Articles | Volume 8, issue 6
Atmos. Chem. Phys., 8, 1445–1482, 2008

Special issue: Air Ice Chemical Interactions (AICI)

Atmos. Chem. Phys., 8, 1445–1482, 2008
12 Mar 2008
12 Mar 2008

A synthesis of atmospheric mercury depletion event chemistry in the atmosphere and snow

A. Steffen1,2, T. Douglas3, M. Amyot4, P. Ariya5, K. Aspmo6, T. Berg6,7, J. Bottenheim1, S. Brooks8, F. Cobbett9, A. Dastoor1, A. Dommergue10, R. Ebinghaus2,11, C. Ferrari10, K. Gardfeldt12, M. E. Goodsite13, D. Lean14, A. J. Poulain4, C. Scherz15, H. Skov16, J. Sommar12, and C. Temme11 A. Steffen et al.
  • 1Environment Canada, Air Quality Research Division, 4905 Dufferin Street, Toronto, Ontario, M3H 5T4, Canada
  • 2Universität Lüneburg, Scharnhorststraße 1/13, 21335, Luneburg, Germany
  • 3US Army Cold Regions Research and Engineering Laboratory Fort Wainwright, Alaska, USA
  • 4Département de Sciences Biologiques, Université de Montréal, Pavillon Marie-Victorin, Montréal (QC) H3C 3J7, Canada
  • 5Departments of Chemistry and Atmospheric and Oceanic Sciences, McGill University, 801 Sherbrooke St. W., Montreal, PQ, H3A 2K6, Canada
  • 6Norwegian Institute for Air Research, Instituttveien 18, 2027 Kjeller, Norway
  • 7Norwegian University of Science and Technology, Department of Chemistry, 7491 Trondheim, Norway
  • 8National Oceanic and Atmospheric Administration, Atmospheric Turbulence and Diffusion Division, Oak Ridge, TN, USA
  • 9School of Engineering, University of Guelph, Guelph, ON, N1G 2W1, Canada
  • 10Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE) and Universite Joseph Fourier, France
  • 11GKSS-Forschungszentrum Geesthacht GmbH, Institute for Coastal Research, Department for Environmental Chemistry, Max-Planck-Str. 1, 21052 Geesthacht, Germany
  • 12Göteborg University and Chalmers University of Technology, 412 96 Göteborg, Sweden
  • 13University of Southern Denmark, Department of Physics and Chemistry Campusvej 55, 5230 Odense M, Denmark
  • 14University of Ottawa, Department of Biology, Centre for Advanced Research in Environmental Genomics, P.O. Box 450 Station A. 20 Marie Curie, Ottawa, ON K1N 6N5, Canada
  • 154 Hollywood Crescent, Toronto, M4L 2K5, Canada
  • 16National Environmental Research Institute, Frederiksborgvej 399, 4000 Roskilde, Denmark

Abstract. It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). This phenomenon is termed atmospheric mercury depletion events (AMDEs) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. Shortly after the discovery was made in Canada, AMDEs were confirmed to occur throughout the Arctic, sub-Artic and Antarctic coasts. It is now known that, through a series of photochemically initiated reactions involving halogens, GEM is converted to a more reactive species and is subsequently associated to particles in the air and/or deposited to the polar environment. AMDEs are a means by which Hg is transferred from the atmosphere to the environment that was previously unknown. In this article we review Hg research taken place in Polar Regions pertaining to AMDEs, the methods used to collect Hg in different environmental media, research results of the current understanding of AMDEs from field, laboratory and modeling work, how Hg cycles around the environment after AMDEs, gaps in our current knowledge and the future impacts that AMDEs may have on polar environments. The research presented has shown that while considerable improvements in methodology to measure Hg have been made but the main limitation remains knowing the speciation of Hg in the various media. The processes that drive AMDEs and how they occur are discussed. As well, the role that the snow pack and the sea ice play in the cycling of Hg is presented. It has been found that deposition of Hg from AMDEs occurs at marine coasts and not far inland and that a fraction of the deposited Hg does not remain in the same form in the snow. Kinetic studies undertaken have demonstrated that bromine is the major oxidant depleting Hg in the atmosphere. Modeling results demonstrate that there is a significant deposition of Hg to Polar Regions as a result of AMDEs. Models have also shown that Hg is readily transported to the Arctic from source regions, at times during springtime when this environment is actively transforming Hg from the atmosphere to the snow and ice surfaces. The presence of significant amounts of methyl Hg in snow in the Arctic surrounding AMDEs is important because this species is the link between the environment and impacts to wildlife and humans. Further, much work on methylation and demethylation processes has occurred but these processes are not yet fully understood. Recent changes in the climate and sea ice cover in Polar Regions are likely to have strong effects on the cycling of Hg in this environment; however more research is needed to understand Hg processes in order to formulate meaningful predictions of these changes.

Final-revised paper