AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Compositional Evolution of Secondary Organic Aerosol as Temperature Cycles in Atmospherically Relevant Ranges
Zixu Zhao, Chen Le, Qi Xu, Weihan Peng, Huanhuan Jiang, Ying-Hsuan Lin, David R. Cocker III, HAOFEI ZHANG, University of California, Riverside
Abstract Number: 544 Working Group: Aerosol Chemistry
Abstract Atmospheric secondary organic aerosols (SOA) play an important role in the global particulate matter budget, and their chemical compositions determine critical properties that impact radiative forcing and human health. During atmospheric particles’ temporal and spatial transport, they could undergo ambient temperature change or cycle through various mechanisms that may transform their chemical compositions. Here, we report the compositional evolution of SOA from α-pinene ozonolysis in a smog chamber as the temperature cycles within atmospherically relevant ranges. Combining a number of on-line and off-line aerosol bulk and molecular-level measurements, we conclude that: (1) as the temperature drops, the organic vapor condensation is much less pronounced compared to volatility-based predictions, likely due to the high viscosity of the α-pinene SOA particles; (2) active and complex particle-phase reactions occur reversibly and irreversibly throughout the temperature cycles, substantially modifying concentrations of the SOA constituents and forming new products; and (3) the SOA bulk O:C ratios increase steadily during most temperature cycles in the absence of gas-phase hydroxyl radicals, and we propose a particle-phase isomerization mechanism of alkoxy radicals from organic peroxide decomposition to account for the observations. These findings have important implications for understanding the chemical evolution of SOA in the atmosphere through their lifetime and long-range transport.