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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.
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