AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Moving Beyond the Bulk Phase: Kinetics of SO2 Oxidation in Sub-Micron, Deliquesced Aerosol Particles
TENGYU LIU, Jonathan Abbatt, University of Toronto, Canada
Abstract Number: 74 Working Group: Aerosol Chemistry
Abstract Sulfate aerosol is a major component of fine particulate matter and has important impacts on air quality, climate, and human and ecosystem health. However, current atmospheric models that include gas- and aqueous-phase oxidation pathways of SO2 generally underestimate the sulfate production rate during severe haze events. The reaction rate coefficients for aqueous-phase oxidation pathways in these models have been determined in bulk solution, which may not be applicable to the wet aerosol particles with three to five orders of magnitude lower water content and very much higher ionic strength than that of fog or cloud droplets. Here, we utilize a flow tube system that allows us to directly investigate, to our knowledge for the first time, the aqueous phase oxidation of dissolved SO2 by H2O2 in sub-micron, deliquesced aerosol particles at two different aerosol pH values (2.8 and 5.7) at RH of 74–90% and high ionic strength. The aerosol pH is buffered to minimize the pH changes induced by the sulfate formation. The pH-, SO2-, and H2O2-dependent sulfate formation rates are determined. The kinetics display first-order reactions in sulfur (IV) and H2O2, similar to those in bulk solution. Overall, the sulfate formation rates are 2.2 times of the modeled sulfate formation rates from bulk phase studies at both pH values. The flow tube system is also being used to investigate the SO2 oxidation catalyzed by transition metal ions to give insights on the relative roles of different oxidation pathways during severe haze events. Results from initial studies with transition metal ions will also be presented. Updating the current models with kinetic data for sulfate formation in sub-micron aerosol particles will improve air quality and climate simulations.