(263e) Hydrolysis of Organic Nitrates Formed from Oxidation of Biogenic Volatile Organic Compounds

Organic nitrates play an important role in the cycling of NO_x and secondary organic aerosol (SOA) formation, yet their formation mechanisms and fates remain highly uncertain. Results from ambient studies suggest that organic nitrates have a relatively short lifetime, though corresponding laboratory data are limited. One further reaction of organic nitrates in the particle phase is hydrolysis in the presence of particle water. In this work, we investigate the formation and hydrolysis of organic nitrates from the photooxidation and nitrate radical oxidation of biogenic volatile organic compounds, a-pinene and b-pinene. Experiments are conducted in the Georgia Environmental Chamber facility (GTEC) under dry and humid conditions in the presence of different types of aerosols seeds. Experiments are also design to probe different peroxy radical pathways (RO₂+HO₂ vs RO₂+NO₃). Speciated gas-phase and particle-phase organic nitrates are continuously monitored by a Filter Inlet for Gases and AEROsols High Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (FIGAERO-HR-ToF-CIMS). Bulk aerosol composition is measured by a High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). A large suite of highly oxygenated gas- and particle-phase organic nitrates are formed rapidly in photooxidation experiments in the presence of NO_x as well as from NO₃ oxidation. We find that the oxidation pathway (photooxidation vs. nitrate radical oxidation) plays a more important role than precursor hydrocarbon (a-pinene vs. b-pinene) in the extent of organic nitrate hydrolysis. The dynamics of the speciated organic nitrates over the course of the experiments will also be discussed. Results from this chamber study can be used to interpret organic nitrate fates under humid ambient conditions with the presence of aerosol water.