Abstract View
SOA and Organic Nitrate Formation from the Reaction of α-Pinene with NO3 under Simulated Nighttime Conditions
Kelvin Bates, James Cope, Guy Burke, TRAN NGUYEN, University of California, Davis
Abstract Number: 402
Working Group: Aerosol Chemistry
Abstract
α-Pinene+NO3 is a major oxidation pathway at night, and thought to be responsible for the large number of terpene-derived organonitrates observed in mixed biogenic/anthropogenic areas, including in the aerosol phase. However, previous laboratory studies on SOA formation from this pathway have shown a big discrepancy on yields, which are likely due to the broad spectrum of chemical and physical conditions used in previous chamber studies, many of which were performed under conditions with excessively large [NO3] concentrations. Here, we perform a series of atmospheric chamber experiments to characterize the reaction of α-pinene + NO3 under a range of atmospherically relevant conditions. Specifically, we vary the reaction partners of the first-generation peroxy radicals (NO3, NO, HO2, RO2) and measure the SOA yields from each individual pathway. We show that the RO2 + RO2 pathway produces large quantities of SOA (up to 90% mass yield), while the other pathways have much lower SOA yields. To further characterize the chemical pathways by which these oxidation reactions occur, we use chemical ionization mass spectrometry to quantify yields of some gas-phase products, and collect filters for offline sampling of particle composition using high-resolution Orbitrap mass spectrometry with electrospray ionization. We show that dimer formation is the primary mechanism of SOA production for the RO2 + RO2 pathway, and remains highly competitive with other RO2 fates under simulated nighttime conditions. We present SOA and organic nitrate yields from each RO2 fate branch, and propose mechanisms consistent with the products observed. These results provide important constraints for atmospheric models of aerosol and nitrate formation, and shed light on the factors controlling nighttime SOA production in mixed biogenic/anthropogenic areas.