ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-14-783-2014 Projections of atmospheric mercury levels and their effect on air quality in the United States Lei H. 1 2 3 Wuebbles D. J. 2 Liang X.-Z. 4 Tao Z. https://orcid.org/0000-0003-0608-712X 5 Olsen S. 2 Artz R. 1 Ren X. 1 Cohen M. 1 National Oceanic and Atmospheric Administration (NOAA), Air Resources Laboratory, College Park, Maryland, USA Department of Atmospheric Sciences, University of Illinois, Urbana, Illinois, USA Center for Spatial Information Science and Systems, George Mason University, Fairfax, VA, USA Department of Atmospheric and Oceanic Science, and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA Universities Space Research Association/NASA Goddard Space Flight Center, Greenbelt, Maryland, USA 23 01 2014 14 2 783 795 Copyright: © 2014 H. Lei et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/14/783/2014/acp-14-783-2014.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/14/783/2014/acp-14-783-2014.pdf

The individual and combined effects of global climate change and emissions changes from 2000 to 2050 on atmospheric mercury levels in the United States are investigated by using the global climate-chemistry model, CAM-Chem, coupled with a mercury chemistry-physics mechanism (CAM-Chem/Hg). Three future pathways from the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) are considered, with the A1FI, A1B and B1 scenarios representing the upper, middle and lower bounds of potential climate warming, respectively. The anthropogenic and biomass burning emissions of mercury are projected from the energy use assumptions in the IPCC SRES report. Natural emissions from both land and ocean sources are projected by using dynamic schemes. TGM concentration increases are greater in the low latitudes than they are in the high latitudes, indicative of a larger meridional gradient than in the present day. In the A1FI scenario, TGM concentrations in 2050 are projected to increase by 2.1–4.0 ng m<sup>−3</sup> for the eastern US and 1.4–3.0 ng m<sup>−3</sup> for the western US. This spatial difference corresponds to potential increases in wet deposition of 10–14 μg m<sup>−2</sup> for the eastern US and 2–4 μg m<sup>−2</sup> for the western US. The increase in Hg(II) emissions tends to enhance wet deposition and hence increase the risk of higher mercury entering the hydrological cycle and ecosystem. In the B1 scenario, mercury concentrations in 2050 are similar to present level concentrations; this finding indicates that the domestic reduction in mercury emissions is essentially counteracted by the effects of climate warming and emissions increases in other regions. The sensitivity analyses show that changes in anthropogenic emissions contribute 32–53% of projected changes in mercury air concentration, while the independent contribution by climate change and its induced natural emissions change accounts for 47–68%.

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