Redox Conversion of Elemental Carbon in Soot Remarkably Promotes HONO and Sulfate Formation

Abstract

Abstract Heterogeneous catalytic processes on soot have attracted great attention in recent years due to their accelerating role to the exacerbation of urban haze pollution. However, the surface catalytic mechanism remains largely ambiguous. Here we provide an in-depth exploration of the heterogeneous conversion of NO2 and SO2 on soot. By combining in-situ experiments with density functional theory (DFT) calculations, we demonstrate that the redox conversion of graphene-like elemental carbon (EC) on hole defects in soot can induce the heterogeneous conversion of SO2 and NO2. In particular, SO2 oxidation and NO2 reduction can be mutually promoted with the redox conversion of EC. Through splitting H2O molecules, EC can be oxidized to form hydroxyl-functionalized EC (EC-OH) while simultaneously reducing NO2 to form HONO. Conversely, EC-OH can be re-reduced to EC when photoinduced OH radicals oxidize SO2 to produce sulfate or H2SO4. Our finding highlights the significance of the redox conversion of EC on hole defects in driving the production of HONO and sulfate, which has a significant effect on elevating the atmospheric oxidation capacity and causing fine particle growth.