PRELIMINARY RESULTS FROM NEW MERCURY DEPOSITION NETWORK (MDN) STATIONS IN VIRGINIA: IMPLICATIONS FOR MERCURY WET DEPOSITION LEVELS IN THE MID-ATLANTIC REGION

The National Atmospheric Deposition Program, Mercury Deposition Network (MDN; http//:nadp.sws.uiuc.edu), is a continent-wide program that measures mercury wet deposition on a weekly basis through a network of standardized collection sites. In autumn 2002, two MDN stations began operation in Virginia, helping to fill a significant gap in the network that existed in the Mid-Atlantic region. Station VA-08, located southwest of Culpeper, VA (lat. 38.4222; long. –78.1044; elev. 163 m), is operated jointly by the U.S. Geological Survey and George Mason University. Station VA-28, located at Big Meadows (lat. 38.5225; long. –78.4358; elev. 1074 m), in Shenandoah National Park, is operated by the National Park Service. These stations will help define background total mercury wet deposition levels west of the Washington, DC metropolitan area. The proximity of the two Virginia stations to each other (31 km) should also allow us to compare local mercury deposition at different elevations.

Quarterly results for volume-weighted average total mercury concentrations in precipitation are currently available in preliminary form for the first three quarters of 2003. Preliminary results for the two MDN stations in Virginia, and four nearest stations in southern Pennsylvania, show distinct seasonal variation, with increases in the second and third quarters of 2003 likely attributed to higher levels of oxidants in the atmosphere during the summer months. Initial results for the two Virginia MDN sites are similar to (VA-08) or lower than (VA-28) quarterly volume-weighted average concentrations for the four Pennsylvania sites for the first three quarters of 2003. Data sets representing a longer period of observation are needed to assess more complete seasonal trends and local differences among these sites. The addition of a proposed new MDN site in Maryland will help improve network resolution in the region. Increasing the density of MDN sites in the region will help us distinguish the extent of local or regional “events,” in which weekly concentrations exceed quarterly average mercury concentrations by 2 to 5 times or more.