Quantum Chemical Investigation of Snow-Mercury Interactions and Their Implication of Mercury Deposition in the Arctic

Elemental gaseous Hg is emitted into the atmosphere through various anthropogenic and natural processes. Mercury's different species and respective transport ranges, atmospheric physical and chemical transformations, and interaction with the earth's surfaces all contribute to the global cycling of toxic mercury. Under sunlight, halogens, ozone, and nitro species oxidize the emitted elemental Hg to gaseous Hg (II) molecules, which deposit onto the snow and ice surfaces in the Arctic. To investigate the fate of deposited mercury, a quantum chemical investigation was conducted using first-principles density functional theory (DFT) to analyze the interaction between various mercury molecules and snow clusters of differing sizes. Results show that all oxidized mercury molecules: XHgY, BrHgOX, BrHgXO XHgOH, XHgO₂H, and XHgNO₂, with X, Y = Cl, Br, and I atoms have thermodynamically stable interactions with snow clusters. Further, the adsorption energy of all mercury molecules increases with increasing size of snow clusters. Additionally, the orientations of deposited mercury molecules on the cluster surface also influence the mercury-snow interactions.