Effects of SO₂ on NH₄NO₃ Photolysis: The Role of Reducibility and Acidic Products

The reducibility of SO2 andits acidic productsinhibited the production of reactive nitrogen in the photolysis ofnitrate on different substrates, affecting the renoxification processin the nitrate photolysis. Nitrate photolysis is a vital processin secondary NOxreleaseinto the atmosphere. The heterogeneous oxidation of SO2 due to nitrate photolysis has been widely reported, while the influenceof SO2 on nitrate photolysis has rarely been investigated.In this study, the photolysis of nitrate on different substrates wasinvestigated in the absence and presence of SO2. In thephotolysis of NH4NO3 on the membrane withoutmineral oxides, NO, NO2, HONO, and NH3 decreasedby 17.1, 6.0, 12.6, and 57.1% due to the presence of SO2, respectively. In the photolysis of NH4NO3 on the surface of mineral oxides, SO2 also exhibitedan inhibitory effect on the production of NOx, HONO, and NH3 due to its reducibility and acidic products, while the increasein surface acidity due to the accumulation of abundant sulfate onTiO(2) and MgO promoted the release of HONO. On the photoactiveoxide TiO2, HSO3 (-), generatedby the uptake of SO2, could compete for holes with nitrateto block nitrate photolysis. This study highlights the interactionbetween the heterogeneous oxidation of SO2 and nitratephotolysis and provides a new perspective on how SO2 affectsthe photolysis of nitrate absorbed on the photoactive oxides.