An international study involving the Institute of Molecular Science (ICMOL) of the Universitat de València and the Rocasolano Physical Chemistry Institute (IQRF) of the Spanish National Research Council (CSIC) has identified the photoreduction of oxidized mercury as the main way to reduce the presence of oxidized mercury in the atmosphere. The new process of solar photolysis reduces oxidized mercury to elemental mercury, leading to a significant increase in the lifetime of this metal in our atmosphere and, therefore, an increase in the distances it can reach from their points of origin.

Mercury from industrial, environmental and mining activities accumulates for a long time in our atmosphere as a gas of elemental mercury atoms.  In this form it can live for up to a year. But once in the atmosphere, in the presence of highly reactive molecules, it becomes oxidised mercury compounds and these new compounds, which are highly toxic and polluting, are more soluble with rain and are placed again on the earth's surface with rainfall. Because it can reach places far away from those where it was emitted, it is considered a "global pollutant".  

The work, titled Photoreduction of gaseous oxidized mercury changes global atmospheric mercury speciation, transport and deposition and which has been published in the journal Nature Communications, shows a new phenomenon of conversion of oxidized mercury into elemental, which brings changes in its life cycle in terrestrial and marine ecosystems. The chemical reactions of oxidation and reduction of mercury in the atmosphere are crucial to understand the processes of dispersion and deposition of this metal.  

As Alfonso Saiz-López, CSIC researcher at the Rocasolano Institute of Physical Chemistry, points out, "oxidized mercury compounds formed in the atmosphere can also be destroyed in the presence of solar radiation (photolysis), re-generating elemental mercury and lengthening the presence of the metal in the air. Until now, this photolysis process had not been considered as an option to destroy this metal".  

To arrive at these conclusions, the team of scientists has used advanced methods of theoretical chemistry, laboratory photolysis experiments, as well as complex methods of numerical modeling of atmospheric chemistry, which have helped determine how new photochemical reactions affect the distribution of mercury on our planet.  

According to Daniel Roca-Sanjuán, researcher of the QCEXVAL group at ICMol and responsible for the computational modelling carried out in the work, "quantum chemistry currently allows us, without the need to carry out complex and expensive experiments, to predict how solar radiation affects pollutants present in the atmosphere and thus better understand their consequences for the environment".

Reference:

Photoreduction of gaseous oxidized mercury changes global atmospheric mercury speciation, transport and deposition. Nature Communications. A. Saiz-Lopez, S. P. Sitkiewicz, Sr. Roca-Sanjuán, J. M. Oliva-Enrich, J. Z. Dávalos, R. Notario, M. Jiskra, I. Xu, F. Wang, C. P. Thackray, E. M. Sunderland, Sr. J. Jacob, O. Travnikov, C. A. Cuevas, A. Ulisses Acuña, Sr. Rivero, J. M.C. Plane, Sr. E. Kinnison and J. E. Sonke. DOI: 10.1038/s41467-018-07075-3