A laboratory study of the heterogeneous uptake and oxidation of sulfur dioxide on mineral dust particles

Abstract

The heterogeneous uptake and oxidation of SO2 on particle surfaces representative of mineral dusts found in the atmosphere have been investigated. These particles include metal oxides (e.g., hematite, corundum), calcite, and China loess. FT-IR spectroscopy was used to characterize surface-bound species following exposure to gaseous SO2. It was found that SO2 irreversibly adsorbs as sulfite (SO32-) and/or bisulfite (HSO3-) on all particle surfaces with the exception of SiO2. The adsorbed species can be oxidized to sulfate and/or bisulfate (SO42- and/or HSO4-) upon exposure to ozone. Knudsen cell reactor studies were done to measure heterogeneous uptake coefficients for SO2. Initial uptake coefficients, calculated using BET surface areas, γBET, are found to be lower than that found for water droplets. As shown here, the γBET value for China loess can be predicted from the reactivity of the single component oxide and carbonate particles along with the average composition of the dust sample, with each component weighted by its natural abundance in the sample.