Assessing the contribution of natural sources to regional atmospheric mercury budgets

Contributions to the global atmospheric mercury budget originate from natural and anthropogenic sources. Constraining inputs from anthropogenic point sources has been the emphasis of past research leaving the contribution from diffuse natural and anthropogenic mercury enriched landscapes poorly constrained and underestimated. From September 1--4, 1997 mercury researchers convened in Reno, NV, US to intercompare methods used to determine in situ mercury flux from a naturally enriched landscape. Data collected indicate that naturally mercury-enriched areas constitute a significant atmospheric Hg source term. Mercury fluxes of 30 to 2,000 ng/m{sup 2} h were measured at the Steamboat springs Geothermal Area. These values are one to three orders of magnitude greater than that applied for natural sources in global mercury budgets. Air concentrations measured in the area indicate that natural sources can increase ambient levels above background concentrations. Assessment of these and other data indicate that natural sources constitute a significant source of atmospheric mercury that is available to the global mercury budget, and that the strength of the source is influenced significantly by environmental factors. Determining the contribution of mercury to the atmosphere from diffuse terrestrial sources is necessary to develop local and regional baselines for environmental regulations and risk assessments, and valid emission inventories. A scaling up mercury fluxes measured for diffuse terrestrial surfaces suggests that the natural atmospheric mercury source term in the US is comparable to the anthropogenic source term