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CLEAR SKIES INITIATIVE: RGM DRY DEPOSITION RESEARCH
Impact/Purpose:
The objective of this research is to improve the understanding of gas phase mercury dry deposition phenomenon. Specifically the objectives will be to:
(1) Develop a scientifically sound first principal gas phase mercury dry deposition model
(2) Develop a direct measurement method(s) for gas phase mercury dry deposition
(3) Conduct gas phase mercury dry deposition model validation
Description:
Excessive levels of mercury in the nations waters are the most widespread cause of water quality impairment in the US. Atmospheric emissions and deposition processes drive mercury accumulation in soils and sediments, and are now recognized as the major route of mercury contamination to most aquatic ecosystems. In pioneering studies conducted in South Florida and the Great Lakes Region, rainfall was observed to be the primary pathway for delivery of mercury loads to the Everglades and Lake Michigan, respectively. However, the Everglades and Lake Michigan studies were not able to adequately resolve the relative contribution of gas phase mercury dry-deposition (particularly the impact of divalent reactive gaseous mercury (RGM)) because of limitations in contemporary measurement methods. It was estimated that RGM dry deposition was perhaps equally as important as wet deposition. Atmospheric constituents are scavenged by rainfall for only a small fraction of the year while dry deposition, much less well understood and less tractable to model, is omnipresent. Thus, field studies of mercury dry deposition of any sort are few because of the minuscule but near-continuous nature of dry deposition processes. This lack of basic scientific understanding and appropriate measurement tools has led to widespread and systematic underestimates of the importance of gas phase mercury; and thus, skewed results of the few efforts devoted to understanding of comprehensive accounting of mercury loads from the atmosphere.