PARTICULATE MERCURY IN THE ATMOSPHERE - ITS SIGNIFICANCE, TRANSPORT, TRANSFORMATION AND SOURCES

The importance of particulate mercury (Hg(p)) in the transport, chemistry and deposition of this toxic metal has long been underestimated and largely ignored. While it was once believed to constitute a small percentage of total atmospheric mercury, Hg(p) may contribute a significant portion of the deposition of this metal to adjacent natural waters. Recent measurements of Hg(p) in several urban/industrial areas have documented that Hg can be associated with large particles (> 2.5 mu m) and in concentrations similar to those of the vapor phase Hg (ng/m(3)). As part of ongoing effort to diagnose the sources, transport and deposition of Hg to the Great Lakes and other Great Waters, the University of Michigan Air Quality Laboratory (UMAQL) has investigated the physical and chemical properties of particulate-phase Hg in both urban and rural locations. It appears that particulate Hg may be the one of the most difficult of the Hg measurements to perform, and perhaps the one of the most important for deposition and source apportionment studies. Particulate Hg concentrations measured in rural areas of the Great Lakes Region and Vermont ranged from 1 to 86 pg/m(3) whereas Hg(p) levels in urban/industrialized areas were in the range 15 pg/m(3) to 1.2 ng/m(3).