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.
\r\n\r\nGas-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.
\r\n\r\nOnce 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.
\r\n\r\nFinally, 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.
\r\n", "doi": "10.7907/4J4Q-HP22", "publication_date": "2014", "thesis_type": "phd", "thesis_year": "2014" }, { "id": "thesis:5123", "collection": "thesis", "collection_id": "5123", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12222006-125228", "primary_object_url": { "basename": "Griffin_RJ_2000.pdf", "content": "final", "filesize": 45759393, "license": "other", "mime_type": "application/pdf", "url": "/5123/1/Griffin_RJ_2000.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Experimental and computational studies of secondary organic aerosol formation", "author": [ { "family_name": "Griffin", "given_name": "Robert John", "clpid": "Griffin-R-J" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Dabdub", "given_name": "Donald", "clpid": "Dabdub-D" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "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.\n\nSOA 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.\n\nEfforts 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.", "doi": "10.7907/2F9Q-1772", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" } ]