Natural and anthropogenic sources contribute mercury to the global atmospheric mercury pool. Constraining the contribution of each source to this pool is critical for the development of environmental regulations and controls. Mercury emissions from point sources are more easily constrained than those from broad diffuse mercury-enriched terrains (e.g., areas containing contaminated mine waste, sewage sludge amended soils, geologically enriched substrate). Mercury enriched or contaminated landscapes and most background terrestrial surfaces constitute long-lived continuous sources of mercury to the atmosphere. The first source may be considered “natural” while the latter two sources represent re-emission (of stored waste Hg, or of previously deposited Hg from the atmosphere). The primary form of mercury being emitted from terrestrial landscapes is elemental mercury which enters the global atmospheric mercury pool, while a significant fraction of that being emitted from coal-fired power plants (the largest anthropogenic point source in the United States) occurs as ionic and particulate bound mercury and is likely to be deposited on a local to regional scale. Constraining mercury emissions from broad diffuse mercury-enriched terrain is the objective of this study, and is accomplished through the in situ measurement of Hg flux using field chambers and micrometeorological methods and measurement of flux from representative samples in the laboratory. A data base constraining Hg fluxes from naturally enriched areas and factors controlling flux is needed in order to scale up local flux measurements to estimate the relative contribution of mercury to the atmosphere from naturally enriched areas. A recent field intercomparison and workshop compared Hg fluxes measured using seven field flux chambers and four micrometeorological methods at the Steamboat Springs Geothermal Area, Reno, NV (Figure 1). The results have been published in a special issue of JGR. Related studies of background soil emissions have been performed in Canada, the Great Lakes Region, and the Southeast. Our data base suggests that mercury flux from both background areas (termed re-emission, Figure 2) and from naturally enriched areas with low levels of mercury enrichment (termed natural surface emission) are substantially higher than the mercury emission rates applied in global mercury budgets for naturally enriched terrains. _________________*Supported by the Electric Power Research Institute in collaboration with the University of Nevada at Reno. Reference: Gustin, M.S., S. E. Lindberg, K. Austin, M. Coolbaugh, A. Vette, and H. Zhang. 2000. Assessing the contribution of natural sources to regional atmospheric mercury budgets. Science of the Total Environment 259:61-72. |
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