1Department of Atmospheric Sciences, University of Illinois, Urbana, Illinois, USA
2Department of Atmospheric and Oceanic Science, and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA
3Universities Space Research Association/NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Received: 12 Jan 2013 – Published in Atmos. Chem. Phys. Discuss.: 15 Apr 2013
Abstract. Atmospheric mercury is a toxic air and water pollutant that is of significant concern because of its effects on human health and ecosystems. A mechanistic representation of the atmospheric mercury cycle is developed for the state-of-the-art global climate-chemistry model, CAM-Chem (Community Atmospheric Model with Chemistry). The model simulates the emission, transport, transformation and deposition of atmospheric mercury (Hg) in three forms: elemental mercury (Hg(0)), reactive mercury (Hg(II)), and particulate mercury (PHg). Emissions of mercury include those from human, land, ocean, biomass burning and volcano related sources. Land emissions are calculated based on surface solar radiation flux and skin temperature. A simplified air–sea mercury exchange scheme is used to calculate emissions from the oceans. The chemistry mechanism includes the oxidation of Hg(0) in gaseous phase by ozone with temperature dependence, OH, H2O2 and chlorine. Aqueous chemistry includes both oxidation and reduction of Hg(0). Transport and deposition of mercury species are calculated through adapting the original formulations in CAM-Chem. The CAM-Chem model with mercury is driven by present meteorology to simulate the present mercury air quality during the 1999–2001 period. The resulting surface concentrations of total gaseous mercury (TGM) are then compared with the observations from worldwide sites. Simulated wet depositions of mercury over the continental United States are compared to the observations from 26 Mercury Deposition Network stations to test the wet deposition simulations. The evaluations of gaseous concentrations and wet deposition confirm a strong capability for the CAM-Chem mercury mechanism to simulate the atmospheric mercury cycle. The general reproduction of global TGM concentrations and the overestimation on South Africa indicate that model simulations of TGM are seriously affected by emissions. The comparison to wet deposition indicates that wet deposition patterns of mercury are more affected by the spatial variability of precipitation. The sensitivity experiments show that 22% of total mercury deposition and 25% of TGM concentrations in the United States result from domestic anthropogenic sources, but only 9% of total mercury deposition and 7% of TGM concentrations are contributed by transpacific transport. However, the contributions of domestic and transpacific sources on the western United States levels of mercury are of comparable magnitude.
Revised: 29 Jul 2013 – Accepted: 09 Oct 2013 – Published: 07 Nov 2013
Citation: Lei, H., Liang, X.-Z., Wuebbles, D. J., and Tao, Z.: Model analyses of atmospheric mercury: present air quality and effects of transpacific transport on the United States, Atmos. Chem. Phys., 13, 10807-10825, doi:10.5194/acp-13-10807-2013, 2013.