Towards understanding the role of amines in the SO2 hydration and the contribution of the hydrated product to new particle formation in the Earth's atmosphere

By theoretical calculations, the gas-phase SO2 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 SO2 hydration reaction is lower than the corresponding that of water and ammonia assisted SO2 hydration. In these hydration reactions, nearly barrierless reaction (only a barrier of 0.1 kcal mol-1) can be found in the case of SO2 + 2H2O + DMA. These lead us to conclude that the SO2 hydration reaction assisted by MA and DMA is energetically facile. The temporal evolution for hydrated products (CH3NH3+-HSO3--H2O or (CH3)2NH2+-HSO3--H2O) 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.