transport limitations, cannot be discerned. When the measured size distributions are compared as another indication of transport-limited departure from equilibrium, we find that different size aerosol particles are not in mutual equilibrium. Although the SCAQS data do not indicate a transport-limited departure from equilibrium, they do support our hypothesis that transport considerations are essential to predicting the size distribution of the volatile inorganic species.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/Z6AN-AJ83, author = {Pandis, Spyros N.}, title = {Studies of physicochemical processes in atmospheric particles and acid deposition}, school = {California Institute of Technology}, year = {1991}, doi = {10.7907/Z6AN-AJ83}, url = {https://resolver.caltech.edu/CaltechETD:etd-05062004-154106}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document. Atmospheric particles, or particulate matter, can be solid or liquid with diameters varying from around 0.002[micrometers] to roughly 100[micrometers]. Atmospheric aerosol sources can be classified as primary or secondary, with the primary aerosol being directly emitted from the corresponding sources and the secondary particles being formed in the atmosphere, for example, from gas-phase chemical reactions that produce condensable vapors. At the same time aerosol particles are ultimately connected with the formation of water droplets and equivalently with the formation of clouds and fogs in the atmosphere. The first part of this thesis concerns the mathematical modeling of wet and dry acid deposition and of the relevant physicochemical processes. Acid deposition consists of the delivery of acidic substances, principally sulfuric and nitric acid, from the atmosphere to the earth’s surface. Upon emission to the atmosphere, SO2 and NOx, are photochemically oxidized, yielding sulfuric and nitric acid vapors. Sulfuric acid is rapidly incorporated into aerosol particles, while nitric acid may be scavenged by particles or droplets or remain in the gas phase. Even in the absence of an aqueous phase (no clouds or fog), the acidic gases and dry particles can be transported to and deposited at ground level; this process is called dry deposition. When an aqueous phase is present (inside a cloud or a fog), gas-phase species like SO2, HNO3, NH3 and aerosol particles are scavenged by water droplets resulting in a solution that can be significantly acidic. Additional cloudwater or fogwater acidity beyond that attained purely from scavenging of gases and particles results from aqueous-phase chemistry, most notably oxidation of dissolved SO2 to sulfuric acid. These acidic droplets can reach the earth’s surface either as precipitation or as impacted cloud and fogwater, in the processes termed wet deposition. If they are not rained or deposited out the aqueous droplets can evaporate leaving as residue new aerosol particles that may themselves undergo dry deposition to the earth’s surface. The effects of acid deposition include soil and lake acidification, forest decline and deterioration of cultural monuments. Mathematical models are a major tool in our effort to understand and ultimately control acid deposition. The development of such a mathematical model represents a major challenge as it requires the ability to describe the entire range of atmospheric physicochemical phenomena. As a first step in the modeling, a comprehensive chemical mechanism for aqueous-phase atmospheric chemistry was developed and its detailed sensitivity analysis was performed. The main aqueous-phase reaction pathways for the system are the oxidation of S(IV) to S(VI) by H2O2, OH, HO2, O2 (catalysed by Fe3+ and Mn2+), O3, and […]. The dominant pathway for HNO3(aq) acidity is scavenging of nitric acid from the gas phase. HCOOH is produced because of the reaction of HCHO(aq) with OH(aq). The gas-phase concentrations of SO2, H2O2, HO2, OH, O3, HCHO, NH3, HNO3, and HCl are of primary importance. Increase of the liquid water content of the cloud results in a decrease of the sulfate concentration, but an increase of the total sulfate amount in the aqueous-phase. On the basis of the sensitivity analysis, a condensed mechanism was derived. The next step was the development of a model that actually predicts the amount of liquid water in the atmosphere solving the energy balance. This Lagrangian model combines for the first time a detailed description of gas and aqueous-phase atmospheric chemistry with a treatment of the dynamics of radiation fog, that is the fog that is created due to the radiative cooling of the earth’s surface to the space during the night. The model was evaluated against a well documented radiation fog episode in Bakersfield in the San Joaquin Valley of California over the period January 4-5, 1985. This application showed that the model predictions for temperature profile, fog development, liquid water content, gas-phase concentrations of SO2, HNO3, and NH3, pH, aqueous-phase concentrations of […], […], and […], and finally deposition rates of the above ions match well the observed values. The fog was found to lead to a drastic increase of deposition rates over those in its absence for the major ionic species, with most notable being the increase of sulfate deposition. Several important differences were found to exist between the characteristics of a radiation fog and a representative cloud environment. Radiation fogs typically develop under stable conditions (very low wind speed) resulting in weak mixing and significant vertical gaseous species concentration gradients. Because of the proximity of the fog to ground-level sources of pollutants like SO2 and NOx, the corresponding gas-phase concentrations can reach much higher levels that in a cloud. In such a case, pathways for aqueous-phase sulfate production that are of secondary importance in a cloud environment may become significant in a fog. The next level of treatment beyond assuming that all the water droplets have the size and chemical composition is to explicitly model the size-composition distribution of droplets as a result of nucleation on aerosol particles. A third model was developed to study the distribution of acidity and solute concentration among the various droplet sizes in a fog or a cloud. The major finding of this study was that significant solute concentration differences can occur in aqueous droplets inside a fog or a cloud. For the fog simulated, during the period of dense fog, the solute concentration in droplets larger than 10[micrometers] diameter increased with size, in such a way that droplets of diameter 20[micrometers] attain a solute concentration that is a factor of 3.6 larger than that in the 10[micrometer] droplets. Chemical processes tend to decrease the total solute mass concentration differences among the various droplet sizes. Low cooling rates of the system also tend to decrease these concentration differences while high cooling rates have exactly the opposite effect. The mass/size distribution of the condensation nuclei influences quantitatively, but not qualitatively, the above concentration differences. The effects of equilibration processes on wet and dry deposition were then investigated and furthermore the accuracy of the currently used modelling approaches of these phenomena was examined. Atmospheric equilibration processes between two phases with different deposition velocities have the potential to affect significantly the amount of total material deposited on the ground. The magnitude of the effects of the equilibration processes depends primarily on the ratio of the deposition velocities of the two phases, on the production/emission rate of the gas-phase species, and on the initial distribution of species between the two phases. At this point all the tools were available for the detailed investigation of the cyclical relationship between the aerosol and aqueous droplets; a polluted atmosphere with high aerosol concentration assists the formation of the aqueous phase which itself appears to enhance smog production, visibility reduction and aerosol sulfate levels after its dissipation. A model including descriptions of aerosol and droplet microphysics, gas and aqueous-phase chemistry and deposition was used to study the transformation of aerosol to fog droplets and back to aerosol in an urban environment. Fogs in polluted environments have the potential to increase aerosol sulfate concentrations, but at the same time to cause reductions in the aerosol concentration of nitrate, chloride, ammonium and sodium as well as in the total aerosol mass concentration. The sulfate produced during fog episodes favors the aerosol particles that have access to most of the fog liquid water which are usually the large particles. Aerosol scavenging efficiencies of around 80% were calculated for urban fogs. Sampling and subsequent mixing of fog droplets of different sizes may result in measured concentrations that are not fully representative of the fogwater chemical composition and can introduce errors in the reported values of the ionic species deposition velocities. Differences in the major ionic species deposition velocities can be explained by their distribution over the aerosol size spectrum and can be correlated with the species average diameter. The second part of this work was focused on the experimental study of the mechanisms of formation of secondary aerosol particles due to the atmospheric photooxidation of hydrocarbons. In this smog chamber the aerosol forming potential of natural hydrocarbons was investigated. Natural hydrocarbons like the monoterpenes C10H16 and isoprene C5H8 are emitted by various trees and plants in significant quantities. Isoprene and [Beta]-pinene, at concentration levels ranging from a few ppb to a few ppm were reacted photoehemically with NOx, in the Caltech outdoor smog chamber facility. Aerosol formation from the isoprene photooxidation was found to be negligible even under extreme ambient conditions due to the relatively high vapor pressure of its condensable products. Aerosol carbon yield from the [Beta]-pinene photooxidation is as high as 8% and depends strongly on the initial HC/NOx ratio. The average vapor pressure of the [Beta]-pinene aerosol is estimated to be 37 [plus or minus] 24 ppt at 31?c. Monoterpene photooxidation can be a significant source of secondary aerosol in rural environments and in urban areas with extended natural vegetation.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/efdm-c587, author = {Wolfenbarger, J. Kenneth}, title = {Aerosol Data Inversion: Optimal Solutions and Information Content}, school = {California Institute of Technology}, year = {1990}, doi = {10.7907/efdm-c587}, url = {https://resolver.caltech.edu/CaltechETD:etd-11092007-094509}, abstract = {
The determination of an aerosol size distribution is presently difficult because current aerosol instruments cannot perfectly discriminate aerosols based on size and because a only limited number of data can be obtained. As a result, for a given set of data the relationship between the unknown distribution and the data is a finite Fredholm integral equation. If the size distribution is desired, then one should answer the following
• What measurements should be taken?
• How should the measurements be used to determine a size distribution?
In this thesis, we shed some light on the answers to these questions by finding optimal solutions to the Fredholm integral equation, and by characterizing the size of the solution set.
The questions of existence and uniqueness of solutions subject to linear inequality constraints are examined. Optimal solutions based on regularization are developed, and numerical methods for finding these solutions are described. Numerical experiments are presented that demonstrate the importance of
• describing dependent error sources.
• considering the magnitude of the errors in the data when there are few data.
• using generalized cross validation when there are many data and the magnitude of the errors is unknown.
An analysis that uses some simple information concepts is presented for examining the size of the solution set. An example is presented that demonstrates the effect of dependent errors on the information provided by the data, and some illustrative experiment design studies are presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/9gn5-p598, author = {Yin, Fangdong}, title = {Atmospheric photooxidation of organosulphur compounds}, school = {California Institute of Technology}, year = {1990}, doi = {10.7907/9gn5-p598}, url = {https://resolver.caltech.edu/CaltechETD:etd-11192007-092214}, abstract = {
NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
The atmospheric chemistry of organosulfur compounds is of fundamental importance to understanding the biogeochemical sulfur cycle as well as environmental issues such as acid precipitation and sulfur aerosol formation in the atmosphere. The research goal of the present work is to elucidate the atmospheric reaction mechanisms of conversion of organosulfur compounds to sulfur-containing aerosols.
