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

Peroxy radical reactions (RO2 + RO2) 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 RO2 + HO2 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, carbonyland alcohol-forming, and organic peroxide-forming channels of the RO2 + RO2 reaction are found to be ∼ 18–38 %, ∼ 59–77 %, and ∼ 3–4 %, respectively. HO2 formation in this system is lower than has been previously assumed. Addition of RO2 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.