Mass and Physical Property Changes of Organic Aerosol (OA) Induced by Photolytic Aging

BIN BAI, Yuchen Wang, Nara Shin, Yaowei Li, Frank Keutsch, Nga Lee Ng, Pengfei Liu, Georgia Institute of Technology

     Abstract Number: 285
     Working Group: Aerosol Chemistry

Abstract
Organic aerosols (OA) constitute a significant fraction of the atmospheric particulate mass. Previous studies have shown that solar radiation in UV wavelengths can directly break the chemical bonds of OA species. This process, defined as OA photolytic aging herein, has been reported as a potentially important chemical removal pathway that can largely shorten the OA lifetime and affect the particle mass loading. This process can also influence the oxidation state, volatility, viscosity, and optical properties of OA. However, the kinetics and underlying chemical processes of photolytic aging remain unclear. The relationships between the mass loss, which involves the formation of volatile organic vapors, and changes in the remaining particle-phase species have not been comprehensively studied. Here, we have simultaneously monitored the mass decay, volatility, and hygroscopicity change of lab-generated OA samples illuminated by UV light under atmospheric-relevant humidity using a high-sensitivity quartz crystal microbalance (QCM-D). We have observed a rapid mass decay accompanied by significant particle volatility and hygroscopicity change for limonene ozonolysis OA and isoprene photo-oxidation OA. A unified box model by lumping OA species based on decadal volatility has been developed to reproduce the measured changes in OA mass, volatility, and hygroscopicity during photolytic aging. These results could help mitigate the knowledge gap in understanding the atmospheric fate and burden of OA, and help evaluating their environmental effects.