@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105173, title ="Acetonyl Peroxy and Hydro Peroxy Self- and Cross- Reactions: Kinetics, Mechanism, and Chaperone Enhancement from the Perspective of the Hydroxyl Radical Product", author = "Zuraski, Kristen and Hui, Aileen O.", journal = "Journal of Physical Chemistry A", month = "August", year = "2020", doi = "10.1021/acs.jpca.0c06220", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200831-130459139", note = "© 2020 American Chemical Society. \n\nPublication Date: August 27, 2020. \n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA), supported by the Upper Atmosphere Research and Tropospheric Chemistry Programs. The contribution of K.Z. was supported by the appointment to the NASA Postdoctoral Program at the NASA Jet Propulsion Laboratory, administered by the Universities Space Research Association under contract with NASA. The contribution from A.H. was supported in part by the National Science Foundation (NSF Grant No. CHE-1413712), and the NASA Earth and Science Fellowship (NESSF). M.D.S. was supported by the NASA Earth and Space Science Fellowship (NNX16AO36H). This research was also supported by an appointment of F.J.G. to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA and a SURP grant from Pomona College for E.D. The work by HGK was funded by the Independent Research Fund Denmark. \n\nAuthor contributions: S.S. and M.O. conceived and designed the research. K.Z. conducted the experiments and performed the data analysis. F.A.F. assisted with the IRKS instrumental upgrades. C.J.P. helped with experimental planning and the model mechanism. A.O.H., F.J.G., and E.D. conducted the early experiments and F.J.G. performed the data analysis on the part of that work presented here. M.D.S. wrote the original kinetic analysis library. K.H.M. and H.G.K. contributed the RRKM-ME and MESMER modeling work. K.Z. and F.G. wrote the paper. All authors contributed to the scientific discussion and preparation of the manuscript.", revision_no = "10", abstract = "Pulsed laser photolysis coupled with infrared (IR) wavelength modulation spectroscopy and ultraviolet (UV) absorption spectroscopy was used to study the kinetics and branching fractions for the acetonyl peroxy (CH₃C(O)CH₂O₂) self-reaction and its reaction with hydro peroxy (HO₂) at a temperature of 298 K and pressure of 100 Torr. Near-IR and mid-IR lasers simultaneously monitored HO₂ and hydroxyl, OH, respectively, while UV absorption measurements monitored the CH₃C(O)CH₂O₂ concentrations. The overall rate constant for the reaction between CH₃C(O)CH₂O₂ and HO₂ was found to be (5.5 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and the branching fraction for OH yield from this reaction was directly measured as 0.30 ± 0.04. The CH₃C(O)CH₂O₂ self-reaction rate constant was measured to be (4.8 ± 0.8) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and the branching fraction for alkoxy formation was inferred from secondary chemistry as 0.33 ± 0.13. An increase in the rate of the HO₂ self-reaction was also observed as a function of acetone (CH₃C(O)CH₃) concentration which is interpreted as a chaperone effect resulting from hydrogen-bond complexation between HO₂ and CH₃C(O)CH₃. The chaperone enhancement coefficient for CH₃C(O)CH₃ was determined to be k”A = (4.0 ± 0.2) x 10⁻²⁹ cm⁶ molecule⁻² s⁻¹ and the equilibrium constant for HO₂•CH₃C(O)CH₃ complex formation was found to be K_c(R15) = (2.0 ± 0.89) × 10⁻¹⁸ cm³ molecule⁻¹; from these values the rate constant for the HO₂ + HO₂•CH₃C(O)CH₃ reaction was estimated to be (2 ± 1) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Results from UV absorption cross-section measurements of CH₃C(O)CH₂O₂ and prompt OH radical yields arising from possible oxidation of the CH₃C(O)CH₃-derived alkyl radical are also discussed. Using theoretical methods, no likely pathways for the observed prompt OH radical formation have been found and thus remains unexplained.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/101998, title ="Remote sensing of angular scattering effect of aerosols in a North American megacity", author = "Zeng, Zhao-Cheng and Xu, Feng", journal = "Remote Sensing of Environment", volume = "242", pages = "Art. No. 111760", month = "June", year = "2020", doi = "10.1016/j.rse.2020.111760", issn = "0034-4257", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200319-123810926", note = "© 2020 Elsevier Inc. \n\nReceived 26 June 2019, Revised 27 February 2020, Accepted 9 March 2020, Available online 18 March 2020. \n\nWe thank the reviewers for their constructive comments and suggestions that helped improve the manuscript. The CLARS project receives support from the California Air Resources Board and the NIST GHG and Climate Science Program. V. N. acknowledges support from the NASA Earth Science Division US Participating Investigator program (solicitation NNH16ZDA001N-ESUSPI). F. X. acknowledges support from the NASA Remote Sensing Theory program under grant 14-RST14-0100. We are also thankful for the support from the Jet Propulsion Laboratory Research and Technology Development Program. AERONET data for the Caltech site are available from https://aeronet.gsfc.nasa.gov/new_web/photo_db_v3/CalTech.html. We also thank Jochen Stutz from UCLA and his staff for their effort in establishing and maintaining the AERONET Caltech site. MERRAero is available from NASA GMAO at https://gmao.gsfc.nasa.gov/reanalysis/MERRA/. CLARS-FTS data are available from the authors upon request, and part of the data are available from the NASA Megacities Project at https://megacities.jpl.nasa.gov. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Z. C. Zeng would like to dedicate this paper to his newborn daughter Judith Zeng. \n\nCredit author statement:\nZ.-C. Zeng: Conceptualization, Methodology, Software, Writing-Original draft preparation;\nF. Xu: Software, Validation, Methodology;\nV. Natraj: Software, Validation, Writing - Review & Editing;\nT. Pongetti: Data curation;\nR.-L. Shia: Software, Validation;\nQ. Zhang: Software, Validation;\nS. Sander: Supervision;\nY. Yung: Supervision. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "16", abstract = "The angle-dependent scattering effect of aerosols in the atmosphere not only influences climate through radiative forcing effects but also impacts trace gas remote sensing by modifying the path of radiation through the atmosphere. The aerosol phase function, which characterizes the angular signature of scattering, has been continuously monitored from ground-based and space-borne observations. However, the range of scattering angles these instruments can sample is very limited. Here, we report multi-year measurements from a mountain-top remote sensing instrument: the California Laboratory for Atmospheric Remote Sensing Fourier Transform Spectrometer (CLARS-FTS), which overlooks the Los Angeles megacity. The observational geometries of CLARS-FTS provide a wide range of scattering angles, from about 20° (forward) to about 140° (backward), which is larger than the range provided by any existing aerosol remote sensing instrument. We then quantify the aerosol angular scattering effect using the O₂ ratio, which is the ratio of retrieved O₂ Slant Column Density (SCD) to geometric O₂ SCD. The O₂ ratio quantifies the light path modification due to aerosol scattering, with a value of 1 representing an aerosol-free scenario. The lower the O₂ ratio value than 1, the stronger the aerosol loading. CLARS-FTS measurements are highly sensitive to the angular scattering effect of aerosols in the Los Angeles (LA) urban atmosphere, due to the long light path going through the boundary layer and the wide range of observational angles. The differences in aerosol scattering between different surface reflection points targeted by CLARS-FTS can be explained by differences in their angular scattering geometries. The correlation between measurements at different targets can be used to quantify the strength of the angular dependence of the aerosol phase function. Applying the correlation technique to CLARS-FTS measurements, we find that, from 2011 to 2018, there is no significant trend in the aerosol phase function in the LA megacity. Overall, this study provides a practical observing strategy for quantifying the angular dependence of aerosol scattering in urban atmospheres that could potentially contribute towards improved greenhouse gas remote sensing in megacities.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99661, title ="Constraining the vertical distribution of coastal dust aerosol using OCO-2 O₂ A-band measurements", author = "Zeng, Zhao-Cheng and Chen, Sihe", journal = "Remote Sensing of Environment", volume = "236", pages = "Art. No. 111494", month = "January", year = "2020", doi = "10.1016/j.rse.2019.111494", issn = "0034-4257", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191105-084121561", note = "© 2019 Elsevier Inc. \n\nReceived 12 August 2019, Revised 19 October 2019, Accepted 23 October 2019, Available online 5 November 2019. \n\nWe thank Run-Lie Shia at Caltech, Suniti Sanghavi at JPL, and Chao Liu at NUIST for stimulating discussions. The OCO-2 Forward model is available at https://github.com/nasa/RtRetrievalFramework. The L1bSc OCO-2 radiances are available online from the NASA Goddard GES DISC at https://disc. gsfc.nasa.gov/datacollection/OCO2_ L1B_Science_7.html. MERRAero monthly 3-h averaged dust column density data can be downloaded from (https://portal.nccs.nasa.gov/cgi-lats4d/webform.cgi?&i=GEOS-5/MERRAero/monthly/tavg3hr_2d_aer_Nx). S. C. acknowledges support from the SURF program at the California Institute of Technology and from the National University of Singapore. V. N. acknowledges support from the NASA Earth Science US Participating Investigator program (solicitation NNH16ZDA001N-ESUSPI). F. X. acknowledges support from the NASA Remote Sensing Theory program under grant 14-RST14-0100. A. M. acknowledges support from NASA grant award 80NSSC18K0891 as part of the NASA Science Team for the OCO missions. Z. C. Zeng would like to dedicate this paper to his newborn daughter Judy Zeng. We thank the support from the Jet Propulsion Laboratory Research and Technology Development Program. We also thank the three reviewers for their constructive comments and suggestions. \n\nDeclaration of competing interest: None.", revision_no = "15", abstract = "Quantifying the vertical distribution of atmospheric aerosols is crucial for estimating their impact on the Earth's energy budget and climate, improving forecast of air pollution in cities, and reducing biases in the retrieval of greenhouse gases (GHGs) from space. However, to date, passive remote sensing measurements have provided limited information about aerosol extinction profiles. In this study, we propose the use of a spectral sorting approach to constrain the aerosol vertical structure using spectra of reflected sunlight absorption within the molecular oxygen (O₂) A-band collected by the Orbiting Carbon Observatory-2 (OCO-2). The effectiveness of the approach is evaluated using spectra acquired over the western Sahara coast by comparing the aerosol profile retrievals with lidar measurements from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Using a radiative transfer model to simulate OCO-2 measurements, we found that high-resolution O₂ A-band measurements have high sensitivity to aerosol optical depth (AOD) and aerosol layer height (ALH). Retrieved estimates of AOD and ALH based on a look up table technique show good agreement with CALIPSO measurements, with correlation coefficients of 0.65 and 0.53, respectively. The strength of the proposed spectral sorting technique lies in its ability to identify spectral channels with high sensitivity to AOD and ALH and extract the associated information from the observed radiance in a straightforward manner. The proposed approach has the potential to enable future passive remote sensing missions to map the aerosol vertical distribution on a global scale.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97168, title ="Atmospheric methane emissions correlate with natural gas consumption from residential and commercial sectors in Los Angeles", author = "He, Liyin and Zeng, Zhao‐Cheng", journal = "Geophysical Research Letters", volume = "46", number = "14", pages = "8563-8571", month = "July", year = "2019", doi = "10.1029/2019gl083400", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190716-102712163", note = "© 2019 American Geophysical Union. \n\nReceived 19 APR 2019; Accepted 10 JUL 2019; Accepted article online 15 JUL 2019. \n\nThis research was supported by NIST, CARB, and NASA. We gratefully acknowledge discussions with M. Fischer, G. Heath, J. Hedelius, M. Weitz, and V. Camobreco. L.H. thanks the Resnick Sustainability Institute at Caltech for fellowship support. We thank A. Andrews and E. Dlugokencky for providing the NOAA flask measurements at Mt. Wilson Observatory (National Oceanic and Atmospheric Administration, 2019). CLARS‐FTS data are available from the NASA Megacities Project (https://megacities.jpl.nasa.gov). The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. L. H., Z. C. Z., T. P., C. W., and S. S. carried out the data acquisition and analysis, J. L. and K. G. provided the Hestia inventory, S. S., L. H., and Z. C. Z. wrote the paper, and all authors contributed to the analysis and discussion of the results. The authors declare no competing financial interests.", revision_no = "25", abstract = "Legislation in the State of California mandates reductions in emissions of short‐lived climate pollutants of 40% from 2013 levels by 2030 for CH_4. Identification of the sector(s) responsible for these emissions and their temporal and spatial variability is a key step in achieving these goals. Here, we determine the emissions of CH_4 in Los Angeles from 2011–2017 using a mountaintop remote sensing mapping spectrometer. We show that the pattern of CH_4 emissions contains both seasonal and nonseasonal contributions. We find that the seasonal component peaks in the winter and is correlated (R^2 = 0.58) with utility natural gas consumption from the residential and commercial sectors and not from the industrial and gas‐fired power plant sectors. The nonseasonal component is (22.9 ± 1.4) Gg CH_4/month. If the seasonal correlation is causal, about (1.4 ± 0.1)% of the commercial and residential natural gas consumption in Los Angeles is released into the atmosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94887, title ="Quantification of Nitric Acid Using Photolysis Induced Fluorescence for use in Chemical Kinetic Studies", author = "Winiberg, Frank A. F. and Percival, Carl J.", journal = "Chemical Physics Letters: X", volume = "3", pages = "Art. No. 100029", month = "July", year = "2019", doi = "10.1016/j.cpletx.2019.100029", issn = "2590-1419", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190423-094241715", note = "© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license\n(http://creativecommons.org/licenses/BY/4.0/).\n\nReceived 27 November 2018, Revised 19 March 2019, Accepted 20 March 2019, Available online 22 April 2019. \n\nThe experimental research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA), and was supported by the Upper Atmosphere Research Program. Frank Winiberg’s research was supported by an appointment to the NASA Postdoctoral Program, administered by Universities Space Research Association under contract with NASA. \n\nConflicts of Interest: There are no conflicts to declare.", revision_no = "14", abstract = "Previous laboratory investigations have predominantly relied on UV absorption measurement of [HNO_3]. Whilst direct, this measurement is difficult at temperatures <298 K, where heterogeneous loss to cold surfaces is significant. Single and two photon photodissociation of HNO_3 was studied in N_2 and He at 193 and 248 nm, and a unique HNO_3 detection method was established using two photons at 248 nm, with good reproducibility and limit of detection (∼1.25 × 10^(14) cm^(-3)). Emissions from excited products have been identified spectroscopically, over a range of pressures and laser energies to support the HNO_3 quantification method.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/95497, title ="Temperature Dependence of the Reaction of Chlorine Atoms with CH_3OH and CH_3CHO", author = "Hui, Aileen O. and Okumura, Mitchio", journal = "Journal of Physical Chemistry A", volume = "123", number = "23", pages = "4964-4972", month = "June", year = "2019", doi = "10.1021/acs.jpca.9b00038", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190515-080040718", note = "© 2019 American Chemical Society. \n\nReceived: January 2, 2019; Revised: May 1, 2019; Published: May 15, 2019. \n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). The authors thank the National Science Foundation (NSF Grant No. CHE-1413712), the\nNASA Earth and Space Science Fellowship (NESSF), and NASA’s Upper Atmospheric Research Program (UARP Grant No. NNX12AE01G) and Tropospheric Chemistry Program for financial support. Copyright 2018, California Institute of Technology. \n\nThe authors declare no competing financial interest.", revision_no = "19", abstract = "Rate constants of the reactions Cl + CH_3OH → CH_2OH + HCl (k_1) and Cl + CH_3CHO → CH_3C(O) + HCl (k_3) were measured at 100 Torr over the temperature range 230.3 - 297.1 K. Radical chemistry was initiated by pulsed laser photolysis of Cl_2 in mixtures of CH_3OH and CH_3CHO in a flow reactor. Heterodyne near-IR (NIR) wavelength modulation spectroscopy was used to directly detect HO_2 produced from the subsequent reaction of CH_2OH with O_2 in real-time to determine the rate of reaction of Cl with CH_3OH. The rate of Cl + CH_3CHO was measured relative to that of the Cl + CH_3OH reaction. Secondary chemistry, including that of the adducts HO_2·CH_3OH and HO_2·CH_3CHO, were taken into account. The Arrhenius expressions were found to be k_1(T) = 5.02^(+1.8)_(-1.5)×10^(-11)exp[(20±88)/T] cm^3 molecule^(-1) s^(-1) and k_3(T) =6.38^(+2.4)_(-2.0)×10^(-11)exp[(56±90)/T] cm^3 molecule^(-1) s^(-1) (2σ uncertainties). The average values of the rate constants over this temperature range were k_1 = (5.45±0.37)×10^(-11) cm^3 molecule^(-1) s^(-1) and k_3 = (8.00±1.27)×10^(-11)cm^3 molecule^(-1) s^(-1) (2σ uncertainties), consistent with current literature values.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96023, title ="Spatio-temporally Resolved Methane Fluxes From the Los Angeles Megacity", author = "Yadav, Vineet and Duren, Riley", journal = "Journal of Geophysical Research. Atmospheres", volume = "124", number = "9", pages = "5131-5148", month = "May", year = "2019", doi = "10.1029/2018JD030062", issn = "2169-897X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190603-081853649", note = "Published 2019. This article is a U.S. Government work and is in the public domain in the USA. \n\nReceived 1 DEC 2018; Accepted 29 MAR 2019; Accepted article online 8 APR 2019; Published online 13 MAY 2019. \n\nA portion of the research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). Additional support was provided by the National Institute of Standards and Technology (NIST) Greenhouse Gas and Climate Science Measurements program. Measurements at SBC were supported by the California Air Resourced Board project (11‐306) at LBNL, operating under U.S. Department of Energy (DOE) contract DE‐AC02‐05CH11231. The authors also acknowledge support from NASA's Carbon Monitoring System program and the Prototype Methane Monitoring System for California project. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose. The views expressed in this article are those of the authors and do not represent the views or policies of the California Air Resources Board.", revision_no = "15", abstract = "We combine sustained observations from a network of atmospheric monitoring stations with inverse modeling to uniquely obtain spatiotemporal (3‐km, 4‐day) estimates of methane emissions from the Los Angeles megacity and the broader South Coast Air Basin for 2015–2016. Our inversions use customized and validated high‐fidelity meteorological output from Weather Research Forecasting and Stochastic Time‐Inverted Lagrangian model for South Coast Air Basin and innovatively employ a model resolution matrix‐based metric to disentangle the spatiotemporal information content of observations as manifested through estimated fluxes. We partially track and constrain fluxes from the Aliso Canyon natural gas leak and detect closure of the Puente Hills landfill, with no prior information. Our annually aggregated fluxes and their uncertainty excluding the Aliso Canyon leak period lie within the uncertainty bounds of the fluxes reported by the previous studies. Spatially, major sources of CH_4 emissions in the basin were correlated with CH_4‐emitting infrastructure. Temporally, our findings show large seasonal variations in CH_4 fluxes with significantly higher fluxes in winter in comparison to summer months, which is consistent with natural gas demand and anticorrelated with air temperature. Overall, this is the first study that utilizes inversions to detect both enhancement (Aliso Canyon leak) and reduction (Puente Hills) in CH_4 fluxes due to the unintended events and policy decisions and thereby demonstrates the utility of inverse modeling for identifying variations in fluxes at fine spatiotemporal resolution.