1Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA
2Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
3Copenhagen Center for Atmospheric Chemistry, Department of Chemistry, University of Copenhagen, 2100 Copenhagen Ø, Denmark
4Division of Geology and Planetary Science, California Institute of Technology, Pasadena, CA 91125, USA
*now at: Energy Storage Division, NEXT ENERGY EWE-Forschungszentrum für Energietechnologie e.V., 26129 Oldenburg, Germany
**now at: Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA 94720, USA
***now at: School of Chemical and Biomolecular Engineering and School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
Abstract. 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 ~42–62%. 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 dimer-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 dimer 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.