Are mercury emissions from geologic sources significant? A status report.

Geologic sources of atmospheric mercury include areas of fossil and current geothermal activity, recent volcanic activity, precious and base metal deposits, and organic rich sedimentary rocks. Early estimates of emissions from these sources were not based on measurements of mercury fluxes but implied based on the difference between emissions from anthropogenic point sources and wet/dry deposition estimates. In the past approximately 7 years significant progress has been made in development of methods for the measurement of mercury emissions, definition of those parameters most important in controlling emissions and scaling up emissions from natural source areas. This paper summarizes the work done on scaling of emissions from discrete areas of natural enrichment and from the State of Nevada, which is situated within a global belt of mercury enrichment. Preliminary data indicate that elemental mercury is the predominant (>95%) form of mercury being emitted from these sources. Scaling results suggest that the value used in early models to represent emissions from global mercuriferous belts is too low by at least three times.