Based on the fundamental chemistry and the available kinetic and mechanistic information from experimental studies, detailed chemical reaction mechanisms have been developed for the atmospheric photooxidation of dimethyl sulfide, […], dimethyl disulfide, […], methanethiol, […], and diethyl sulfide, […]. Predictions of the developed mechanisms by computer simulation are compared with available data on laboratory photooxidation of organosulfur compounds to identify critical uncertainties in chemical pathways and reaction rate constants. Further experimental studies have been designed based on the findings from computer modeling work. Using the outdoor smog chamber reactor, the dynamic behavior of various chemical species and particle nucleation and growth have been investigated in detail under well-defined atmospheric conditions for systems […] and […]. Through analysis of the experimental data from outdoor smog chamber experiments by computer simulation, the mechanisms developed for photooxidation of […] and […] have been evaluated and reformulated. The key problems regarding the initial reactions, secondary reactions of RSOX radicals and […] radicals, and the major chemical pathways for the formation of […] and […] compounds have been elucidated and the discrepancies of the experimental results between different investigators have been resolved. Critical uncertatinties regarding chemical path- ways and reaction rate constants have been identified and further detailed kinetic experimental studies have been recommended.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/h2d4-tq78, author = {Webb, Christopher John}, title = {Robust Control Strategies for a Fixed Bed Chemical Reactor}, school = {California Institute of Technology}, year = {1990}, doi = {10.7907/h2d4-tq78}, url = {https://resolver.caltech.edu/CaltechETD:etd-11132007-110352}, abstract = {This thesis addresses the practical application of robust control design to an experimental fixed bed reactor. Controllers are designed using robust control theory, specifically, Structured Singular Value analysis and Internal Model Control theory. These controllers are guaranteed to be stable and have good performance even when there is plant-model mismatch. To understand the sources of model mismatch and how model mismatch affects a fixed bed reactor’s control design, an experimental methanation reactor was constructed.
The reactor is non-adiabatic with a constant wall temperature. A series of thermo couples located inside an axial thermowell are used to measure bed temperatures, and a gas chromatograph is used to measure gas concentrations. The pilot plant includes a feed-effluent heat exchanger and a product recycle line for positive feedback of both mass and energy.
A mathematical model of the reactor is developed from first principles. This dynamic model is a three dimensional heterogenous model. It consists of four non-linear coupled partial differential equations. Finite difference methods are used to approximate these equations with a series of ordinary differential equations. The temperature profiles simulated using the model compare favorably with the profiles obtained from the experimental reactor.
Two control configurations are studied: the control of the hot spot temperature using the flow rate of an inert gas, and the control of the outlet concentration and temperature by manipulating the recycle flow rate and power supplied to an inlet heater. For both of these experiments, the control objective is to maintain stability and acceptable performance for a variety of operating conditions. Bounds of the amount of model uncertainty are explicitly incorporated in the controller design.
A new methodology for computing frequency domain uncertainty bounds for single-input single-output systems is presented. This new methodology uses spectral analysis to identify a series of non-parametric frequency domain models and a “regions-mapping” technique to bound the frequency by frequency description of these models in the complex plane. The methodology is compared to existing non-parametric techniques and shown to be superior for identifying the uncertainty bound associated with a nonlinear system. This methodology is then applied to the hot spot temperature identification problem of the fixed bed reactor. A robust controller with a single adjustable parameter is designed for the reactor using Internal Model Control (IMC) theory. The computed uncertainty bounds are experimentally validated using the IMC controller.
A simple procedure is presented for designing a robust controller when one or more of the control variables must be inferred from other process measurements. As part of this procedure, a robust measurement selection scheme determines which process measurements should be used for inference. The measurement selection scheme is based on Structured Singular Value analysis. This procedure is successfully applied to the outlet concentration control for the experimental methanation reactor.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Morari, Manfred and Seinfeld, John H.}, } @phdthesis{10.7907/pmy6-3d94, author = {Kreidenweis-Dandy, Sonia Maria}, title = {Experimental and Theoretical Studies of Binary Nucleation and Condensation}, school = {California Institute of Technology}, year = {1989}, doi = {10.7907/pmy6-3d94}, url = {https://resolver.caltech.edu/CaltechETD:etd-02132007-092817}, abstract = {Many gas-to-particle conversion processes occurring in the atmosphere (and in technological applications) involve more than one gaseous species. An understanding of how gas-to-particle conversion occurs in multicomponent systems is necessary to predict the evolution of atmospheric aerosols. Of particular interest is the validity of binary nucleation theory in describing particle formation from two interacting vapors.
Chapter II presents a modeling study of heat and mass transfer to aqueous droplets dried under various conditions, and discusses the applicability of common assumptions in describing such processes. A method for the separation, into droplets containing different solutes, of an aerosol composed of two types of aqueous droplets is proposed.
Next, in Chapter III, an experimental study of binary nucleation theory using two similar organics (dibutylphthalate and dioctylphthalate) is presented, and compared with the predictions of an integral model that describes particle formation using binary nucleation theory. It was found that the number concentrations of particles formed in the presence of both vapors was higher than could be attributed to single-component nucleation of either organic, suggesting that binary nucleation was the mechanism for particle formation. Model predictions using the theoretical binary nucleation rates, modified by suitable (species-dependent) enhancement factors, were able to represent the data well.
Attention was next focused on an environmentally-important organosulfur compound, dimethylsulfide, and its oxidation under atmospheric-type conditions. In particular, the aerosol-forming ability of the two major sulfur containing products, methanesulfonic acid and sulfuric acid, was investigated theoretically. Binary nucleation and multicomponent condensation theories were used to predict particle formation and growth in the chemically reacting system at 36% relative humidity, and model predictions were compared with published experimental smog chamber measurements of dimethylsulfide photooxidation. It was found that the experimental results could be well represented by a model that allowed for binary nucleation of aqueous sulfuric acid droplets, and ternary growth of these droplets by condensation of water, methanesulfonic acid, and sulfuric acid vapors. This investigation is presented in Chapter IV.
The calculations presented in Chapter IV are some of the first estimates of particle formation in the methanesulfonic acid/water binary vapor system. In order to assess the validity of binary nucleation theory in describing this particle formation, an experimental program was initiated for the investigation of binary nucleation phenomena in this system. A continuous-flow, mixing-type device was proposed that would yield information not only on the critical saturation ratios required for observable particle formation, but the actual variation of nucleation rate with the gas-phase concentration of each species. The experimental apparatus that was constructed and used for this purpose and a summary and analysis of the experimental results are found in Chapter V. Particle formation was observed at moderate relative humidities and undersaturated acid vapor concentrations, demonstrating that methanesulfonic acid is able to undergo binary nucleation with water vapor. The adequacy of classical binary nucleation theory in predicting the nucleation rates is discussed in detail. The second major goal of the experimental program that was realized was the demonstration of the usefulness of this device in the investigation of binary nucleation phenomena, particularly for corrosive materials, which are difficult to work with in conventional systems.
Because of its successful application to the methanesulfonic acid/water vapor system, this device shows great promise for future applications in the study of binary nucleation phenomena. Suggestions for the modification and improvement of the apparatus that emerged from laboratory experience and from the data analysis are presented in Chapter VI.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/417v-ke62, author = {Stern, Jennifer E.}, title = {Aerosol Formation and Growth in Aromatic Hydrocarbon/NOₓ Systems}, school = {California Institute of Technology}, year = {1988}, doi = {10.7907/417v-ke62}, url = {https://resolver.caltech.edu/CaltechETD:etd-12282004-153051}, abstract = {The formation of secondary organic aerosol in the atmosphere remains one of the most poorly understood aspects of the air pollution problem in urban areas. Photooxidation of gas-phase emissions produces low vapor pressure species that are converted to the aerosol phase either by homogeneous nucleation of new particles or by condensation onto existing particles. One of the goals in studying aerosol dynamics in atmospheric systems is to determine the factors that govern which of these two pathways dominates in the conversion of gas-phase species to the aerosol phase.
We have conducted an extensive series of experiments aimed at elucidating the physics of atmospheric organic aerosol formation. An outdoor smog chamber was used to study the formation and growth of secondary aerosol resulting from the photooxidation of aromatic hydrocarbons (toluene, m-xylene, ethyl benzene, and 1,3,5-trimethyl benzene) in the presence of NOₓ. In the experiments, particular emphasis was given to the effect of primary aerosol on the subsequent aerosol evolution in the system. We observed that with a sufficient number concentration of initial seed particles in the system, homogeneous nucleation could be suppressed and all gas-to-particle conversion occurred via condensation onto the seed particles.
Aerosol yields by mass from the gas phase were calculated for each experiment. These yields were somewhat dependent on the initial hydrocarbon/NOₓ ratio in each experiment, which is an indication of the system reactivity. Average yields for each aromatic species were: toluene - 4.8%, m-xylene - 3.5%, ethyl benzene - 1.9%, and 1,3,5-trimethyl benzene - 2.4%. These results are in good agreement with previous determinations of aerosol yield for the toluene and m-xylene systems.
Several models were used to describe the observed aerosol dynamics. An integral model assuming a monodisperse aerosol, developed by Warren and Seinfeld (1984, 1985b), was used to determine apparent saturation vapor pressures of condensible species from the observations of nucleation events. Overall predictions of final number concentrations with the integral model, based on these saturation vapor pressures, were fairly close to the experimentally observed number concentrations.
An analysis of the rate of aerosol growth was carried out for those experiments exhibiting uniform condensational growth. This analysis provided estimates for the gas-phase partial pressures of the condensible species, which could be compared with the integral model vapor pressures to give approximate saturation ratios during these periods of growth.
Full aerosol size distribution simulations were performed using the sectional model ESMAP (Warren and Seinfeld, 1985a), based on the work of Gelbard et al. (1980). Number concentrations resulting from these predictions were higher than those of the integral model, since the condensation rate on a polydisperse aerosol is smaller than that on a monodisperse distribution, leading to a higher nucleation rate. Comparisons of predicted and observed size, distributions during the course of each experiment were limited in accuracy by the numerical diffusion associated with current versions of the sectional model.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/t5w6-2r52, author = {Pilinis, Christodoulos}, title = {Mathematical Modeling of the Dynamics and Thermodynamics of Multicomponent Atmospheric Aerosols}, school = {California Institute of Technology}, year = {1988}, doi = {10.7907/t5w6-2r52}, url = {https://resolver.caltech.edu/CaltechETD:etd-11072007-140642}, abstract = {Atmospheric aerosols consist of particles with sizes between 0.01 and 10µm. These particles, when occurring in urban areas, consist, in general, of aqueous solutions of sulfate, nitrate, ammonium, chloride, sodium and other ionic species, as well as of primary and secondary organics.