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94395, title ="Temperature Dependence Study of the Kinetics and Product Yields of the HO_2 + CH_3C(O)O_2 Reaction by Direct Detection of OH and HO_2 Radicals Using 2f-IR Wavelength Modulation Spectroscopy", author = "Hui, Aileen O. and Fradet, Mathieu", journal = "Journal of Physical Chemistry A", volume = "123", number = "17", pages = "3655-3671", month = "May", year = "2019", doi = "10.1021/acs.jpca.9b00442", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190403-092708652", note = "© 2019 American Chemical Society. Copyright 2018, California Institute of Technology. \n\nReceived: January 15, 2019; Revised: March 14, 2019; Published: April 3, 2019. \n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). The authors thank the Microdevices Lab (MDL) at the Jet Propulsion Laboratory (JPL), and in particular Mathieu Fradet and Siamak Forouhar, who were responsible for the fabrication of our mid-IR OH detection laser. Finally, A.O.H. thanks the National Science Foundation (NSF), the NASA Earth and Space Science Fellowship (NESSF), and NASA’s Upper Atmospheric Research Program (UARP) and Tropospheric Chemistry Program for financial support. \n\nThe authors declare no competing financial interest.", revision_no = "20", abstract = "The HO_2 + CH_3C(O)O_2 reaction consists of three product channels: CH_3C(O)OOH + O_2 (R1a), CH_3C(O)OH + O_3 (R1b), and OH + CH_3C(O)O + O_2 (R1c). The overall rate constant (k_1) and product yields (α_(1a), α_(1b), and α_(1c)) were determined over the atmospherically-relevant temperature range of 230 - 294 K at 100 Torr in N_2. Time resolved kinetics measurements were performed in a pulsed laser photolysis experiment in a slow flow cell employing simultaneous infrared (IR) and ultraviolet (UV) absorption spectroscopy. HO_2 and CH_3C(O)O_2 were formed by Cl-atom reactions with CH_3OH and CH_3CHO, respectively. Heterodyne near- and mid-infrared (NIR and MIR) wavelength modulation spectroscopy (WMS) was employed to selectively detect HO_2 and OH radicals. Ultraviolet absorption at 225 nm and 250 nm was used to detect various peroxy radicals as well as ozone (O_3). These experimental techniques enabled direct measurements of α_(1c) and α_(1b) via time-resolved spectroscopic detection in the MIR and the UV, respectively. At each temperature, experiments were performed at various ratios of initial HO_2 and CH_3C(O)O_2 concentrations to quantify the secondary chemistry. The Arrhenius expression was found to be k1(T) = 1.38^(+1.17)_(-0.63)×10^(-12)exp[(730±170)/T] cm^(-3) molecule^(-1) s^(-1). Α_(1a) was temperature-independent while α_(1b) and α_(1c) increased and decreased, respectively, with increasing temperatures. These trends are consistent with the current recommendation by the IUPAC data evaluation. Hydrogen-bonded adducts of HO_2 with the precursors, HO_2.CH_3OH and HO_2.CH_3CHO, played a role at lower temperatures; as part of this work, kinetics of the adducts were also measured.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/90156, title ="Constraining Aerosol Vertical Profile in the Boundary Layer Using Hyperspectral Measurements of Oxygen Absorption", author = "Zeng, Zhao-Cheng and Natraj, Vijay", journal = "Geophysical Research Letters", volume = "45", number = "19", pages = "10772-10780", month = "October", year = "2018", doi = "10.1029/2018gl079286", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181008-135406047", note = "© 2018 American Geophysical Union. \n\nReceived 20 JUN 2018; Accepted 23 SEP 2018; Accepted article online 27 SEP 2018; Published online 12 OCT 2018. \n\nWe thank Jack Margolis, Chao Liu, Yuan Wang, Siteng Fan, Suniti Sanghavi, Mike Gunson, and Annmarie Eldering for stimulating discussions. V. N. acknowledges support from the NASA Earth Science US Participating Investigator program (solicitation NNH16ZDA001N‐ESUSPI). F. X. acknowledges support from NASA Remote Sensing Theory program under grant 14‐RST14‐0100. We are also thankful for the support from the Jet Propulsion Laboratory Research and Technology Development Program. Part of the research in this study was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The CLARS project receives support from the California Air Resources Board and the NIST GHG and Climate Science Program. The MiniMPL was supported by the KISS Program at Caltech; data are available from the NASA Megacity project data portal: https://megacities.jpl.nasa.gov/portal/. AERONET data for the Caltech site are available from https://aeronet.gsfc.nasa.gov/new_web/photo_db_v3/CalTech.html. We also thank Jochen Stutz from UCLA and his staff for their effort in establishing and maintaining the AERONET Caltech site. CLARS‐FTS data are available from the authors upon request, and part of the data are available from the NASA Megacities Project at https://megacities.jpl.nasa.gov. We are grateful to the two anonymous reviewers whose comments helped improve the paper.", revision_no = "24", abstract = "This study attempts to infer aerosol vertical structure in the urban boundary layer using passive hyperspectral measurements. A spectral sorting technique is developed to retrieve total aerosol optical depth (AOD) and effective aerosol layer height (ALH) from hyperspectral measurements in the 1.27‐μm oxygen absorption band by the mountaintop Fourier Transform Spectrometer at the California Laboratory for Atmospheric Remote Sensing instrument (1,673 m above sea level) overlooking the LA basin. Comparison to AOD measurements from Aerosol Robotic Network and aerosol backscatter profile measurements from a Mini MicroPulse Lidar shows agreement, with coefficients of determination (r^2) of 0.74 for AOD and 0.57 for effective ALH. On average, the AOD retrieval has an error of 24.9% and root‐mean‐square error of 0.013, while the effective ALH retrieval has an error of 7.8% and root‐mean‐square error of 67.01 m. The proposed method can potentially be applied to existing and future satellite missions with hyperspectral oxygen measurements to constrain aerosol vertical distribution on a global scale.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/81117, title ="Resolving the model-observation discrepancy in the mesospheric and stratospheric HO_x chemistry", author = "Li, King-Fai and Zhang, Qiong", journal = "Earth and Space Science", volume = "4", number = "9", pages = "607-624", month = "September", year = "2017", doi = "10.1002/2017EA000283", issn = "2333-5084", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170905-074402925", note = "© 2017 American Geophysical Union. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. \n\nReceived 12 APR 2017; Accepted 28 AUG 2017; Accepted article online 4 SEP 2017; Published online 27 SEP 2017.\n\nWe thank P. Wennberg, R. -L. Shia, S. Newman, and P. Kopparla for helpful comments. We acknowledge the support of the NASA Aura Science Team. S. W., Q. Z., and Y. L. Y. acknowledge partial support by NASA's LWS Program grant NNX16AK63G. K. F. L. was supported partly by the Jack Eddy Fellowship managed by the University Corporation for Atmospheric Research and partly by the NASA grant NNX14AR40G. We thank the two anonymous reviewers, whose comments significantly improved this manuscript. Additional support was provided by the NASA Upper Atmosphere Research and Tropospheric Chemistry Programs. MLS data are available at https://mls.jpl.nasa.gov/products/oh_product.php.", revision_no = "19", abstract = "We examine the middle atmospheric odd-hydrogen (HO_x) chemistry by comparing the Aura Microwave Limb Sounder (MLS) OH and HO_2 measurements with a photochemical model simulation. The model underestimates mesospheric OH and HO_2 concentrations if the standard chemical kinetic rates are used, whether the model H_2O and O_3 are constrained with observations or not. To resolve the discrepancies, we adjust the kinetic rate coefficients of three key reactions (O + OH → O_2 + H, OH + HO_2 → H_2O + O_2, and H + O_2 + M → HO_2 + M) and the O2photo absorption cross section at Lyman-α (121.57 nm) using the Bayesian optimal estimation. A much better model-observation agreement can be achieved if the kinetic rate coefficients for H + O_2 + M → HO_2 + M is increased by 134–310%, and the O_2 photo absorption cross section at Lyman-α is reduced by 33–54%, while the kinetic rate coefficients for O + OH → O_2 + H and OH + HO_2 → H_2O + O_2 remain consistent with the current laboratory values. The kinetic rate coefficient for H + O_2 + M → HO_2 + M requires a very large adjustment beyond the uncertainty limits recommended in the NASA Data Evaluation, suggesting the need for future laboratory measurements. An alternative explanation is that the radiative association reaction, H + O_2 → HO_2 + hν, plays a significant role, which has never been measured. Our results demonstrate that high quality satellite observations can be used to constrain photochemical parameters and help improve our understanding of atmospheric chemistry.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/75555, title ="Aerosol scattering effects on water vapor retrievals over the Los Angeles Basin", author = "Zeng, Zhao-Cheng and Zhang, Qiong", journal = "Atmospheric Chemistry and Physics", volume = "17", number = "4", pages = "2495-2508", month = "February", year = "2017", doi = "10.5194/acp-17-2495-2017", issn = "1680-7324", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170330-153453156", note = "© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License. \n\nReceived: 08 Jun 2016 – Discussion started: 20 Jun 2016. Revised: 27 Jan 2017 – Accepted: 27 Jan 2017 – Published: 17 Feb 2017. \n\nWe thank M. Gunson and A. Eldering for stimulating discussions and support, and M. Gerstell for proofreading the manuscript. Part of the research in this study was performed at the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), under a contract with the National Aeronautics and Space Administration (NASA). Support from the Caltech KISS Megacity project, the NIST GHG and Climate Science Program and NASA’s Carbon Cycle Science Program through the JPL is gratefully acknowledged. Zhao-Cheng Zeng was supported by a postgraduate studentship for overseas academic exchange from the Chinese University of Hong Kong. We thank Jochen Stutz and his staff for their effort in establishing and maintaining the AERONET Caltech site. We also thank the anonymous reviewers whose comments helped improve the paper significantly. \n\nData availability: The AERONET data for this paper can be downloaded online (http://aeronet.gsfc.nasa.gov); CLARS-FTS data are available from the authors upon request. \n\nThe Supplement related to this article is available online at doi:10.5194/acp-17-2495-2017-supplement. The copyright of individual parts of the supplement might differ from the CC-BY 3.0 licence. \n\nThe authors declare that they have no conflict of interest.", revision_no = "18", abstract = "In this study, we propose a novel approach to describe the scattering effects of atmospheric aerosols in a complex urban environment using water vapor (H_2O) slant column measurements in the near infrared. This approach is demonstrated using measurements from the California Laboratory for Atmospheric Remote Sensing Fourier Transform Spectrometer on the top of Mt. Wilson, California, and a two-stream-exact single scattering (2S-ESS) radiative transfer (RT) model. From the spectral measurements, we retrieve H_2O slant column density (SCD) using 15 different absorption bands between 4000 and 8000\u202fcm^(−1). Due to the wavelength dependence of aerosol scattering, large variations in H_2O SCD retrievals are observed as a function of wavelength. Moreover, the variations are found to be correlated with aerosol optical depths (AODs) measured at the AERONET-Caltech station. Simulation results from the RT model reproduce this correlation and show that the aerosol scattering effect is the primary contributor to the variations in the wavelength dependence of the H_2O SCD retrievals. A significant linear correlation is also found between variations in H_2O SCD retrievals from different bands and corresponding AOD data; this correlation is associated with the asymmetry parameter, which is a first-order measure of the aerosol scattering phase function. The evidence from both measurements and simulations suggests that wavelength-dependent aerosol scattering effects can be derived using H_2O retrievals from multiple bands. This understanding of aerosol scattering effects on H_2O retrievals suggests a promising way to quantify the effect of aerosol scattering on greenhouse gas retrievals and could potentially contribute towards reducing biases in greenhouse gas retrievals from space.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/72566, title ="Monthly trends of methane emissions in Los Angeles from 2011 to 2015 inferred by CLARS-FTS observations", author = "Wong, Clare K. and Pongetti, Thomas J.", journal = "Atmospheric Chemistry and Physics", volume = "16", number = "20", pages = "13121-13130", month = "October", year = "2016", doi = "10.5194/acp-16-13121-2016", issn = "1680-7324", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161205-142301578", note = "© 2016 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. \n\nReceived: 16 Mar 2016 – Published in Atmos. Chem. Phys. Discuss.: 29 Apr 2016; Revised: 06 Sep 2016 – Accepted: 10 Sep 2016 – Published: 26 Oct 2016. \n\nThe research in this study was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Clare K. Wong thanks the California Air Resources Board, NIST GHG and Climate Science Program, and the W. M. Keck Institute for Space Studies for support. The authors would like to acknowledge our colleagues at JPL and California Institute of Technology, and Risa Patarasuk at Arizona State University for helpful comments and suggestions.", revision_no = "14", abstract = "This paper presents an analysis of methane emissions from the Los Angeles Basin at monthly timescales across a 4-year time period – from September 2011 to August 2015. Using observations acquired by a ground-based near-infrared remote sensing instrument on Mount Wilson, California, combined with atmospheric CH_4–CO_2 tracer–tracer correlations, we observed −18 to +22\u202f% monthly variability in CH_4\u202f:\u202fCO_2 from the annual mean in the Los Angeles Basin. Top-down estimates of methane emissions for the basin also exhibit significant monthly variability (−19 to +31\u202f% from annual mean and a maximum month-to-month change of 47\u202f%). During this period, methane emissions consistently peaked in the late summer/early fall and winter. The estimated annual methane emissions did not show a statistically significant trend over the 2011 to 2015 time period.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/90301, title ="Los Angeles megacity: a high-resolution land–atmosphere modelling system for urban CO_2 emissions", author = "Feng, Sha and Lauvaux, Thomas", journal = "Atmospheric Chemistry and Physics", volume = "16", number = "14", pages = "9019-9045", month = "July", year = "2016", doi = "10.5194/acp-16-9019-2016", issn = "1680-7316", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181016-153903710", note = "© Author(s) 2016. This work is distributed under the Creative Commons Attribution 3.0 License. \n\nReceived: 15 Feb 2016 – Discussion started: 21 Mar 2016 – Revised: 22 Jun 2016 – Accepted: 04 Jul 2016 – Published: 22 Jul 2016. \n\nA portion of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The Megacities Carbon Project is sponsored in part by the National Institute of Standards and Technology (NIST). Sally Newman acknowledges funding from the Caltech/JPL President & Director’s Research and Development Fund. Kevin R. Gurney thanks NIST grant 70NANB14H321. Ravan Ahmadov was supported by the US Weather Research Program within the NOAA/OAR Office of Weather and Air Quality. Seongeun Jeong and Marc L. Fischer acknowledge the support by the Laboratory Directed Research and Development Program, Office of Science, of the US Department of Energy under contract no. DE-AC02-05CH11231. Thanks to W. Angevine at NOAA for radar wind profiler data, K. Aikin at NOAA for Aircraft WP-3D data, and B. Lefer at University of Houston for ceilometer data. \n\nEdited by: R. Cohen. Reviewed by: I. Super and one anonymous referee. \n\nAuthor contributions. Sha Feng and Thomas Lauvaux designed the model experiments, evaluated the model performance, and developed the assessment of the measuring network; Sally Newman provided the calibrated CO_2 measurements and support for the model evaluations. Preeti Rao, Risa Patarasuk, Darragh O’Keeffe, Jianhua Huang, Yang Song, and Kevin R. Gurney developed and prepared the Vulcan and Hestia emission products; Ravan Ahmadov contributed to the development of the WRF-VPRM model and relevant guidance; Aijun Deng provided quality control for the observations from the National Weather Stations; Liza I. Díaz-Isaac tested PBL algorithms; Seongeun Jeong and Marc L. Fischer provided the background CO_2 concentration for the LA megacity (region); Riley M. Duren, Christoph Gerbig, Zhijin Li, Charles E. Miller, Stanley P. Sander, Kam W. Wong, and Yuk L. Yung provided comments and discussion on the results of the study. \n\nData availability: The model output can be accessed by request (sfeng@psu.edu). Both the Vulcan and Hestia fossil fuel CO_2 emissions data products can be accessed by request (kevin.gurney@asu.edu). Access and information about National Weather Service data can be found at www.weather.gov. Access and information about CalNex data can be found at http://www.esrl.noaa.gov/csd/groups/csd7/measurements/2010calnex/.", revision_no = "10", abstract = "Megacities are major sources of anthropogenic fossil fuel CO_2 (FFCO_2) emissions. The spatial extents of these large urban systems cover areas of 10000 km^2 or more with complex topography and changing landscapes. We present a high-resolution land–atmosphere modelling system for urban CO_2 emissions over the Los Angeles (LA) megacity area. The Weather Research and Forecasting (WRF)-Chem model was coupled to a very high-resolution FFCO_2 emission product, Hestia-LA, to simulate atmospheric CO_2 concentrations across the LA megacity at spatial resolutions as fine as \u2009∼\u20091 km. We evaluated multiple WRF configurations, selecting one that minimized errors in wind speed, wind direction, and boundary layer height as evaluated by its performance against meteorological data collected during the CalNex-LA campaign (May–June 2010). Our results show no significant difference between moderate-resolution (4 km) and high-resolution (1.3 km) simulations when evaluated against surface meteorological data, but the high-resolution configurations better resolved planetary boundary layer heights and vertical gradients in the horizontal mean winds. We coupled our WRF configuration with the Vulcan 2.2 (10 km resolution) and Hestia-LA (1.3 km resolution) fossil fuel CO_2 emission products to evaluate the impact of the spatial resolution of the CO_2 emission products and the meteorological transport model on the representation of spatiotemporal variability in simulated atmospheric CO_2 concentrations. We find that high spatial resolution in the fossil fuel CO_2 emissions is more important than in the atmospheric model to capture CO_2 concentration variability across the LA megacity. Finally, we present a novel approach that employs simultaneous correlations of the simulated atmospheric CO_2 fields to qualitatively evaluate the greenhouse gas measurement network over the LA megacity. Spatial correlations in the atmospheric CO_2 fields reflect the coverage of individual measurement sites when a statistically significant number of sites observe emissions from a specific source or location. We conclude that elevated atmospheric CO_2 concentrations over the LA megacity are composed of multiple fine-scale plumes rather than a single homogenous urban dome. Furthermore, we conclude that FFCO_2 emissions monitoring in the LA megacity requires FFCO_2 emissions modelling with \u2009∼\u20091 km resolution because coarser-resolution emissions modelling tends to overestimate the observational constraints on the emissions estimates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/68534, title ="Matrix-isolated infrared absorption spectrum of CH_2BrOO radical", author = "Zhang, Xu and Sander, Stanley P.", journal = "Chemical Physics Letters", volume = "657", pages = "131-134", month = "July", year = "2016", doi = "10.1016/j.cplett.2016.05.060", issn = "0009-2614", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160620-131343215", note = "© 2016 Elsevier B.V. Copyright 2016 California Institute of Technology. Government sponsorship is acknowledged. \n\nReceived 22 March 2016; In final form 26 May 2016; Available online 27 May 2016. \n\nThis work was supported by the NASA Tropospheric Chemistry and Upper Atmosphere Research Programs. Additional support for this work to J.F.S. comes from the U.S. Department of Energy (Contract Number DE-FG02-07ER15884) and the Robert A. Welch Foundation of Houston, TX (Grant F-1284). The authors would also like to thank Dr. Kyle Bayes and Prof. Barney Ellison for their helpful discussions. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.\n", revision_no = "8", abstract = "The bromomethylperoxy radical, CH_2BrOO, has been generated in cryogenic matrices. Six fundamental bands for CH_2BrOO have been observed in an argon matrix at 5 K. The experimental frequencies (cm^(−1)) are: ν_4 = 1274.3, ν_5 = 1229.4, ν_6 = 1086.7, ν_7 = 961.8, ν_8 = 879.9, and ν_(10) = 515.4, two of which are detected for the first time. Ab initio calculations have been performed employing coupled-cluster methods. The experimental frequencies are shown to be in good agreement with the computation as well as the four bands (ν_4, ν_6, ν_7 and ν_8) observed by Huang and Lee in the gas phase.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91290, title ="X_(CO2) retrieval error over deserts near critical surface albedo", author = "Zhang, Qiong and Shia, Run-Lie", journal = "Earth and Space Science", volume = "3", number = "2", pages = "36-45", month = "February", year = "2016", doi = "10.1002/2015ea000143", issn = "2333-5084", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181128-113131152", note = "©2016. The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. \n\nReceived 21 OCT 2015. Accepted 28 DEC 2015. Accepted article online 3 JAN 2016. Published online 3 FEB 2016. \n\nWe thank A. Eldering, M. Gunson, V. Natraj, J. Margolis, S. Newman, and K.‐F. Li for their helpful comments. We also thank the Editor, F.C. Seidel, and an anonymous reviewer whose comments helped improve the manuscript significantly. This research was supported in part by NASA grant NNX13AK34G to the California Institute of Technology, a grant from the OCO 2 mission at Jet Propulsion Laboratory, and the KISS program at Caltech. The OCO 2 data used in this study can be downloaded from http://oco.jpl.nasa.gov/science/ocodatacenter/.", revision_no = "8", abstract = "Large retrieval errors in column‐weighted CO_2 mixing ratio (X_(CO2)) over deserts are evident in the Orbiting Carbon Observatory 2 version 7 L2 products. We argue that these errors are caused by the surface albedo being close to a critical surface albedo (α_c). Over a surface with albedo close to α_c, increasing the aerosol optical depth (AOD) does not change the continuum radiance. The spectral signature caused by changing the AOD is identical to that caused by changing the absorbing gas column. The degeneracy in the retrievals of AOD and X_(CO2) results in a loss of degrees of freedom and information content. We employ a two‐stream‐exact single scattering radiative transfer model to study the physical mechanism of X_(CO2) retrieval error over a surface with albedo close to α_c. Based on retrieval tests over surfaces with different albedos, we conclude that over a surface with albedo close to α_c, the X_(CO2) retrieval suffers from a significant loss of accuracy. We recommend a bias correction approach that has significantly improved the X_(CO2) retrieval from the California Laboratory for Atmospheric Remote Sensing data in the presence of aerosol loading.