Photoinduced Uptake and Oxidation of SO on Beijing Urban PM.

Sulfate, as a major component of aerosol particles, greatly contributes to haze formation and affects global climate change. Although formation pathways of sulfate aerosols from the conversion of SO have been extensively studied, the discrepancy between field observations and model simulations suggests that there are still unknown sulfate sources. Herein, we report for the first time a photoinduced SO uptake and oxidation pathway in Beijing urban PM aerosols. In comparison with the NO- and O-induced SO oxidation pathways, this SO photo-oxidation in Beijing urban PM could make an important contribution to the daytime sulfate formation. Reactive species, such as OH radicals and HO, are the major oxidants leading to sulfate formation in PM. The water-soluble matter (WSM) and water-insoluble organic matter (WISOM) in PM were identified as the main photo-oxidant producers. Our work highlights an important daytime sulfate source in the atmosphere and provides new insight into the photochemical aging of ambient aerosols.