AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Sulfate Formation from SO2 Uptake onto Organic Aerosol
Shunyao Wang, William Tsui, V. Faye McNeill, Jonathan Abbatt, ARTHUR W. H. CHAN, University of Toronto
Abstract Number: 294 Working Group: Aerosol Chemistry
Abstract Particulate matter is dominated by sulfate and organic aerosol (OA). Secondary formation of these components are often studied and modeled separately, but the observed correlations between their concentrations suggest synergistic reactions. Previous laboratory studies show that secondary organic aerosol (SOA) yields are higher when formed in the presence of SO2, but the mechanisms by which SO2 reacts are not known. In this work, we conducted bulk solution experiments of S(IV) oxidation by organic peroxides to investigate the kinetics and mechanisms of sulfate formation, and chamber experiments of SO2 uptake onto peroxide-containing OA.
The bulk reaction rate constants of SO2 with commercially available organic peroxides (cumene hydroperoxide, benzoyl peroxide and 2-butanone hydroperoxide) are quantified as a function of pH, and are shown to be similar to that with H2O2. Using isotopically labeled reagents and ion-mobility mass spectrometry (IMS-TOF), we show that organosulfates are formed from ROOH + SO2 at a substantial yield of 40%. This mechanism is unique from previously proposed pathways for organosulfate formation, which require inorganic sulfate as a reactant. Further experiments are conducted in the aerosol phase by generating SOA in the flow tube and measuring SO2 uptake onto SOA in the chamber. The uptake coefficients are measured for different SOA containing different types and amounts of organic peroxides. Organosulfate speciation using IMS-TOF is examined and compared to the backbone of SOA precursors. The mechanisms and kinetic parameters derived from this work are applied in an aerosol kinetic model (GAMMA) to understand the rate of SO2 uptake and inorganic and organic sulfate formation in the aerosol. Preliminary modeling results suggest that this reaction can account for all of the observed SO2 uptake onto SOA from limonene ozonolysis, and results for other SOA systems and implications on atmospheric chemistry will be discussed.