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/63339, title ="First evidence of middle atmospheric HO_2 response to 27 day solar cycles from satellite observations", author = "Wang, Shuhui and Zhang, Qiong", journal = "Geophysical Research Letters", volume = "42", number = "22", pages = "10004-10009", month = "November", year = "2015", doi = "10.1002/2015GL065237", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160104-135519357", note = "© 2015 American Geophysical Union. \n\nReceived 6 JUL 2015; Accepted 12 OCT 2015; Accepted article online 14 OCT 2015; Published online 16 NOV 2015. \n\nWe acknowledge the support of the\nNASA Aura Science Team, Upper\nAtmosphere Research, and\nTropospheric Chemistry programs.\nWork at the Jet Propulsion Laboratory,\nCalifornia Institute of Technology, was\ndone under contract to the National\nAeronautics and Space Administration.\nWe acknowledge the LASP Interactive\nSolar Irradiance Datacenter (LISIRD) for\nLyman α record (http://lasp.colorado.\nedu/lisird/).", revision_no = "19", abstract = "HO_2 and OH, also known as HO_x, play an important role in controlling middle atmospheric O_3. Due to their photochemical production and short chemical lifetimes, HO_x are expected to respond rapidly to solar irradiance changes, resulting in O_3 variability. While OH solar cycle signals have been investigated, HO_2 studies have been limited by the lack of reliable observations. Here we present the first evidence of HO_2 variability during solar 27\u2009day cycles by investigating the recently developed HO_2 data from the Aura Microwave Limb Sounder (MLS). We focus on 2012–2015, when solar variability is strong near the peak of Solar Cycle 24. The features of HO_2 variability, with the strongest signals at 0.01–0.068\u2009hPa, correlate well with those of solar Lyman α. When continuous MLS OH observations are not available, the new HO_2 data could be a promising alternative for investigating HO_x variability and the corresponding impacts on O_3 and the climate.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/63123, title ="Simulated retrievals for the remote sensing of CO_2, CH_4, CO, and H_2O from geostationary orbit", author = "Xi, X. and Natraj, V.", journal = "Atmospheric Measurement Techniques", volume = "8", number = "11", pages = "4817-4830", month = "November", year = "2015", doi = "10.5194/amt-8-4817-2015", issn = "1867-8548", url = "https://resolver.caltech.edu/CaltechAUTHORS:20151222-083951345", note = "© 2015 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. \n\nReceived: 21 April 2015 – Published in Atmos. Meas. Tech. Discuss.: 12 June 2015; Revised: 3 September 2015 – Accepted: 5 October 2015 – Published: 18 November 2015. \n\nThe authors would like to thank Renyu Hu, Pushkar Kopparla, Michael Wong, Le Kuai, Clare (Kam Weng) Wong, and Dejian Fu for helpful discussions. The authors also appreciate technical support from Michael Black and administrative support from Margaret Carlos and Irma Black. Valuable comments and suggestions from two reviewers are greatly appreciated. This research was supported in part by NASA grant NNX13AK34G to the California Institute of Technology, grant P1367828 from the Jet Propulsion Laboratory, and the KISS program at California Institute of Technology.", revision_no = "12", abstract = "The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution spectra of reflected sunlight in three near-infrared bands centered around 0.76, 1.6, and 2.3 μm and to deliver simultaneous retrievals of column-averaged dry air mole fractions of CO_2, CH_4, CO, and H_2O (denoted XCO_2, XCH_4, XCO, and XH_2O, respectively) at different times of day over North America. In this study, we perform radiative transfer simulations over both clear-sky and all-sky scenes expected to be observed by GeoFTS and estimate the prospective performance of retrievals based on results from Bayesian error analysis and characterization. \n\nWe find that, for simulated clear-sky retrievals, the average retrieval biases and single-measurement precisions are < 0.2 % for XCO_2, XCH_4, and XH_2O, and < 2 % for XCO, when the a priori values have a bias of 3 % and an uncertainty of 3 %. In addition, an increase in the amount of aerosols and ice clouds leads to a notable increase in the retrieval biases and slight worsening of the retrieval precisions. Furthermore, retrieval precision is a strong function of signal-to-noise ratio and spectral resolution. This simulation study can help guide decisions on the design of the GeoFTS observing system, which can result in cost-effective measurement strategies while achieving satisfactory levels of retrieval precisions and biases. The simultaneous retrievals at different times of day will be important for more accurate estimation of carbon sources and sinks on fine spatiotemporal scales and for studies related to the atmospheric component of the water cycle.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48801, title ="Accounting for aerosol scattering in the CLARS retrieval of column averaged CO_2 mixing ratios", author = "Zhang, Qiong and Natraj, Vijay", journal = "Journal of Geophysical Research. Atmospheres", volume = "120", number = "14", pages = "7205-7218", month = "July", year = "2015", doi = "10.1002/2015JD023499", issn = "2169-897X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140822-092514611", note = "© 2015 American Geophysical Union. \n\nReceived 13 APR 2015; Accepted 2 JUL 2015; Accepted article online 3 JUL 2015; Published online 29 JUL 2015. \n\nWe thank Paul Wennberg, C. Wong, J. Margolis, S. Newman, C. Miller, D. Crisp, M. Gerstell, X. Xi, P. Kopparla, P. Gao, R. Hu, and L. Kuai for their helpful comments. We thank Jochen Stutz and his staff for establishing and maintaining the AERONET Caltech site used in this investigation. We also thank the anonymous reviewers whose comments helped improve the manuscript significantly. This research was supported in part by NASA grant NNX13AK34G to the California Institute of Technology, grant P1367828 from the Jet Propulsion Laboratory, and the KISS program at Caltech. Support for CLARS from the California Air Resources Board, NOAA Climate Program, NIST GHG and Climate Science Program, NASA Carbon Cycle Science Program, and JPL Earth Science and Technology Directorate is gratefully acknowledged. TCCON data were obtained from the TCCON Data Archive, hosted by the Carbon Dioxide Information Analysis Center—tccon.onrl.gov. AERONET data for this paper can be downloaded online. CLARS‐FTS data are available from the authors upon request.", revision_no = "29", abstract = "The California Laboratory for Atmospheric Remote Sensing Fourier transform spectrometer (CLARS‐FTS) deployed at Mount Wilson, California, has been measuring column abundances of greenhouse gases in the Los Angeles (LA) basin in the near‐infrared spectral region since August 2011. CLARS‐FTS measures reflected sunlight and has high sensitivity to absorption and scattering in the boundary layer. In this study, we estimate the retrieval biases caused by aerosol scattering and present a fast and accurate approach to correct for the bias in the CLARS column averaged CO2 mixing ratio product, X_(CO2). The high spectral resolution of 0.06\u2009cm^(−1) is exploited to reveal the physical mechanism for the bias. We employ a numerical radiative transfer model to simulate the impact of neglecting aerosol scattering on the CO_2 and O_2 slant column densities operationally retrieved from CLARS‐FTS measurements. These simulations show that the CLARS‐FTS operational retrieval algorithm likely underestimates CO_2 and O_2 abundances over the LA basin in scenes with moderate aerosol loading. The bias in the CO_2 and O_2 abundances due to neglecting aerosol scattering cannot be canceled by ratioing each other in the derivation of the operational product of X_(CO2). We propose a new method for approximately correcting the aerosol‐induced bias. Results for CLARS X_(CO2) are compared to direct‐Sun X_(CO2) retrievals from a nearby Total Carbon Column Observing Network (TCCON) station. The bias‐correction approach significantly improves the correlation between the X_(CO2) retrieved from CLARS and TCCON, demonstrating that this approach can increase the yield of useful data from CLARS‐FTS in the presence of moderate aerosol loading.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100362, title ="Does the reaction of HO₂ with NO produce HONO₂ and HOONO", author = "Mertens, Laura A. and Allen, Hannah M.", pages = "PHYS-519", month = "March", year = "2015", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191218-144653179", note = "© 2015 American Chemical Society.", revision_no = "10", abstract = "HO_x (HO₂ and OH) and NO_x (NO₂ and NO) radicals are key intermediates in chem. throughout the atm.; the HO_x and NO_x cycles catalyze ozone depletion in the stratosphere and ozone and photochem. smog prodn. in the troposphere. Interconversion within the HO_x family and within the NO_x family happens continuously, partially through the reaction of HO₂ and NO to form OH and NO₂. Since these radicals are continually recycled, even a small branching yield of nitric acid (HONO₂) from the reaction of HO₂ with NO would impact radical concns. predicted in the troposphere and stratosphere, by cumulatively sequestering radicals in a stable reservoir species. Butkovskaya et al. obsd. a small yield of HONO₂ from the reaction of HO₂ with NO (0.5 ˆat 1 atm and 298 K) in a turbulent flow reactor using Chem.-Ionization Mass Spectrometry. We investigated this reaction by an alternative method: detecting the HONO₂ - as well as its weakly bound isomer HOONO - with Pulsed-Cavity Ringdown spectroscopy. HO₂ radicals were produced by Pulsed Laser Photolysis of Cl₂ in a slow flow cell, in the presence of methanol or formaldehyde. Addn. of 700 torr of CO prevented unwanted HONO₂ formation from the reaction of OH and NO₂. Our expts. provide a complementary approach, allowing detection of products spectroscopically on short time-scales in the absence of any wall reactions. Our results raise doubts about the magnitude of the HONO₂ yields obsd. by Butovskaya et al.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100358, title ="Reactions of atmospheric peroxy radicals studied by synchrotron VUV multiplexed photoionization mass spectrometry", author = "Dodson, Leah G. and Shen, Linhan", pages = "PHYS-556", month = "March", year = "2015", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191218-140316314", note = "© 2015 American Chemical Society.", revision_no = "10", abstract = "Peroxy radicals are key intermediates in the oxidn. chem. of both anthropogenic and biogenic Volatile Org. Compds.(VOCs) in the troposphere. These species are central in the formation of photochem. smog and org. aerosols, and can be formed from abstraction reactions or from addn. reactions with unsatd. hydrocarbons. Lab. studies of the kinetics of peroxy radical reactions are complicated by the many competing self- and cross-reactions that typically occur. The large no. of possible products, esp. chain-propagating radical channels, further complicates the chem. Here we describe recent expts. using time-resolved photoionization mass spectrometry (PIMS) with ionization by VUV synchrotron radiation. This method provides a powerful, highly sensitive technique for studying the product branching ratios and reaction rates, by selective time-resolved detection of many of the reactants, intermediates, and primary products. We report investigations of peroxy radical reactions in a laser-photolysis low-pressure flow cell expt. that utilizes tunable VUV radiation generated at the Advanced Light Source synchrotron at the Lawrence Berkeley Lab., coupled to the Sandia multiplexed PIMS app. We have performed expts. on the reactions of the acetyl peroxy radicals, as well as the selfreaction of the Et peroxy radical. We are able to det. relative product yields based on measurements of abs. radical concns., new abs. photoionization cross sections, with the aid of kinetic modeling.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/55030, title ="VUV Photoionization Cross Sections of HO_2, H_2O_2, and H_2CO", author = "Dodson, Leah G. and Shen, Linhan", journal = "Journal of Physical Chemistry A", volume = "119", number = "8", pages = "1279-1291", month = "February", year = "2015", doi = "10.1021/jp508942a", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150219-145521644", note = "© 2015 American Chemical Society. \n\nReceived: September 4, 2014. Revised: January 22, 2015. Publication Date (Web): January 26, 2015. \n\nAcknowledgment\nThe Caltech effort was supported by the National Science Foundation grants CHE-0957490 and CHE-1413712 and the National Aeronautics and Space Administration’s (NASA) Upper Atmospheric Research Program grant NNX12AI01G. L.G.D. was supported by an EPA STAR Fellowship and a Sandia Campus Executive Fellowship. N.C.E. was supported in part by a Dreyfus Foundation Postdoctoral Fellowship in Environmental Chemistry. Part of this research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The participation of D.L.O., J.D.S., O.W., and C.A.T. and the development and maintenance of the MPIMS apparatus are supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under contract DE-AC04-94-AL85000. The research conducted used resources of the Advanced Light Source, which is a DOE Office of Science User Facility at Lawrence Berkeley National Laboratory under contract DE-AC02-05CH11231. \n\nThe authors declare no competing financial interest.", revision_no = "24", abstract = "The absolute vacuum ultraviolet (VUV) photoionization spectra of the hydroperoxyl radical (HO_2), hydrogen peroxide (H_2O_2), and formaldehyde (H_2CO) have been measured from their first ionization thresholds to 12.008 eV. HO_2, H_2O_2, and H_2CO were generated from the oxidation of methanol initiated by pulsed-laser-photolysis of Cl_2 in a low-pressure slow flow reactor. Reactants, intermediates, and products were detected by time-resolved multiplexed synchrotron photoionization mass spectrometry. Absolute concentrations were obtained from the time-dependent photoion signals by modeling the kinetics of the methanol oxidation chemistry. Photoionization cross sections were determined at several photon energies relative to the cross section of methanol, which was in turn determined relative to that of propene. These measurements were used to place relative photoionization spectra of HO_2, H_2O_2, and H_2CO on an absolute scale, resulting in absolute photoionization spectra.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/90300, title ="Mapping CH_4 : CO_2 ratios in Los Angeles with CLARS-FTS from Mount Wilson, California", author = "Wong, K. W. and Fu, D.", journal = "Atmospheric Chemistry and Physics", volume = "15", number = "1", pages = "241-252", month = "January", year = "2015", doi = "10.5194/acp-15-241-2015", issn = "1680-7316", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181016-153903592", note = "© Author(s) 2015. This work is distributed under the Creative Commons Attribution 3.0 License. \n\nReceived: 23 May 2014 – Discussion started: 26 Jun 2014 – Revised: 16 Sep 2014 – Accepted: 18 Oct 2014 – Published: 12 Jan 2015. \n\nThe authors thank our colleagues at JPL, Q. Zhang (California Institute of Technology), D. Wunch (California Institute of Technology), P. Wennberg (California Institute of Technology), C. Roehl (California Institute of Technology), J. Stutz (University of California, Los Angeles) and G. Keppel-Aleks (University of Michigan) for helpful comments. Support from the\nNASA Postdoctoral Program, California Air Resources Board, NOAA Climate Program, NIST GHG and Climate Science Program and JPL Earth Science and Technology Directorate is gratefully acknowledged. Y. L. Yung was supported in part by NASA grant NNX13AK34G to the California Institute of Technology and the KISS program of Caltech. \n\nEdited by: R. Harley", revision_no = "12", abstract = "The Los Angeles megacity, which is home to more than 40% of the population in California, is the second largest megacity in the United States and an intense source of anthropogenic greenhouse gases (GHGs). Quantifying GHG emissions from the megacity and monitoring their spatiotemporal trends are essential to be able to understand the effectiveness of emission control policies. Here we measure carbon dioxide (CO_2) and methane (CH_4) across the Los Angeles megacity using a novel approach – ground-based remote sensing from a mountaintop site. A Fourier transform spectrometer (FTS) with agile pointing optics, located on Mount Wilson at 1.67 km above sea level, measures reflected near-infrared sunlight from 29 different surface targets on Mount Wilson and in the Los Angeles megacity to retrieve the slant column abundances of CO_2, CH_4 and other trace gases above and below Mount Wilson. This technique provides persistent space- and time-resolved observations of path-averaged dry-air GHG concentrations, XGHG, in the Los Angeles megacity and simulates observations from a geostationary satellite. In this study, we combined high-sensitivity measurements from the FTS and the panorama from Mount Wilson to characterize anthropogenic CH_4 emissions in the megacity using tracer–tracer correlations. During the period between September 2011 and October 2013, the observed XCH_4 : XCO_2 excess ratio, assigned to anthropogenic activities, varied from 5.4 to 7.3 ppb CH_4 (ppm CO_2)^(−1), with an average of 6.4 ± 0.5 ppb CH_4 (ppm CO_2)^(−1) compared to the value of 4.6 ± 0.9 ppb CH_4 (ppm CO_2)^(−1) expected from the California Air Resources Board (CARB) bottom-up emission inventory. Persistent elevated XCH_4 : XCO_2 excess ratios were observed in Pasadena and in the eastern Los Angeles megacity. Using the FTS observations on Mount Wilson and the bottom-up CO_2 emission inventory, we derived a top-down CH_4 emission of 0.39 ± 0.06 Tg CH_4 year^(−1) in the Los Angeles megacity. This is 18–61% larger than the state government's bottom-up CH_4 emission inventory and consistent with previous studies.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48327, title ="Laboratory experiments of HO_2 reactions with peroxy radicals using infrared kinetic spectroscopy (IRKS)", author = "Hui, Aileen O. and Grieman, Frederick J.", pages = "PHYS 95", month = "August", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140811-133839521", note = "© 2014 American Chemical Society.", revision_no = "12", abstract = "The reaction of HO_2 with acetyl peroxy radical, CH_3C(O)O_2, has been suggested to proceed via three channels [1]:(a) HO_2 + CH_3C(O)O_2 → CH_3C(O)O_2H + O_2(b) HO_2 + CH_3C(O)O_2 → CH_3C(O)OH + O_3(c) HO_2 + CH_3C(O)O_2 → CH_3C(O)O + OH + O_2Channel (c) is of particular interest not only because of the lack of prodn. of ozone, but also the formation of the hydroxyl radical, OH, a key oxidizing radical in the earth's atm. The results from several independent studies [2,3,4] have shown that the branching ratio of (c) is close to 0.40. Although the results show strong evidence that channel (c) is a significant branch of the reaction of acetyl peroxy radical with HO_2, all expts. were only done at room temp. (298 K) and none of the expts. used techniques that allowed for the measurement of either of the two reacting species. Another concern is that the overall reaction rates of acetyl peroxy radical with HO_2 obtained by the expts. have shown large discrepancies. Furthermore, there is very little information on the temp. dependence of this reaction at upper troposphere temps. The results have led to upper and lower bound ests. by the JPL Data Evaluation panel that differ by almost an order of magnitude. The current study has employed a powerful method called IR Kinetic Spectroscopy (IRKS) for studying radical reactions. In the presented work, this technique is used to study the consumption of HO2 by CH_3C(O)O_2. Specifically, the kinetic rate consts. of this reaction is detd. as a function of temp. (220 to 298 K) and pressure (50 to 400 torr) by simultaneously measuring the disappearance of HO_2 using near-IR spectroscopy and of CH_3C(O)O_2 using UV spectroscopy at a wavelength where HO_2 does not absorb.[1] Hasson, A. S., Tyndall, G. S., Orlando, J. A, 2004, 108 (28), 5979-5989.[2] Crawford, M. A., Wallington, T. J., Szente, J. J., Maricq, M. A, 1999, 103 (3), 365-378.[3] Dillon, T. And Crowley, J. Discuss., 2008, 8, 7111-7148.[4] Moortgat, G. K., Veyret, B., Lesclaux, R. 1989, 160 (4) 18, 443-447.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48583, title ="Pressure and temperature dependences of rate coefficients for the reaction OH + NO_2 + M → products", author = "Liu, Yingdi and Sander, Stanley P.", pages = "ENVR 420", month = "August", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140815-074943119", note = "© 2014 American Chemical Society.", revision_no = "10", abstract = "The OH + NO_2 reaction is a critically important process for radical chain termination in the atm. with a major impact on the ozone budgets of the troposphere and stratosphere. Rate consts. for the reaction of OH + NO_2 + → products have been measured under conditions relevant to the upper troposphere/lower stratosphere with a Pulsed Laser Photolysis - Pulsed Laser Induced Fluorescence technique augmented by in situ optical spectroscopy for quantification of [NO_2]. The expts. are carried out over the temp. range of 230K - 330K and the pressure range 40-800 Torr of air and N_2. The reaction was studied under pseudo first-order conditions, monitoring the decay of OH in the presence of a large excess of NO_2. The obsd. pressure and temp. dependences are analyzed to quantify the falloff behavior and to derive parameters for Troe falloff expressions. The atm. implications are discussed.