Interactions between Heterogeneous Uptake and Adsorption of Sulfur Dioxide and Acetaldehyde on Hematite.

Sulfur dioxide and organic aldehydes in the atmosphere are ubiquitous and often correlated with mineral dust aerosols. Heterogeneous uptake and adsorption of one of these species on mineral aerosols can potentially change the properties of the particles and further affect the subsequent heterogeneous reactions of the other species on the coating particles. In this study, the interactions between heterogeneous uptake and adsorption of sulfur dioxide and acetaldehyde on hematite are investigated by using in situ diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) at room temperature. It is found that the preadsorption of SO2 on α-Fe2O3 can significantly hinder the subsequent heterogeneous oxidation of CH3CHO to acetate, while the preadsorption of CH3CHO significantly suppresses the heterogeneous reaction of large amounts of SO2 on the surface of α-Fe2O3 and has a little influence on the uptake of small amount of SO2. The heterogeneous reactions of SO2 on α-Fe2O3 preadsorbed by CH3CHO change the existing acetate on the particle surface into chemisorbed acetic acid, for the enhancement of surface acidity after the uptake of SO2. During these processes, different surface hydroxyl groups showed different reactivities. Atmospheric implications of this study are discussed.