This thesis attempts to describe the evolution and fate of atmospheric aerosol particles. The size-composition distribution of atmospheric aerosols is governed by a combination of kinetics and thermodynamics, which, because of their complexity, can be analyzed only with computer simulations. At first, a solution of the General Dynamic Equation in the case of small coagulation, using perturbation techniques, is developed.
In subsequent work, a comprehensive size-sectionalized trajectory aerosol model was developed for simulating the evolution of a multicomponent aerosol size-composition distribution through homogeneous heteromolecular nucleation, condensational growth, coagulation and deposition. The model was employed along a trajectory from Anaheim to Rubidoux, California.
In the process of analyzing this model it became apparent that a detailed treatment of the thermodynamics of the sodium/ sulfate/ nitrate/ ammonium/ chloride/ water system is very important in aerosol predictions. Thus, an equilibrium model for this system that takes into account differences in the composition among particles of different sizes was developed and tested.
Finally, the same theory was used in a Eulerian framework, thus producing a three-dimensional Eulerian Urban Gas-Aerosol Model, which was used to predict the aerosol concentration and size distribution throughout the Los Angeles Basin on August 30, 1982. Its prediction is compared with measured values and a statistical evaluation study is presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/8cpt-ce77, author = {Adkins, Carol Leslie Jones}, title = {Use of a Continuous Stirred Tank Reactor for the Study of Aqueous Aerosol Chemistry}, school = {California Institute of Technology}, year = {1988}, doi = {10.7907/8cpt-ce77}, url = {https://resolver.caltech.edu/CaltechTHESIS:12042009-080025691}, abstract = {
Atmospheric aerosol chemistry is important in areas ranging from urban air pollution to cloud formation. It has long been supposed that droplet-phase reactions account for a significant fraction of the atmospheric conversion of SO₂ to sulfate. Among such reactions is the manganese-catalyzed aqueous-phase oxidation of SO₂. Whereas the role of aqueous phase SO₂ oxidation in the dilute solutions characteristic of fog and cloud droplets (diameter > 10 µm) has been reasonably well established, the role of comparable reaction in submicron aerosols is uncertain. In this thesis a reactor system is developed to carry out gas-aerosol reactions under humid, ambient-like conditions. The apparatus consists of a continuous stirred tank reactor (CSTR) in which the growth of the aqueous aerosol is measured. Absence of mass transfer limitation, coagulation, and nucleation ensure that particle growth is direct evidence of reaction. Special care is taken to minimize size biasing of the aqueous aerosol in the electrostatic classifier used to measure the reactor feed and effluent distributions. Aerosol behavior in the reactor is modeled assuming an ideal CSTR and, given the solution thermodynamics and equilibrium chemistry, the effluent distribution can be predicted using one of the proposed reaction rate mechanisms.
Experiments were performed using a pure MnSO₄ or a MnSO₄-Na₂SO₄ mixture feed aerosol. The relative humidity ranged from 86 to 94% and 0.1 ppm < pSO₂, < 50 ppm. The slow, approximately constant reaction rate of Bronikowski and Pasiuk-Bronikowska (1981) (R ~ 2 x 10⁻⁴ Ms⁻¹) was found to best predict the observed growth over the entire range of operating conditions. The various rate expressions proposed for this system in the literature resulted in varying estimates of growth. When reactor conditions were similar to those at which the rate expression was determined, the agreement between the predicted and observed distributions improved. This indicates that use of a rate expression beyond its specified range may result in erroneous predictions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/gs7z-gy70, author = {Lee, Tai-yong}, title = {Estimation of Petroleum Reservoir Properties}, school = {California Institute of Technology}, year = {1987}, doi = {10.7907/gs7z-gy70}, url = {https://resolver.caltech.edu/CaltechETD:etd-03012008-135126}, abstract = {
Numerical algorithms are developed to estimate petroleum reservoir properties such as absolute permeability, porosity, and relative permeabilities based on the noisy pressure and flow data. Regularization and spline approximation of spatially varying parameters are employed to convert the ill-posed nature of the problem to a well-posed one. A stabilizing functional with gradient operator is used to measure the non-smoothness of the parameter estimates. The number of spline coefficients along each spatial direction is chosen to be as much as the number of meshes for the reservoir PDE’s. New history matching algorithms are developed that determine the regularization parameter during the computation without requiring a priori information and improve the parameter estimates stepwise. A partial conjugate gradient method is employed for the estimation of a single set of parameters, and the steepest descent algorithm is used for the simultaneous estimation of absolute and relative permeabilities. A rough parametric sensitivity analysis is carried out for the simultaneous estimation to improve the convergence. Numerical tests are carried out to estimate the parameters in single- and two-phase reservoirs for the different choices of the stabilizing functionals, the regularization parameters, and the degrees of spline approximation; and the effects of the observation error, the observation time, and the configuration of the observation points are investigated. The results show that the new algorithms generate better parameter estimates over the various possible choices of the estimation conditions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/de8x-sp79, author = {Sageev Grader, Gideon}, title = {Fourier Transform Infrared Spectroscopy of a Single Aerosol Particle}, school = {California Institute of Technology}, year = {1987}, doi = {10.7907/de8x-sp79}, url = {https://resolver.caltech.edu/CaltechETD:etd-03052008-111804}, abstract = {Throughout this thesis, the phenomenon of radiation-induced particle size change is studied both on a theoretical as well as experimental level. The thrust of this study is aimed at using the size changes due to heat absorption to develop a technique for obtaining the particle chemical composition.
The experiments here involve charged particles, generated with an impulse jet, and trapped by the electric field of an electrodynamic balance. The particles under study are all aqueous solutions of non-volatile salts, where upon heating a partial evaporation of water occurs. The evaporation and subsequent condensation processes are modeled in both the continuum and the transition regimes. The models developed are tested and the agreement between theory and experimental results is demonstrated. The models are also used to extract the values of the water, thermal, and mass accommodation coefficients from the data. The results for the thermal accommodation show that its value is near unity, however the corresponding results for the mass accommodation are not conclusive.
A method is developed for obtaining the molecular composition of a single suspended microparticle by Fourier transform infrared spectroscopy. The particle is irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The laser is tuned to an edge of an optical resonance of the particle while the IR beam is chopped. Through evaporation and condensation the chopped IR beam causes a size modulation of the droplet, which in turn induces a fluctuation in the laser light scattered from the particle. The scattered light is detected at 90° with a photomultiplier, and the amplitude of the light fluctuation is measured with a lock-in amplifier. The lock-in signal is then inverted by a discrete fast Fourier transform routine (FFT), to yield the particle absorption spectrum. Spectra of (NH4)2SO4 droplets at different solute concentrations are presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/czeb-7c12, author = {Mandler, Jorge Anibal}, title = {Robust Control System Design for a Fixed-Bed Catalytic Reactor}, school = {California Institute of Technology}, year = {1987}, doi = {10.7907/czeb-7c12}, url = {https://resolver.caltech.edu/CaltechETD:etd-03212008-092922}, abstract = {
The design of control systems in the face of model uncertainty is addressed. A methodology for the design of robust control schemes is outlined, which employs the Structured Singular Value as an analysis tool and Internal Model Control as the synthesis framework. This methodology is applied to the design of control systems for a fixed-bed, laboratory, catalytic methanation reactor. The design procedure allows a clear insight on the fundamental limits to closed-loop performance and provides controllers with explicit stability and performance guarantees for the case of plant-model mismatch.
The overall controller design effort is initiated with a careful mathematical modeling of the system. The original nonlinear partial differential equations are converted through collocation techniques into a nonlinear ordinary-differential/algebraic equation system amenable to dynamic simulation. Interactive software is developed for the open- and closed-loop simulation of general nonlinear differential-algebraic systems, which provides an efficient means to simulate the reactor model. Linearization and control-relevant model reduction techniques are applied to arrive at models appropriate for the control studies.
Both the single-input single-output and the multivariable case are addressed. Three different control configurations are investigated in the context of the single- pass operation of the reactor. In each case-study presented, the controller design procedure is divided into four steps: first, the definition of the control objectives, which not only leads to the selection of the appropriate control configuration but also determines the most adequate design techniques to employ; second, a nominal design step, in which the system-inherent limitations to the closed-loop performance are highlighted; third, a characterization of the uncertainty and the use of this information in the design of robust controllers; and, fourth, the evaluation of the designs through nonlinear simulations.
The thesis describes the first application of structured singular value-based analysis techniques to a chemical reactor system and is in essence the first comprehensive study of the application of robust control to fixed-bed reactors. The power of the new mathematical theory for robust control system design is demonstrated. It is shown that the design of control systems for complex, distributed systems such as the methanation reactor can be addressed in a practical way, and low-order controllers be adequately obtained, which possess near-optimal characteristics when applied in a realistic environment of uncertainty and unavailability of measurements.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/5ZEY-MH91, author = {Cohen, Mark Daniel}, title = {Studies of Concentrated Electrolyte Solutions Using the Electrodynamic Balance}, school = {California Institute of Technology}, year = {1987}, doi = {10.7907/5ZEY-MH91}, url = {https://resolver.caltech.edu/CaltechETD:etd-03202008-105002}, abstract = {
An electrodynamic balance has been used to measure the water activity as a function of solute concentration at 20 °C for eleven single-electrolyte aqueous solutions - NaCl, NaBr, KCl, KBr, NH4Cl, Na2SO4, (NH4)2SO4, CaCl2, MnCl2, MnSO4 and FeCl3 - and three mixed-electrolyte aqueous solutions - NaCl-KCl, NaCl-KBr, and NaCl-(NH4)2SO4. The measurements were performed by levitating single, charged, 20-micron diameter droplets of these solutions within the balance and measuring the mass of the particles as a function of the surrounding relative humidity. The deliquescence behavior of the particles was also observed.
Heterogeneous nucleation was inhibited due to the absence of container walls and because the small droplets were less likely than a bulk sample to contain foreign particles. Thus, this technique allowed the thermodynamics of highly concentrated solutions to be studied. For most of the solutions, water activity measurements were made to higher solute concentrations than have previously been reported. At low concentrations, the results were consistent with previously published data. Nucleation theory was used to estimate the surface excess free energy and critical nucleus size from the measured supersaturation at which nucleation occurred.
