Ozone production chemistry in the presence of urban plumes

W. H. Brune; B. C. Baier; J. Thomas; X. Ren; R. C. Cohen; S. E. Pusede; E. C. Browne; A. H. Goldstein; D. R. Gentner; F. N. Keutsch; J. A. Thornton; S. Harrold; F. D. Lopez-Hilfiker; P. O. Wennberg

doi:10.1039/C5FD00204D

Ozone production chemistry in the presence of urban plumes†

W. H. Brune,*^a B. C. Baier,^a J. Thomas,^ab X. Ren,^c R. C. Cohen,^d S. E. Pusede,^de E. C. Browne,^df A. H. Goldstein,^g D. R. Gentner,^h F. N. Keutsch,ⁱ J. A. Thornton,^j S. Harrold,^jk F. D. Lopez-Hilfiker^jl and P. O. Wennberg^m

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* Corresponding authors

^a Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA
E-mail: whb2@psu.edu

^b Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA

^c NOAA Air Resources Laboratory, College Park, MD, USA

^d Departments of Chemistry and Earth and Planetary Science, University of California, Berkeley, CA 94720, USA

^e Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA

^f Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA

^g Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA

^h Department of Chemical and Environmental Engineering, Yale University, New Haven, CT 06511, USA

ⁱ Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA

^j Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA

^k Puget Sound Clean Air Agency, Seattle, WA 98101, USA

^l Paul Scherrer Institut, Villigen, PSI, Switzerland

^m The Linde Center for Global Environmental Science, Caltech, Pasadena, CA 91125, USA

Abstract

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 NO_x-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 NO_x-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.

This article is part of the themed collection: Chemistry in the Urban Atmosphere

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Ozone production chemistry in the presence of urban plumes†

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