Peroxy radical chemistry and OH radical production during the NO 3-initiated oxidation of isoprene

Abstract

Peroxy radical reactions (RO 2 + RO 2) from the NO 3-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 C10-organic peroxide compounds (ROOR). The nitrooxy, allylic, and C5 peroxy radicals present in this system exhibit different behavior than the limited suite of peroxy radicals that have been studied to date. © 2012 Author(s).