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Journal of Geophysical Research: Atmospheres

Ozone and organic nitrates over the eastern United States: Sensitivity to isoprene chemistry

Authors

  • Jingqiu Mao,

    Corresponding author
    1. Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey, USA
    2. Geophysical Fluid Dynamics Laboratory/National Oceanic and Atmospheric Administration, Princeton, New Jersey, USA
    • Corresponding author: J. Mao, NOAA/GFDL, 201 Forrestal Road, Princeton, NJ 08540, USA. (Jingqiu.Mao@noaa.gov)

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  • Fabien Paulot,

    1. School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
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  • Daniel J. Jacob,

    1. School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
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  • Ronald C. Cohen,

    1. Department of Chemistry and Department of Earth and Planetary Science, University of California, Berkeley, California, USA
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  • John D. Crounse,

    1. Division of Engineering and Applied Science and Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
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  • Paul O. Wennberg,

    1. Division of Engineering and Applied Science and Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
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  • Christoph A. Keller,

    1. School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
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  • Rynda C. Hudman,

    1. Department of Chemistry and Department of Earth and Planetary Science, University of California, Berkeley, California, USA
    2. Now at Environmental Protection Agency Region IX, San Francisco, California, USA
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  • Michael P. Barkley,

    1. EOS Group, Department of Physics & Astronomy, University of Leicester, Leicester, UK
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  • Larry W. Horowitz

    1. Geophysical Fluid Dynamics Laboratory/National Oceanic and Atmospheric Administration, Princeton, New Jersey, USA
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Abstract

[1] We implement a new isoprene oxidation mechanism in a global 3-D chemical transport model (GEOS-Chem). Model results are evaluated with observations for ozone, isoprene oxidation products, and related species from the International Consortium for Atmospheric Research on Transport and Transformation aircraft campaign over the eastern United States in summer 2004. The model achieves an unbiased simulation of ozone in the boundary layer and the free troposphere, reflecting canceling effects from recent model updates for isoprene chemistry, bromine chemistry, and HO2 loss to aerosols. Simulation of the ozone-CO correlation is improved relative to previous versions of the model, and this is attributed to a lower and reversible yield of isoprene nitrates, increasing the ozone production efficiency per unit of nitrogen oxides (NOx ≡ NO + NO2). The model successfully reproduces the observed concentrations of organic nitrates (∑ANs) and their correlations with HCHO and ozone. ∑ANs in the model is principally composed of secondary isoprene nitrates, including a major contribution from nighttime isoprene oxidation. The correlations of ∑ANs with HCHO and ozone then provide sensitive tests of isoprene chemistry and argue in particular against a fast isomerization channel for isoprene peroxy radicals. ∑ANs can provide an important reservoir for exporting NOx from the U.S. boundary layer. We find that the dependence of surface ozone on isoprene emission is positive throughout the U.S., even if NOx emissions are reduced by a factor of 4. Previous models showed negative dependences that we attribute to erroneous titration of OH by isoprene.

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