ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-4779-2011 Worldwide trend of atmospheric mercury since 1995 Slemr F. 1 Brunke E.-G. 2 Ebinghaus R. 3 Kuss J. 4 Max-Planck-Institut für Chemie, P.O. Box 3060, 55020 Mainz, Germany South African Weather Service c/o CSIR, P.O. Box 320, Stellenbosch 7599, South Africa GKSS Forschungszentrum Geesthacht GmbH, Max-Planck-Strasse, 21502 Geesthacht, Germany Leibniz Institute for Baltic Sea Research, Seestrasse 15, 18119 Rostock-Warnemünde, Germany 23 05 2011 11 10 4779 4787 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/4779/2011/acp-11-4779-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/4779/2011/acp-11-4779-2011.pdf

Concern about the adverse effects of mercury on human health and ecosystems has led to tightening emission controls since the mid 1980s. But the resulting mercury emissions reductions in many parts of the world are believed to be offset or even surpassed by the increasing emissions in rapidly industrializing countries. Consequently, concentrations of atmospheric mercury are expected to remain roughly constant. Here we show that the worldwide atmospheric mercury concentrations have decreased by about 20 to 38 % since 1996 as indicated by long-term monitoring at stations in the Southern and Northern Hemispheres combined with intermittent measurements of latitudinal distribution over the Atlantic Ocean. The total reduction of the atmospheric mercury burden of this magnitude within 14 years is unusually large among most atmospheric trace gases and is at odds with the current mercury emission inventories with nearly constant anthropogenic emissions over this period. This suggests a major shift in the biogeochemical cycle of mercury including oceans and soil reservoirs. Decreasing reemissions from the legacy of historical mercury emissions are the most likely explanation for this decline since the hypothesis of an accelerated oxidation rate of elemental mercury in the atmosphere is not supported by the observed trends of other trace gases. Acidification of oceans, climate change, excess nutrient input and pollution may also contribute by their impact on the biogeochemistry of ocean and soils. Consequently, models of the atmospheric mercury cycle have to include soil and ocean mercury pools and their dynamics to be able to make projections of future trends.

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