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Atmosphere 2013, 4(2), 113-131; doi:10.3390/atmos4020113

Decreases in Mercury Wet Deposition over the United States during 2004–2010: Roles of Domestic and Global Background Emission Reductions

*  and
Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA
* Author to whom correspondence should be addressed.
Received: 8 April 2013 / Revised: 26 April 2013 / Accepted: 6 May 2013 / Published: 10 May 2013
(This article belongs to the Special Issue Atmospheric Mercury)
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Wet deposition of mercury (Hg) across the United States is influenced by changes in atmospheric conditions, domestic emissions and global background emissions. We examine trends in Hg precipitation concentrations at 47 Mercury Deposition Network (MDN) sites during 2004–2010 by using the GEOS-Chem nested-grid Hg simulation. We run the model with constant anthropogenic emissions and subtract the model results from the observations. This helps to remove the variability in observed Hg concentrations caused by meteorological factors, including precipitation. We find significant decreasing trends in Hg concentrations in precipitation at MDN sites in the Northeast (−4.1 ± 0.49% yr−1) and Midwest (−2.7 ± 0.68% yr−1). Over the Southeast (−0.53 ± 0.59% yr−1), trends are weaker and not significant, while over the West, trends are highly variable. We conduct model simulations assuming a 45% decrease in Hg emissions from domestic sources in the modeled period and a uniform 12% decrease in background atmospheric Hg concentrations. The combination of domestic emission reductions and decreasing background concentrations explains the observed trends over the Northeast and Midwest, with domestic emission reductions accounting for 58–46% of the decreasing trends. Over the Southeast, we overestimate the observed decreasing trend, indicating potential issues with our assumption of uniformly decreasing background Hg concentrations.
Keywords: mercury; wet deposition; trend; GEOS-Chem; nested-grid model mercury; wet deposition; trend; GEOS-Chem; nested-grid model
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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Zhang, Y.; Jaeglé, L. Decreases in Mercury Wet Deposition over the United States during 2004–2010: Roles of Domestic and Global Background Emission Reductions. Atmosphere 2013, 4, 113-131.

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