Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

Creators: Wennberg, Paul O.; Bates, Kelvin H.; Crounse, John D.; Dodson, Leah G.; McVay, Renee C.; Mertens, Laura A.; Nguyen, Tran B.; Praske, Eric; Schwantes, Rebecca H.; Smarte, Matthew D.; St. Clair, Jason M.; Teng, Alexander P.; Zhang, Xuan; Seinfeld, John H.

Abstract

Isoprene carries approximately half of the flux of non-methane volatile organic carbon emitted to the atmosphere by the biosphere. Accurate representation of its oxidation rate and products is essential for quantifying its influence on the abundance of the hydroxyl radical (OH), nitrogen oxide free radicals (NO_x), ozone (O_3), and, via the formation of highly oxygenated compounds, aerosol. We present a review of recent laboratory and theoretical studies of the oxidation pathways of isoprene initiated by addition of OH, O_3, the nitrate radical (NO_3), and the chlorine atom. From this review, a recommendation for a nearly complete gas-phase oxidation mechanism of isoprene and its major products is developed. The mechanism is compiled with the aims of providing an accurate representation of the flow of carbon while allowing quantification of the impact of isoprene emissions on HO_x and NO_x free radical concentrations and of the yields of products known to be involved in condensed-phase processes. Finally, a simplified (reduced) mechanism is developed for use in chemical transport models that retains the essential chemistry required to accurately simulate isoprene oxidation under conditions where it occurs in the atmosphere—above forested regions remote from large NO_x emissions.

Additional Information

© 2018 American Chemical Society. Received: July 21, 2017; Publication Date (Web): March 9, 2018. Additional Data: Additional detailed treatments of the reactions can be found at http://dx.doi.org/10.22002/D1.247, where the full and reduced mechanisms are made available as computer-readable codes for communal use and development. We acknowledge support for this study by the Electric Power Research Institute, the National Science Foundation (AGS-1240604 and CHE-1508526), and the National Aeronautics and Space Administration (NNX14AP46G). P.O.W. thanks the University of Copenhagen and Henrik Kjaergaard for hosting his sabbatical during which much of this work was completed. He further thanks Henrik Kjaergaard, Kristian Møller, and Rasmus Otkjær for help with the H-shift chemistry. T.B.N. thanks the National Science Foundation AGS Postdoctoral Research Fellowship for support (AGS-1331360). L.G.D. was supported by an EPA STAR Fellowship and a Sandia Campus Executive Laboratory Directed Research and Development (LDRD) project. K.H.B. and M.D.S. acknowledge support from the National Science Foundation Graduate Research Fellowship program. The National Center for Atmospheric Research is sponsored by the National Science Foundation. Finally, we acknowledge the heroic effort of the anonymous reviewers; they provided excellent feedback that substantially improved our manuscript. The authors declare no competing financial interest.

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