Part 1: A Summary and Review Mercury Emissions, Deposition and Air Chemistry Basic Atmospheric Chemistry

Understanding the sources of mercury deposition is fundamental to assessing how to control mercury deposition, in order to protect human health. Uptake of mercury by the general population is largely through fish consumption. The present source of “new mercury ” is mainly from atmospheric deposition. However, the sources of deposition in various areas of the country are unclear, and the roles of long-range global transport and deposition versus local and regional deposition are critical questions that are not clearly understood today. Mercury in the atmosphere is largely (~95%) elemental mercury [Hg(0)]. Background concentrations of Hg(0) in the atmosphere are on the order of 1-2 ng/m3 (Slemr and Langer, 1992; Lin and Pehkonen, 1999). It is a gaseous, relatively insoluble form is the form of mercury most subject to long-range transport and least subject to deposition. The overall, global average residence time for Hg(0) is estimated to be as low as 4 to 7 months (Sommar et al. 2001), but is generally considered to be 6 months to 2 years (Schroeder and Munthe 1998).1 Some deposition occurs via stomatal uptake by plants (Mosbaek et al. 1988; Brown