For the single-electrolyte solutions, the dependence of the solute activity coefficient on concentration was calculated, and the features of this dependence are discussed in relationship to ionic hydration and association. Several semi-empirical electrolyte solution models were tested against the data, and it was found that salt-specific model parameters estimated from low concentration data could not be reliably used to predict the solution behavior at high concentrations. However, with estimated parameters based on the full range of the data, the models were able to represent the experimental data for single-electrolyte solutions to within the uncertainty in the measurements.
Three models of mixed-electrolyte solutions — the Zdanovskii-Stokes-Robinson, Reilly-Wood-Robinson and Pitzer methods — agreed well with the experimental data for the NaCl-KCl and NaCl-KBr systems over the range of concentration that the models could be applied. The mixing rules’ predictions were consistent with the experimental observations for the NaCl-(NH4)2SO4 particles assuming a small amount of water was retained in the dry state.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/71dn-x264, author = {Georgopoulos, Panagiotis Gerasimou}, title = {Mathematical Studies of Photochemical Air Pollution}, school = {California Institute of Technology}, year = {1986}, doi = {10.7907/71dn-x264}, url = {https://resolver.caltech.edu/CaltechETD:etd-02012007-092322}, abstract = {In Part I a new, comprehensive model for a chemically reacting plume, is presented, that accounts for the effects of incomplete turbulent macro- and micro- mixing on chemical reactions between plume and ambient constituents. This “Turbulent Reacting Plume Model” (TRPM) is modular in nature, allowing for the use of different levels of approximation of the phenomena involved. The core of the model consists of the evolution equations for reaction progress variables appropriate for evolving, spatially varying systems (“local phenomenal extent of reaction”). These equations estimate the interaction of mixing and chemical reaction and require input parameters characterizing internal plume behavior, such as relative dispersion and fine scale plume segregation. The model addresses deficiencies in previous reactive plume models. Calculations performed with the TRPM are compared with the experimental data of P.J.H. Builtjes for the reaction between NO in a point source plume and ambient O3, taking place in a wind tunnel simulating a neutral atmospheric boundary layer. The comparison shows the TRPM capable of quantitatively predicting the retardation imposed on the evolution of nonlinear plume chemistry by incomplete mixing. Part IA (Chapters 1 to 3) contains a detailed description of the TRPM structure and comparisons of calculations with measurements, as well as a literature survey of reactive plume models. Part IB (Chapters 4 to 7) contains studies on the turbulent dispersion and reaction phenomena and plume dynamics, thus exposing in detail the underlying concepts and methods relevant to turbulent reactive plume modeling. New formulations for describing in-plume phenomena, such as the “Localized Production of Fluctuations Model” for the calculation of the plume concentration variance are included here.
Part II (Chapter 8) presents a collection of distribution-based statistical methods that are appropriate for characterizing extreme events in air pollution studies. Applications to the evaluation of air quality standards, formulation of rollback calculations, and to the use of plume models are included here.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/0edp-5481, author = {Warren, Dale Ross}, title = {Nucleation and Growth of Aerosols}, school = {California Institute of Technology}, year = {1986}, doi = {10.7907/0edp-5481}, url = {https://resolver.caltech.edu/CaltechETD:etd-03212008-085926}, abstract = {This thesis discusses the formation of aerosol particles by homogeneous nucleation of supersaturated vapor, and the subsequent or simultaneous growth of particles by condensation. Experiments, theory, and numerical simulations are used to approach the underlying goal of understanding the aerosol evolution process in photochemically reactive systems, such as Los Angeles smog.
A comprehensive size-sectionalized model was developed for simulating the evolution of a multicomponent aerosol size distribution through homogeneous nucleation, condensational growth, coagulation, and various deposition mechanisms. When applied to atmospheric photochemistry, the model predicted that the number of new particles nucleated is controlled by the ratio between the rates of homogeneous nucleation and condensational growth. A simple model was devised for predicting the number and size evolution of particles which would be formed by a burst of homogeneous nucleation. An interesting aspect of the model was its prediction of suppression of homogeneous nucleation by seed aerosol through bulk vapor depletion. Later these predictions were verified qualitatively in two systems. One was a physiochemically well characterized system where nucleation was driven by a high initial supersaturation ratio, in which nucleation was faster than predicted by classical nucleation theory, and suppression of nucleation was only slight. The second system was our outdoor smog chamber.
In a large outdoor smog chamber, toluene and NOx were allowed to photochemically react. Gas phase concentrations and the resulting aerosol distribution were followed with time, for various initial concentrations of reactants and seed aerosol. A few thousand seed particles per cm3 (sub-ambient concentrations) were sufficient to suppress homogeneous nucleation that would have resulted in several times as many particles. Operation of the chamber in dual mode allowed the influence of a single parameter, varied between the two sides of the bag, to be clearly observed, thus avoiding many of the difficulties that arise from comparing experiments conducted at different times and different temperature and sunlight histories.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/swb9-yg26, author = {Leone, Joseph Anthony}, title = {Studies in Photochemical Smog Chemistry: I. Atmospheric Chemistry of Toluene. II. Analysis of Chemical Reaction Mechanisms for Photochemical Smog}, school = {California Institute of Technology}, year = {1985}, doi = {10.7907/swb9-yg26}, url = {https://resolver.caltech.edu/CaltechETD:etd-12042006-093443}, abstract = {This study focuses on two related topics in the gas phase organic chemistry of importance in urban air pollution. Part I describes an experimental and modeling effort aimed at developing a new explicit reaction mechanism for the atmospheric photooxidation of toluene. This mechanism is tested using experimental data from both indoor and outdoor smog chamber facilities. The predictions of the new reaction mechanism are found to be in good agreement with both sets of experimental data. Additional simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where our understanding is not complete. The outdoor experimental facility, which was built to provide the second set of experimental data, consists of a 65 cubic meter teflon smog chamber together with full instrumentation capable of measuring ozone, nitrogen dioxide, nitric oxide, peroxyacetyl nitrate (PAN), carbon monoxide, relative humidity, temperature, aerosol size distributions, and of course toluene and its photooxidation products.
In Part II, we present a theoretical analysis of lumped chemical reaction mechanisms for photochemical smog. Included is a description of a new counter species analysis technique which can be used to analyze any complex chemical reaction mechanism. When applied to mechanisms for photochemical smog, this analysis is shown capable of providing answers to previously inaccessible questions such as the relative contributions of individual organics to photochemical ozone formation. The counter species analysis is applied to six existing mechanisms for photochemical smog to determine why they predict substantially different degrees of emission controls to achieve the same desired air quality under identical conditions. For each mechanism critical areas are identified that when altered bring the predictions of the various mechanisms into much closer agreement. Finally, a new lumped mechanism for photochemical smog is developed and tested against experimental data from two smog chamber facilities. Advantages of this mechanism relative to the existing lumped mechanisms are discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/VK3Y-QN30, author = {Khanna, Rohit}, title = {Control Model Development for Packed Bed Chemical Reactors}, school = {California Institute of Technology}, year = {1984}, doi = {10.7907/VK3Y-QN30}, url = {https://resolver.caltech.edu/CaltechETD:etd-05152003-160535}, abstract = {
Although control algorithms have been conceived for industrial chemical systems, their acceptance by industry has been slow due to a lack of direct experimental evidence of their effectiveness and to volumes of conflicting, or at least incompatible, recommendations on control structure design. This thesis provides the basis for a concerted theoretical and experimental program in multivariable process control structure design for packed bed chemical reactors by presenting an in-depth control analysis of a practical, multivariable, distributed parameter system-the heat conduction problem defined by the simple diffusion equation-using both frequency-domain and time-domain analyses and the formulation, numerical solution, and analysis of a detailed model for packed bed reactors, along with reduction to a low-order state-space representation suitable for on-line process control.
The study of the heat conduction system allowed for consideration of various control design techniques and the relation between measurement structure and control system design. This study shows that the choice of measurements and their locations significantly affects the optimal control design and the usefulness of the different design techniques and the importance of an accurate process model and the necessity of model reduction to a low-order state-space representation for control structure design and implementation.
The second portion of this study provides a detailed mathematical modeling analysis of packed bed catalytic reactors that significantly extends previous studies in the detail of the model and in the consideration of all aspects of the model development and reduction to a state-space control representation. The general view that modeling simplifications are desired since they lead to a reduction in numerical solution effort is contested, and it is shown that many simplifications are no longer necessary with today’s advanced computational capabilities. A unified approach to dynamic reactor modeling is developed and its importance in the accurate description of dynamic and steady state reactor behavior, in the investigation of reactor start-up or the effects of process disturbances, and in the development of an accurate reduced state-space model for the design of control structures to stabilize the reactor under various disturbances or to provide optimal system recovery from input changes is shown.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/m0kv-m285, author = {Kravaris, Constantine}, title = {Identification of Spatially-Varying Parameters in Distributed Parameter Systems}, school = {California Institute of Technology}, year = {1984}, doi = {10.7907/m0kv-m285}, url = {https://resolver.caltech.edu/CaltechETD:etd-01092007-104956}, abstract = {
Identification of spatially-varying parameters in distributed parameter systems given an observation of the state is as a rule an ill-posed problem in the sense of Hadamard. Even in case when the solution is unique, it does not depend continuously on the data. The identification problem that motivated this work arises in the description of petroleum reservoirs and subsurface aquifers; it consists of identifying the spatially-varying parameter α(x,y) in the diffusion equation ut = (αux)x + (αuy)y + f given an observation of u at a discrete set of spatial locations.
The question of uniqueness of α (identifiability problem) is first investigated. The analysis is restricted to the one-dimensional version of the above equation i.e. to ut = (αux)x + f and an observation of u at a single point. The identifiability problem is formulated as an inverse Sturm-Liouville problem for (αy’)’ + λy = 0. It is proved that the eigenvalues and the normalizing constants determine the above Sturm-Liouville operator uniquely. Identifiability and non-identifiability results are obtained for three special cases.