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48314, title ="Temperature dependent branching ratios of HONO_2 and HOONO from HO_x and NO_x cross reactions found using pulsed cavity-\u200bringdown spectroscopy", author = "Mertens, Laura A. and Okumura, Mitchio", pages = "PHYS 468", month = "August", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140811-131530295", note = "© 2014 American Chemical Society.", revision_no = "14", abstract = "The HO_x (HO_2 and OH) and NO_x (NO and NO_2) cycles have major roles in both ozone loss in the stratosphere and pollution from hydrocarbon oxidn. in the troposphere. Two of the central reactions in the atm. are OH + NO_2 -> HONO_2 and HO_2 + NO -> OH + NO_2.. Formation of stable compds., like HNO_3, by chain termination steps decrease radical concns. in the stratosphere and troposphere and provide sinks for both HO_x and NO_x. We employed pulsed-laser-photolysis (PLP) to generate radicals in a temp.-controlled slow flow cell and mid-IR detection of intermediates and products in real time using cavity-ringdown spectroscopy (CRDS). We have investigated the yields for HONO_2 and HOONO products, extending our previous work on the OH + NO_2 reaction at room temp. Our expts. also shed light on the branching ratio of HONO_2 from HO_2 + NO.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45314, title ="Kinetics and product yields of the acetyl peroxy + HO_2 radical reaction studied by photoionization mass spectrometry", author = "Dodson, Leah G. and Shen, Linhan", pages = "ENVR-98", month = "March", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140429-131752018", note = "© 2014 American Chemical Society.", revision_no = "18", abstract = "The acetyl peroxy radical (CH_3C(O)O_2) is a key intermediate in the oxidn. of carbonyl-contg. hydrocarbons in\nthe troposphere. Reaction of acetyl peroxy radicals with HO_2 has been suggested as a source of OH radicals\nin low-NO_x conditions. Previous work on this reaction obsd. only two product channels forming (1) peracetic\nacid and (2) acetic acid. Recent expts. have shown that there is a third channel that generates the radicals OH\nand acetoxy: CH_3C(O)O_2 + HO_2 → (1) CH_3C(O)OOH + O_2 (2) CH_3C(O)OH + O_3 (3) CH_3C(O)O + O_2 + OH\nThis last pathway to OH formation would then contribute to the apparent isoprene OH recycling suggested by\ndiscrepancies between atm. models and field observations of OH. There have, however, been significant\ndisagreements among expts. on the yield of OH in this reaction. We report our preliminary studies of acetyl\nperoxy reaction with itself and HO_2. Expts. were conducted at the Advanced Light Source synchrotron at the\nLawerence Berkeley National Lab. using tunable VUV ionizing radiation coupled to the Sandia National Lab.\npulsed-laser-photolysis multiplexed photoionization mass spectrometer to detect time-resolved photofragmets of\nreactants, intermediates, and products. From these results, we report new values for the branching fractions of\nthe three product channels in the acetyl peroxy + HO_2 radical reaction.", } @misc {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/65030, title ="Airships: A New Horizon for Science", author = "Miller, Sarah H. and Fesen, Robert", journal = "arXiv", month = "February", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160303-135927410", note = "While we acknowledge specific contributions to this report above, all study members listed on the title page participated in\ninvaluable ways to our brain-storming discussions, conclusions, and recommendations over the course of the study period. In\naddition to the study members who contributed to the Short Course presentations (Robert Fesen, Jens Kauffmann, Steve\nLord, Randy Friedl, Geoff Blake, Paul Goldsmith, and Sarah Miller), we also thank Michael Werner for his presentation.\nThe members of this study would like to extend their gratitude to Michele Judd, Managing Director of the Keck Institute for\nSpace Studies, and her excellent team, for creating an optimal working environment during the workshops and meetings of\nthis study. Judd played a pivotal role in the creation of our new airship science community over the course of the study period.\nWe also thank the director of the Keck Institute for Space Studies, Tom Prince, as well as the Steering Committee for selecting\nour proposal from the 2013 study program candidates. The Institute provided a unique opportunity to bring key science and\nindustry leaders together to make this comprehensive evaluation and report possible.\nWe thank the larger science community for their participation during the Short Course of this study, and their continued\ninterest and support in new airship and stratospheric tether platforms for science. We thank the public for their interest and\nparticipation in the public component of this study.\nWe acknowledge NASA's Jet Propulsion Laboratory and the California Institute of Technology for their internal support of the\nprocess and program of the Keck Institute for Space Studies.\nFinally, we would like to thank the W. M. Keck Foundation for establishing and sustaining the Keck Institute for Space Studies", revision_no = "21", abstract = "The \"Airships: A New Horizon for Science\" study at the Keck Institute for\nSpace Studies investigated the potential of a variety of airships currently\noperable or under development to serve as observatories and science\ninstrumentation platforms for a range of space, atmospheric, and Earth science.\nThe participants represent a diverse cross-section of the aerospace sector,\nNASA, and academia. Over the last two decades, there has been wide interest in\ndeveloping a high altitude, stratospheric lighter-than-air (LTA) airship that\ncould maneuver and remain in a desired geographic position (i.e.,\n\"station-keeping\") for weeks, months or even years. Our study found\nconsiderable scientific value in both low altitude (< 40 kft) and high altitude\n(> 60 kft) airships across a wide spectrum of space, atmospheric, and Earth\nscience programs. Over the course of the study period, we identified\nstratospheric tethered aerostats as a viable alternative to airships where\nstation-keeping was valued over maneuverability. By opening up the sky and\nEarth's stratospheric horizon in affordable ways with long-term flexibility,\nairships allow us to push technology and science forward in a project-rich\nenvironment that complements existing space observatories as well as aircraft\nand high-altitude balloon missions.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/42874, title ="Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy\nRadical", author = "Sprague, Matthew K. and Mertens, Laura A.", journal = "Journal of Physical Chemistry A", volume = "117", number = "39", pages = "10006-10017", month = "October", year = "2013", doi = "10.1021/jp400390y ", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131206-082335728", note = "© 2013 American Chemical Society. Received: January 12, 2013. Revised: May 3, 2013. Publication Date (Web): May 3, 2013. Financial support was provided by the National Aeronautics and Space Administration (NASA) Upper Atmosphere Research Program (grants NNX09AE21G and NNX12AI01G), the National Science Foundation (NSF, Grant CHE-0957490 for experimental work at Caltech and Grant CHE-1213347 for computational work by ABM), and the NASA Tropospheric Chemistry Program. Part of this research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). We acknowledge support of a National Defense Science and Engineering Graduate Fellowship for M.K.S., an NSF Graduate Fellowship for L.A.M., and the Caltech Student-Faculty Programs office for H.N.W. through the Summer Undergraduate Research Fellowship program. We thank Dr. Andrew Mollner, who performed the initial setup of the experiment and the formaldehyde sampling system, Dr. Ralph Page for vital technical assistance and optimization of the spectrometer optics, Michael Roy for machining support, and Richard Gerhart for glassware construction and repair. We\nacknowledge the inspiration provided by Takeshi Oka for this\nwork. \n\nThe authors declare no competing financial interest.\n\nNote that there was a sign error in the last term in eq 2 of ref 48.", revision_no = "19", abstract = "We report vibrational and electronic spectra of the hydroxy-methyl-peroxy radical (HOCH_2OO^• or HMP), which was formed as the primary product of the reaction of the hydroperoxy radical, HO_2^•, and formaldehyde, HCHO. The ν_1 vibrational (OH stretch) spectrum and the à ← X electronic spectrum of HMP were detected by infrared cavity ringdown spectroscopy (IR-CRDS), and assignments were verified with density functional calculations. The HMP radical was generated in reactions of HCHO with HO_2^•. Free radical reactions were initiated by pulsed laser photolysis (PLP) of Cl_2 in the presence of HCHO and O_2 in a flow reactor at 300–330 Torr and 295 K. IR-CRDS spectra were measured in mid-IR and near-IR regions over the ranges 3525–3700 cm^(–1) (ν_1) and 7250–7800 cm^(–1) (à ← X) respectively, at a delay time 100 μs after photolysis. The ν_1 spectrum had an origin at 3622 cm^(–1) and exhibited partially resolved P- and R-branch contours and a small Q-branch. At these short delay times, spectral interference from HOOH and HCOOH was minimal and could be subtracted. From B3LYP/6-31+G(d,p) calculations, we found that the anharmonic vibrational frequency and band contour predicted for the lowest energy conformer, HMP-A, were in good agreement with the observed spectrum. In the near-IR, we observed four well spaced vibronic bands, each with partially resolved rotational contours. We assigned the apparent origin of the à ← X electronic spectrum of HMP at 7389 cm^(–1) and two bands to the blue to a progression in ν15′, the lowest torsional mode of the à state (ν_(15′) = 171 cm^(–1)). The band furthest to the red was assigned as a hot band in ν^(15″), leading to a ground state torsional frequency of (ν^(15″) = 122 cm^(–1)). We simulated the spectrum using second order vibrational perturbation theory (VPT2) with B3LYP/6-31+G(d,p) calculations at the minimum energy geometries of the HMP-A conformer on the X and à states. The predictions of the electronic origin frequency, torsional frequencies, anharmonicities, and rotational band contours matched the observed spectrum. We investigated the torsional modes more explicitly by computing potential energy surfaces of HMP as a function of the two dihedral angles τ_(HOCO) and τ_(OOCO). Wave functions and energy levels were calculated on the basis of this potential surface; these results were used to calculate the Franck–Condon factors, which reproduced the vibronic band intensities in the observed electronic spectrum. The transitions that we observed all involved states with wave functions localized on the minimum energy conformer, HMP-A. Our calculations indicated that the observed near-IR spectrum was that of the lowest energy X state conformer HMP-A, but that this conformer is not the lowest energy conformer in the à state, which remains unobserved. We estimated that the energy of this lowest conformer (HMP-B) of the à state is E_0 (Ã, HMP-B) ≈ 7200 cm^(–1), on the basis of the energy difference E_0(HMP-B) – E_0(HMP-A) on the à state computed at the B3LYP/6-31+G(d,p) level.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/37807, title ="Midlatitude atmospheric OH response to the most recent 11-y solar cycle", author = "Wang, Shuhui and Li, King-Fai", journal = "Proceedings of the National Academy of Sciences of the United States of America", volume = "110", number = "6", pages = "2023-2028", month = "February", year = "2013", doi = "10.1073/pnas.1117790110 ", issn = "0027-8424", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130408-133142312", note = "© 2013 National Academy of Sciences.\n\nEdited by Steven C. Wofsy, Harvard University, Cambridge, MA, and approved December 19, 2012 (received for review November 1, 2011).\nPublished online before print January 22, 2013.\nWe thank the NASA Aura Science Team and the Upper Atmosphere Research and Tropospheric Chemistry programs for\ntheir support. We thank R. C. Willson for providing the ACRIM TSI composite (www.acrim.com) and the Laboratory for Atmospheric and Space Physics Interactive Solar Irradiance Datacenter for composites of Lyman-α and Mg-II indices (http://lasp.colorado.edu/lisird/). We also acknowledge\nreceipt of a TSI dataset from the PMOD (www.pmodwrc.ch/)\nand receipt of unpublished data from the Variability of Solar Irradiance and Gravity Oscillations on board the Solar and Heliospheric Observatory. Some FTUVS OH data from early years were collected by R. P. Cageao. We thank H. M. Pickett, the principal investigator (retired) for the MLS OH measurements and a NASA Aura Science Team project. We\nalso thank R.-L. Shia and S. Newman for help with the models and error analysis and insightful discussions. Work at the Jet Propulsion Laboratory, California Institute of Technology, was done under contract to NASA. Support from an Australian Research Council Linkage International\ngrant is gratefully acknowledged.\n\nAuthor contributions: S.W., K.-F.L., S.P.S., Y.L.Y., and F.P.M. designed research; S.W., K.-F.L.,\nand T.J.P. performed research; M.-C.L., J.W.H., and M.S. contributed new reagents/analytic\ntools; S.W., T.J.P., N.J.L., M.L.S., J.W.H., and M.S. analyzed data; and S.W. and K.-F.L. wrote\nthe paper.", revision_no = "24", abstract = "The hydroxyl radical (OH) plays an important role in middle atmospheric photochemistry, particularly in ozone (O_3) chemistry. Because it is mainly produced through photolysis and has a short chemical lifetime, OH is expected to show rapid responses to solar forcing [e.g., the 11-y solar cycle (SC)], resulting in variabilities in related middle atmospheric O_3 chemistry. Here, we present an effort to investigate such OH variability using long-term observations (from space and the surface) and model simulations. Ground-based measurements and data from the Microwave Limb Sounder on the National Aeronautics and Space Administration’s Aura satellite suggest an ∼7–10% decrease in OH column abundance from solar maximum to solar minimum that is highly correlated with changes in total solar irradiance, solar Mg-II index, and Lyman-α index during SC 23. However, model simulations using a commonly accepted solar UV variability parameterization give much smaller OH variability (∼3%). Although this discrepancy could result partially from the limitations in our current understanding of middle atmospheric chemistry, recently published solar spectral irradiance data from the Solar Radiation and Climate Experiment suggest a solar UV variability that is much larger than previously believed. With a solar forcing derived from the Solar Radiation and Climate Experiment data, modeled OH variability (∼6–7%) agrees much better with observations. Model simulations reveal the detailed chemical mechanisms, suggesting that such OH variability and the corresponding catalytic chemistry may dominate the O_3 SC signal in the upper stratosphere. Continuing measurements through SC 24 are required to understand this OH variability and its impacts on O_3 further. ", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33431, title ="Low temperatures and pressure dependence study of OH and CO reaction", author = "Liu, Yingdi and Sander, Stanley P.", pages = "PHYS-131", month = "August", year = "2012", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120822-074655130", revision_no = "14", abstract = "OH radical and CO reaction is of crucial importance in the atmospheres of Mars and Earth. In this work, the reaction is studied under pseudo first-order conditions, monitoring the decay of OH by laser-induced fluorescence in the presence of a large excess of CO. We measured rate coeffs. for the reaction of OH with CO using laser photolysis/laser-induced fluorescence in 180K - 295K temp. under 100 to 200 torr. The pressure dependence study is ranging from 50 to 800 torr with Ar, He or N2 as bath gas. The biexponential decay of OH signal is obsd. and it is analyzed to derive information about the equil. const. for reaction: OH + CO ↔HOCO.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/32446, title ="Kinetics of n-Butoxy and 2-Pentoxy Isomerization and Detection of Primary Products by Infrared Cavity Ringdown Spectroscopy", author = "Sprague, Matthew K. and Garland, Eva R.", journal = "Journal of Physical Chemistry A", volume = "116", number = "24", pages = "6327-6340", month = "June", year = "2012", doi = "10.1021/jp212136r", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120716-075316620", note = "© 2012 American Chemical Society. Special Issue: A. R. Ravishankara Festschrift. Received: December 15, 2011. \nRevised: April 23, 2012. Publication Date (Web): April 24, 2012. Financial support was provided by the NASA Upper\nAtmosphere Research Program Grants NAG5-11657,\nNNG06GD88G, and NNX09AE21G, National Science Foundation\ngrant CHE-0957490 and the California Air Resources\nBoard Contracts 03-333 and 07-730. Part of this research was\ncarried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration. M.K.S. thanks the Department of Defense NDSEG Graduate Fellowship for funding. E.R.G. was supported by an EPA STAR Graduate Research Fellowship. Support from the NASA UARP and Tropospheric\nChemistry Program is acknowledged. A.K.M. thanks the\nNASA Earth System Science and NSF Graduate Research\nFellowship programs. M.L.W. thanks the Caltech Student-\nFaculty Programs office for funding through the Summer\nUndergraduate Research Fellowship program. We thank Todd\nFuelberth and Dave Natzic for building the OPA crystal\nrotation mechanism and other technical assistance, David\nRobichaud for LabVIEW programming, Ralph Page for\noptimization of the spectrometer optics, Nathan Eddingsaas\nfor assistance with FTIR analysis of the 2-pentyl nitrite, Michael Roy for machining of the CRDS mirror mounts, Tom Dunn for electronics assistance, and Richard Gerhart for glassware\nconstruction and repair. ", revision_no = "21", abstract = "The primary products of n-butoxy and 2-pentoxy isomerization in the presence and absence of O_2 have been detected using pulsed laser photolysis-cavity ringdown spectroscopy (PLP-CRDS). Alkoxy radicals n-butoxy and 2-pentoxy were generated by photolysis of alkyl nitrite precursors (n-butyl nitrite or 2-pentyl nitrite, respectively), and the isomerization products with and without O_2 were detected by infrared cavity ringdown spectroscopy 20 μs after the photolysis. We report the mid-IR OH stretch (ν_1) absorption spectra for δ-HO-1-C_4H_8•, δ-HO-1-C_4H_8OO•, δ-HO-1-C_5H_(10)•, and δ-HO-1-C_5H_(10)OO•. The observed ν_1 bands are similar in position and shape to the related alcohols (n-butanol and 2-pentanol), although the HOROO• absorption is slightly stronger than the HOR• absorption. We determined the rate of isomerization relative to reaction with O_2 for the n-butoxy and 2-pentoxy radicals by measuring the relative ν_1 absorbance of HOROO• as a function of [O_2]. At 295 K and 670 Torr of N_2 or N_2/O_2, we found rate constant ratios of k_(isom)/k_(O2) = 1.7 (±0.1) × 10^(19) cm^(–3) for n-butoxy and k_(isom)/k_(O2) = 3.4(±0.4) × 10^(19) cm^(–3) for 2-pentoxy (2σ uncertainty). Using currently known rate constants k_(O2), we estimate isomerization rates of k_(isom) = 2.4 (±1.2) × 10^5 s^(–1) and k_(isom) ≈ 3 × 10^5 s^(–1) for n-butoxy and 2-pentoxy radicals, respectively, where the uncertainties are primarily due to uncertainties in k_(O2). Because isomerization is predicted to be in the high pressure limit at 670 Torr, these relative rates are expected to be the same at atmospheric pressure. Our results include corrections for prompt isomerization of hot nascent alkoxy radicals as well as reaction with background NO and unimolecular alkoxy decomposition. We estimate prompt isomerization yields under our conditions of 4 ± 2% and 5 ± 2% for n-butoxy and 2-pentoxy formed from photolysis of the alkyl nitrites at 351 nm. Our measured relative rate values are in good agreement with and more precise than previous end-product analysis studies conducted on the n-butoxy and 2-pentoxy systems. We show that reactions typically neglected in the analysis of alkoxy relative kinetics (decomposition, recombination with NO, and prompt isomerization) may need to be included to obtain accurate values of k_(isom)/k_(O2).", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/57374, title ="The Geostationary Carbon Process Mapper", author = "Keys, Richard and Sander, Stanley", pages = "1-16", month = "March", year = "2012", doi = "10.1109/AERO.2012.6187029", isbn = "978-1-4577-0556-4", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150508-102328349", note = "Copyright 2012, California Institute of Technology. Government sponsorship acknowledged. Date of Conference: 3-10 March 2012.\n\nThe research described in this publication was carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration.", revision_no = "14", abstract = "The Geostationary Carbon Process Mapper (GCPM) is an earth science mission to measure key atmospheric trace gases and process tracers related to climate change and human activity. The measurement strategy delivers a process based understanding of the carbon cycle that is accurate and extensible from city to regional and continental scales. This understanding comes from contiguous maps of carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), and chlorophyll fluorescence (CF) collected up to 10 times per day at high spatial resolution (~4km × 4km) from geostationary orbit (GEO). These measurements will capture the spatial and temporal variability of the carbon cycle across diurnal, synoptic, seasonal and interannual time scales. The CO2/CH4/CO/CF measurement suite has been specifically selected because their combination provides the information needed to disentangle natural and anthropogenic contributions to atmospheric carbon concentrations and to minimize key uncertainties in the flow of carbon between the atmosphere and surface since they place constraints on both biogenic uptake and release as well as on combustion emissions. Additionally, GCPM's combination of high-resolution mapping and high measurement frequency provide quasi-continuous monitoring, effectively eliminating atmospheric transport uncertainties from source/sink inversion modeling. GCPM uses a single instrument, the “Geostationary Fourier Transform Spectrometer (GeoFTS)” to make measurements in the near infrared spectral region at high spectral resolution. The GeoFTS is a half meter cube size instrument designed to be a secondary “hosted” payload on a commercial GEO satellite. NASA and other government agencies have adopted the hosted payload implementation approach because it substantially reduces the overall mission cost. This paper presents a hosted payload implementation approach for measuring the major carbon-containing gases in the atmosphere from the geostationary vantage point, to affordably advance the scientific understating of carbon cycle processes and climate change.