Diesel soot photooxidation enhances the heterogeneous formation of H2SO4

Both field observation and experimental simulation have implied that black carbon or soot plays a remarkable role in the catalytic oxidation of SO2 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 SO2 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 SO2 to H2SO4, mainly through the heterogeneous reaction between SO2 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 (center dot O-2(-)) as an intermediate. Our results extend the known sources of atmospheric H2SO4 and provide insight into the internal photochemical oxidation mechanism of SO2 on DBC. Potential source of H2SO4 remains unclear in the atmosphere. This work first demonstrates that the formation of photoinduced center dot OH radical can directly promote the heterogeneous conversion of SO2 to H2SO4 on real diesel soot under light irradiation, extending the known sources of atmospheric H2SO4.

Automated summary

This study investigates the conversion of SO2 on diesel soot under light irradiation. The results show that the presence of soot can promote the conversion of SO2 to H2SO4 through the reaction with photo-induced OH radicals. The formation of OH radicals is related to the electron transfer in soot and the generation of reactive superoxide radicals.