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Project Title: Assessing Methods of Alleviating Impacts
from Mercury on Human Health and Environment in the Great Lakes Basin
Chemicals Studied: Mercury
Geographic Areas: The Great Lakes Region
Synopsis: The purpose of this project was to conduct regional-scale modeling analysis to provide an improved understanding of the fate and transport of mercury within the Great Lakes region. The research team developed a comprehensive budget of elemental mercury (Hg0), reactive gaseous mercury (RGM), particulate mercury (Hgp), and mercury wet deposition across the Great Lake region, including sources, sinks, atmospheric lifetimes, burdens, and advective fluxes. Updated emissions inventories for global and continental emissions were investigated to support the regional-scale modeling. Using the updated global emissions inventory, global modeling was conducted to provide initial and boundary conditions for the regional chemical transport modeling (CTM). The regional chemical transport modeling (MM5-SMOKE-CMAQ) was performed to provide an improved understanding of the fate and potential ecological impacts of mercury in the Great Lakes region. Water-air exchange flux calculations were also performed to simulate and improve understanding of how local, regional, and global emissions of mercury cycle through the atmospheric and aquatic environment in the Great Lakes basin.
To strengthen the initial findings and provide a more sound approach, a more in-depth modeling study was conducted with updated emissions and enhancements to the treatment of mercury chemistry in the chemical transport model. The U.S. EPA MODELS-3 (MM5-SMOKE-CMAQ4.7.1) was utilized to simulate mercury deposition and transport for the year 2005 with 36-km grid domain which included a 148 by 112 grid array over the United States, Southern Canada, and Northern Mexico. Simulations included: a base case and three sensitivity evaluations including: zero-out runs of point sources (PT-IPM), Chinese emissions, and global background concentrations.
In general, the global background concentrations had the highest contribution to the RGM deposition in the Great Lakes (27-97%). However, a significant impact of PM-IPM on wet deposition to Lake Erie, Lake Huron, and southern tip of Lake Michigan was observed. High PM-IPM contributions to the wet and dry RGM deposition were observed during the winter season on the Great Lakes with maximum influence in Lake Erie. A high localized PM-IPM impact on wet and dry RGM deposition to Lake Erie was observed throughout the year, varying from 2 to 58%. RGM deposition to Lake Superior was mostly influenced by global contributions, varying from 75-97%, predominantly in the fall season. Other lakes also observed high global contributions except Lake Erie. Chinese emissions contributed 0.05-9% to RGM deposition in the Great Lakes with maximum effect on wet deposition in winter.
Sensitivity analysis on net loading to the Great Lakes was also conducted. Chinese emissions, PM-IPM emissions, and global background concentrations were used as individual scenarios to assess the percent change in net mercury loadings when the individual source contributions change by seasons. The change in the net loading is most sensitive to the global background with a maximum of 214% increase due to global contributions. The PM-IPM sources showed the least sensitivity with net percent change ranging from 1.8 to 12.4%. Chinese emissions results in a maximum change of 21.4% in Lake Superior and a minimum of 2.3% change in Lake Ontario in spring 2005.
Preliminary project results have been presented during the 2010-11 GLAD webinar series.
Kevin Crist, Ph.D.