The problem of constructing stable approximate solutions to identification problems in distributed parameter systems is next investigated. The concept of regularization, widely used in solving linear Fredholm integral equations, is developed for the solution of such problems. A general regularization identification theory is presented and applied to the identification of parabolic systems. Two alternative numerical approaches for the minimization of the smoothing functional are investigated: (i) classical Banach space gradient methods and (ii) discretized minimization methods. The latter use finite-dimensional convergent approximations in Sobolev spaces and are based on an appropriate convergence theorem. The performance of the regularization identification method is evaluated by numerical experiments on the identification of spatially-varying diffusivity α in the diffusion equation.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/9mvc-2t06, author = {Bassett, Mark Elliott}, title = {Mathematical Modeling of Atmospheric Aerosol Equilibria and Dynamics}, school = {California Institute of Technology}, year = {1984}, doi = {10.7907/9mvc-2t06}, url = {https://resolver.caltech.edu/CaltechETD:etd-11092005-105529}, abstract = {Atmospheric aerosols consist of submicron-sized particles occurring at number concentrations of the order of 105 cm-3 and mass concentrations of the order of 100 µg m-3. These aerosols, when occurring in urban areas, consist of aqueous solutions of sulfate, nitrate, ammonium, organic constituents, and certain metals. This thesis is a contribution toward our ability to describe mathematically the formation and growth of such atmospheric aerosols. Since a substantial fraction of the mass of urban aerosols consists of sulfate, nitrate, ammonium and water (Stelson and Seinfeld, 1981), the description of the dynamics of such an aerosol is an important place to initiate the development of aerosol models. The size and composition distribution of atmospheric aerosols are governed by a combination of thermodynamics and kinetics. A detailed treatment of the thermodynamics of the atmospheric sulfate/nitrate/ammonium/water system is presented. Based on this treatment, models are developed to predict the equilibrium quantity, composition, state, and size of the aerosol given gas phase properties. Aerosol kinetics are approached by solution of the General Dynamic Equation for the aerosol sized distribution using the sectional method of Gelbard and Seinfeld. In the most general kinetic model presented, the evolution of the size and composition of an atmospheric sulfate aerosol is predicted under power plant plume conditions. Users manuals for the computer codes comprising the models developed here are given in the Appendix.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/yd9e-2s32, author = {Crump, James Gleason, III}, title = {Aerosol Deposition, Growth, and Dynamics in the Continuous Stirred Tank Reactor}, school = {California Institute of Technology}, year = {1983}, doi = {10.7907/yd9e-2s32}, url = {https://resolver.caltech.edu/CaltechETD:etd-09122006-145635}, abstract = {This work examines three related topics in aerosol science. First, a continuous stirred tank reactor (CSTR) for studying the dynamics of chemically reacting aerosol systems is described. This apparatus is designed to allow aerosols to react under conditions of controlled temperature and relative humidity and is applied to the study of growth of aqueous manganese sulfate aerosols in a humid atmosphere containing sulfur dioxide. From experimental data the rate of conversion of sulfur dioxide to sulfuric acid in manganese sulfate aerosols is deduced.
Second, a new algorithm for inversion of aerosol size distribution data is presented. This algorithm is well suited to the ill-posed nature of the data inversion problem and is shown to give results superior to those obtained using conventional methods. This inversion technique is applied to the analysis of aerosol growth data.
Finally, the general steady state coagulation equations with particle sources and sinks are examined and shown to admit physically unrealistic solutions in some cases. General conditions are then given which insure the existence of physically acceptable solutions and these solutions are shown to have large particle tails that decay exponentially.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/X6ZW-RA12, author = {Pesthy, Andrew John}, title = {Aerosol Formation and Growth in Laminar Flow}, school = {California Institute of Technology}, year = {1983}, doi = {10.7907/X6ZW-RA12}, url = {https://resolver.caltech.edu/CaltechETD:etd-09062006-080949}, abstract = {A detailed theoretical analysis of aerosol nucleation and growth in laminar flow, including the important aspects of mass and energy transfer and aerosol size distribution dynamics, is presented. Simulations of dibutyl phthalate aerosol formation and growth in a laminar flow cooled tube, in the presence and absence of seed particles, are carried out using the classical and Lothe-Pound theories of homogeneous nucleation. The competition between new particle formation and vapor growth onto seed particles is explored in detail. The mathematical model is compared to experimental measurements of aerosol volume distribution and dibutyl phthalate mass balance for a laminar flow cooled tube without seed particles. The model with Lothe-Pound theory shows fair agreement with the mass balance data, but over-predicts the total aerosol number concentration by four orders of magnitude.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/m9ac-pe87, author = {Stelson, Arthur Wesley}, title = {Thermodynamics of Aqueous Atmospheric Aerosols}, school = {California Institute of Technology}, year = {1982}, doi = {10.7907/m9ac-pe87}, url = {https://resolver.caltech.edu/CaltechETD:etd-09062006-113244}, abstract = {A novel application of classical thermodynamics is presented to understand the distribution of aerosol forming material between the gas and aerosol phases in the polluted troposphere. The particular system studied involves NH4NO3 and its interactions with the environmental variables, temperature, relative humidity, droplet pH and aqueous (NH4)2SO4 concentration. In Chapter 1, the theoretical temperature dependence of the solid NH4NO3 dissociation constant is compared to ambient ammonia-nitric acid partial pressure products and general agreement is shown. Also, temperature is demonstrated to be a determining factor for ambient aerosol nitrate formation. Chapter 2 discusses how an urban aerosol can be chemically characterized and that the aqueous electrolytic aerosol solutions are very concentrated (> 8 molal). Thus, any attempt to model ion interactions in aerosol solutions must be able to represent the concentrated solution regime. The ammonia-nitric acid partial pressure product for concentrated NH4NO3-HNO3-H2O solutions is shown to be sensitive to relative humidity but not to pH (1-7) in Chapter 3. Since the ammonia-nitric acid partial pressure product is insensitive to pH, the NH4NO3 dissociation constant over NH4NO3-H2O solutions should typify the ammonia-nitric acid partial pressure product above slightly acidic solutions. The NH4NO3 dissociation constant temperature and relative humidity dependence is evaluated and compared to ambient data in Chapter 4. General agreement between the predictions and the data exists but the possible effect of additional solutes in aerosol droplets is evident. Since NH4NO3 and (NH4)2SO4 are present in atmospheric particles of similar size, it is appropriate to calculate the effect of (NH4)2SO4 on the relative humidity dependence of the NH4NO3 dissociation constant. Chapter 5 shows the presence of (NH4)2SO4 reduces the amount of ammonia and nitric acid in the gas phase and that the NH4NO3 dissociation constant is only 40% less for a 0.5 (NH4)2SO4 ionic strength fraction in aqueous solution. Also, methods for predicting the particle growth, the solution density and the refractive index of NH4NO3-(NH4)2SO4-H2O solutions are outlined in Chapter 5. Good accordance between experimental data and predictions is demonstrated indicating the possible applicability of these techniques to more complex multicomponent solutions.
In the Appendices, a density prediction technique for (NH4)2SO4-H2SO4-H2O solutions is presented since this aspect of ambient aerosols is not contained in the major thrust of this work.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/n8p7-f149, author = {McRae, Gregory John}, title = {Mathematical Modeling of Photochemical Air Pollution}, school = {California Institute of Technology}, year = {1981}, doi = {10.7907/n8p7-f149}, url = {https://resolver.caltech.edu/CaltechETD:etd-05042006-134537}, abstract = {Air pollution is an environmental problem that is both pervasive and difficult to control. An important element of any rational control approach is a reliable means for evaluating the air quality impact of alternative abatement measures. This work presents such a capability, in the form of a mathematical description of the production and transport of photochemical oxidants within an urban airshed. The combined influences of advection, turbulent diffusion, chemical reaction, emissions and surface removal processes are all incorporated into a series of models that are based on the species continuity equations. A delineation of the essential assumptions underlying the formulation of a three-dimensional, a Lagrangian trajectory, a vertically integrated and single cell air quality model is presented. Since each model employs common components and input data the simpler forms can be used for rapid screening calculations and the more complex ones for detailed evaluations.
The flow fields, needed for species transport, are constructed using inverse distance weighted polynomial interpolation techniques that map routine monitoring data onto a regular computational mesh. Variational analysis procedures are then employed to adjust the field so that mass is conserved. Initial concentration and mixing height distributions can be established with the same interpolation algorithms.
Subgrid scale turbulent transport is characterized by a gradient diffusion hypothesis. Similarity solutions are used to model the surface layer fluxes. Above this layer different treatments of turbulent diffusivity are required to account for variations in atmospheric stability. Convective velocity scaling is utilized to develop eddy diffusivities for unstable conditions. The predicted mixing times are in accord with results obtained during sulfur hexafluoride (SF6) tracer experiments. Conventional models are employed for neutral and stable conditions.
A new formulation for gaseous deposition fluxes is presented that provides a means for estimating removal rates as a function of atmospheric stability. The model satisfactorily reproduces measured deposition velocities for reactive materials. In addition it is shown how computational cell size influences the representation of surface removal.
Chemical interactions between twenty nine chemical species are described by a 52 step kinetic mechanism. The atmospheric hydrocarbon chemistry is modeled by the reactions of six lumped classes: alkanes, ethylene, other olefins, aromatics, formaldehyde and other aldehydes; a grouping that enables representation of a wide range of smog chamber experiments and atmospheric conditions. Chemical lumping minimizes the number of species while maintaining a high degree of detail for the inorganic reactions. Variations in rate data, stoichiometric coefficients and initial conditions have been studied using the Fourier Amplitude Sensitivity Test.
The wide variation in time scales, non-linearity of the chemistry and differences in transport processes complicates selection of numerical algorithms. Operator splitting techniques are used to decompose the governing equation into elemental steps of transport and chemistry. Each transport operator is further split into advective and diffusive components so that linear finite element and compact finite difference schemes can be applied to their best advantage. Because most of the computer time is consumed by the chemical kinetics those species that could be accurately described by pseudo-steady state approximations were identified reducing the number of species, described by differential equations, to 15.
While the mathematical formulation of the complete system contains no regional or area specific information, performance evaluation studies were carried out using data measured in the South Coast Air Basin of Southern California. Detailed emissions and meteorological information were assembled for the period 26-28 June 1974. A comparison between predictions and observed air quality, during multi-day periods, indicates that the model can satisfactorily describe urban scale atmospheric concentration dynamics.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/004X-2856, author = {Watson, Albert Theodore}, title = {Estimation of two-phase petroleum reservoir properties}, school = {California Institute of Technology}, year = {1980}, doi = {10.7907/004X-2856}, url = {https://resolver.caltech.edu/CaltechETD:etd-10102006-104201}, abstract = {The estimation of petroleum reservoir properties on the basis of production rate and pressure observations at the wells is an essential component in the prediction of reservoir behavior. The reservoir properties to be estimated appear as parameters in the partial differential equations describing the flow of fluids in the reservoir. The estimation of these properties is referred to variously as the inverse or identification problem or as history matching. In this dissertation, new results have been obtained pertaining to the estimation of petroleum reservoir properties.
