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The hydration of SO3 plays an important role in atmospheric sulfuric acid formation. Some atmospheric species can be involved in and facilitate the reaction. In this work, using quantum chemical calculations, we show that oxalic acid, the most common dicarboxylic acid in the atmosphere, can effectively catalyze the hydration of SO3. The energy barrier of the SO3 hydration reaction catalyzed by oxalic acid (cTt, tTt, tCt and cCt conformers) is a little higher or less than 1 kcal mol -1 , which is lower than the energy barrier of 5.17 kcal mol -1 for water-catalyzed SO3 hydration. Compared with the rates of the SO3 hydration reaction catalyzed by oxalic acid and water, it can be found that in the upper troposphere the OA-catalyzed SO3 hydration can play an important role in promoting SO3 hydration. It leads us to conclude that the involvement of oxalic acid in SO3 hydration to form H2SO4 is significant in the atmosphere. [ABSTRACT FROM AUTHOR]

By theoretical calculations, the gas-phase SO 2 hydration reaction assisted by methylamine (MA) and dimethylamine (DMA) was investigated, and the potential contribution of the hydrated product to new particle formation (NPF) also was evaluated. The results show that the energy barrier for aliphatic amines (MA and DMA) assisted SO 2 hydration reaction is lower than the corresponding that of water and ammonia assisted SO 2 hydration. In these hydration reactions, nearly barrierless reaction (only a barrier of 0.1 kcal mol −1 ) can be found in the case of SO 2 + 2H 2 O + DMA. These lead us to conclude that the SO 2 hydration reaction assisted by MA and DMA is energetically facile. The temporal evolution for hydrated products (CH 3 NH 3 + -HSO 3 - -H 2 O or (CH 3 ) 2 NH 2 + -HSO 3 - -H 2 O) in molecular dynamics simulations indicates that these complexes can self-aggregate into bigger clusters and can absorb water and amine molecules, which means that these hydrated products formed by the hydration reaction may serve as a condensation nucleus to initiate the NPF. [ABSTRACT FROM AUTHOR]