AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Effect of SO2 on the Yields and Optical Properties of Secondary Organic Aerosol from Limonene Ozonolysis
JIANHUAI YE, Jonathan Abbatt, Arthur W. H. Chan, University of Toronto, Toronto, Canada
Abstract Number: 449 Working Group: Aerosol Chemistry
Abstract Ozonolysis of monoterpenes is an important source of atmospheric biogenic secondary organic aerosol (BSOA). While enhanced BSOA formation has been repeatedly observed under sulfate-rich conditions, the underlying mechanisms, as well as the chemical and physical properties of BSOA formed remain poorly understood. In this study, the role of SO2, an anthropogenic gaseous pollutant, on the yields and optical properties of BSOA was examined. BSOA was produced from limonene ozonolysis in a 1-m3 smog chamber or a 10-L quartz flow tube reactor in the presence of SO2. Enhanced SOA formation was observed through interactions with SO2. Over the course of experiments, SO2 was consumed at time scales consistent with oxidation by Criegee intermediates, indicating that gaseous SO2 interacts directly with reactive intermediates during ozonolysis. A considerable fraction of SO2 (14-70%) was found to be oxidized by sCIs even under humid conditions. In addition to the reaction with Criegee, reactive uptake of SO2 may also be significant. SO2 depletion was observed when excess HCOOH was added as Criegee scavenger. This proposed SO2 uptake increased significantly under more humid conditions. Light-absorbing components were also observed in the presence of SO2. Preliminary results show that the averaged mass absorption coefficient of these components (~ 500 cm3 g-1) is comparable to those of 'brown carbon' in other studies with biogenic precursors. Our results demonstrate the synergistic effect between BSOA formation and SO2 oxidation through Criegee/SO2 chemistry and SO2 uptake on organic aerosol. It is highlighted that not only does SO2 increase the efficiency of SOA formation from limonene ozonolysis, SO2 also enhances the potential formation of light-absorbing materials in BSOA and increases its ability to absorb radiation and affect global climate.