Unveiling a Photochemical Mechanism of Mercury Re-emission in the Arctic through Computational Chemistry and Kinetic Modelling

In the polar regions, atmospheric mercury depletion events (AMDEs) efficiently convert elemental mercury into oxidized mercury (Hg(II)) via bromine oxidation. Hg(II) subsequently deposits onto snow and ice. While polar field observations have measured that a large percentage of the deposited mercury is re-emitted from the ice to the atmosphere by a photoinduced process, the fundamental photochemistry that drives the re-emission has remained elusive. In this study, the light-induced chemistry of bromide-containing mercury species in polar snowpacks during these events is analysed using computational chemistry and kinetic modelling. The authors propose a mechanism that involves the photoreduction of these bromide-based compounds to explain the mercury reemissions. Focusing on the Arctic environment, their modelling results suggest that the proposed mechanism can play a significant role in mercury reemissions from the ice surface to the atmosphere, helping to bridge a decades-long gap in the understanding of ice-atmosphere mercury exchange.

Reference:
Carmona-García, J., Saiz-Lopez, A., Mahajan, A.S., et al. (2025). Photoreduction of mercuric bromides in polar ice. PNAS, 122(10), e2422885122. https://doi.org/10.1073/pnas.2422885122