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/27147, title ="Determination of Equilibrium Constants for the Reaction between Acetone and HO_2 Using Infrared Kinetic Spectroscopy", author = "Grieman, Fred J. and Noell, Aaron C.", journal = "Journal of Physical Chemistry A", volume = "115", number = "38", pages = "10527-10538", month = "September", year = "2011", doi = " 10.1021/jp205347s", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111010-152528326", note = "© 2011 American Chemical Society.\n\nReceived: June 7, 2011; revised: August 8, 2011; published: August 9, 2011.\n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). This work was supported by the NASA Upper Atmosphere Research and Tropospheric Chemistry Programs and the NASA Graduate Student Research Program (GSRP). This research was supported by an appointment of Fred Grieman to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA and a SURP grant from Pomona College for C.D.-V. A. We acknowledge the vital technical support of Dave Natzic. Government sponsorship is acknowledged.", revision_no = "21", abstract = "The reaction between the hydroperoxy radical, HO_2, and acetone may play an important role in acetone removal and the budget of HO_x radicals in the upper troposphere. We measured the equilibrium constants of this reaction over the temperature range of 215–272 K at an overall pressure of 100 Torr using a flow tube apparatus and laser flash photolysis to produce HO_2. The HO_2 concentration was monitored as a function of time by near-IR diode laser wavelength modulation spectroscopy. The resulting [HO_2] decay curves in the presence of acetone are characterized by an immediate decrease in initial [HO_2] followed by subsequent decay. These curves are interpreted as a rapid (<100 μs) equilibrium reaction between acetone and the HO_2 radical that occurs on time scales faster than the time resolution of the apparatus, followed by subsequent reactions. This separation of time scales between the initial equilibrium and ensuing reactions enabled the determination of the equilibrium constant with values ranging from 4.0 × 10^(–16) to 7.7 × 10^(–1)8 cm^3 molecule^(–1) for T = 215–272 K. Thermodynamic parameters for the reaction determined from a second-law fit of our van’t Hoff plot were Δ_(r)H°_(245) = −35.4 ± 2.0 kJ mol^(–1) and Δ_(r)S°_(245) = −88.2 ± 8.5 J mol^(–1) K^(–1). Recent ab initio calculations predict that the reaction proceeds through a prereactive hydrogen-bonded molecular complex (HO_2–acetone) with subsequent isomerization to a hydroxy–peroxy radical, 2-hydroxyisopropylperoxy (2-HIPP). The calculations differ greatly in the energetics of the complex and the peroxy radical, as well as the transition state for isomerization, leading to significant differences in their predictions of the extent of this reaction at tropospheric temperatures. The current results are consistent with equilibrium formation of the hydrogen-bonded molecular complex on a short time scale (100 μs). Formation of the hydrogen-bonded complex will have a negligible impact on the atmosphere. However, the complex could subsequently isomerize to form the 2-HIPP radical on longer time scales. Further experimental studies are needed to assess the ultimate impact of the reaction of HO_2 and acetone on the atmosphere.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33270, title ="Gas phase reactions of the hydroperoxyl radical HO_2 with carbonyl compounds", author = "Okumura, M. and Sander, S. P.", month = "December", year = "2010", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120816-130547267", note = "© 2012 American Chemical Society.", revision_no = "14", abstract = "The hydroperoxyl radical HO2 is a key member of the hydrogen (HOx) radical family and is present throughout the\nenvironment. It is often the dominant HOx species throughout the atm., where its chem. influences ozone concns. and\nair pollution. Simple carbonyl compds. such as formaldehyde, acetaldehyde, and acetone are among the most abundant\nreactive orgs. in the free troposphere. Their primary degrdn. paths; reaction with OH and photolysis. Reactions of HO2\nwith carbonyls in the gas phase are believed to proceed through a hydrogen bonded adduct. The adduct can then\nundergo an intramol. rearrangement to form a peroxy radical (see figure). The reaction of HO2 with formaldehyde,\nHCHO, has been well studied, yet the spectroscopic evidence for the rearrangement lies in a broad, featureless UV\nspectrum. The reaction of HO2 with acetone, however, was found not to proceed at room temp., and its significance in\nthe atm. was thus not considered. Recent theor. calcns., however, predict that HO2 may react at lower temps. relevant\nto the free troposphere, conditions which favor adduct formation. The computations suggest that this reaction may in fact\nbe another important sink for acetone near the tropopause. Here we report spectroscopic evidence for formation of the\nhydroxy-Me peroxyl radical, the intermediate formed from reaction of HO2 with HCHO. We observe both the mid-IR OH\nstretch band, and the characteristic A-X near IR electronic band of the peroxyl radical, and compare to calcns. In a\nsecond set of expts., we obtain equil. data on the HO2 + acetone reaction using the IR-Kinetic Spectroscopy (IRKS)\ninstrument at the NASA Jet Propulsion Lab. Using diode laser spectroscopy to detect HO2, we det. the DrH and DrS.\nThese results shed light on the atm. relevance of this reaction for carbonyl loss in the atm.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33264, title ="Isoflurane, desflurane, and sevoflurane and global climate change: Atmospheric chemistry and environmental impact of inhaled anesthetics", author = "Sulbaek Andersen, M. P. and Karpichev, B.", month = "December", year = "2010", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120816-111919047", note = "© 2012 American Chemical Society.", revision_no = "13", abstract = "The atm. chem. of isoflurane, desflurane and sevoflurane has been investigated using FTIR/smog chamber and laser\nphotolysis/laser induced fluorescence techniques. The rates of reactions with OH radicals and Cl atoms, have been\nmeasured and the products resulting from the OH radicals and chlorine atom initiated oxidn. have been identified. For\nthe first time, measured absorption cross sections of the anesthetics were weighted by an instantaneous cloudy-sky\nradiative forcing calcd. for a model atm., allowing for a more accurate evaluation of the global warming potentials for this\nselection of important medical compds. The results will be discussed with respect to the impact of inhaled anesthetics on\nthe radiative forcing of climate change.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20894, title ="Rate of Gas Phase Association of Hydroxyl Radical and Nitrogen Dioxide", author = "Mollner, Andrew K. and Valluvadasan, Sivakumaran", journal = "Science", volume = "330", number = "6004", pages = "646-649", month = "October", year = "2010", doi = "10.1126/science.1193030 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101118-114740373", note = "© 2010 American Association for the Advancement of Science.\n\nReceived for publication 1 June 2010; accepted for publication 24 September 2010.\n\nThis work was supported by National Aeronautics and Space Administration (NASA) grants NAG5-11657, NNG06GD88G, and NNX09AE21G; California Air Resources Board contracts 03-333 and 07-730; National Science Foundation grant CHE-0515627/0848242 (A.B.M.); a NASA Earth Systems Science Fellowship (A.K.M.); and a Department of Defense National Defense Science and Engineering Graduate Fellowship (M.K.S.). Research at JPL was supported by the NASA Upper Atmosphere Research and Tropospheric Chemistry\nPrograms. This work was carried out in part at JPL,\nCalifornia Institute of Technology, under contract with NASA.", revision_no = "21", abstract = "The reaction of OH and NO_2 to form gaseous nitric acid (HONO_2) is among the most influential in atmospheric chemistry. Despite its importance, the rate coefficient remains poorly determined under tropospheric conditions because of difficulties in making laboratory rate measurements in air at 760 torr and uncertainties about a secondary channel producing peroxynitrous acid (HOONO). We combined two sensitive laser spectroscopy techniques to measure the overall rate of both channels and the partitioning between them at 25°C and 760 torr. The result is a significantly more precise value of the rate constant for the HONO_2 formation channel, 9.2 (±0.4) × 10^(−12) cm^3 molecule^(−1) s^(−1) (1 SD) at 760 torr of air, which lies toward the lower end of the previously established range. We demonstrate the impact of the revised value on photochemical model predictions of ozone concentrations in the Los Angeles airshed. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91264, title ="Direct Sun measurements of NO_2 column abundances from Table Mountain, California: Intercomparison of low- and high-resolution spectrometers", author = "Wang, Shuhui and Pongetti, Thomas J.", journal = "Journal of Geophysical Research. Atmospheres", volume = "115", number = "D13", pages = "Art. No. D13305", month = "July", year = "2010", doi = "10.1029/2009jd013503", issn = "2169-897X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181127-160004188", note = "© 2010 by the American Geophysical Union. \n\nReceived 4 November 2009; revised 3 March 2010; accepted 10 March 2010; published 15 July 2010. \n\nWe acknowledge the support of the NASA Upper Atmosphere Research and Aura Validation programs to each of these groups: JPL, WSU, and GSFC. We also wish to thank the staff at JPL's Table Mountain Facility, especially Pam Glatfelter and Bruce Williamson, for their exceptional support during the intercomparison campaign. The WSU group thanks Robert Gibson for help in the field. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology; Washington State University; and the Goddard Space Flight Center under contract to the National Aeronautics and Space Administration.", revision_no = "24", abstract = "The NO_2 total column abundance, C_(NO_2) was measured with a direct Sun viewing technique using three different instruments at NASA Jet Propulsion Laboratory's (JPL) Table Mountain Facility in California during an instrument intercomparison campaign in July 2007. The instruments are a high‐resolution (∼0.001 nm) Fourier transform ultraviolet spectrometer (FTUVS) from JPL and two moderate‐resolution grating spectrometers, multifunction differential optical absorption spectroscopy (MF‐DOAS) (∼0.8 nm) from Washington State University and Pandora (∼0.4 nm) from NASA Goddard Space Flight Center. FTUVS uses high spectral resolution to determine the absolute NO_2 column abundance independently from the exoatmospheric solar irradiance using rovibrational NO_2 absorption lines. The NO_2 total column is retrieved after removing the solar background using Doppler‐shifted spectra from the east and west limbs of the Sun. The FTUVS measurements were used to validate the independently calibrated measurements of multifunction differential optical absorption spectroscopy (MF‐DOAS) and Pandora. The latter two instruments start with measured high‐Sun spectra as solar references to retrieve relative NO_2 columns and then apply modified Langley or “bootstrap” methods to determine the amounts of NO_2 in the references to obtain the absolute NO_2 columns. The calibration offset derived from the FTUVS measurements is consistent with the values derived from Langley and bootstrap calibration plots of the NO_2 slant column measured by the grating spectrometers. The calibrated total vertical column abundances of NO_2, C_(NO_2) from all three instruments are compared showing that MF‐DOAS and Pandora data agree well with each other, and both data sets agree with FTUVS data to within (1.5 ± 4.1)% and (6.0 ± 6.0)%, respectively.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/19124, title ="Near-Infrared Kinetic Spectroscopy of the HO_2 and C_2H_5O_2 Self-Reactions and Cross Reactions", author = "Noell, A. C. and Alconcel, L. S.", journal = "Journal of Physical Chemistry A", volume = "114", number = "26", pages = "6983-6995", month = "July", year = "2010", doi = "10.1021/jp912129j", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100720-104159802", note = "© 2010 American Chemical Society. \n\nPublished In Issue July 08, 2010; Article ASAP June 04, 2010; Received: December 23, 2009; Revised: April 29, 2010. \n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). This work was supported by the NASA Upper Atmosphere Research and Tropospheric Chemistry Programs and the NASA Graduate Student Research Program (GSRP). The authors would like to thank Dave Natzic for extensive laboratory support and Dr. Lance Christensen and the Okumura group for many discussions. \n\nNote Added after ASAP Publication. This article posted ASAP on June 4, 2010. Tables 1 and 3 have been revised. The correction version posted on June 11, 2010.", revision_no = "24", abstract = "The self-reactions and cross reactions of the peroxy radicals HO_2 and C_2H_5O_2 and HO_2 were monitored using simultaneous independent spectroscopic probes to observe each radical species. Wavelength modulation (WM) near-infrared (NIR) spectroscopy was used to detect HO_2, and UV absorption monitored HO_2 and C_2H_5O_2. The temperature dependences of these reactions were investigated over a range of interest to tropospheric chemistry, 221−296 K. The Arrhenius expression determined for the cross reaction, k_2(T) = (6.01^(+1.95)_(−1.47)) × 10^(−13) exp((638 ± 73)/T) cm^3 molecules^(−1) s^(−1) is in agreement with other work from the literature. The measurements of the HO_2 self-reaction agreed with previous work from this lab and were not further refined.(1) The C_2H_5O_2 self-reaction is complicated by secondary production of HO_2. This experiment performed the first direct measurement of the self-reaction rate constant, as well as the branching fraction to the radical channel, in part by measurement of the secondary HO_2. The Arrhenius expression for the self-reaction rate constant is k_3(T) = (1.29^(+0.34)_(−0.27)) × 10^(−13)exp((−23 ± 61)/T) cm^3 molecules^(−1) s^(−1), and the branching fraction value is α = 0.28 ± 0.06, independent of temperature. These values are in disagreement with previous measurements based on end product studies of the branching fraction. The results suggest that better characterization of the products from RO_2 self-reactions are required.\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/12946, title ="Atmospheric hydroxyl radical (OH) abundances from ground-based ultraviolet solar spectra: an improved retrieval method", author = "Cheung, Ross and Li, King-Fai", journal = "Applied Optics", volume = "47", number = "33", pages = "6277-6284", month = "November", year = "2008", doi = "10.1364/AO.47.006277", issn = "0003-6935", url = "https://resolver.caltech.edu/CaltechAUTHORS:CHEao08", note = "© 2008 Optical Society of America. \n\nReceived 5 November 2007; revised 17 September 2008; accepted 19 September 2008; posted 19 September 2008 (Doc. ID 89379); published 19 November 2008. \n\nWe thank Run-Lie Shia for many valuable discussions on the numerical methods used in this work. We acknowledge the support of the NASA Undergraduate Student Research Program (USRP), the Caltech Summer Undergraduate Research Fellowship (SURF) program, and the NASA Upper Atmosphere Research, Aura Validation, Solar Occultation Satellite Science, and Tropospheric Chemistry Programs. Work at the Jet Propulsion Laboratory, California Institute of Technology, is under contract to the National Aeronautics and Space Administration (NASA).", revision_no = "13", abstract = "The Fourier Transform Ultraviolet Spectrometer (FTUVS) instrument has recorded a long-term data record of the atmospheric column abundance of the hydroxyl radical (OH) using the technique of high resolution solar absorption spectroscopy. We report new efforts in improving the precision of the OH measurements in order to better model the diurnal, seasonal, and interannual variability of odd hydrogen (HOx) chemistry in the stratosphere, which, in turn, will improve our understanding of ozone chemistry and its long-term changes. Until the present, the retrieval method has used a single strong OH absorption line P1(1) in the near-ultraviolet at 32,341 cm−1. We describe a new method that uses an average based on spectral fits to multiple lines weighted by line strength and fitting precision. We have also made a number of improvements in the ability to fit a model to the spectral feature, which substantially reduces the scatter in the measurements of OH abundances.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/12764, title ="Validation of Aura Microwave Limb Sounder OH measurements with Fourier Transform Ultra-Violet Spectrometer total OH column measurements at Table Mountain, California", author = "Wang, Shuhui and Pickett, Herbert M.", journal = "Journal of Geophysical Research D", volume = "113", pages = "D22301", month = "November", year = "2008", doi = "10.1029/2008JD009883", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:WANjgrd08", note = "© 2008. American Geophysical Union. \n\nReceived 29 January 2008; accepted 26 August 2008; published 19 November 2008. \n\nWe acknowledge the support of the NASA Upper Atmosphere Research, Aura Validation, Solar Occultation Satellite Science, and Tropospheric Chemistry Programs, the NASA Undergraduate Student Research Program (USRP) and the Caltech Summer Undergraduate Research Fellowship (SURF) program. We also wish to thank King Fai Li and Run-Lie Shia (Caltech) for helpful discussions. Alyn Lambert (JPL) is kindly acknowledged for helping with the orthogonal linear fit. Work at the Jet Propulsion Laboratory, California Institute of Technology, is under contract to the National Aeronautics and Space Administration.", revision_no = "14", abstract = "The first seasonal and interannual validation of OH measurements from the Aura Microwave Limb Sounder (MLS) has been conducted using ground-based OH column measurements from the Fourier Transform Ultra-Violet Spectrometer (FTUVS) over the Jet Propulsion Laboratory's Table Mountain Facility (TMF) during 2004–2007. To compare with FTUVS total column measurements, MLS OH vertical profiles over TMF are integrated to obtain partial OH columns above 21.5 hPa, which covers nearly 90% of the total column. The tropospheric OH and the lower stratopheric OH not measured by MLS are estimated using GEOS (Goddard Earth Observing System)-Chem and a Harvard 2-D model implemented within GEOS-Chem, respectively. A number of field observations and calculations from a photochemical box model are compared to OH profiles from these models to estimate the variability in the lower atmospheric OH and thus the uncertainty in the combined total OH columns from MLS and models. In general, the combined total OH columns agree extremely well with TMF total OH columns, especially during seasons with high OH. In winter with low OH, the combined columns are often higher than TMF measurements. A slightly weaker seasonal variation is observed by MLS relative to TMF. OH columns from TMF and the combined total columns from MLS and models are highly correlated, resulting in a mean slope of 0.969 with a statistically insignificant intercept. This study therefore suggests that column abundances derived from MLS vertical profiles have been validated to within the mutual systematic uncertainties of the MLS and FTUVS measurements.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91244, title ="First satellite observations of lower tropospheric ammonia and methanol", author = "Beer, Reinhard and Shephard, Mark W.", journal = "Geophysical Research Letters", volume = "35", number = "9", pages = "Art. No. L09801", month = "May", year = "2008", doi = "10.1029/2008gl033642", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181127-154248588", note = "© 2008 American Geophysical Union. \n\nReceived 14 February 2008; revised 28 March 2008; accepted 1 April 2008; published 1 May 2008. \n\nThis work was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, under contract with the National Aeronautics and Space Administration. We also wish to thank G. Guerova (U. Wollongong) and D. Millet (Harvard U.) for kindly providing the profiles of ammonia and methanol on which these analyses rest and to the two reviewers for their helpful suggestions. All TES data are available at http://eosweb.larc.nasa.gov/PRODOCS/tes/table_tes.html.", revision_no = "9", abstract = "The Tropospheric Emission Spectrometer (TES) on the EOS Aura satellite makes global measurements of infrared radiances which are used to derive profiles of species such as O_3, CO, H_2O, HDO and CH_4 as routine standard products. In addition, TES has a variety of special modes that provide denser spatial mapping over a limited geographical area. A continuous‐coverage mode (called “transect”, about 460 km long) has now been used to detect additional molecules indicative of regional air pollution. On 10 July 2007 at about 05:37 UTC (13:24 LMST) TES conducted such a transect observation over the Beijing area in northeast China. Examination of the residual spectral radiances following the retrieval of the TES standard products revealed surprisingly strong features attributable to enhanced concentrations of ammonia (NH3) and methanol (CH_3OH), well above the normal background levels. This is the first time that these molecules have been detected in space‐based nadir viewing measurements that penetrate into the lower atmosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91263, title ="First observations of iodine oxide from space", author = "Saiz-Lopez, Alfonso and Chance, Kelly", journal = "Geophysical Research Letters", volume = "34", number = "12", pages = "Art. No. L12812", month = "June", year = "2007", doi = "10.1029/2007gl030111", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181127-160004088", note = "© 2007 by the American Geophysical Union. \n\nReceived 22 March 2007; revised 30 April 2007; accepted 1 June 2007; published 29 June 2007. \n\nA. Saiz‐Lopez was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with the National Aeronautics and Space Administration (NASA). Research at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA, was supported by the NASA Upper Atmosphere Research and Tropospheric Chemistry Programs. Research at the Smithsonian Astrophysical Observatory was supported by NASA and the Smithsonian Institution. We thank Chris Sioris for providing help with SCIAMACHY data. We are also grateful for the ongoing cooperation of the European Space Agency and the German Aerospace Center in the SCIAMACHY program.", revision_no = "8", abstract = "We present retrievals of IO total columns from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite instrument. We analyze data for October 2005 in the polar regions to demonstrate for the first time the capability to measure IO column abundances from space. During the period of analysis (i.e. Southern Hemisphere springtime), enhanced IO vertical columns over 3 × 10^(13) molecules cm^(−2) are observed around coastal Antarctica; by contrast during that time in the Artic region IO is consistently below the calculated instrumental detection limit for individual radiance spectra (2–4 × 10^(12) molecules cm^(−2) for slant columns). The levels reported here are in reasonably good agreement with previous ground‐based measurements at coastal Antarctica. These results also demonstrate that IO is widespread over sea‐ice covered areas in the Southern Ocean. The occurrence of elevated IO and its hitherto unrecognized spatial distribution suggest an efficient iodine activation mechanism at a synoptic scale over coastal Antarctica.