ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-7117-2012 An assessment of atmospheric mercury in the Community Multiscale Air Quality (CMAQ) model at an urban site and a rural site in the Great Lakes Region of North America Holloway T. 1 Voigt C. 1 Morton J. 1 Spak S. N. 2 Rutter A. P. 3 Schauer J. J. 4 Nelson Institute Center for Sustainability and the Global Environment (SAGE), University of Wisconsin-Madison, Madison, WI, USA Public Policy Center (PPC), University of Iowa, Iowa City, IA USA Civil and Environmental Engineering, Rice University, Houston, TX, USA Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, WI, USA 07 08 2012 12 15 7117 7133 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/12/7117/2012/acp-12-7117-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/7117/2012/acp-12-7117-2012.pdf

Quantitative analysis of three atmospheric mercury species – gaseous elemental mercury (Hg<sup>0</sup>), reactive gaseous mercury (RGHg) and particulate mercury (PHg) – has been limited to date by lack of ambient measurement data as well as by uncertainties in numerical models and emission inventories. This study employs the Community Multiscale Air Quality Model version 4.6 with mercury chemistry (CMAQ-Hg), to examine how local emissions, meteorology, atmospheric chemistry, and deposition affect mercury concentration and deposition the Great Lakes Region (GLR), and two sites in Wisconsin in particular: the rural Devil's Lake site and the urban Milwaukee site. Ambient mercury exhibits significant biases at both sites. Hg<sup>0</sup> is too low in CMAQ-Hg, with the model showing a 6% low bias at the rural site and 36% low bias at the urban site. Reactive mercury (RHg = RGHg + PHg) is over-predicted by the model, with annual average biases >250%. Performance metrics for RHg are much worse than for mercury wet deposition, ozone (O<sub>3</sub>), nitrogen dioxide (NO<sub>2</sub>), or sulfur dioxide (SO<sub>2</sub>). Sensitivity simulations to isolate background inflow from regional emissions suggests that oxidation of imported Hg<sup>0</sup> dominates model estimates of RHg at the rural study site (91% of base case value), and contributes 55% to the RHg at the urban site (local emissions contribute 45%).

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