Articles | Volume 12, issue 14
Atmos. Chem. Phys., 12, 6095–6111, 2012

Special issue: Atmospheric mercury processes: papers from the 10th ICMGP

Atmos. Chem. Phys., 12, 6095–6111, 2012

Research article 16 Jul 2012

Research article | 16 Jul 2012

Nested-grid simulation of mercury over North America

Y. Zhang1, L. Jaeglé1, A. van Donkelaar2, R. V. Martin2,3, C. D. Holmes4, H. M. Amos5, Q. Wang6, R. Talbot7, R. Artz8, S. Brooks8, W. Luke8, T. M. Holsen9, D. Felton10, E. K. Miller11, K. D. Perry12, D. Schmeltz13, A. Steffen14, R. Tordon14, P. Weiss-Penzias15, and R. Zsolway16 Y. Zhang et al.
  • 1Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA
  • 2Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada
  • 3Harvard Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
  • 4Department of Earth System Sciences, University of California, Irvine, CA, USA
  • 5Department of Earth and Planetary Sciences, Harvard University, Cambridge MA, USA
  • 6School of Engineering and Applied Sciences, Harvard University, Cambridge MA, USA
  • 7Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA
  • 8NOAA Air Resources Laboratory, Silver Spring, MD, USA
  • 9Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY, USA
  • 10New York State Department of Environmental Conservation, Division of Air Resources, Albany, NY, USA
  • 11Ecosystems Research Group, Norwich, VT, USA
  • 12Department of Atmospheric Sciences, University of Utah, Salt Lake City, UT, USA
  • 13Office of Atmospheric Programs, US Environmental Protection Agency, Washington DC, USA
  • 14Environment Canada, Air Quality Research Division, Toronto, Ontario, Canada
  • 15Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA, USA
  • 16Division of Environmental Regulation, Bureau of Air Quality Monitoring, New Jersey Department of Environmental Protection, Trenton, NJ, USA

Abstract. We have developed a new nested-grid mercury (Hg) simulation over North America with a 1/2° latitude by 2/3° longitude horizontal resolution employing the GEOS-Chem global chemical transport model. Emissions, chemistry, deposition, and meteorology are self-consistent between the global and nested domains. Compared to the global model (4° latitude by 5° longitude), the nested model shows improved skill at capturing the high spatial and temporal variability of Hg wet deposition over North America observed by the Mercury Deposition Network (MDN) in 2008–2009. The nested simulation resolves features such as higher deposition due to orographic precipitation, land/ocean contrast and and predicts more efficient convective rain scavenging of Hg over the southeast United States. However, the nested model overestimates Hg wet deposition over the Ohio River Valley region (ORV) by 27%. We modify anthropogenic emission speciation profiles in the US EPA National Emission Inventory (NEI) to account for the rapid in-plume reduction of reactive to elemental Hg (IPR simulation). This leads to a decrease in the model bias to −2.3% over the ORV region. Over the contiguous US, the correlation coefficient (r) between MDN observations and our IPR simulation increases from 0.60 to 0.78. The IPR nested simulation generally reproduces the seasonal cycle in surface concentrations of speciated Hg from the Atmospheric Mercury Network (AMNet) and Canadian Atmospheric Mercury Network (CAMNet). In the IPR simulation, annual mean gaseous and particulate-bound Hg(II) are within 140% and 11% of observations, respectively. In contrast, the simulation with unmodified anthropogenic Hg speciation profiles overestimates these observations by factors of 4 and 2 for gaseous and particulate-bound Hg(II), respectively. The nested model shows improved skill at capturing the horizontal variability of Hg observed over California during the ARCTAS aircraft campaign. The nested model suggests that North American anthropogenic emissions account for 10–22% of Hg wet deposition flux over the US, depending on the anthropogenic emissions speciation profile assumed. The modeled percent contribution can be as high as 60% near large point sources in ORV. Our results indicate that the North American anthropogenic contribution to dry deposition is 13–20%.

Final-revised paper