AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Hydrolysis of Daytime and Nighttime Organic Nitrates from α-Pinene and β-Pinene
MASAYUKI TAKEUCHI, Gamze Eris, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 194 Working Group: There Must be Something in the Water: Cloud, Fog and Aerosol Aqueous Chemistry for Aerosol Production
Abstract Particulate organic nitrates (ONs) have been observed ubiquitously across different continents and their contributions to the mass fraction of organic aerosols are found to be substantial in various field studies. Since ONs serve as a NOx reservoir and/or sink, the fate of ONs could affect the NOx cycle and O3 production. One known loss process of particulate ONs is hydrolysis in the presence of aerosol water. Results from recent field studies suggested that BVOC-derived particulate ONs in the Southeast U.S. have a short lifetime of a few hours. Although several laboratory studies have investigated the hydrolysis of speciated ONs in bulk solutions, hydrolysis of particulate ONs in aerosol water is largely unexplored. In this study, we conducted a series of chamber experiments to investigate the hydrolysis of ONs from α-pinene and β-pinene under two oxidation conditions: photooxidation in the presence of NOx (i.e. daytime) and NO3 oxidation (i.e. nighttime). The HR-ToF-AMS is used to monitor changes in the mass fraction of ONs in total organic aerosols and the HR-ToF-FIGAERO-CIMS provides speciated molecular information of ONs. Our results suggest that nighttime ONs undergo negligible hydrolysis whereas some fractions of daytime ONs appear to hydrolyze, suggesting that the type of oxidants may play a more important role than the identity of the precursor hydrocarbon in determining the hydrolysis of particulate ONs. Oxidation conditions (OH vs. NO3) could be responsible for the differences in chemical structures of ONs; nighttime chemistry favorably generates primary and/or secondary ONs that undergo slow hydrolysis while daytime chemistry forms tertiary ONs that undergo more rapid hydrolysis. Our work provides the fundamental data to understand and evaluate the fates of ONs formed under different oxidations in ambient environments.