Relative Importance of Mercury Dry Deposition to MD08 in Western Maryland

Chris Moore, Mark Castro
University of Maryland Center for Environmental Science Appalachian Laboratory, 301 Braddock Rd., Frostburg, MD

John Sherwell
Maryland Department of Natural Resources, Annapolis, MD

Mark Garrison
3ERM, Exton, PA


Mercury is constantly being deposited from the atmosphere to the Earth’s surface, even in seemingly remote areas. The wet component of mercury deposition has been measured nationwide by the NADP Mercury Deposition Network. However, the dry component of mercury deposition has been sparsely measured. Estimates of dry deposition of mercury to the Piney Creek Reservoir in western Maryland (MD08) were obtained using three different models: CALPUFF, ‘big leaf’, and TEAM. In addition, we estimated dry deposition at MD08 using ambient air mercury concentrations (Hg(o), RGM and Hg-part) and different deposition velocities.. In the first scenario, a deposition velocity of 0.01cm s-1 was used for Hg(o), 0.1 cm s-1 for Hg-part and 0.5 cm s-1 for RGM. In the second scenario, the deposition velocity of RGM was increased to 2.0cm/s to reflect the maximum range in observed RGM deposition velocities over land. The preliminary estimates using CALPUFF resulted in a total dry deposition of 19 µg m-2 yr-1 to MD08, while the ‘big leaf’ and TEAM models estimated 10-15 µg m-2 yr-1. Our total dry deposition estimate using the first scenario was 6.5 ug m-2 yr-1, with 26 % from RGM, 71 % from Hg (o) and 3 % from Hg-part. For scenario two, total dry deposition was 11.9 µg m-2 yr-1, with 60% from RGM, 39% from Hg(o), and less than 2% from Hg-part. These estimates vary by a factor of three and emphasize the uncertainty in current estimates of mercury dry deposition. The dry component of mercury deposition is similar to wet deposition at MD08, but the modeled dry component is highly variable. To improve model estimates and to obtain more accurate estimates of total mercury deposition to western Maryland, we need to measure dry deposition mercury at MD08. This information is also critical to assess the effectiveness of reductions in mercury emissions from power plants in the United States.