1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
2School of Engineering and Applied Sciences, Harvard University, Boston, MA, USA
3Department of Earth System Science, University of California, Irvine, CA, USA
4Air Quality Research Division, Environment Canada, Toronto, Ont., Canada
5Civil and Environmental Engineering Department, Rice University, Houston, TX, USA
6Department of Natural Resources and Environmental Sciences, University of Nevada, Reno, NV, USA
7Department of Civil and Environmental Engineering, University of Wisconsin, Madison, WI, USA
8Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
9Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA
10Atmospheric Research & Analysis, Inc., Cary, NC, USA
11Department of Atmospheric Sciences, University of Washington, Seattle, USA
12Department of Environmental Health, Harvard University, Boston, MA, USA
Received: 19 Oct 2011 – Published in Atmos. Chem. Phys. Discuss.: 31 Oct 2011
Abstract. Atmospheric deposition of Hg(II) represents a major input of mercury to surface environments. The phase of Hg(II) (gas or particle) has important implications for deposition. We use long-term observations of reactive gaseous mercury (RGM, the gaseous component of Hg(II)), particle-bound mercury (PBM, the particulate component of Hg(II)), fine particulate matter (PM2.5), and temperature (T) at five sites in North America to derive an empirical gas-particle partitioning relationship log10(K−1) = (10±1)–(2500±300)/T where K = (PBM/PM2.5)/RGM with PBM and RGM in common mixing ratio units, PM2.5 in μg m−3, and T in K. This relationship is within the range of previous work but is based on far more extensive data from multiple sites. We implement this empirical relationship in the GEOS-Chem global 3-D Hg model to partition Hg(II) between the gas and particle phases. The resulting gas-phase fraction of Hg(II) ranges from over 90 % in warm air with little aerosol to less than 10 % in cold air with high aerosol. Hg deposition to high latitudes increases because of more efficient scavenging of particulate Hg(II) by precipitating snow. Model comparison to Hg observations at the North American surface sites suggests that subsidence from the free troposphere (warm air, low aerosol) is a major factor driving the seasonality of RGM, while elevated PBM is mostly associated with high aerosol loads. Simulation of RGM and PBM at these sites is improved by including fast in-plume reduction of Hg(II) emitted from coal combustion and by assuming that anthropogenic particulate Hg(p) behaves as semi-volatile Hg(II) rather than as a refractory particulate component. We improve the simulation of Hg wet deposition fluxes in the US relative to a previous version of GEOS-Chem; this largely reflects independent improvement of the washout algorithm. The observed wintertime minimum in wet deposition fluxes is attributed to inefficient snow scavenging of gas-phase Hg(II).
Revised: 30 Dec 2011 – Accepted: 02 Jan 2012 – Published: 11 Jan 2012
Amos, H. M., Jacob, D. J., Holmes, C. D., Fisher, J. A., Wang, Q., Yantosca, R. M., Corbitt, E. S., Galarneau, E., Rutter, A. P., Gustin, M. S., Steffen, A., Schauer, J. J., Graydon, J. A., Louis, V. L. St., Talbot, R. W., Edgerton, E. S., Zhang, Y., and Sunderland, E. M.: Gas-particle partitioning of atmospheric Hg(II) and its effect on global mercury deposition, Atmos. Chem. Phys., 12, 591-603, doi:10.5194/acp-12-591-2012, 2012.