Diesel soot photooxidation enhances the heterogeneous formation of HSO.

Both field observation and experimental simulation have implied that black carbon or soot plays a remarkable role in the catalytic oxidation of SO for the formation of atmospheric sulfate. However, the catalytic mechanism remains ambiguous, especially that under light irradiation. Here we systematically investigate the heterogeneous conversion of SO on diesel soot or black carbon (DBC) under light irradiation. The experimental results show that the presence of DBC under light irradiation can significantly promote the heterogeneous conversion of SO to HSO, mainly through the heterogeneous reaction between SO and photo-induced OH radicals. The detected photo-chemical behaviors on DBC suggest that OH radical formation is closely related to the abstraction and transfer of electrons in DBC and the formation of reactive superoxide radical (•O) as an intermediate. Our results extend the known sources of atmospheric HSO and provide insight into the internal photochemical oxidation mechanism of SO on DBC.