Effects of SO2 on NH4NO3 Photolysis: The Role of Reducibility and Acidic Products
Qing Cao1,2, Biwu Chu1,2,3, Peng Zhang1,2,3
1State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Abstract:
Nitrate photolysis is a vital process in secondary NOx release into the atmosphere. The heterogeneous oxidation of SO2 due to nitrate photolysis has been widely reported, while the influence of SO2 on nitrate photolysis has rarely been investigated. In this study, the photolysis of nitrate on different substrates was investigated in the absence and presence of SO2. In the photolysis of NH4NO3 on the membrane without mineral oxides, NO, NO2, HONO, and NH3 decreased by 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 exhibited an inhibitory effect on the production of NOx, HONO, and NH3 due to its reducibility and acidic products, while the increase in surface acidity due to the accumulation of abundant sulfate on TiO2 and MgO promoted the release of HONO. On the photoactive oxide TiO2, HSO3-, generated by the uptake of SO2, could compete for holes with nitrate to block nitrate photolysis. This study highlights the interaction between the heterogeneous oxidation of SO2 and nitrate photolysis and provides a new perspective on how SO2 affects the photolysis of nitrate absorbed on the photoactive oxides.
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