The Formation and Aerosol Uptake of Isoprene Nitrooxyhydroxyepoxide (INHE), a Newly Identified Product from the RO2 + HO2 Pathway of Isoprene NO3 Oxidation

Wednesday, 17 December 2014: 11:35 AM
Rebecca Schwantes, Alex Teng, Tran Nguyen, Matthew Mitchell Coggon, Xuan Zhang, Katherine Schilling-Fahnestock, John Crounse, Jason Michael St Clair, John Seinfeld and Paul O Wennberg, California Institute of Technology, Pasadena, CA, United States
Isoprene (C5H8) reacts with the nitrate radical (NO3) during the night to produce a peroxy nitrate radical (RO2). This RO2 can react with nitrogen oxides (i.e., NO, NO2, or NO3) and other RO2 radicals to form isoprene nitrates or with the hydroperoxyl radical (HO2) to form nitrooxyhydroperoxide (INP). Both model and field studies have found that in the ambient atmosphere much of the RO2 radical reacts with HO2. More specifically, during the 2013 SOAS field campaign, INP was one of the main species that increased at sunset suggesting the RO2 + HO2 pathway from NO3 oxidation is important in the southeastern US and similar areas. However, chamber studies so far have been run under conditions that optimize RO2 + NO3 reactions and/or RO2 + RO2 reactions. In this work, we present a new way to run NO3 oxidation chamber experiments that optimize for the RO2 + HO2 pathway creating a more atmospherically relevant product distribution. The gas phase formation of INP and subsequent oxidation products were monitored using a chemical ionization mass spectrometer (CIMS). Because isoprene nitrates formed from NO3 oxidation react slowly with ozone (O3) and NO3, many of these nitrates will remain in the atmosphere until the sun rises and hydroxyl radical (OH) begins to form. Results from these chamber experiments suggest that OH will react with INP to form nitrooxyhydroxyepoxide (INHE), a newly identified product from INP. We suspect INHE could be important for Secondary Organic Aerosol (SOA) production due to its similarity to isoprene epoxydiol (IEPOX), a product from isoprene OH oxidation that has been shown to be a significant SOA precursor. We studied the uptake of INHE onto various seed types, and found that as expected INHE rapidly partitions to highly acidic seed aerosol due to an acid catalyzed ring opening. A time-of-flight aerosol mass spectrometer (ToF-AMS) was used to understand the chemical composition of the aerosol produced from the various seed types.