Hydrocarbon Removal in Power Plant Plumes Shows Nitrogen Oxide Dependence of Hydroxyl Radicals

J. A. de Gouw, D. D. Parrish, S. S. Brown, Peter Edwards, J. B. Gilman, M. Graus, T. F. Hanisco, J. Kaiser, F. N. Keutsch, S. -W. Kim, B. M. Lerner, J. A. Neuman, J. B. Nowak, I. B. Pollack, J. M. Roberts, T. B. Ryerson, P. R. Veres, G. M. Wolfe

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During an airborne study in the Southeast United States, measured mixing ratios of biogenic hydrocarbons were systematically lower in air masses containing enhanced nitrogen oxides from power plants, which we attribute to increased concentrations of hydroxyl (OH) radicals within the power plant plumes. Plume transects at successively further downwind distances provide a decreasing gradient of nitrogen oxides (NO x) concentrations, which together with the implied loss rates of isoprene, constrains the OH dependence on NO x. We find that OH concentrations were highest at nitrogen dioxide concentrations near 1–2 ppbv and decreased at higher and at lower concentrations. These findings agree with the dependence of OH on NO x concentrations expected from known chemical reactions but are not consistent with some studies reporting direct OH measurements higher than expected in regions of the atmosphere with low NO x (NO < 0.08 and NO 2 < 0.46 ppbv) and high biogenic hydrocarbon emissions.

Original languageEnglish
Pages (from-to)7752-7760
Number of pages9
JournalGeophysical Research Letters
Issue number13
Early online date19 Jun 2019
Publication statusPublished - 16 Jul 2019

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