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Published August 17, 2012 | Published
Journal Article Open

Peroxy radical chemistry and OH radical production during the NO_3-initiated oxidation of isoprene


Peroxy radical reactions (RO_2 + RO_2) from the NO3-initiated oxidation of isoprene are studied with both gas chromatography and a chemical ionization mass spectrometry technique that allows for more specific speciation of products than in previous studies of this system. We find high nitrate yields (~ 80%), consistent with other studies. We further see evidence of significant hydroxyl radical (OH) formation in this system, which we propose comes from RO_2 + HO_2 reactions with a yield of ~38–58%. An additional OH source is the second generation oxidation of the nitrooxyhydroperoxide, which produces OH and a dinitrooxyepoxide with a yield of ~35%. The branching ratio of the radical propagating, carbonyl- and alcohol-forming, and organic peroxide-forming channels of the RO_2 + RO_2 reaction are found to be ~18–38%, ~59–77%, and ~3–4%, respectively. HO_2 formation in this system is lower than has been previously assumed. Addition of RO_2 to isoprene is suggested as a possible route to the formation of several isoprene C_(10)-organic peroxide compounds (ROOR). The nitrooxy, allylic, and C_5 peroxy radicals present in this system exhibit different behavior than the limited suite of peroxy radicals that have been studied to date.

Additional Information

© 2012 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 20 December 2011. Published in Atmos. Chem. Phys. Discuss.: 24 January 2012. Revised: 22 June 2012. Accepted: 7 July 2012. Published: 17 August 2012. This research is funded by the US Department of Energy Biological and Environmental Research Program DE-FG02-05ER63983. Also, this material is based upon work supported by the National Science Foundation (NSF) under grant ATM-0432377 and an NSF Graduate Research Fellowship (AJK). The authors would like to thank C. D. Vecitis, J. Cheng, M. R. Hoffmann, K. Takematsu, and M. Okumura for experimental assistance, J. D. Crounse, N. H. Donahue, N. C. Eddingsaas, F. Paulot, and H. O. T. Pye for helpful discussions, and the anonymous reviewers for helpful comments on the original manuscript. Edited by: J. B. Burkholder.

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