Modelling the Role of Particulate Nitrate Photolysis on Tropospheric Sulfate Formation

Recent studies have suggested that particulate nitrate photolysis could be an important source of atmospheric oxidants. Products of nitrate photolysis, NOx and N(III), are proposed to be major contributors to the heterogenous oxidation of SO2 in laboratory studies. Regional and chemical kinetic modelling studies suggest that the enhanced production of sulfate in relation to nitrate photolysis is a potential missing source of the high sulfate concentration in polluted areas in North China during winter haze events. However, the formation mechanism of sulfate and its relationship with re-noxification due to nitrate photolysis over different regions remain unexplored. In this study, we implement a detail model representation of sulfate formation via nitrate photolysis into a global chemical transport model (GEOS-Chem). The model results suggest two potential pathways for sulfate formation due to nitrate photolysis: 1) via direct oxidation by N(III), and 2) via altering the concentrations of NOx, OH, and ozone. The overall impact of nitrate photolysis on global burden and distribution of sulfate and oxidants are investigated.