Mercury (Hg) is a heavy metal that is present naturally in various chemical forms. It forms toxic methylmercury compounds that bioaccumulate up aquatic food chains, leading to elevated levels in fish and piscivorous mammals. Resultantly, mercury holds threatening neurological effects on human health, identifying it as an environmental pollutant of global concern. The respective transport ranges of mercury species, atmospheric physical and chemical transformations, and interaction with Earth’s surfaces, contributes to the global cycling of toxic mercury. In arctic springtime, elemental Hg(0) is oxidized by halogens, ozone, and nitro species under ultraviolet light into reactive Hg (II) that is deposited onto snow through atmospheric mercury depletion events (AMDE). As a result, the Arctic seasonal snowpack is suspected to contribute to the contamination of aquatic life during snowmelt. However, the exact pathway mercury follows succeeding deposition and the extent of atmospherically deposited mercury influencing the Arctic through snow remains unclear. To understand the fate of deposited mercury, reactions between mercury and snow surfaces was analyzed through adsorption processes. A quantum-chemical investigation was carried out by mimicking optimized structures of different snow cluster dimensions and observing the interaction of various oxidized mercury compounds to the snow surfaces. Density-functional theory was applied to analyze the strength at which these compounds bind to the snow cluster of varying sizes. Results showed that BrHgXO (X representing Br, Cl, and I) compounds had the strongest interaction for clusters consisting of five, twelve and thirty-nine snow molecules. Oxygen containing compounds overall had higher adsorption energies than those that are lacking due to O-H hydrogen bonding. The adsorption values confirm that mercury dissociates onto snow, and enters the arctic water supply.

Quantum chemical investigation of the adsorption of oxidized mercury on snow surfaces

ACS Spring Meeting 2021

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