The objective of the MDN is to develop a national database of weekly concentrations of
total mercury in precipitation and the seasonal and annual flux of total mercury in wet
deposition. The data will be used to develop information on spatial and seasonal trends in
mercury deposited to surface waters, forested watersheds, and other sensitive receptors.
Analysis of precipitation samples for total- and methylmercury is performed by
Frontier
Geosciences, Inc., Seattle WA, USA. Frontier Geosciences provides the environmental
sciences community with uncompromisingly high-quality contract research, project design
and management, and analytical chemistry services concerned with the sources, fate and
effects of trace metals.
The MDN began a transition network of 13 sites in
1995. Beginning in 1996, MDN became an official network in NADP with 26 sites in
operation. Over 85 sites currently are in operation (see site map). The network uses
standardized methods for collection and analyses. Weekly
precipitation samples are collected in a modified Aerochem Metrics model 301 collector.
The "wet-side" sampling glassware is removed from the collector every Tuesday
and mailed to the Hg Analytical Laboratory (HAL) at Frontier Geosciences in
Seattle, WA for analysis by cold vapor atomic fluorescence. The MDN provides data for
total mercury, but also includes methylmercury if desired by a site sponsor.
The following journal articles and presentations describe the network design, including
the sampling and analytical protocols, used in the MDN:
Lindberg, S. and Vermette, S. 1995. Workshop on Sampling Mercury in Precipitation for
the National Atmospheric Deposition Program. Atmospheric Environment. 29, 1219-1220.
Vermette, S., Lindberg, S., and Bloom, N. 1995. Field Tests for a Regional Mercury
Deposition Network - Sampling Design and Preliminary Test Results. Atmospheric
Environment. 29, 1247-1251.
Welker, M. and Vermette, S.J., 1996. Mercury Deposition Network: QA/QC
Protocols. Paper 96-RP129.01, Proceedings of the 89th Annual Meeting of the Air and Waste
Management Association, A&WMA, Pittsburgh, PA.
Sweet, C.W. and Prestbo, E. 1999. Wet Deposition of Mercury in the U.S. and
Canada. Presented at "Mercury in the Environment Specialty
Conference", September 15-17, 1999, Minneapolis, MN. Proceedings
published by Air and Waste Management Association, Pittsburgh, PA.
(Available from NADP Program Office)