Reductive Adsorption of Atmospheric Oxidized Mercury on Ice: Insights from Density Functional Calculations

Abstract

The fate of atmospheric mercury (Hg) has been intensively investigated due to concerns about its global dispersion. The reduction of reactive oxidized Hg (Hg-II) to the stable form (Hg-0) is a significant process, in that it extends the mean atmospheric lifetime of Hg and allows for its long-range transport. While the reduction mechanisms of Hg-II in aqueous, particulate, and gas phases have drawn much attention, the reaction pathway and mechanism of Hg-II reduction in icy environments are still elusive, despite that ice particles have been expected to play an active role, from field and laboratory observations. With density functional theory calculations, we reveal the adsorptive and dissociative pathways of Hg-II on ice, including the catalytic role of the ice surface that facilitates the dissociative adsorption of Hg dihalides. Because ice is the most common phase of water in the upper atmosphere and cryosphere, its influence on Hg speciation can have profound implications on the global Hg cycle.