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Science 7 August 2009:
Vol. 325. no. 5941, pp. 730 - 733
DOI: 10.1126/science.1172910
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Reports

Unexpected Epoxide Formation in the Gas-Phase Photooxidation of Isoprene

Fabien Paulot,1,* John D. Crounse,2 Henrik G. Kjaergaard,3,4 Andreas Kürten,1,{dagger} Jason M. St. Clair,1 John H. Seinfeld,1,2 Paul O. Wennberg1,5

Emissions of nonmethane hydrocarbon compounds to the atmosphere from the biosphere exceed those from anthropogenic activity. Isoprene, a five-carbon diene, contributes more than 40% of these emissions. Once emitted to the atmosphere, isoprene is rapidly oxidized by the hydroxyl radical OH. We report here that under pristine conditions isoprene is oxidized primarily to hydroxyhydroperoxides. Further oxidation of these hydroxyhydroperoxides by OH leads efficiently to the formation of dihydroxyepoxides and OH reformation. Global simulations show an enormous flux—nearly 100 teragrams of carbon per year—of these epoxides to the atmosphere. The discovery of these highly soluble epoxides provides a missing link tying the gas-phase degradation of isoprene to the observed formation of organic aerosols.

1 Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA.
2 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
3 Department of Chemistry, University of Otago, Dunedin, New Zealand.
4 Department of Chemistry, University of Copenhagen, Copenhagen, Denmark.
5 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.

{dagger} Present address: Institute for Atmospheric and Environmental Sciences, Goethe University, Frankfurt am Main, Germany.

* To whom correspondence should be addressed. E-mail: paulot{at}caltech.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Epoxying Isoprene Chemistry.
T. E. Kleindienst (2009)
Science 325, 687-688
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