Gaseous elemental mercury (Hg0) is a globally distributed air toxin with a long atmospheric residence time. Any process that reduces its atmospheric lifetime increases its potential accumulation in the biosphere. Our data from Barrow, AK, at 71 degrees N show that rapid, photochemically driven oxidation of boundary-layer Hg0 after polar sunrise, probably by reactive halogens, creates a rapidly depositing species of oxidized gaseous mercury in the remote Arctic troposphere at concentrations in excess of 900 pg m(-3). This mercury accumulates in the snowpack during polar spring at an accelerated rate in a form that is bioavailable to bacteria and is released with snowmelt during the summer emergence of the Arctic ecosystem. Evidence suggests that this is a recent phenomenon that may be occurring throughout the earth's polar regions.

Mercury pollution control has become a global goal. The accurate estimate of long-term mercury emissions in China is critical to evaluate the global mercury budget and the emission reduction potentials. In this study, we used a technology-based approach to compile a consistent series of China's atmospheric mercury emissions at provincial level from 1978 to 2014. China totally emitted 13 294 t of anthropogenic mercury to air during 1978-2014, in which gaseous elemental mercury, gaseous oxidized mercury, and particulate-bound mercury accounted for 58.2%, 37.1%, and 4.7%, respectively. The mercury removed during this period were 2085 t in coal-fired power plants (counting 49% of mercury input), 7259 t in Zn smelting (79%), 771 t in coal-fired industrial boilers (25%), and 658 t in cement production plants (27%), respectively. Annual mercury emissions increased from 147 t in 1978 to 530 t in 2014. Both sectoral and spatial emissions of atmospheric mercury experienced significant changes. The largest mercury emission source evolved from coal-fired industrial boilers before 1998, to zinc smelting during 1999-2004, coal-fired power plants during 2005-2008, finally to cement production after 2009. Coal-fired industrial boilers and cement production have become critical hotpots for China's mercury pollution control.

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The isotopic composition of atmospheric total gaseous mercury (TGM) and particle-bound mercury (PBM) and mercury (Hg) in litterfall samples have been determined at urban/industrialized and rural sites distributed over mainland China for identifying Hg sources and transformation processes. TGM and PBM near anthropogenic emission sources display negative δ(202)Hg and near-zero Δ(199)Hg in contrast to relatively positive δ(202)Hg and negative Δ(199)Hg observed in remote regions, suggesting that different sources and atmospheric processes force the mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) in the air samples. Both MDF and MIF occur during the uptake of atmospheric Hg by plants, resulting in negative δ(202)Hg and Δ(199)Hg observed in litter-bound Hg. The linear regression resulting from the scatter plot relating the δ(202)Hg to Δ(199)Hg data in the TGM samples indicates distinct anthropogenic or natural influences at the three study sites. A similar trend was also observed for Hg accumulated in broadleaved deciduous forest foliage grown in areas influenced by anthropogenic emissions. The relatively negative MIF in litter-bound Hg compared to TGM is likely a result of the photochemical reactions of Hg(2+) in foliage. This study demonstrates the diagnostic stable Hg isotopic composition characteristics for separating atmospheric Hg of different source origins in China and provides the isotopic fractionation clues for the study of Hg bioaccumulation.