Most of the prior analysis of the reservoir parameter estimation problem has been confined to reservoirs containing a single fluid phase, e.g., oil. We consider here reservoirs that contain two fluid phases, e.g., oil and water. The parameters to be estimated in such a case are the porosity and permeability, which depend on spatial location, and the saturation-dependent relative permeabilities. In this work we treat two basic problems in reservoir parameter estimation: (1) establishing the ability to estimate the desired parameters (so-called identifiability), and (2) developing and testing a new algorithm, based on optimal control theory, to carry out the estimation.
In regard to problem (1), we have extended the classic analytical (Buckley-Leverett) solution for incompressible flow to heterogeneous reservoirs. Analysis for an incompressible water flooding situation shows that the spatially varying properties at locations behind the saturation front have an effect on the pressure solution. The spatially varying properties can be uniquely determined based on data taken up to the time of water breakthrough. Only an integral value of the porosity can be determined from the water-oil ratio data alone; however, the spatially varying porosity may be determined when the initial saturation varies with location. The values of the relative permeabilities which are identifiable, and the information about the relative permeabilities obtained for other intervals of saturation, is established. Analytical expressions are derived for the sensitivity of the pressure and water-oil ratio observations to parameters appearing in functional forms of the relative permeabilities. When the relative permeabilities are represented as exponential functions, the coefficients and exponents can be uniquely determined.
For problem (2), an algorithm is developed for the estimation of porosity, permeability and the relative permeabilities for two-phase, compressible reservoirs. This work represents the first study for which relative permeabilities have been estimated based on a model generally used to represent fluid flow in petroleum reservoirs. An objective function, composed of the weighted sum of squares of the deviations between the observed and calculated values of pressure and water-oil ratio, is minimized by a first-order gradient method based on optimal control theory. The algorithm is tested for one and two-dimensional hypothetical water floods. The algorithm performed well for problems in which the porosity, permeability and relative permeability exponents were simultaneously estimated. The increase from one to two spatial variables does not appear to change the properties of the estimation problem. Small observation errors are shown not to significantly affect the convergence of the estimates.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Gavalas, George R.}, } @phdthesis{10.7907/9BZ5-X071, author = {Sander, Stanley Paul}, title = {Kinetics studies of bromine monoxide and methylperoxy free radicals by flash photolysis}, school = {California Institute of Technology}, year = {1980}, doi = {10.7907/9BZ5-X071}, url = {https://resolver.caltech.edu/CaltechETD:etd-11032006-131828}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
A flash photolysis-ultraviolet absorption system was constructed to study the kinetics of gas-phase free radical reactions over a wide range of pressure and temperature. Because of their atmospheric importance, the reactions of methylperoxy (CH302) and bromine monoxide (BrO) radicals with themselves, and with NO and NO2 were investigated:
[…].
The rate constants for reactions 1 - 6 were determined by measuring the first-order or second-order decay rates of BrO and CH3O2 radicals by ultraviolet absorption spectrophotometry. The rate constants for reactions 3 and 6 were found to vary significantly with pressure, indicating the formation of a stable adduct. The pressure dependence of the rate constants was discussed in terms of the Troe theory of unimolecular reactions. Measurements of the branching ratio of reaction 4 were used to develop a detailed reaction mechanism for the disproportionation of BrO radicals. Upper limits were also obtained for the rate constants for the reactions
[…].
The atmospheric implications of the rate constant measurements are discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/WJMB-2D76, author = {Gelbard, Fred}, title = {The general dynamic equation for aerosols}, school = {California Institute of Technology}, year = {1979}, doi = {10.7907/WJMB-2D76}, url = {https://resolver.caltech.edu/CaltechTHESIS:12112012-114024411}, abstract = {This work focusses on developing and solving the conservation equations for a spatially homogeneous aerosol. We begin by developing the basic equations, and in doing so, a new form of the conservation equation or General Dynamic Equation (GDE), termed the discrete-continuous GDE, is presented. In this form, one has the ability to simulate aerosol dynamics in systems in which processes are occurring over a broad particle size spectrum, typical of those found in the atmosphere. All the necessary kinetic coefficients needed to solve the GDE are discussed and the mechanisms for gas-to-particle conversion are also elucidated.
Particle growth rates limited by gas phase diffusion, surface and volume reactions are discussed. In the absence of coagulation, analytic solutions for the above particle growth rates, arbitrary initial and boundary conditions, arbitrary sources, and first order removal mechanisms are developed.
To account for all processes, numerical solutions are required. Therefore, numerical techniques and the errors associated with the numerical solution of the GDE are discussed in detail. By comparing the numerical solution to both analytical solutions for simplified cases and smog chamber data, it is shown that the numerical techniques are highly accurate and efficient.
Techniques for simulating a sulfuric acid and water aerosol are presented. By application of the discrete-continuous GDE, the effect of neglecting cluster-cluster agglomeration, and the effect of a preexisting aerosol on the nucleation rate of a sulfuric acid and water aerosol are studied. The effects of coagulation are also elucidated by simulating the system with the full continuous GDE and the analytic solution to the continuous GDE in the absence of coagulation. Fairly good agreement between the predicted and experimentally observed distributions is obtained.
Finally, an exact solution to the continuous form of the GDE for a multicomponent aerosol for simplified cases is developed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/7DC3-EX92, author = {Shah, Piyush Chimanlal}, title = {Estimation of properties in petroleum reservoirs}, school = {California Institute of Technology}, year = {1977}, doi = {10.7907/7DC3-EX92}, url = {https://resolver.caltech.edu/CaltechETD:etd-12042006-081055}, abstract = {
The determination of parameters in a dynamical system, on the basis of noisy observations of its state is variously known as parameter estimation, identification or the inverse problem. In this work, the determination of porous rock property distribution in a petroleum reservoir using the production rate records and observed pressures (the history matching problem) is considered.
The history matching problem is inherently underdetermined because of the large number of unknown parameters relative to the available data. The number of unknowns can be reduced by representing the distributions by a small number of parameters (parameterization). The commonly used zonation approach involves a parameterization, but introduces a considerable modeling error. In chapter 1, Bayesian estimation theory is extended to history matching as an alternative to zonation; it is sought to alleviate the underdeterminacy through specification of a priori statistical information about the unknown parameters. Application of Bayesian estimation and zonation to the problem of porosity and permeability estimation in a one-dimensional single-phase reservoir indicates that the former yields superior estimates; this holds true even when the prior statistics involve large errors. The application of the conjugate gradient and the Gauss-Newton (or Marquardt’s) algorithms for history matching is investigated, and the numerical effort for zonation and Bayesian estimation in one- and two-dimensional reservoirs is estimated in detail.
In chapter 2, analytic expressions are derived for the sensitivities of an observed oil pressure to small, arbitrary changes in the porosity and permeability distributions in a one-dimensional reservoir. The results indicate that highly oscillatory components of either have very small influence on the pressure and thus cannot be determined by history matching. Further, the dependence of all the observed pressures on the unknown parameters is linearized, for small deviation, about two reference property distributions. The linear relation is analyzed to yield quantitative information concerning the statistical properties of the problem. Iterative corrections in the history matching algorithms are identified with various pseudo-inverses of the linear relation, thus explaining the properties of the resulting estimates. The nature of the linear relation is found to be not strongly dependent on the reference property distributions used for linearization; thus such analysis can be performed prior to estimation. It is discussed how the linearized analysis can be used to determine the determinacy of any given parameterization.
The information derived from the linearized analysis and that in the a priori statistics is synthesized in chapter 3 to predict covariances for the zonation and Bayesian estimates. Since the results of the linearized analysis depend only weakly on the reference distribution, the predicted covariances are valid for a class of reservoirs having “true” property distributions with identical prior statistics. A good agreement is found when the predicted variances are compared with actual mean square estimate errors in simulations with four distributions with given prior statistics. The sensitivity of the estimates and their covariance to changes and errors in the specification of the prior statistics are investigated in considerable detail. The determination of zonation with smallest trace of estimate covariance for a given problem is considered. The design of Marquardt’s algorithm to yield the smallest expected total estimate error for a given zonation is discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H. and Gavalas, George R.}, } @phdthesis{10.7907/47d4-nd32, author = {Robertson, Grant Earl}, title = {Combined Forced and Free Convection in Stratified and Unstratified Flows}, school = {California Institute of Technology}, year = {1975}, doi = {10.7907/47d4-nd32}, url = {https://resolver.caltech.edu/CaltechTHESIS:10062021-232305217}, abstract = {The laminar, steady, horizontal flow past a hot or cold two-dimensional body is examined; the fluid is unbounded, diffusive, and viscous. The presence of significant ambient stable temperature (or density) stratification, or significant buoyancy-induced convection, or both, is considered. A detailed understanding of the fundamental structure of such flows is obtained by developing effective analytical and numerical solution procedures.
