Journal of Geophysical Research: Atmospheres

Detailed chemical characterization of unresolved complex mixtures in atmospheric organics: Insights into emission sources, atmospheric processing, and secondary organic aerosol formation

Authors

  • Arthur W. H. Chan,

    Corresponding author
    1. Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
    2. Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada
    • Corresponding author: A. W. H. Chan, Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College St., Toronto, ON M5S 3E5, Canada. (arthurwh.chan@utoronto.ca)

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  • Gabriel Isaacman,

    1. Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
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  • Kevin R. Wilson,

    1. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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  • David R. Worton,

    1. Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
    2. Aerosol Dynamics Inc., Berkeley, California, USA
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  • Christopher R. Ruehl,

    1. Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
    2. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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  • Theodora Nah,

    1. Department of Chemistry, University of California, Berkeley, California, USA
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  • Drew R. Gentner,

    1. Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA
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  • Timothy R. Dallmann,

    1. Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA
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  • Thomas W. Kirchstetter,

    1. Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA
    2. Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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  • Robert A. Harley,

    1. Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA
    2. Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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  • Jessica B. Gilman,

    1. Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Chemical Sciences Division, NOAA, Boulder, Colorado, USA
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  • William C. Kuster,

    1. Chemical Sciences Division, NOAA, Boulder, Colorado, USA
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  • Joost A. de Gouw,

    1. Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Chemical Sciences Division, NOAA, Boulder, Colorado, USA
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  • John H. Offenberg,

    1. National Exposure Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
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  • Tadeusz E. Kleindienst,

    1. National Exposure Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
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  • Ying H. Lin,

    1. Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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  • Caitlin L. Rubitschun,

    1. Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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  • Jason D. Surratt,

    1. Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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  • Patrick L. Hayes,

    1. Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, Colorado, USA
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  • Jose L. Jimenez,

    1. Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, Colorado, USA
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  • Allen H. Goldstein

    1. Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
    2. Department of Civil and Environmental Engineering, University of California, Berkeley, California, USA
    3. Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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Abstract

[1] Recent studies suggest that semivolatile organic compounds (SVOCs) are important precursors to secondary organic aerosol (SOA) in urban atmospheres. However, knowledge of the chemical composition of SVOCs is limited by current analytical techniques, which are typically unable to resolve a large number of constitutional isomers. Using a combination of gas chromatography and soft photoionization mass spectrometry, we characterize the unresolved complex mixture (UCM) of semivolatile aliphatic hydrocarbons observed in Pasadena, California (~16 km NE of downtown Los Angeles), and Bakersfield, California, during the California Research at the Nexus of Air Quality and Climate Change 2010. To the authors' knowledge, this work represents the most detailed characterization of the UCM in atmospheric samples to date. Knowledge of molecular structures, including carbon number, alkyl branching, and number of rings, provides important constraints on the rate of atmospheric processing, as the relative amounts of branched and linear alkanes are shown to be a function of integrated exposure to hydroxyl radicals. Emissions of semivolatile branched alkanes from fossil fuel-related sources are up to an order of magnitude higher than those of linear alkanes, and the gas-phase OH rate constants of branched alkanes are ~30% higher than their linear isomers. Based on a box model considering gas/particle partitioning, emissions, and reaction rates, semivolatile branched alkanes are expected to play a more important role than linear alkanes in the photooxidation of the UCM and subsequent transformations into SOA. Detailed speciation of semivolatile compounds therefore provides essential understanding of SOA sources and formation processes in urban areas.

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