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Fine-scale simulation of ammonium and nitrate over the South Coast Air Basin and San Joaquin Valley of California during CalNex-2010

Authors

  • James T. Kelly,

    Corresponding author
    1. Office of Air Quality Planning and Standards, U.S. EPA, Research Triangle Park, North Carolina, USA
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  • Kirk R. Baker,

    1. Office of Air Quality Planning and Standards, U.S. EPA, Research Triangle Park, North Carolina, USA
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  • John B. Nowak,

    1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
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  • Jennifer G. Murphy,

    1. Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
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  • Milos Z. Markovic,

    1. Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
    2. Now at NOAA and University of Colorado, Boulder, Colorado, USA
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  • Trevor C. VandenBoer,

    1. Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
    2. Now at Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
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  • Raluca A. Ellis,

    1. Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
    2. Now at Climate and Urban Systems Partnership, Franklin Institute, Philadelphia, Pennsylvania, USA
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  • J. Andrew Neuman,

    1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
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  • Rodney J. Weber,

    1. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
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  • James M. Roberts,

    1. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
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  • Patrick R. Veres,

    1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
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  • Joost A. de Gouw,

    1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
    2. Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
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  • Melinda R. Beaver,

    1. Environmental Science and Engineering, California Institute of Technology, Pasadena, California, USA
    2. Now at National Exposure Research Laboratory, U. S. EPA, Research Triangle Park, North Carolina, USA
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  • Sally Newman,

    1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
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  • Chris Misenis

    1. Office of Air Quality Planning and Standards, U.S. EPA, Research Triangle Park, North Carolina, USA
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  • This article was corrected on 23 JUL 2014. See the end of the full text for details.

Abstract

National ambient air quality standards (NAAQS) have been set for PM2.5 due to its association with adverse health effects. PM2.5 design values in the South Coast Air Basin (SoCAB) and San Joaquin Valley of California exceed NAAQS levels, and NH4+ and NO3 make up the largest fraction of total PM2.5 mass on polluted days. Here we evaluate fine-scale simulations of PM2.5 NH4+ and NO3 with the Community Multiscale Air Quality model using measurements from routine networks and the California Research at the Nexus of Air Quality and Climate Change 2010 campaign. The model correctly simulates broad spatial patterns of NH4+ and NO3 including the elevated concentrations in eastern SoCAB. However, areas for model improvement have been identified. NH3 emissions from livestock and dairy facilities appear to be too low, while those related to waste disposal in western SoCAB may be too high. Analyses using measurements from flights over SoCAB suggest that problems with NH3 predictions can influence NO3 predictions there. Offline ISORROPIA II calculations suggest that overpredictions of NHx in Pasadena cause excessive partitioning of total nitrate to the particle phase overnight, while underpredictions of Na+ cause too much partitioning to the gas phase during the day. Also, the model seems to underestimate mixing during the evening boundary layer transition leading to excessive nitrate formation on some nights. Overall, the analyses demonstrate fine-scale variations in model performance within and across the air basins. Improvements in inventories and spatial allocations of NH3 emissions and in parameterizations of sea spray emissions, evening mixing processes, and heterogeneous ClNO2 chemistry could improve model performance.

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