Ozone production chemistry in the presence of urban plumes.
Ozone pollution affects human health, especially in urban areas on hot sunny days. Its basic photochemistry has been known for decades and yet it is still not possible to correctly predict the high ozone levels that are the greatest threat. The CalNex_SJV study in Bakersfield CA in May/June 2010 provided an opportunity to examine ozone photochemistry in an urban area surrounded by agriculture. The measurement suite included hydroxyl (OH), hydroperoxyl (HO2), and OH reactivity, which are compared with the output of a photochemical box model. While the agreement is generally within combined uncertainties, measured HO2 far exceeds modeled HO2 in NOx-rich plumes. OH production and loss do not balance as they should in the morning, and the ozone production calculated with measured HO2 is a decade greater than that calculated with modeled HO2 when NO levels are high. Calculated ozone production using measured HO2 is twice that using modeled HO2, but this difference in calculated ozone production has minimal impact on the assessment of NOx-sensitivity or VOC-sensitivity for midday ozone production. Evidence from this study indicates that this important discrepancy is not due to the HO2 measurement or to the sampling of transported plumes but instead to either emissions of unknown organic species that accompany the NO emissions or unknown photochemistry involving nitrogen oxides and hydrogen oxides, possibly the hypothesized reaction OH + NO + O2 → HO2 + NO2.
Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA. whb2@psu.edu.
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Brune
Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA. whb2@psu.edu.
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Baier
Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA. whb2@psu.edu and Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA.
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Thomas
NOAA Air Resources Laboratory, College Park, MD 20740, USA.
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Ren
Departments of Chemistry and Earth and Planetary Science, University of California, Berkeley, CA 94720, USA.
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Cohen
Departments of Chemistry and Earth and Planetary Science, University of California, Berkeley, CA 94720, USA and Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA.
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Pusede
Departments of Chemistry and Earth and Planetary Science, University of California, Berkeley, CA 94720, USA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA.
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Browne
Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA.
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Goldstein
Department of Chemical and Environmental Engineering, Yale University, New Haven, CT 06511, USA.
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Gentner
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
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Keutsch
Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA.
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Thornton
Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA and Puget Sound Clean Air Agency, Seattle, WA 98101, USA.
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Harrold
Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA and Paul Scherrer Institut, Villigen, PSI, Switzerland.
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Lopez-Hilfiker
The Linde Center for Global Environmental Science, Caltech, Pasadena, CA 91125, USA.
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Wennberg