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Journal of Geophysical Research: Atmospheres

Los Angeles Basin airborne organic aerosol characterization during CalNex

Authors

  • J. S. Craven,

    1. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
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  • A. R. Metcalf,

    1. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA
    2. Now at the Combustion Research Facility, Sandia National Laboratories, Livermore, California, USA
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  • R. Bahreini,

    1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA
    3. Now at the Department of Environmental Sciences, University of California, Riverside, California, USA
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  • A. Middlebrook,

    1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA
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  • P. L. Hayes,

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

    1. Department of Chemical and Environmental Engineering, University of Arizona, Tucson, Arizona, USA
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  • A. Sorooshian,

    1. Department of Chemical and Environmental Engineering, University of Arizona, Tucson, Arizona, USA
    2. Department of Atmospheric Sciences, University of Arizona, Tucson, Arizona, USA
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  • J. L. Jimenez,

    1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA
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  • R. C. Flagan,

    1. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
    2. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA
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  • J. H. Seinfeld

    1. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
    2. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA
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Corresponding author: J. H. Seinfeld, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA. (seinfeld@caltech.edu)

Abstract

[1] We report airborne organic aerosol (OA) measurements over Los Angeles carried out in May 2010 as part of the CalNex field campaign. The principal platform for the airborne data reported here was the CIRPAS Twin Otter (TO); airborne data from NOAA WP-3D aircraft and Pasadena CalNex ground-site data acquired during simultaneous TO flybys are also presented. Aerodyne aerosol mass spectrometer measurements constitute the main source of data analyzed. The increase in organic aerosol oxidation from west to east in the basin was sensitive to OA mass loading, with a greater spatial trend in O:C associated with lower mass concentration. Three positive matrix factorization (PMF) components (hydrocarbon-like organic aerosol (HOA), semi-volatile oxidized organic aerosol (SVOOA), and low volatility oxidized organic aerosol (LVOOA)) were resolved for the one flight that exhibited the largest variability in estimated O:C ratio. Comparison of the PMF factors with two optical modes of refractory black carbon (rBC)-containing aerosol revealed that the coating of thinly coated rBC-containing aerosol, dominant in the downtown region, is likely composed of HOA, whereas more thickly coated rBC-containing aerosol, dominant in the Banning pass outflow, is composed of SVOOA and LVOOA. The correlation of water-soluble organic mass to oxidized organic aerosol (OOA) is higher in the outflows than in the basin due to the higher mass fraction of OOA/OA in the outflows. By comparison, the average OA concentration over Mexico City MILAGRO (Megacity Initiative: Local and Global Research Observations) campaign was ∼7 times higher than the airborne average during CalNex.

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