Chapter 2: This chapter considers the general problem of stably stratified, Oseen flow at large distances upstream and downstream of a body which is represented as a line sink of horizontal or vertical momentum, or as a line heat source or heat dipole. The analysis is focused on the general properties of the horizontal velocity component, as well as on explicit calculation of the horizontal velocity profiles and disturbance streamfunction fields for varying degrees of stratification. For stable stratifications, the flow fields for all four types of singularities exhibit the common feature of multiple recirculating rotors of finite thicknesses, which leads to an alternating jet structure. both upstream and downstream for the horizontal velocity component and to lee-waves in the overall flow. Self-similar formulae for the velocity, temperature, and pressure at very large distances upstream and downstream are also derived and compared with the Oseen solutions
Chapter 3: The simultaneous forced and free convection flow of a neutrally- or stably-stratified fluid past a hot or cold horizontal flat plate is investigated by numerically solving the full equations of motion and thermal energy subject only to the Boussinesq approximation. The solutions span the parameter ranges 10 ≤ Re ≤ 100, 0.1 ≤ Pr ≤ 10, -2.215 ≤ Gr/Re5/2 ≤ +2.215, and O ≤ Ri ≤ 6.325, where Re, Pr, Gr, and Ri are based on the overall plate length ℓ and the ambient free stream fluid properties evaluated at the plate level. For all degrees of stratification a hot plate causes an acceleration of the boundary flow near the plate surface relative to the corresponding forced convection flow, thereby increasing both the local skin friction and heat transfer coefficients. On the other hand, the boundary flow adjacent to a cold plate is decelerated and the local skin friction and heat transfer rate are decreased. This deceleration effect is enhanced by either further cooling or increasing the amount of ambient stratification, Ri, leading to boundary-layer separation in some cases. When the effect of the ambient stratification dominates that of local heating or cooling, the boundary-layer displacement increases for decreasing Ri, due to the buoyancy restoring force lessening, thus diminishing the drag. The dimunition in the drag, for the same decrease in Ri, lessens (increases) by slightly heating (cooling) the plate. When the effect of local heating or cooling dominates that of the ambient stratification, the drag is diminished by increasing Ri. A wave-structure exists only for stably-stratified fluids, with the amplitudes and wavelengths of the waves being decreased for increasing Ri.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Leal, L. Gary}, } @phdthesis{10.7907/132p-k784, author = {Cormack, Donald Edward}, title = {Topics in Geophysical Fluid Dynamics: I. Natural Convection in Shallow Cavities. II. Studies of a Phenomenological Turbulence Model}, school = {California Institute of Technology}, year = {1975}, doi = {10.7907/132p-k784}, url = {https://resolver.caltech.edu/CaltechTHESIS:01212022-000323683}, abstract = {Part I
The problem of natural convection in a cavity of small aspect ratio with differentially heated end walls is considered. It is shown by use of matched asymptotic expansions that the flow consists of two distinct regimes: a parallel flow in the core region and a second, non-parallel flow near the ends of the cavity. An analytical solution valid at all orders in the aspect ratio, A, is found for the core region, while the first several terms of the appropriate asymptotic expansion are obtained for the end regions. Parametric limits of validity for the parallel flow structure are discussed. Asymptotic expressions for the Nusselt number and the single free parameter of the parallel flow solution, valid in the limit as A → O, are derived.
Also presented are numerical solutions of the full Navier-Stokes equations, which cover the parameter range Pr = 6.983, 10 ≤ Gr ≤ 2 X 10⁴ and 0.05 ≤ A ≤ 1. A comparison with the asymptotic theory shows excellent agreement between the analytical and numerical solutions provided that A ≾ 0.1 and Gr²Pr²A³ ~ 10⁵. In addition, the numerical solutions demonstrate the transition between the shallow-cavity limit and the boundary-layer limit, A fixed Gr → ∞.
Finally, the effect of upper surface boundary conditions on the flow structure within differentially heated shallow cavities is examined. Matched asymptotic solutions, valid for small cavity aspect ratios are presented for the cases of uniform shear stress with zero heat flux, uniform heat flux with zero shear stress, and a heat flux linearly dependent on surface temperature with zero shear stress. It is shown that these changes in surface boundary conditions have an important influence on temperature and flow structure within the cavity.
Part II
The rational closure technique proposed by Lumley and Khajeh-Nouri (1974), in which each unknown correlation is represented as an expansion about the homogeneous, isotropic state, is applied to the approximate closure of the mean Reynolds stress tensor, and rate of dissipation equations for turbulent flows. The high Reynolds number turbulence model which results is similar in many respects to that presented by Lumley et al. However, a more detailed effort is made to evaluate systematically the numerous parameters. Particular emphasis is placed on the suitability and quality of the experimental data which is used for the estimation of model parameters and on the uniqueness and universality of the resulting parameters.
A quantitative comparison of the present turbulence model to those proposed by Daly and Harlow (1970), Hanjalic and Launder (1972b), Shir (1973) and Wyngaard, Cote and Rao (1973), indicates that the present model gives the best overall prediction of the dynamic response for the homogeneous flows of Uberoi (1956, 1957), Champagne, Harris and Corrsin (1970) and Tucker and Reynolds (1968). A further comparison, which evaluates the ability of these turbulence models to predict profiles of the triple-velocity correlation, the rate of intercomponent transfer and the rate of turbulence energy dissipation for inhomogeneous flows indicates that, of the previous turbulence models, that of Hanjalic and Launder is most consistent with the data examined. However, the present model shows promise to yield an even better approximation to the experimental data.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Leal, L. Gary and Seinfeld, John H.}, } @phdthesis{10.7907/6XF8-F790, author = {Chen, Wen Hsiung}, title = {Estimation of parameters in partial differential equations – with applications to petroleum reservoir description}, school = {California Institute of Technology}, year = {1974}, doi = {10.7907/6XF8-F790}, url = {https://resolver.caltech.edu/CaltechETD:etd-10252005-143807}, abstract = {The determination of parameters in dynamical systems, on the basis of noisy experimental data, is called the parameter estimation problem or inverse problem. In this dissertation, several methods for parameter estimation are derived for systems governed by partial differential equations, so-called distributed parameter systems.
The first class of problems, investigated in Chapter II, is that in which the parameters to be estimated are constants. This class of problems is important for it includes most cases of practical interest. Techniques based on gradient optimization, quasilinearization, and collocation methods are developed. A method of determining confidence intervals for parameter estimates is presented, a method which enables one to design experiments (and measurements) that lead to the best estimates of the parameters. The effectiveness of these methods for estimating constant parameters is illustrated through the estimation of the diffusivity in the heat equation, the estimation of the activation energy for a single reaction from dynamic plug flow reactor data, and the estimation of the permeabilities in a two-region reservoir model. The numerical results also show the advantage of using data taken at optimally chosen measurement locations to estimate the parameters.
Many physical systems contain spatially varying parameters, for example, the permeability distribution in a petroleum reservoir model. In Chapter III, two approaches are presented for the estimation of spatially varying parameters. The first is a method of steepest descent based on consideration of the unknown parameter vector as a control vector. The second is based on treating the parameter as an additional state vector and employing least square filtering. The key feature of the former method is that the parameters are considered as continuous functions of position rather than as constant in a certain number of spatial regions. This technique may offer significant savings in computing time over conventional gradient optimization methods, such as steepest descent and Gauss-Newton in which the parameters are considered as uniform in a certain number of zones. Two examples are presented to illustrate the use of the method and its comparison to other algorithms.
In certain cases, the location of the boundary of a system may not be known, such as the boundary of a petroleum reservoir. In the case of oil reservoirs it is very important to be able to estimate the area and shape (or the location of the boundary) of a reservoir so that the production policies can be optimized. A method based on the variation of a functional defined on a variable region is developed in Chapter IV. The computational applications of this method are illustrated in determining the locations of the boundaries of a one-dimensional and a two-dimensional petroleum reservoir.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/dx1x-j848, author = {Reynolds, Steven Diggs}, title = {Mathematical Modeling of Photochemical Air Pollution}, school = {California Institute of Technology}, year = {1974}, doi = {10.7907/dx1x-j848}, url = {https://resolver.caltech.edu/CaltechTHESIS:04152021-211653038}, abstract = {A model is presented for predicting the dynamic behavior of both inert and chemically reacting air pollutants in an urban atmosphere. Pollutants of interest include carbon monoxide, nitric oxide, nitrogen dioxide, ozone, and high and low reactivity hydrocarbons. The model is developed for a general urban area and then applied to the Los Angeles airshed. To evaluate the model, six smoggy days occurring in Los Angeles in 1969 are simulated followed by a comparison of the predictions with the numerous air quality measurements reported by the local air pollution control agencies. In addition, since evaluation of emission control strategies is an important potential use of the model, simulation results are also given demonstrating the possible impact on air quality in the Los Angeles area resulting from implementation of the U.S. Environmental Protection Agency’s control strategy for the South Coast Air Basin proposed in July of 1973.
The governing equations of the model are based on the general mass conservation relationships for a chemically reactive species in a three-dimensional, turbulent atmospheric boundary layer. These equations are solved independently of the coupled Navier-Stokes and energy equations; meteorological parameters in the model are estimated from measured wind and mixing depth data. Reaction rate expressions for the reacting species are derived from a concise, fifteen step kinetic mechanism describing the important chemical reactions that take place in the atmosphere. A detailed discussion is included of the treatment of the winds and temperature inversion in the Los Angeles area.
Since pollutant emissions are an essential input to the model, a general model and comprehensive inventory of contaminant emissions for Los Angeles is presented. Considered in this study are the spatial and temporal distribution of emissions from motor vehicles, aircraft, and fixed sources (including power plants, refineries, etc.).
Because of the nonlinear nature of the chemical kinetics, the governing equations themselves are nonlinear. Thus, a finite difference scheme based on the method of fractional steps is developed to solve the equations. A detailed exposition of all difference equations and their manner of solution is given.
As mentioned previously, an evaluation study of the model is performed by making extensive comparisons of predictions and measurements for Los Angeles. It is found that local pollutant sources near monitoring stations can hamper the comparison of spatially averaged predictions with point measurements. In an effort to account for sub-grid scale effects, a “microscale” model is developed to predict the concentration elevation observed at a monitoring site caused by local sources, such as traffic on nearby streets and freeways. In general, it is found that the model predicts pollutant concentrations reasonably well considering the complexity of the problem and the uncertainty in many of the parameters in the model.
Finally, possible future applications of the model are discussed, including the short range forecast of pollutant concentrations (say up to a few days in the future) and the evaluation of the impact of regional planning decisions and emission control strategies on air quality. To gain experience in applying the model to evaluate emission control strategies, simulations of the Los Angeles region are performed using an emission inventory based on control measures proposed by EPA for the region in 1977. The model results indicate that ozone concentrations will be reduced. substantially from 1969 levels; however, definitive statements with regard to air quality in 1977 must await further refinement of the model and better understanding of the effects of the various proposed control strategies on pollutant emissions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/H6WX-2303, author = {Kyan, Chwan Pein}, title = {Determination of Optimal Air Pollution Control Strategies}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/H6WX-2303}, url = {https://resolver.caltech.edu/CaltechTHESIS:11122019-165102707}, abstract = {One of the important environmental problems facing urban officials today is the selection and enforcement of air pollutant emission control measures. These measures take two forms: long-term controls (multi-year legislation, such as the Federal new car emission standards through 1976) and short-term controls (action taken over a period of hours to days to avoid an air pollution episode). What is required for each form of control is a methodology for the systematic determination of the “best” strategy from among all those possible. In this thesis, a general theoretical framework for the determination of optimal air pollution control strategies is presented for both long-term and real-time controls.
