An international research team, including the Quantum Chemistry of Excited States Group (QCEXVAL) from the Institute of Molecular Science (ICMol) Universitat de València, has unveiled a crucial mechanism that explains how mercury deposited in Arctic snow returns to the atmosphere with the arrival of spring. The study, published in Proceedings of the National Academy of Sciences (PNAS), provides a key piece in understanding the global mercury cycle—a toxic pollutant with adverse effects on both human health and the environment.

When sunlight reaches the Arctic, atmospheric mercury—originating from both anthropogenic and natural sources—is deposited on polar surfaces through photochemical reactions. However, scientific observations have shown that this metal does not remain trapped in the ice, but rather re-emerges into the atmosphere shortly after deposition. Until now, the mechanism behind this phenomenon had not been clearly identified.

The research, conducted using advanced computational chemistry techniques, reveals that the photoreduction of mercury and bromine compounds present in polar snow plays a fundamental role in the re-emission of mercury into the atmosphere. When sunlight hits these compounds, processes in excited states are triggered, leading to molecular dissociation and the release of mercury in gaseous form.

The study employed multiconfigurational quantum models to accurately simulate what happens in Arctic snow during the early moments of sunlight exposure. By integrating this data into atmospheric models, scientists gain a more complete understanding of mercury behavior in the cryosphere and its impact on the global circulation of this pollutant.

The discovery—led by researchers from ICMol, the Spanish National Research Council (CSIC), and the University of Pennsylvania—marks a significant step forward in understanding the biogeochemical cycle of mercury, particularly in the context of climate change. The progressive warming of the Arctic could significantly alter this cycle, with direct implications for ecosystems and global public health.

About the QCEXVAL Group

The Quantum Chemistry of Excited States Group (QCEXVAL), based at the Institute of Molecular Science (ICMol) of the University of Valencia, is currently led by Dr. Daniel Roca-Sanjuán, Dr. Javier Segarra-Martí, and Dr. Antonio Francés-Monerris. The group is a pioneer in the use of advanced computational chemistry techniques applied to photochemistry, specializing in simulating light-induced processes in molecular systems of biological, medical, nanotechnological, and environmental interest.

Founded in 1993 within the Theoretical Chemistry Research Unit of the Department of Physical Chemistry at the University of Valencia, the group was previously led by renowned scientists such as Dr. Manuela Merchán and Dr. Luis Serrano-Andrés, both awarded by the Royal Spanish Society of Chemistry. Since its inception, QCEXVAL has combined scientific excellence with a strong international focus and a solid track record in fundamental research on the excited states of complex molecules.