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46637, title ="Precision requirements for space-based X_(CO_2) data", author = "Miller, C. E. and Crisp, D.", journal = "Journal of Geophysical Research D", volume = "112", number = "D10", pages = "Art. No. D10314", month = "May", year = "2007", doi = "10.1029/2006JD007659", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140702-113242262", note = "© 2007 American Geophysical Union. \n\nReceived 15 June 2006; revised 16 September 2006; accepted 11 January 2007; article first published online 26 May 2007. \n\nThis work was supported by the Orbiting Carbon Observatory (OCO) project through NASA’s Earth System Science Pathfinder (ESSP) program. SCO and JTR were supported by a NASA IDS grant (NAG5-9462) to JTR. We thank R. Frey for the assistance with the MODIS cloud data.\nPlease note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.", revision_no = "18", abstract = "Precision requirements are determined for space-based column-averaged CO_2 dry air mole fraction (X_(CO)_2) data. These requirements result from an assessment of spatial and temporal gradients in (X_(CO)_2) the relationship between (X_(CO)_2) precision and surface CO_2 flux uncertainties inferred from inversions of the (X_(CO)_2) data, and the effects of (X_(CO)_2) biases on the fidelity of CO_2 flux inversions. Observational system simulation experiments and synthesis inversion modeling demonstrate that the Orbiting Carbon Observatory mission design and sampling strategy provide the means to achieve these (X_(CO)_2) data precision requirements.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48894, title ="Retrieval of ozone profile from ground-based measurements with polarization: A synthetic study", author = "Guo, Xin and Natraj, Vijay", journal = "Journal of Quantitative Spectroscopy and Radiative Transfer", volume = "103", number = "1", pages = "175-192", month = "January", year = "2007", doi = "10.1016/j.jqsrt.2006.05.008", issn = "0022-4073", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140826-090755061", note = "© 2006 Elsevier Ltd. Received 6 May 2006. Revised 27 May 2006. Accepted 30 May 2006. Available online 30 June 2006. We appreciate the helpful comments from J. Margolis, M. Newchurch, K. Chance, X. Liu, F. Mills, J. Herman, L. Li, X. Jiang, Y. Jiang, S. Herman, C. Kolb and two anonymous reviewers. This research is supported in part by NASA Grant NAG1-02081 and JPL Grant P421407 to California Institute of\nTechnology.", revision_no = "14", abstract = "We perform a retrieval based on optimal estimation theory to retrieve the vertical distribution of ozone from simulated spectra in the Huggins bands. The model atmosphere includes scattering by aerosol as well as Rayleigh scattering. The virtual instrument is ground-based and zenith-viewing. Using this algorithm, we show that it is possible to retrieve the ozone profile provided that the spectral resolution is at least 0.2 nm and the signal to noise ratio greater than 500. Our synthetic retrievals suggest that if we are able to measure the Stokes parameters Q, U and V with accuracy comparable to that of the intensity, the information contained in the measurements, and therefore the inversion, will improve. Furthermore, we find that the measurement of the full Stokes vector from the ground-based instrument will especially enhance the retrieval of tropospheric ozone. Utilizing concepts from information theory, our arguments are confirmed by increases in the degrees of freedom and the Shannon information content in the simulated measurements.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77970, title ="Experimental and ab Initio Study of the HO_2·CH_3OH Complex: Thermodynamics and Kinetics of Formation", author = "Christensen, Lance E. and Okumura, Mitchio", journal = "Journal of Physical Chemistry A", volume = "110", number = "21", pages = "6948-6959", month = "June", year = "2006", doi = "10.1021/jp056579a", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170606-131245100", note = "© 2006 American Chemical Society. \n\nReceived 14 November 2005. Published online 19 April 2006. Published in print 1 June 2006. \n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). This work was supported by the NASA Upper Atmosphere Research and Tropospheric Chemistry Programs and the NASA Graduate Student Research Program (GSRP). This research has also been supported in part by a grant from the U.S. Environmental Protection Agency National Center for Environmental Research's Science to Achieve Results (STAR) program, through grant R826236-01-0. It has not been subjected to any EPA review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. We would like to acknowledge the indispensable scientific advice of Barna László, Kyle Bayes, Brian Drouin, and Herbert Pickett, the vital technical support of Dave Natzic and Jürgen Linke, and all the exceptional work of Siamak Forouhar, Kamjou Mansour, and Sam Keo of the Microdevices Laboratory in the manufacture and testing of the diode laser. We thank David Rowley and Daniel Stone for helpful discussions of their data. \n\nNote Added in Proof:\u2009 Very recently, rotational transitions of HO2·H2O have been observed (Suma et al. Science 2006, 311, 1278).", revision_no = "10", abstract = "Near-infrared spectroscopy was used to monitor HO_2 formed by pulsed laser photolysis of Cl_2−O_2−CH_3OH−N_2 mixtures. On the microsecond time scale, [HO_2] exhibited a time dependence consistent with a mechanism in which [HO_2] approached equilibrium via HO_2 + HO_3OH^M⇆_M HO_2·CH_3OH (3, −3). The equilibrium constant for reaction 3, Kp, was measured between 231 and 261 K at 50 and 100 Torr, leading to standard reaction enthalpy and entropy values (1 σ) of Δ_rH°_(246K) = −37.4 ± 4.8 kJ mol^(-1) and Δ_rS°_(246K) = −100 ± 19 J mol^(-1) K^(-1). The effective bimolecular rate constant, k_3, for formation of the HO_2·CH_3OH complex is 2.8^(+7.5)_(-2.0)·10^(-15)·exp[(1800 ± 500)/T] cm^3 molecule^(-1) s^(-1) at 100 Torr (1 σ). Ab initio calculations of the optimized structure and energetics of the HO_2·CH_3OH complex were performed at the CCSD(T)/6-311++G(3df,3pd)//MP2(full)/6-311++G(2df,2pd) level. The complex was found to have a strong hydrogen bond (D_e = 43.9 kJ mol^(-1)) with the hydrogen in HO_2 binding to the oxygen in CH_3OH. The calculated enthalpy for association is Δ_rH°_(245K) = −36.8 kJ mol^(-1). The potentials for the torsion about the O_2−H bond and for the hydrogen-bond stretch were computed and 1D vibrational levels determined. After explicitly accounting for these degrees of freedom, the calculated Third Law entropy of association is Δ_rS°_(245K) = −106 J mol^(-1) K^(-1). Both the calculated enthalpy and entropy of association are in reasonably good agreement with experiment. When combined with results from our previous study (Christensen et al. Geophys. Res. Lett. 2002, 29; doi:10.1029/2001GL014525), the rate coefficient for the reaction of HO_2 with the complex, HO_2 + HO_2·CH_3-OH, is determined to be (2.1 ± 0.7) × 10^(-11) cm^3 molecule^(-1) s^(-1). The results of the present work argue for a reinterpretation of the recent measurement of the HO_2 self-reaction rate constant by Stone and Rowley (Phys. Chem. Chem. Phys. 2005, 7, 2156). Significant complex concentrations are present at the high methanol concentrations used in that work and lead to a nonlinear methanol dependence of the apparent rate constant. This nonlinearity introduces substantial uncertainty in the extrapolation to zero methanol.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48776, title ="OH column abundance over Table Mountain Facility, California: AM-PM diurnal asymmetry", author = "Li, King-Fai and Cageao, Richard P.", journal = "Geophysical Research Letters", volume = "32", number = "13", pages = "Art. No. L13813", month = "July", year = "2005", doi = "10.1029/2005GL022521", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140821-120128252", note = "© 2005 The American Geophysical Union.\n\nReceived 23 January 2005; Revised 13 May 2005; Accepted 23 May 2005; Published 8 July 2005.\n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. KFL and EMK acknowledge support from the Caltech Summer Undergraduate Research Fellowship program. This work was supported by the NASA Upper Atmosphere Research Program (JPL), by NASA Grant NAG1-02081\n(California Institute of Technology), and by the Australian Research Council (ANU).", revision_no = "14", abstract = "Observations of the OH column abundance have been made by the Fourier Transform Ultraviolet Spectrometer at the JPL Table Mountain Facility (TMF) near Los Angeles since July 1997. In the January 1998–December 2003 data set we used five OH lines to derive the OH column abundance in the atmosphere. This data set was used to quantify the OH morning/afternoon asymmetry (AMPMDA). An analysis of summer and winter data showed that the daily OH maximum occurred 26–36 minutes after solar transit. This phase lag appears to be the primary reason why OH in the afternoon is larger than at corresponding solar zenith angles in the morning throughout the year. A simple heuristic model suggests that the asymmetry is a direct consequence of the finite lifetime of OH. Comparison of the TMF data with earlier results from Fritz Peak Observatory, Colorado, by Burnett et al. reveals significant differences in the behavior of the AMPMDA between the two sites.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46805, title ="Ground-based photon path measurements from solar absorption spectra of the O_2 A-band", author = "Yang, Z. and Wennberg, P. O.", journal = "Journal of Quantitative Spectroscopy and Radiative Transfer", volume = "90", number = "3-4", pages = "309-321", month = "February", year = "2005", doi = "10.1016/j.jqsrt.2004.03.020", issn = "0022-4073", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140703-101456060", note = "© 2004 Elsevier Ltd. \n\nReceived 6 October 2003; accepted 13 March 2004. \n\nWe thank Linda Brown, Camy-Peyret and David Crisp for many helpful discussions, Rebecca Washenfelder for providing comparison spectra. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Paul Wennberg, Geoff Toon, and Zhonghua Yang acknowledge support from NASA’s ACMAP and Terrestrial Ecology Programs (NAG5-11739; NAG12247). Stan Sander, Rich Cageao, and Tom Pongetti acknowledge support from the NASA’s Upper Atmosphere Research Program.", revision_no = "18", abstract = "High-resolution solar absorption spectra obtained from Table Mountain Facility (TMF, 34.38°N, 117.68°W, 2286 m elevation) have been analyzed in the region of the O_2 A-band. The photon paths of direct sunlight in clear sky cases are retrieved from the O_2 absorption lines and compared with ray-tracing calculations based on the solar zenith angle and surface pressure. At a given zenith angle, the ratios of retrieved to geometrically derived photon paths are highly precise (∼0.2%), but they vary as the zenith angle changes. This is because current models of the spectral lineshape in this band do not properly account for the significant absorption that exists far from the centers of saturated lines. For example, use of a Voigt function with Lorentzian far wings results in an error in the retrieved photon path of as much as 5%, highly correlated with solar zenith angle. Adopting a super-Lorentz function reduces, but does not completely eliminate this problem. New lab measurements of the lineshape are required to make further progress.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77929, title ="Temperature and Pressure Dependence of High-Resolution Air-Broadened Absorption Cross Sections of NO_2(415−525 nm)", author = "Nizkorodov, S. A. and Sander, S. P.", journal = "Journal of Physical Chemistry A", volume = "108", number = "22", pages = "4864-4872", month = "June", year = "2004", doi = "10.1021/jp049461n", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170605-071525697", note = "© 2004 American Chemical Society. \n\nReceived 5 February 2004. Published online 8 May 2004. Published in print 1 June 2004. \n\nThis research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This work was supported by the NASA EOS/Aura Validation, Upper Atmosphere Research and Tropospheric Chemistry Programs. S.A.N. thanks the Camille and Henry Dreyfus Foundation for the postdoctoral scholarship. The authors thank M. Dulick for experimental assistance and G. Mount and J. Harder for helpful discussions.", revision_no = "72", abstract = "Cross sections of air-broadened NO_2 in the 415−525 nm region are reported. These are retrieved from 21 absorption spectra recorded at 0.060 cm^(-1) resolution with the McMath−Pierce Fourier Transform Spectrometer located on Kitt Peak in Arizona. The measurements are obtained for pressures (1−760 Torr) and temperatures (220−298 K) that are representative of typical tropospheric and stratospheric conditions. Two sigma uncertainty (95% confidence interval ≈ 2σ_(mean)) for the absolute absorption cross sections is below ±7% over the reported wavelength range. The average integrated intensity of all our data is 〈σ〉_(400-500 nm) = 4.53 × 10^(-17) cm^2 nm, which is within 0.2% of the averaged value from the recent literature. The wavelength (referred to vacuum) accuracy is 0.011 cm^(-1) (2.8 × 10^(-4) nm at 500 nm) and precision is 0.0022 cm^(-1) throughout the investigated wavelength range. In agreement with previous observations, high-resolution features in the NO_2 absorption spectrum display a strong pressure dependence with an effective pressure broadening parameter of 0.116 ± 0.003 cm^(-1)/atm (the rate of increase of Lorentzian half width at half-maximum with pressure). Temperature has a relatively minor effect on the shapes of individual high-resolution features, but it exerts a complex dependence on the relative line intensities. Absorption cross sections reported here represent the highest resolution data available over a substantial (>100 nm) wavelength range for quantitative analysis of NO_2 atmospheric column absorption spectra.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48865, title ="Modeling of atmospheric radiative transfer with polarization and its application to the remote sensing of tropospheric ozone", author = "Jiang, Yibo and Yung, Yuk L.", journal = "Journal of Quantitative Spectroscopy and Radiative Transfer", volume = "84", number = "2", pages = "169-179", month = "March", year = "2004", doi = "10.1016/S0022-4073(03)00140-7", issn = "0022-4073", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140825-153132188", note = "© 2003 Elsevier Ltd. Received 21 October 2002, Accepted 11 March 2003, Available online 21 November 2003. We would like to express our appreciation to Mark Allen, Richard Cageao and Andy Ingersoll for their valuable comments, and to Mimi Gerstell for a critical reading of the manuscript. This work\nwas supported in part by NASA grant NAGW 2204 to the California Institute of Technology and was carried out there and at JPL, under contract with NASA.", revision_no = "12", abstract = "Light reflected or transmitted by a planetary atmosphere contains information about particles and molecules in the atmosphere. Therefore, accurate modeling of the radiation field may be used to retrieve information on atmospheric composition. In this paper, a multi-layer model for a vertically inhomogeneous atmosphere is implemented by using the doubling-adding method for a plane-parallel atmosphere. By studying the degree of linear polarization of the transmitted and reflected solar light in the Huggins bands, we find significant differences between tropospheric ozone and stratospheric ozone. The effects of tropospheric ozone change on the linear polarization are 10 times more than that of the same amount of stratospheric ozone change. We also show the aerosol effect on the linear polarization, but this effect is wavelength independent as compared to that caused by the tropospheric ozone change. The results provide a theoretical basis for the retrieval of tropospheric ozone from measurement of linear polarization of the scattered sunlight both from the ground and from a satellite.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77692, title ="Measurements of the Rate Constant of HO_2 + NO_2 + N_2 → HO_2NO_2 + N_2 Using Near-Infrared Wavelength-Modulation Spectroscopy and UV−Visible Absorption Spectroscopy", author = "Christensen, Lance E. and Okumura, Mitchio", journal = "Journal of Physical Chemistry A", volume = "108", number = "1", pages = "80-91", month = "January", year = "2004", doi = "10.1021/jp035905o", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170524-082812028", note = "© 2004 American Chemical Society. \n\nReceived: July 2, 2003; In Final Form: October 21, 2003. Publication Date (Web): December 5, 2003. \n\nThis research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This work was supported by the NASA Upper Atmosphere Research and Tropospheric Chemistry Programs and the NASA Graduate Student Researcher Program (GSRP). This research has also been supported in part by a grant from the U.S. Environmental Protection Agency National Center for Environmental Research's Science to Achieve Results (STAR) program, through Grant R826236-01-0. It has not been subjected to any EPA review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. We acknowledge the scientific and technical support of Barna László, Dave Natzic, Jürgen Linke, Siamak Forouhar, Dave Dougherty, and Sam Keo of the Jet Propulsion Laboratory. ", revision_no = "9", abstract = "Rate coefficients for the reaction HO_2 + NO_2 + N_2 → HO_2NO_2 + N_2 (reaction 1) were measured using simultaneous near-IR and UV spectroscopy from 220 to 298 K and from 45 to 200 Torr. Using the data acquired in the present experiment, the low-pressure and high-pressure limit rate constants for reaction 1 were determined to be k_o = (2.1 ± 0.1) × 10^(-31) × (T/300)^(-(3.1±0.3)) cm^6 molecule^(-2) s^(-1) and k∞ = (2.4 ± 0.1) × 10^(-12) × (T/300))^(-(1.9±0.5)) cm^3 molecule^(-1) s^(-1), using the expressions for rate constants adopted by the NASA data evaluation panel (F_c = 0.6). The reaction rate was significantly enhanced in the presence of methanol due to a chaperone effect involving an HO_2·CH_3OH complex. Enhancement parameters for this process were quantified as a function of temperature. During the course of our studies, we observed an unexpected time-dependent UV absorption unaccounted for in previous examinations of reaction 1 that employed UV spectroscopy to monitor HO_2. We show that this absorption, which may have led to errors in those prior studies, is due to the process NO_2 + NO_2 ⇄ N_2O_4 (reaction 3). Using UV−visible spectroscopy, we determine k_(-3) to be (36 ± 10) s^(-1) at 231 K and 100 Torr using the NASA-recommended equilibrium constant for the dimerization of NO_2. This represents the first measurement of k_(-3) at T < 250 K.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48724, title ="OH column abundance over Table Mountain Facility, California: Intra-annual variations and comparisons to model predictions for 1997–2001", author = "Mills, Franklin P. and Cageao, Richard P.", journal = "Journal of Geophysical Research D", volume = "108", number = "D24", pages = "Art. No. 4785", month = "December", year = "2003", doi = "10.1029/2003JD003481", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140820-105110108", note = "© 2003 The American Geophysical Union.\n\nReceived 4 February 2003; Revised 14 July 2003; Accepted 11 August 2003; Published 24 December 2003.\n\nThe research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology. Support received from the NASA Upper Atmosphere Research Program, the California Institute of Technology President’s Fund, the Naval Research Laboratory, and NASA grants NAG1-1806 and NAG1-2151 to the California Institute of Technology is gratefully acknowledged. The authors thank Vassilli Nemtchinov and Yibo Jiang for their contributions to the collection and processing of the OH column measurements, Timothy Canty for his assistance in comparing the TMF and FPO measurements, and Fok-Yan Leung for assistance with the final versions of figures. Helpful\nsuggestions from an anonymous reviewer are gratefully acknowledged. The HALOE data were obtained via http://haloedata.larc.nasa.gov.", revision_no = "55", abstract = "Measurements of the OH column abundance over the Jet Propulsion Laboratory's Table Mountain Facility (TMF) have been made since July 1997 at 10°–80° solar zenith angle using a Fourier transform ultraviolet spectrometer. The measured OH column at any solar zenith angle is typically larger in the afternoon than in the morning. The variations observed in the OH column abundance appear to result from changes in atmospheric conditions on a daily or longer timescale. The larger observed variations are statistically significant. Sensitivity coefficients describing how the OH column abundance is expected to change in response to changes in the concentrations of H_2O, O_3, NO, CO, and CH_4 have been calculated on the basis of an analytic model. On the basis of these sensitivity coefficients and Halogen Occultation Experiment observations of O_3, the net sensitivity of the OH column abundance to variations in O_3 should be close to zero. The observed OH column abundance over TMF increased by about 25% from July 1997 to December 2001. This interannual trend in OH column abundance is not consistent with calculations that incorporate observed trends in H_2O and O_3 and is at least a factor of 2 larger than the calculated difference between solar minimum and maximum. Comparisons between measured and calculated normalized OH column abundances suggest that the sensitivity of OH to variations in H_2O may be a factor of 2 larger than predicted in present models and that there is some other major driver for the observed variability in the OH column abundance that was not included in the present analysis.