ICMol team discovers a mechanism for re-emission of mercury from ice into the atmosphere in polar spring

An international research team that includes a group from the Institute of Molecular Science (ICMol), located in the scientific-academic area of the Science Park of the University of Valencia (PCUV), has discovered a mechanism by which mercury deposited on polar ice, with the arrival of spring in the Arctic, returns to the atmosphere almost entirely. The finding, obtained through computational chemistry techniques and published in the journal 'PNAS', provides a new data for the understanding of the biogeochemical cycle of mercury, a global contaminant and an element toxic to the nervous system of living beings

Mercury is released into the atmosphere through anthropogenic and geological activity. This metal is distributed throughout the planet, including the polar zones, using the atmosphere as a means of transport. During the spring, when the first rays of sunlight arrive, so-called mercury deposition events occur from the atmosphere to the polar surface. This is due to the oxidation of mercury by bromine radicals generated by sunlight. Field measurements indicate that mercury is not removed from the atmosphere in such events, but much of this toxic metal returns to planetary circulation.

The Excited State Quantum Chemistry group (QCEXVAL) of the Institute of Molecular Science (ICMol), located in the Science Park of the University of Valencia, is part of the international team that has discovered a mechanism responsible for this process, which has been misunderstood by science for decades.

The results of work published by the journal PNAS (Proceedings of the National Academy of Sciences), carried out using state-of-the-art computational chemistry tools, suggest that the photoreduction of mercury and bromine compounds -mercury bromides -, present in polar snowpacks, plays a key role in the re-emission of mercury from the ice surface to the atmosphere. "The techniques we have contributed to allow us to predict directly with computers what happens to the pollutants present in the troposphere and stratosphere when sunlight reaches them," says Daniel Roca-Sanjuán, researcher of the Institute of Molecular Science (ICMol) of the Universitat de València and co-founder of the project. "We can estimate the rate at which molecules break down, due to the absorption of sunlight, and also know what new compounds appear," adds the scientist.

"The techniques we have contributed to allow us to predict directly with computers what happens to pollutants in the troposphere and stratosphere when sunlight hits them. We can estimate the speed at which molecules break down due to sunlight absorption, and also know what new compounds appear", Daniel Roca-Sanjuán, researcher at the Molecular Science Institute (ICMol) and co-leader of the project"

According to the article, the work combines multiconfigurational quantum chemistry with computational procedures capable of determining the 'excited state chemistry' that occurs in the Arctic ice sheet at the arrival of spring. These excited states generated by sunlight have an important influence on the behaviour and distribution of pollutants throughout the planet.

The study has as its first author Javier Carmona García, newly PhD by UV, and is co-led by Daniel Roca-Sanjuán (UV), Alfonso Saiz-López (CSIC) and Joseph S. Francisco (University of Pennsylvania, USA). The collaborative team has been working for years to understand the cycle of mercury in the atmosphere, adding to atmospheric and climatic modelling data on 'sunlight-induced excited state chemistry', Quantum information rarely considered in current models.

Mercury pollution is a global concern and, according to the authors of the study, understanding its biogeochemical cycle is necessary for effective mitigation measures. "This is especially important as climate change is causing an amplified regional warming of the Arctic, disrupting the cycle of mercury in the cryosphere, soils, ocean and atmosphere. Therefore, there is a clear need to develop mechanistic biogeochemical models to predict how mercury pollution in the Arctic will evolve in future global change scenarios," concludes the paper.

Source: UV News