Heterogeneous Reactions of SO3 on Ice: An Overlooked Sink for SO3 Depletion

The reaction between SO3 and water in the gas phase has always been of great interest as it has important implications to atmos-pheric and environment science. Compared to gas-phase water, however, heterogeneous hydration of SO3 on the surfaces of con-densed phase of water/ice are relatively less explored. Here, we present a systematic study of the reaction between SO3 and three different phases of water, namely, water vapor, surface of liquid water droplet, and the {1 1 -2 0} plane of hexagonal ice (Ih). The computation results show that contrary to the gas-phase water, the surface of water droplet and {1 1 -2 0} plane of Ih ice play a distinctly different role in the reaction, in which the HSO4-/H3O+ is formed within a few picoseconds. Moreover, the SO3 hydration exhibits multiple reaction pathways on the surface of water drop-let and {1 1 -2 0} plane of Ih ice, including the newly observed chemical mechanism without the formation of water-loop struc-tures. Considering temperature effects (winter vs. su...