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Peroxy radical chemistry and OH radical production during the NO3-initiated oxidation of isoprene

by A J Kwan, Chan A W H., N Ng, H G Kjaergaard, J H Seinfeld, P O Wennberg
Atmos. Chem. Phys. ()

Abstract

Peroxy radical reactions (RO2 + RO2 ) from the NO3 -initiated oxidation\nof isoprene are studied with both gas chromatography and a chemical\nionization mass spectrometry technique that allows for more specific\nspeciation of products than in previous studies of this system. We\nfind high nitrate yields (∼ 80 %), consistent with other studies.\nWe further see evidence of significant hydroxyl radical (OH)formation\nin this system, which we propose comes from RO2 + HO2 reactions with\na yield of ∼ 38–58 %. An additional OH source is the second generation\noxidation of the nitrooxyhydroperoxide, which produces OH and a dinitrooxyepoxide\nwith a yield of ∼ 35 %. The branching ratio of the radical propagating,\ncarbonyl- and alcohol-forming, and organic peroxide-forming channels\nof the RO2 + RO2 reaction are found to be ∼ 18–38 %, ∼ 59–77 %, and\n∼ 3–4 %, respectively. HO2 formation in this system is lower than\nhas been previously assumed. Addition of RO2 to isoprene is suggested\nas a possible route to the formation of several isoprene C10 -organic\nperoxide compounds (ROOR). The nitrooxy, allylic, and C5 peroxy radicals\npresent in this system exhibit different behavior than the limited\nsuite of peroxy radicals that have been studied to date.

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