Peroxy radical chemistry and OH radical production during the NOsub3/sub-initiated oxidation of isoprene

摘要

Peroxy radical reactions (RO₂ + RO₂) from theNO₃-initiated oxidation of isoprene are studied with both gaschromatography and a chemical ionization mass spectrometry technique thatallows for more specific speciation of products than in previous studies ofthis system. We find high nitrate yields (~ 80%), consistent withother studies. We further see evidence of significant hydroxyl radical (OH)formation in this system, which we propose comes from RO₂ + HO₂reactions with a yield of ~38–58%. An additional OH source is thesecond generation oxidation of the nitrooxyhydroperoxide, which produces OHand a dinitrooxyepoxide with a yield of ~35%. The branching ratio ofthe radical propagating, carbonyl- and alcohol-forming, and organic peroxide-formingchannels of the RO₂ + RO₂ reaction are found to be~18–38%, ~59–77%, and ~3–4%, respectively. HO₂formation in this system is lower than has been previously assumed. Additionof RO₂ to isoprene is suggested as a possible route to the formationof several isoprene C₁₀-organic peroxide compounds (ROOR). The nitrooxy, allylic, andC₅ peroxy radicals present in this system exhibit different behaviorthan the limited suite of peroxy radicals that have been studied to date.