For the long-term control problem, it is assumed that emission control procedures are changed on a year-to-year basis. The problem considered is to determine the set of control measures that minimizes the total cost of control while maintaining specified levels of air quality each year. It is assumed that an airshed model exists which is capable of predicting pollutant concentrations as a function of source emissions in the airshed. Both single-year and multi-year problems are treated. Computational methods are developed based on mathematical programming techniques. The theory and computational methods developed are applied to the evaluation of long-term air pollution control strategies for the Los Angeles basin. Optimal strategies for the control of carbon monoxide, nitrogen dioxide and ozone for 1973 to 1975 in the Los Angeles basin have been obtained.
The problem of determining real-time (short-term) air pollution control strategies for an urban airshed is posed as selecting those control measures from among all possible such that air quality is maintained at a certain level over a given time period and the total control imposed is a minimum. The real-time control is based on meteorological predictions made over a several hour to several day period. A computational algorithm is developed for solving the class of control problems that result.
Typical control measures include restrictions on the number of motor vehicles allowed on a freeway, reduced operation of power plants, and substitution of low emission fuel (e.g. natural gas) for high emission fuel (e.g. coal) in power plants. The control strategy is assumed to be enforced over a certain period, say, one hour, based on meteorological predictions made at the beginning of the period. The strategy for each time period could be determined by an air pollution control agency by means of a computer implementing the algorithm presented. The theory is applied to a hypothetical study of implementation of the optimal control on September 29, 1969 in the Los Angeles basin.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/NEJT-CW55, author = {Hecht, Thomas Arnold}, title = {Development of a Generalized Kinetic Mechanism for Photochemical Smog}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/NEJT-CW55}, url = {https://resolver.caltech.edu/CaltechTHESIS:08172018-124115870}, abstract = {In this dissertation a generalized kinetic mechanism for photochemical smog is formulated and validated. There are two basic objectives for pursuing this work. First, kinetic mechanisms are a critical component of airshed simulation models whose uses include the evaluation of alternative control strategies for photochemical smog. Second, kinetic mechanisms provide a means of understanding the chemistry of smog formation. In addition to developing the kinetic mechanism, extensive consideration is given here to further experimental studies of the kinetics of elementary reactions and to procedural aspects of smog chamber experiments which will aid in reducing uncertainty in future mathematical simulation studies.
The most important feature of the kinetic mechanism which 1s presented in Chapter I lies in its general nature; that is, the mechanism has been written so as to be applicable to a large number of hydrocarbons – and, ultimately, the entire atmospheric hydrocarbon mix – rather than just a specific hydrocarbon such as propylene. The rationale for the lumping procedure is described in detail. By design the resultant mechanism takes advantage of the general features typical of smog formation to maintain at a minimum the number of reactions and species included while at the same time retaining a high degree of detail, especially as concerns the chemistry of the inorganic species. In essence a careful balance between compactness of form and accuracy of prediction is sought. The mechanism is then validated using n-butane-NOx, propylene-NOx, and n-butane-propylene- NOx smog chamber data at 13 different sets of initial reactant concentrations and a wide variety of hydrocarbon to NOx ratios.
Several sources of potential uncertainty in the predictions of the mechanism are discussed. Of these the two most serious – and the two most amenable to correction – are gaps in our knowledge of rate constants and mechanisms of key elementary reactions and effects related to smog chamber systems which either alter or incorrectly monitor the course of smog formation in controlled experimenta1 studies. These sources of uncertainty along with recommendations for future studies to minimize them are the topics of Chapters II and III.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, } @phdthesis{10.7907/C7W5-8C39, author = {Yu, Thomas King Lin}, title = {Optimal filtering for systems governed by coupled ordinary and partial differential equations}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/C7W5-8C39}, url = {https://resolver.caltech.edu/CaltechTHESIS:10202017-140716441}, abstract = {
The recursive estimation of states or parameters of stochastic dynamical systems with partial and imperfect measurements is generally referred to as filtering. The estimator itself is called the filter. In this dissertation optimal filters are derived for three important classes of nonlinear stochastic dynamical systems.
The first class of systems, considered in Chapter II, is that governed by stochastic nonlinear hyperbolic and parabolic partial differential equations in which the dynamical disturbances in the system and in the boundary conditions can be both additive and nonadditive. This class of systems is important for it encompasses a large group of systems of practical interest, such as chemical reactors and heat exchangers. The optimal filter obtained can estimate, not only the state, but also constant parameters appearing at the boundary and in the volume of the system. The computational application of this filter is illustrated in an example of the feedback control of a styrene polymerization reactor.
Many physical systems contain time delays in one form or another. Often, this kind of delay system is accompanied by some other processes such as dissipation of mass and energy, fluid mixing, and chemical reaction. In Chapter III within a single framework new optimal filters are obtained for the following classes of stochastic systems:
The performance of the filter is illustrated through estimates of the temperatures in a system consisting of a well-stirred chemical reactor and an external heat exchanger.
In Chapter IV filtering equations are derived for a completely general class of stochastic systems governed by coupled nonlinear ordinary and partial differential equations of either first order hyperbolic or parabolic type with both volume and boundary random disturbances. Thus, the results of Chapter III can be shown to be a special case of those obtained in Chapter IV.
A related important concept to filtering is observability. For deterministic linear lumped parameter systems, observability refers to the ability to recover some prior state of a dynamical system based on partial observations of the state over some period of time. Under certain conditions, observability of the corresponding deterministic system is a sufficient condition for convergence of the optimal linear filter for a linear system with white noise disturbances. In Chapter V the concept of observability and filter convergence is developed for a class of stochastic linear distributed parameter systems whose solutions can be expressed as eigenfunction expansions. Two important questions examined are: (1) the effect of measurement locations on observability, and (2) the optimal location of measurements for state estimation.
An economic air pollution control model, which determines the least cost of reaching various air quality levels, is formulated. The model takes the form of a general, nonlinear, mathematical programming problem. Primary contaminant emission levels are the independent variables. The objective function is the cost of attaining various emission levels and is to be minimized subject to constraints that given air quality levels be attained.
The model is applied to a simplified statement of the photochemical smog problem in Los Angeles County in 1975 with emissions specified by a two-dimensional vector, total reactive hydrocarbon, (RHC), and nitrogen oxide, (NOx), emissions. Air quality, also two-dimensional, is measured by the expected number of days per year that nitrogen dioxide, (NO2), and mid-day ozone, (O3), exceed standards in Central Los Angeles.
The minimum cost of reaching various emission levels is found by a linear programming model. The base or “uncontrolled” emission levels are those that will exist in 1975 with the present new car control program and with the degree of stationary source control existing in 1971. Controls, basically “add-on devices”, are considered here for used cars, aircraft, and existing stationary sources. It is found that with these added controls, Los Angeles County emission levels [(1300 tons/day RHC, 1000 tons /day NOx) in 1969] and [(670 tons/day RHC, 790 tons/day NOx) at the base 1975 level], can be reduced to 260 tons/day RHC (minimum RHC program) and 460 tons/day NOx (minimum NOx program).
“Phenomenological” or statistical air quality models provide the relationship between air quality and emissions. These models estimate the relationship by using atmospheric monitoring data taken at one (yearly) emission level and by using certain simple physical assumptions, (e. g., that emissions are reduced proportionately at all points in space and time). For NO2, (concentrations assumed proportional to NOx emissions), it is found that standard violations in Central Los Angeles, (55 in 1969), can be reduced to 25, 5, and 0 days per year by controlling emissions to 800, 550, and 300 tons /day, respectively. A probabilistic model reveals that RHC control is much more effective than NOx control in reducing Central Los Angeles ozone. The 150 days per year ozone violations in 1969 can be reduced to 75, 30, 10, and 0 days per year by abating RHC emissions to 700, 450, 300, and 150 tons/day, respectively, (at the 1969 NOx emission level).
The control cost-emission level and air quality-emission level relationships are combined in a graphical solution of the complete model to find the cost of various air quality levels. Best possible air quality levels with the controls considered here are 8 O3 and 10 NO2 violations per year (minimum ozone program) or 25 O3 and 3 NO2 violations per year (minimum NO2 program) with an annualized cost of $230,000,000 (above the estimated $150,000,000 per year for the new car control program for Los Angeles County motor vehicles in 1975).
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {List, E. John}, } @phdthesis{10.7907/BG3X-F787, author = {Hwang, Myung Kyu}, title = {Estimation and Control of Stochastic Chemical Systems}, school = {California Institute of Technology}, year = {1971}, doi = {10.7907/BG3X-F787}, url = {https://resolver.caltech.edu/CaltechTHESIS:05252018-085149423}, abstract = {
Chapter II
The control of nonlinear lumped-parameter systems is considered with unknown random inputs and measurement noise. A scheme is developed whereby a nonlinear filter is included in the control loop to improve system performance. Pure time delays in the control loop are also examined. A computational example is presented for the proportional control on temperature of a CSTR subject to random disturbances, applying a nonlinear least square filter.
Chapter III
Least square filtering and interpolation algorithms are derived for states and parameters in nonlinear distributed systems with unknown additive volume, boundary and observation noises, and with volume and boundary dynamical inputs governed by stochastic ordinary differential equations. Observations are assumed to be made continuously in time at continuous or discrete spatial locations. Two methods are presented for derivation of the filter. One is the limiting procedure of the finite dimensional description of partial differential equation systems along the spatial axis, applying known filter equations in ordinary differential equation systems. The other is to define a least square estimation criterion and convert the estimation problem into an optimal control problem, using extended invariant imbedding technique in partial differential equations. As an example, the derived filter is used to estimate the state and parameter in a nonlinear hyperbolic system describing a tubular plug flow chemical reactor. Also a heat conduction problem is studied with the filtering and interpolation algorithms.
Chapter IV
New necessary and sufficient conditions are presented for the observability of systems described by nonlinear ordinary differential equations with nonlinear observations. The conditions are based on extension of the necessary and sufficient conditions for observability of time-varying linear systems to the linearized trajectory of the nonlinear system. The result is that the local observability of any initial condition can be readily determined, and the observability of the entire initial domain can be computed. The observability of constant parameters appearing in the differential equations is also considered.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Seinfeld, John H.}, }