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77686, title ="Cavity Ringdown Spectroscopy of cis-cisHOONO and the HOONO/HONO_2 Branching Ratio in the Reaction OH + NO_2+ M", author = "Bean, Brian D. and Mollner, Andrew K.", journal = "Journal of Physical Chemistry A", volume = "107", number = "36", pages = "6974-6985", month = "September", year = "2003", doi = "10.1021/jp034407c", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170524-071408780", note = "© 2003 American Chemical Society. \n\nReceived 17 February 2003. Published online 19 August 2003. Published in print 1 September 2003. \n\nThis work was supported by NASA Grants NAG5-11657 and NAGW-3911 and the Upper Atmospheric Research and Tropospheric Chemistry Programs. A.K.M. acknowledges support of an NSF Graduate Research Fellowship, G.N. support by a Caltech SURF Fellowship, and G.N. and S.A.N. by the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry. Calculations were supported by the NASA JPL Supercomputing Project. We thank D. M. Golden and J. R. Barker for sharing their results prior to publication and A. Goldman for providing spectral data.", revision_no = "9", abstract = "The termolecular association reaction OH + NO_2 + M was studied in a low-pressure discharge flow reactor, and both HONO_2 and HOONO products were detected by infrared cavity ringdown spectroscopy (IR-CRDS). The absorption spectrum of the fundamental ν1 band of the cis-cis isomer of HOONO (pernitrous or peroxynitrous acid) was observed at 3306 cm^(-1), in good agreement with matrix isolation studies and ab initio predictions. The rotational contour of this band was partially resolved at 1 cm^-1 resolution and matched the profile predicted by ab initio calculations. The integrated absorbances of the ν^1 bands of the cis-cis HOONO and HONO_2 products were measured as a function of temperature and pressure. These were converted to product branching ratios by scaling the experimentally observed absorbances with ab initio integrated cross sections for HOONO and HONO_2 computed at the CCSD(T)/cc-pVTZ level. The product branching ratio for cis-cis HOONO to HONO_2 was 0.075 ± 0.020(2σ) at room temperature in a 20 Torr mixture of He/Ar/N_2 buffer gas. The largest contribution to the uncertainty is from the ab initio ratio of the absorption cross sections, computed in the double harmonic approximation, which is estimated to be accurate to within 20%. The branching ratio decreased slightly with temperature over the range 270 to 360 K at 20 Torr. Although trans-perp HOONO was not observed, its energy was computed at the CCSD(T)/cc-pVTZ level to be E_0 = +3.4 kcal/mol relative to the cis-cis isomer. Statistical rate calculations showed that the conformers of HOONO should reach equilibrium on the time scale of this experiment. These results suggested that essentially all isomers had converted to cis-cis HOONO; thus, the reported branching ratio is a lower bound for and may represent the entire HOONO yield.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91262, title ="Measurements of quantum yields of bromine atoms in the photolysis of bromoform from 266 to 324 nm", author = "Bayes, Kyle D. and Toohey, Darin W.", journal = "Journal of Geophysical Research. Atmospheres", volume = "108", number = "D3", pages = "Art. No. 4095", month = "February", year = "2003", doi = "10.1029/2002jd002877", issn = "2169-897X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181127-160003989", note = "© 2003 by the American Geophysical Union. \n\nReceived 23 August 2002; revised 4 November 2002; accepted 4 December 2002; published 5 February 2003. \n\nThe authors would like to thank Joseph Francisco and William Jackson for prepublication copies of their manuscripts and David Natzic for expert assistance in constructing the flow tube. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration.", revision_no = "11", abstract = "The quantum yield for the formation of bromine atoms in the photolysis of bromoform, CHBr_3, has been measured between 266 and 324 nm. For 303 to 306 nm the quantum yields are unity within the experimental uncertainty of the measurements. At longer wavelengths, where the bromoform cross sections decrease rapidly, an apparent trend to slightly lower quantum yields is probably the result of systematic and random errors or incorrect CHBr_3 absorption cross sections. Support for a unit quantum yield for all wavelengths longer than 300 nm comes from the recent theoretical calculations of Peterson and Francisco. At 266 nm the bromine atom quantum yield is 0.76 (±0.03), indicating that at least one additional dissociation channel becomes important at shorter wavelengths. For modeling of the troposphere, it is recommended that a quantum yield of unity be used for wavelengths of 300 nm and longer.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50825, title ="Kinetics of HO_2 + HO_2 → H_2O_2 + O_2: Implications for Stratospheric H_2O_2", author = "Christensen, L. E. and Okumura, M.", journal = "Geophysical Research Letters", volume = "29", number = "9", pages = "Art. No. 1299", month = "May", year = "2002", doi = "10.1029/2001GL014525", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141027-085804530", note = "Copyright 2002 by the American Geophysical Union. \n\nReceived 6 December 2001; accepted 28 December 2001; published 7 May 2002. \n\nThis work was supported by the NASA Upper Atmosphere Research and Tropospheric Chemistry Programs and the NASA Graduate Student Researchers Program (GRSP). We wish to thank The National Scientific Balloon Facility (NSBF), Palestine, TX, for use of their facility and resources for the MkIV and FIRS-2 instruments. We also wish to thank D. J. Jacob and F. Ravetta for insight into the effect of k_1 on tropospheric chemistry, J. S. Francisco and J. C. Hansen for calculations regarding hydrogen-bonding between methanol and HO_2, and D. B. Natzic for his invaluable experimental contributions. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.", revision_no = "14", abstract = "The reaction HO_2 + HO_2 → H_2O_2 + O_2(1) has been studied at 100 Torr and 222 K to 295 K. Experiments employing photolysis of Cl_2/CH_3OH/O_2/N_2 and F_2/H_2/O_2/N_2 gas mixtures to produce HO_2 confirmed that methanol enhanced the observed reaction rate. At 100 Torr, zero methanol, k_1 = (8.8 ± 0.9) 10^(−13) × exp[(210 ± 26)/T] cm^3 molecule^(−1) s^(−1) (2σ uncertainties), which agrees with current recommendations at 295 K but is nearly 2 times slower at 231 K. The general expression for k_1, which includes the dependence on bath gas density, is k_1 = (1.5 ± 0.2) × 10^(−12) × exp[(19 ± 31)/T] + 1.7 × 10^(−33) × [M] × exp[1000/T], where the second term is taken from the JPL00-3 recommendation. The revised rate largely accounts for a discrepancy between modeled and measured [H_2O_2] in the lower to middle stratosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/2916, title ="High-Resolution Fourier-Transform Ultraviolet-Visible Spectrometer for the Measurement of Atmospheric Trace Species: Application to OH", author = "Cageao, Richard P. and Blavier, Jean-Francois", journal = "Applied Optics", volume = "40", number = "12", pages = "2024-2030", month = "April", year = "2001", doi = "10.1364/AO.40.002024", issn = "0003-6935", url = "https://resolver.caltech.edu/CaltechAUTHORS:CAGao01", note = "© 2001 Optical Society of America \n\nReceived 20 March 2000; revised manuscript received 17 October 2000. \n\nThe research described in this paper was conducted at the JPL, California Institute of Technology. It was supported by grants from the NASA Upper Atmosphere Research Program, the U.S. Naval Research Laboratory, and by the JPL Director’s Discretionary Fund. We thank R. Beer, B. Farmer, R. Norton, R. Friedl, D. Peterson, and G. Toon of JPL and G. Wyntjes and J. Engel of Optra, Inc. for many valuable discussions. We also thank D. Miller, J. MacConnell, G. A. Al-Jumaily, D. Natzic, J. D. Rex, R. Chave, R. Marquedant, J. Voeltz, and B. Wilson for their assistance with the instrument design and fabrication.", revision_no = "8", abstract = "A compact, high-resolution Fourier-transform spectrometer for atmospheric near-ultraviolet spectroscopy has been installed at the Jet Propulsion Laboratory s Table 1 Mountain Facility (34.4 N, 117.7 W, elevation 2290 m). This instrument is designed with an unapodized resolving power near 500,000 at 300 nm to provide high-resolution spectra from 290 to 675 nm for the quantification of column abundances of trace atmospheric species. The measurement technique used is spectral analysis of molecular absorptions of solar radiation. The instrument, accompanying systems designs, and results of the atmospheric hydroxyl column observations are described.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/76682, title ="NO_2 Quantum Yield from the 248 nm Photodissociation of Peroxynitric Acid (HO_2NO_2)", author = "Roehl, Coleen M. and Mazely, Troy L.", journal = "Journal of Physical Chemistry A", volume = "105", number = "9", pages = "1592-1598", month = "March", year = "2001", doi = "10.1021/jp001982x", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170419-110417967", note = "© 2001 American Chemical Society. \n\nReceived: May 31, 2000; In Final Form: October 31, 2000.\nPublication Date (Web): December 22, 2000. \n\nWe acknowledge the technical support of Mr. Dave Natzic. The supercomputer used in this investigation was provided by funding from the NASA Offices of Earth Science, Aeronautics and Space Science. The research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Support from the NASA Upper Atmosphere Research, Tropospheric Chemistry and Atmospheric Effects of Aircraft Programs is acknowledged.", revision_no = "9", abstract = "Peroxynitric acid (PNA) was photolyzed at 248 nm, and the NO_2 photoproduct was detected by laser-induced fluorescence (LIF). The quantum yield for the production of NO_2 was determined by comparison with HNO_3 photolysis data taken under identical experimental conditions. Measurements made over a range of pressures, flows, and precursor concentrations resulted in an NO_2 quantum yield of 0.56 ± 0.17, where the statistical uncertainty is 2 standard deviations. Calculations of potential energy curves for several low-lying singlet and triplet states of PNA are presented. The calculations show that while the singlet excitations occur via an n−π* transition on the NO_2 moiety, the dissociative channels forming OH + NO_3 and HO_2 + NO_2 likely occur via predissocation on different surfaces. Excitation energies at the MRCI and CCSD(T) level of theory show that excited states of PNA are not accessible at wavelengths longer than 407 nm (∼3.0 eV).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46496, title ="Intensity of the second and third OH overtones of H_2O_2, HNO_3, and HO_2NO_2", author = "Zhang, Hui and Roehl, Coleen M.", journal = "Journal of Geophysical Research D", volume = "105", number = "D11", pages = "14593-14598", month = "June", year = "2000", doi = "10.1029/2000JD900118", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140625-075632457", note = "© 2000 American Geophysical Union. \n\nReceived November 23, 1999; revised February 9, 2000; accepted February 11, 2000. \n\nPaper number 2000JD900118. \n\nThis work is partly supported by NASA grant SA98-0055. We thank R.J. Salawitch for help on the HO_2NO_2 photolysis rate calculations. Useful communications with D. J. Donaldson are greatly appreciated.", revision_no = "14", abstract = "The 3ν_(OH) and 4ν_(OH) of H_2O_2, HNO_3, and HO_2NO_2 have been observed. The band strengths of 3ν_(OH) are (7.0±1.8) × 10^(−20), (2.9±0.7) × 10^(−20), and (3.8±1.1) × 10^(−20) cm^2 molecules^(−1) cm^(−1) for H_2O_2, HNO_3, and HO_2NO_2, respectively. Those of 4ν_(OH) are (4.5± .6) × 10^(−21), (2.8± .0) × 10^(−21), and (3.0±1.8) × 10^(−21) cm^2 molecules^(−1) cm^(−1) for H_2O_2, HNO_3, and HO_2NO_2, respectively. The uncertainty is for one standard deviation. Assuming excitation of these modes by solar absorption is dissociative for HO_2NO_2, these measurements confirm that this process will play a small role in the atmospheric photochemistry of the lower stratosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/75190, title ="Temperature Dependence of the HO_2 + ClO Reaction. 1. Reaction Kinetics by Pulsed Photolysis-Ultraviolet Absorption and ab Initio Studies of the Potential Surface", author = "Nickolaisen, Scott L. and Roehl, Coleen M.", journal = "Journal of Physical Chemistry A", volume = "104", number = "2", pages = "308-319", month = "January", year = "2000", doi = "10.1021/jp992753h", issn = "1089-5639", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170316-161356188", note = "© 2000 American Chemical Society. \n\nReceived: August 4, 1999; In Final Form: October 29, 1999. Publication Date (Web): December 16, 1999. \n\nWe acknowledge the expert technical assistance of Mr. Dave Natzic in the setup and execution of these experiments. We have benefited greatly from frequent discussions with Dr. M. Okumura (Caltech), Dr. R. Salawitch, and members of the JPL Chemical Kinetics and Photochemistry Group. Support for L. Blakeley was provided under an NIH Minority Access to Research Careers (MARC) Grant, no. GM08228. The supercomputer used in this investigation was provided by funding from the NASA Offices of Earth Science, Aeronautics and Space Science. The research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.", revision_no = "11", abstract = "The kinetics of the HO_2 + ClO reaction was studied using the flash photolysis/ultraviolet absorption technique over the temperature range 203−364 K and pressure range 50−700 Torr of N_2. In contrast to previous work, the temperature dependence displayed linear Arrhenius behavior over the entire temperature range with the rate constant being described by the expression k(T) = 2.84 × 10^(-12) exp{(312 ± 60)/T} cm^3 molecule^(-1) s^(-1). Ab initio calculations of intermediates and transition states have been carried out on the singlet and triplet potential energy surfaces. These calculations show that the reaction proceeds mainly through the ClO−HO_2 complex on the triplet surface; however, collisionally stabilized HOOOCl formed on the singlet surface will possess an appreciable lifetime due to large barriers toward decomposition to HCl and HOCl. Termolecular rate calculations using ab initio parameters lead to a strong collision rate constant of ∼5 × 10^(-32) cm^6 molecule^(-2) s^(-1) for HOOOCl formation. This intermediate may be important under both laboratory and atmospheric conditions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91346, title ="Ozone depletion potential of CH_3Br", author = "Ko, Malcolm K. W. and Sze, Nien Dak", journal = "Journal of Geophysical Research. Atmospheres", volume = "103", number = "D21", pages = "28187-28195", month = "November", year = "1998", doi = "10.1029/98jd02537", issn = "2169-897X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181129-163705207", note = "© 1998 American Geophysical Union. \n\n(Received February 6, 1998; revised July 23, 1998; accepted July 28, 1998.) \n\nPaper number 98JD02537. \n\nWork at AER is supported by the Methyl Bromide Global Coalition and by the National Aeronautics and Space Administration (NASA) Atmospheric Chemistry Modeling and Analysis Program (ACMAP, NAS5-97039). The authors benefited from numerous discussions with participants at the Methyl Bromine State of the Science Workshop, 1997. Their contributions are gratefully acknowledged. We would also like to thank Martyn Chipperfield for sharing his results prior to their publication.", revision_no = "9", abstract = "The ozone depletion potential (ODP) of methyl bromide (CH_3Br) can be determined by combining the model‐calculated bromine efficiency factor (BEF) for CH_3Br and its atmospheric lifetime. This paper examines how changes in several key kinetic data affect BEF. The key reactions highlighted in this study include the reaction of BrO + HO_2, the absorption cross section of HOBr, the absorption cross section and the photolysis products of BrONO_2, and the heterogeneous conversion of BrONO_2 to HOBr and HNO_3 on aerosol particles. By combining the calculated BEF with the latest estimate of 0.7 year for the atmospheric lifetime of CH_3Br, the likely value of ODP for CH_3Br is 0.39. The model‐calculated concentration of HBr (∼0.3 pptv) in the lower stratosphere is substantially smaller than the reported measured value of about 1 pptv. Recent publications suggested models can reproduce the measured value if one assumes a yield for HBr from the reaction of BrO + OH or from the reaction of BrO + HO_2. Although the DeMore et al. [1997] evaluation concluded any substantial yield of HBr from BrO + HO_2 is unlikely, for completeness, we calculate the effects of these assumed yields on BEF for CH_3Br. Our calculations show that the effects are minimal: practically no impact for an assumed 1.3% yield of HBr from BrO + OH and 10% smaller for an assumed 0.6% yield from BrO + HO_2.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/28880, title ="Kinetics of the HO_2 + BrO reaction over the temperature range\n233–348 K", author = "Li, Zhuangjie and Friedl, Randall R.", journal = "Journal of the Chemical Society. Faraday Transactions", volume = "93", number = "16", pages = "2683-2691", month = "August", year = "1997", doi = "10.1039/a701583f", issn = "0956-5000", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120120-090859935", note = "© 1997 Royal Society of Chemistry. Received 6th March, 1997.\nThis research was performed by the Jet Propulsion Laboratory, California Institute Technology, under contract with National Aeronautics and Space Administration. We are\ngrateful to J. S. Francisco and S. Guha for providing details of their ab initio calculations on HBrO and to David Natzic 3, and Juergen Linke for their expert technical assistance in this work. ", revision_no = "12", abstract = "The reaction BrO + HO_2 → products is the rate-limiting step in a key catalytic ozone destruction cycle in the lower stratosphere. In this study a discharge-flow reactor coupled with molecular beam mass spectrometry has been used to study the BrO + HO_2 reaction over the temperature range 233-348 K. Rate constants were measured under pseudo-first-order conditions in separate experiments with first HO_2 and then BrO in excess in an effort to identify possible complications in the reaction conditions. At 298 K, the rate constant was determined to be (1.73 ± 0.61) x 10^(-11) cm^3 molecule^(-1) s^(-1) with HO_2 in excess and (2.05 ± 0.64) x 10^(-11) cm^3 molecule^(-1) s^(-1) with BrO in excess. The combined results of the temperature-dependent experiments\ngave the following fit to the Arrhenius expression : k = (3.13 ± 0.33)]10^(-12) exp(536 ± 206/T) where the quoted uncertainties represent two standard deviations. The reaction mechanism is discussed in light of recent ab initio results on the thermochemistry of isomers of possible reaction intermediates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48675, title ="Detection of tropospheric ozone by remote sensing from the ground", author = "Jiang, Yibo and Yung, Yuk L.", journal = "Journal of Quantitative Spectroscopy and Radiative Transfer", volume = "57", number = "6", pages = "811-818", month = "June", year = "1997", doi = "10.1016/S0022-4073(96)00145-8", issn = "0022-4073", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140819-093219098", note = "© 1997 Elsevier Science Ltd. Received 18 July 1996, Available online 16 May 1998. We thank R. S. Stolarski, R. Cageao, M. Allen, R. McPeters, M. Newchurch, and J.-H. Kim for\nvaluable comments. This work was supported by National Science Foundation grant ATM 9526209 and NASA grant\nNAGI-1806 to the California Institute of Technology. Contribution number 5674 from the Division of Geological and\nPlanetary Sciences, California Institute of Technology. After this work was completed, it was pointed out to us by\nR. McPeters that similar ideas were proposed by Green et al.", revision_no = "9", abstract = "Due to larger multiple scattering effects in the troposphere compared to that in the stratosphere, the optical path of tropospheric ozone is markedly enhanced (as compared with that of stratospheric ozone) in the Huggins bands from 310 to 345 nm. Model study of the direct and diffuse solar fluxes on the ground shows differences between tropospheric and stratospheric ozone. The characteristic signature of tropospheric ozone enables us to distinguish a change in troposheric ozone from that of stratospheric ozone. A simple retrieval algorithm is used to recover the tropospheric column ozone from simulated data.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48674, title ="Calculated Hydroxil A^2∑ → X^2Π (0,0) band emission rate factors applicable to atmospheric spectroscopy", author = "Cageao, R. P. and Ha, Y. L.", journal = "Journal of Quantitative Spectroscopy and Radiative Transfer", volume = "57", number = "5", pages = "703-717", month = "May", year = "1997", doi = "10.1016/S0022-4073(96)00105-7", issn = "0022-4073", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140819-091518312", note = "© 1997 Elsevier Science Ltd. Received 26 February 1996; received for publication 3 June 1996. The authors would like to thank Xiaolei Zhu for his efforts in refining the program coding, Drs William Sharp and Randall Friedl for their support, helpful comments, and discussions refining the scope of this paper, and Drs Gary Rottman and Robert Kurucz for illuminating discussions on the solar near ultraviolet spectra. This work was supported by NASA Sounding Rocket Flight Program grant NGR 23-005-36, NASA Graduate Student Researcher's Grant NGT-50010, NASA grant NAGW-2204, a California Institute of Technology Summer Undergraduate Researcher Fund grant and President's Fund grant, and a Jet Propulsion Laboratory Director's Discretionary Fund grant.", revision_no = "12", abstract = "A calculation of the A^2∑ → X^2Π (0, 0) band emission rate factors and line center absorption cross sections of OH applicable to its measurement using solar resonant fluorescence in the terrestrial atmosphere is presented in this paper. The most accurate available line parameters have been used. Special consideration has been given to the solar input flux because of its highly structured Fraunhofer spectrum. The calculation for the OH atmospheric emission rate factor in the solar resonant fluorescent case is described in detail with examples and intermediate results. Results of this calculation of OH emission rate factors for individual rotational lines are, on average, 30% lower than the values obtained in an earlier work.