AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Interaction between SO2 and Criegee Intermediates in Monoterpene Ozonolysis and Effects on Secondary Organic Aerosol Formation
JIANHUAI YE, Arthur Chan, University of Toronto
Abstract Number: 233 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
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 in both field studies and laboratory experiments, the underlying mechanisms remain poorly understood. In this work, the effect of SO2 on BSOA formation from monoterpene ozonolysis was investigated. The role of stabilized Criegee biradicals (sCIs) generated from alkene ozonolysis on SO2 oxidation was examined under different humidity conditions (<5% vs. 50%). Experiments were conducted in a 1 m3 Teflon chamber. BSOA was produced from ozonolysis of alpha-pinene or limonene in the presence of 30 to 100 ppb of SO2. Our results show that BSOA from monoterpene ozonolysis is significantly enhanced in the presence of SO2 under dry conditions. SOA enhancement increases with increasing the concentration of SO2. However, the enhancement becomes negligible as the conditions become more humid. Control experiments show that SO2 is consumed at timescales consistent with oxidation by sCIs indicating that gaseous SO2 interacts directly with reactive intermediates during monoterpene ozonolysis. Organosulfate formation is probed by electrospray ionization-ion mobility time of flight mass spectrometer (ESI-IMS/TOF). Our results clearly indicate that the synergy between BSOA and anthropogenic sulphur can occur through SO2 rather than sulphuric acid, in monoterpene-rich environments. However, humidity plays an important role in modulating this effect.