Interaction of Acrylic Acid and SO2 on the Surface of Mineral Dust Aerosol

Heterogeneous reactions of ubiquitous acidic gases on the surface of mineral dust particles change particulate acidity and therefore affect the atmosphere, soil, and water environments during long-distance transport. Notwithstanding, interactions of inorganic and organic acidic gases in the heterogeneous reactions with aerosols remain poorly understood. In this study, reactions of sulfur dioxide (SO2) and acrylic acid on the surface of titanium dioxide (TiO2) particles under different conditions are investigated using diffuse reflectance infrared Fourier transform spectroscopy. Our analysis shows that in the single-component experiments with only SO2 or acrylic acid, wet condition inhibits the formation of sulfite compared with the dry condition; light can promote the formation of sulfuric acid and sulfate, but has little effect on the reaction of acrylic acid. In the mixed experiments with both SO2 and acrylic acid, acrylic acid can inhibit the heterogeneous reaction of SO2 by competing Lewis acid sites, Lewis basic sites, and OH active sites on the surface of particles, whereas SO2 has little effect on acrylic acid. When there is light in the mixed experiments, photo-excited reactive oxygen species can facilitate the production of sulfuric acid, which displaces acrylic acid, resulting in a decrease in acrylate and an enhancement in adsorbed acrylic acid. The results reveal the interaction of different acidic gases on the surface of particles and advance the understanding of the heterogeneous reaction of trace gases in complex atmospheric environments.