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91269, title ="Interaction of peroxynitric acid with solid H_2O ice", author = "Li, Zhuangjie and Friedl, Randall R.", journal = "Journal of Geophysical Research. Atmospheres", volume = "101", number = "D3", pages = "6795-6802", month = "March", year = "1996", doi = "10.1029/96JD00065", issn = "2169-897X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181128-092706343", note = "© 1996 by the American Geophysical Union. \n\nPaper number 96JD0065. \n\nReceived August 1, 1995; revised December 13, 1995; accepted December 13, 1995. \n\nThe research described in this paper was carried out at Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We thank G. T. Toon, M. R. Gunson, and R. J. Salawitch for providing their unpublished results, R. Zhang, M.-T. Leu, and R. J. Salawitch for helpful discussion on our results, and R. D. May for facility assistance in preparing HNO_4.", revision_no = "8", abstract = "The uptake of peroxynitric acid (PNA), HO_2NO_2 or HNO_4, on solid H_2O ice at 193 K (−80°C) was studied using a fast flow‐mass spectrometric technique. An uptake coefficient of 0.15 ± 0.10 was measured, where the quoted uncertainty denotes 2 standard deviations. The uptake process did not result in the production of gas phase products. The composition of the condensed phase was investigated using programmed heating (3 K min^(−1)) of the substrate coupled with mass spectrometric detection of desorbed species. Significant quantities of HNO_4 and HNO_3 desorbed from the substrates at temperatures above 225 K and 246 K, respectively. The desorbed HNO_3, which was less than 9% of the desorbed HNO_4 and remained unchanged upon incubation of the substrate, was likely due to impurities in the HNO_4 samples rather than reaction of HNO_4 on the substrate. The onset temperatures for HNO_4 desorption increased with increasing H_2O to HNO_4 ratios, indicating that HNO_4, like HNO_3, tends to be hydrated in the presence of water. These observations suggest possible mechanisms for removal of HNO_4 or repartitioning of total odd nitrogen species in the Earth's upper troposphere and stratosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48496, title ="Chloryl Nitrate: A Novel Product of the OCIO + NO_3 + M Recombination", author = "Friedl, Randall R. and Sander, Stanley P.", journal = "Journal of Physical Chemistry", volume = "96", number = "19", pages = "7490-7493", month = "September", year = "1992", doi = "10.1021/j100198a002", issn = "0022-3654", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140813-094930400", note = "© 1992 American Chemical Society. Received: May 20, 1992: In Final Form: July 16, 1992. Part of the research described in this report was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration. Y.L.Y. was supported by NASA Grant NAGW-413 to the California Institute of Technology.", revision_no = "11", abstract = "The products of the reaction of OClO with NO_3 were investigated between 220 and 298 K using a flow reactor and infrared, visible, and ultraviolet analysis. At temperatures below 250 K new infrared and ultraviolet absorption features were observed and assigned to the novel compound chloryl nitrate (O_2ClONO_2). Additionally, ClO and NO_2 were observed as reaction products, indicating the existence of a second reaction channel. O_2ClONO_2 formation predominates at temperatures below 230 K. The reaction rate constant at 220 K is estimated to be on the order of 10^(-14) cm^3 molecule^(-1) s^(-1) in 1-5 Torr of helium. These observations suggest that O_2ClONO_2 may exist in the terrestrial stratosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/58517, title ="Temperature dependence and mechanism of the reaction between atomic O(^3P) and chlorine dioxide", author = "Colussi, A. J. and Sander, S. P.", journal = "Journal of Physical Chemistry", volume = "96", number = "11", pages = "4442-4445", month = "May", year = "1992", doi = "10.1021/j100190a058", issn = "0022-3654", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154806978", note = "© 1992 American Chemical Society. \n\n(Received: September 13, 1991; In Final Form: January 9, 1992) \n\nThe research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.", revision_no = "10", abstract = "Second-order rate constants for the decay of O(^3P) in excess chlorine dioxide, k_(11), were measured by flash photolysis-atomic resonance fluorescence as a function of total pressure (20-600 Torr argon) and temperature (248-312 K). It was found that (1) k_(11) is pressure dependent with a value, k_b, that is nonzero at zero pressure and (2) both the third-order rate constant (dk_(11)/d[M])_(lMl=O) = k_0, and k_b have negative temperature dependences. These results are consistent with an association reaction leading to an intermediate having two decomposition channels: O + OClO ⇌ ClO_3* (1, 2); ClO3_* + M → + ClO_3 + M (3); ClO_3* → ClO + O_2* (4), with E_(o2) > E_(o4). The measured k_0 values were used in conjunction with Troe's expression for unimolecular decomposition rates in the low-pressure limit to derive a critical energy for ClO_3 of 10 700 cm^(-1), which leads to ΔH_f(ClO_3) = 51.9 ± 5 kcal/mol. This is ~4 kcal/mol smaller than the value derived in our previous room temperature study of this reaction.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/58518, title ="Induced ClO vacuum ultraviolet fluorescence", author = "Colussi, A. J. and Sander, S. P.", journal = "Chemical Physics Letters", volume = "187", number = "1-2", pages = "85-92", month = "November", year = "1991", doi = "10.1016/0009-2614(91)90489-V", issn = "0009-2614", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154807222", note = "© 1991 Elsevier. \n\nReceived 23 May 1991; in final form 9 September 1991. \n\nThe work described here was performed at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA, under a contract with the National Aeronautics and Space Administration.", revision_no = "10", abstract = "Some vibronic transitions of ClO such as G(ν′=11)←X(ν″=10), G(ν′=5)←X(ν″=3) and H(ν′=4)←X(ν″=2), which promote overtones of X(^2Π^(3/2)) to bound Rydberg states, are nearly resonant with the 130.6 nm O-atom emission line and possess sizable Franck—Condon factors. On this basis broadband detection of “O atom” fluorescence in experiments involving vibrationally excited ClO(X) is ascribed to the radiative decay of ClO(G, H) rather than to the formation of O atoms; these observations raise the probability of monitoring ClO(X; ν=0) by VUV induced fluorescence.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/58519, title ="Thermodynamics of acetylene van der Waals dimerization", author = "Colussi, A. J. and Sander, S. P.", journal = "Chemical Physics Letters", volume = "178", number = "5-6", pages = "497-503", month = "April", year = "1991", doi = "10.1016/0009-2614(91)87009-Z", issn = "0009-2614", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154807470", note = "© 1991 Elsevier. \n\nReceived 12 December 1990. \n\nThe work described here was performed at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA under a contract with the National Aeronautics and Space Administration. We thank Professor Y.L. Yung for a preprint of ref. [15] and for his interest in this work.", revision_no = "10", abstract = "Integrated band intensities of the 620 cm^(−1) absorption in (C_2H_2)_2 have been measured by FTIR spectroscopy at constant acetylene pressure between 198 and 273 K. These data, in conjunction with ab initio results for (C_2H_2)_2, have been used for the statistical evaluation of the equilibrium constant K_p(T) for acetylene cluster dimerization. Present results are used to clarify the role of molecular clusters in chemical systems at or near equilibrium, in particular in Titan's stratosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48498, title ="Spatial Variation of Ozone Depletion Rates in the Springtime Antarctic Polar Vortex", author = "Yung, Yuk L. and Allen, Mark", journal = "Science", volume = "248", number = "4956", pages = "721-724", month = "May", year = "1990", doi = "10.1126/science.11538181", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140813-100857739", note = "© 1990 American Association for the Advancement of Science.\n24 October 1989; accepted 22 February 1990. We are \ngrateful to R. Stolarski for providing TOMS data before publication and to P. Newman for sending us potential\nvorticity data. We thank K. K. Tung, R. Friedl, J. Rodriguez, M. Schoeberl, and R. L. Shia for illuminating\ndiscussions, S. Solomon for critical comments on systematic errors of TOMS data, and X.-L. Zhu for plotting all the graphs in this report. Part of the research described in this paper was carried out by the Jet Propulsion Laboratory,\nunder contract with the National Aeronautics and Space\nAdministration, and was also supported by NASA grant\nNAGW-413 to the California Institute of Technology. Contribution number 4783 from the Division of Geological\nand Planetary Sciences, California Institute of Technology.", revision_no = "11", abstract = "An area-mapping technique, designed to filter out synoptic perturbations of the Antarctic polar vortex such as distortion or displacement away from the pole, was applied to the Nimbus-7 TOMS (Total Ozone Mapping Spectrometer) data. This procedure reveals the detailed morphology of the temporal evolution of column O_3. The results for the austral spring of 1987 suggest the existence of a relatively stable collar region enclosing an interior that is undergoing large variations. There is tentative evidence for quasi-periodic (15 to 20 days) O_3 fluctuations in the collar and for upwelling of tropospheric air in late spring. A simplified photochemical model of O_3 loss and the temporal evolution of the area-mapped polar O_3 are used to constrain the chlorine monoxide (C1O) concentrations in the springtime Antarctic vortex. The\nconcentrations required to account for the observed loss of O_3 are higher than those previously reported by Anderson et al. but are comparable to their recently revised\nvalues. However, the O_3 loss rates could be larger than deduced here because of underestimates of total O_3 by TOMS near the terminator. This uncertainty, together with the uncertainties associated with measurements acquired during the Airborne Antarctic Ozone Experiment, suggests that in early spring, closer to the vortex center, there may be even larger ClO concentrations than have yet been detected.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49270, title ="Rate of Formation of the ClO Dimer in the Polar Stratosphere: Implications for Ozone Loss", author = "Sander, Stanley P. and Friedl, Randall R.", journal = "Science", volume = "245", number = "4922", pages = "1095-1098", month = "September", year = "1989", doi = "10.1126/science.245.4922.1095 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140905-090620093", note = "© 1989 American Association for the Advancement of Science.\n\nReceived 29 March 1989; accepted 12 July 1989.\n\nPart of the research described in this report was\ncarried out by the Jet Propulsion Laboratory, California\nInstitute of Technology, under contract with\nthe National Aeronautics and Space Administration\n(NASA). Y.L.Y. was supported by NASA grant\nNAGW-413 to the California Institute of Technology.\nWe acknowledge several valuable conversations\nwith M. Allen, W. DeMore, C. B. Farmer, J.\nMargitan, M. Molina, J. Rodriguez, G. Toon, and J.\nSander. We thank D. Hofmann, R. DeZafra, R.\nSchindler, C. B. Farmer, C. Howard, D. McKenna,\nand D. Hartmann for preprints.", revision_no = "14", abstract = "The gas-phase recombination of chlorine monoxide (ClO) has been investigated under the conditions of pressure and temperature that prevail in the Antarctic stratosphere during the period of maximum ozone (O_3) disappearance. Measured rate constants are less than one-half as great as the previously accepted values. One-dimensional model calculations based on the new rate data indicate that currently accepted chemical mechanisms can quantitatively account for the observed O_3 losses in late spring (17 September to 7 October). A qualitative assessment indicates that the existing mechanisms can only account for at most one-half of the measured O3 depletion in the early spring (28 August to 17 September), indicating that there may be additional catalytic cycles, besides those currently recognized, that destroy O_3.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91343, title ="Kinetics and product studies of the BrO + ClO Reaction: Implications for Antarctic chemistry", author = "Sander, Stanley P. and Friedl, Randall R.", journal = "Geophysical Research Letters", volume = "15", number = "8", pages = "887-890", month = "August", year = "1988", doi = "10.1029/gl015i008p00887", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181129-163523694", note = "© 1988 American Geophysical Union. \n\n(Received: May 12, 1988; Revised: June 28, 1988; Accepted: June 30, 1988) \n\nPaper number 8L6857. \n\nThe authors wish to thank Drs. D. W. Toohey and R. J. Salawitch for many helpful discussions. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. \n\nThis article also appears in: Polar Ozone", revision_no = "8", abstract = "The reaction of ClO with BrO has been investigated by two independent techniques, discharge flow‐mass spectrometry and flash photolysis‐UV spectrometry, over the temperature range 220‐400 K and the pressure range 1‐760 torr. Rate constants have been determined for three product channels; a) Br + ClOO, b) Br + OClO, and c) BrCl + O_2. The rate constants for the overall reaction and each reaction branch were found to be inversely dependent on temperature and independent of pressure. The results for the temperature dependence of the overall rate constant from the discharge flow and flash photolysis studies are in excellent agreement, and collectively disagree substantially with the only previous temperature dependence study. Also, in contrast to previous studies, the channel forming BrCl is found to be significant (≃ 8%). These kinetic measurements have an important impact on the modeling of Antarctic chemistry; for temperatures found in the Antarctic stratosphere the rate coefficients for the channels yielding ClOO and OClO are a factor of 2‐3 larger than previously estimated. In addition, the BrCl channel, which has an impact on the nighttime partitioning of BrO_X and the diurnal variability of OClO, has been omitted from previous atmospheric models.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91289, title ="A kinetics study of the homogeneous and heterogeneous components of the HCl + ClONO_2 reaction", author = "Friedl, Randall R. and Goble, James H.", journal = "Geophysical Research Letters", volume = "13", number = "12", pages = "1351-1354", month = "November", year = "1986", doi = "10.1029/gl013i012p01351", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181128-113131044", note = "© 1986 American Geophysical Union. \n\n(Received August 15, 1986; accepted August 21, 1986) \n\nPaper number 6L6331. \n\nThe authors wish to thank Drs. J. J. Hargitan, R. A. Stachnik and M. J. Molina for many helpful discussions. The research described in this paper was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. \n\nThis article also appears in: Antarctic Ozone", revision_no = "8", abstract = "The kinetics of the reaction HCl + ClONO_2 → Cl_2 + HNO_3 were investigated at 298 K using a flow reactor with FTIR analysis to assess the importance of this reaction for stratospheric chemistry. The observed reaction was characteristic of a heterogeneous process; an upper limit of 5 × 10^(−18) cm³ molecule^(−1) s^(−1) was obtained for the homogeneous gas phase rate constant. From calculations of the first order wall rate constant, estimates were made of the reaction rate on stratospheric aerosols. Because both HCl and ClONO_2 need to be adsorbed on the particle surface, the reaction will be of negligible importance under most stratospheric conditions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/11818, title ="Atmospheric Bromine and Ozone Perturbations in the Lower Stratosphere", author = "Yung, Y. L. and Pinto, J. P.", journal = "Journal of the Atmospheric Sciences", volume = "37", number = "2", pages = "339-353", month = "February", year = "1980", doi = "10.1175/1520-0469(1980)037<0339:ABAOPI>2.0.CO;2", issn = "0022-4928", url = "https://resolver.caltech.edu/CaltechAUTHORS:YUNjas80", note = "© 1980 American Meteorological Society. \n\n(Manuscript received May 4, 1979, in final form September 26, 1979) \n\nWe thank A.L. Lazrus and W.A. Sedlacek for permission to use their data prior to publication. We benefited from discussions with W.B. DeMore, H.B. Singh, J.S. Chang, S.C. Liu, N.D. Sze, J.A. Logan, S.C. Wofsy, M.T. Molina and F.S. Rowland. We appreciate the constructive criticisms given by the referees, P.J. Crutzen and R.J. Cicerone in their reviews of this paper. \n\nThis research was supported by NASA Grant NSG 2229 to the California Institute of Technology and NASA Grant NSG 5163 Scope M to Columbia University; this also represents one phase of NASA sponsored research carried out at the Jet Propulsion Laboratory under Contract NAS 7-100. \n\nContribution No. 3215 of the Division of Geological and Planetary Sciences, California Institute of Technology.", revision_no = "13", abstract = "The role of bromine compounds in the photochemistry of the natural and perturbed stratosphere has been reexamined using an expanded reaction scheme and the results of recent laboratory studies of several key reactions. The most important finding is that through the reaction BrO + CIO → Br + Cl + O2, there is a synergistic effect between bromine and chlorine which results in an efficient catalytic destruction of ozone in the lower stratosphere. One-dimensional photochemical model results indicate that BrO is the major bromine species throughout the stratosphere, followed by BrONO2, HBr, HOBr and Br. We show from the foregoing that bromine is more efficient than chlorine as a catalyst for destroying ozone, and discuss the implications for stratospheric ozone of possible future growth in the industrial and agricultural use of bromine. Bromine concentrations of 20 pptv (2 × 10^−11), as suggested by recent observations, can decrease the present-day integrated ozone column density by 2.4%, and can enhance ozone depletion from steady-state chlorofluoromethane release at 1973 rates by a factor of 1.1–1.2.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49982, title ="Pressure and temperature dependence kinetics study of the NO + BrO → NO_2 + Br reaction. Implications for stratospheric bromine photochemistry", author = "Watson, R. T. and Sander, S. P.", journal = "Journal of Physical Chemistry", volume = "83", number = "23", pages = "2936-2944", month = "November", year = "1979", doi = "10.1021/j100486a002", issn = "0022-3654", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140924-094540365", note = "© 1979 American Chemical Society. Received May 21, 1979.\n\nWe thank J. Linke for his indispensable glass blowing services, G. Tennant and M. Patapoff for their expert assistance in constructing the experimental apparatus, and J. Pinto for use of the output of our one dimensional\nphotochemical model prior to publication. We benefited greatly from discussions with W. B. DeMore. This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS7-100, sponsored by the National Aeronautics and Space Administration. Part of this work was supported by NASA Grant NSG 2229 to the California Institute of Technology. ", revision_no = "17", abstract = "The flash photolysis-ultraviolet absorption technique has been utilized to study the reactivity of nitric oxide\nwith BrO radicals over a wide range of pressure (100-700 torr) and temperature (224-398 K). Pseudo-first-order\nconditions were used in order to minimize complications caused by secondary kinetic processes. The reaction\nand its corresponding Arrhenius expression in units of cm^3 molecule^(-1) s^(-1) can be written \nNO + BrO → NO_2 + Br ΔHº_298 = -17.0 kcal mol^(-1)\nk_1 = (1.28 ± 0.23) x 10^(-11)exp((181 ± 46)/T) (T = 224-398 K)\nThe results are compared with previous measurements, and atmospheric implications of the reaction are discussed.\nIt is shown that this reaction is important in controlling the ratios [BrO]/[Br] and [BrO]/[HBr] in the stratosphere\nbut that it does not affect the catalytic efficiency of BrO, in ozone destruction. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/102833, title ="Chemical kinetics of homogeneous atmospheric oxidation of sulfur dioxide", author = "Sander, Stanley P. and Seinfeld, John H.", journal = "Environmental Science and Technology", volume = "10", number = "12", pages = "1114-1123", month = "November", year = "1976", doi = "10.1021/es60122a007", issn = "0013-936X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200428-084748306", note = "© 1976 American Chemical Society. \n\nReceived for review January 5, 1976. Accepted April 26, 1976. \n \nWork supported in part by the Jet Propulsion Laboratory and in part by\nNational Science Foundation Grant 71ENG-02486.", revision_no = "8", abstract = "A systematic evaluation of known homogeneous SO₂ reactions\nwhich might be important in air pollution chemistry\nis carried out. A mechanism is developed to represent the\nchemistry of NO_x/hydrocarbon/SO₂ systems, and the mechanism\nis used to analyze available experimental data appropriate\nfor quantitative analysis of SO₂ oxidation kinetics.\nDetailed comparisons of observed and predicted concentration\nbehavior are presented. In all cases, observed SO₂ oxidation\nrates cannot be explained solely on the basis of those SO₂ reactions\nfor which rate constants have been measured. The role\nof ozone-olefin reactions in SO₂ oxidation is elucidated.", }