Utilization of event precipitation data to establish source-receptor relationships for mercury wet deposited in south Florida.

Abstract

Source-receptor relationships for mercury (Hg) and other trace elements wet-deposited in south Florida were investigated using daily-event precipitation samples collected concurrently at 17 sites from 8/6/95 to 9/6/95. Local anthropogenic sources were found to account for all of the Hg wet-deposited during the study period at measurement sites in the Florida Everglades. Meteorological analyses of precipitation cell path history utilizing WSR-88D radar data found significantly higher volume-weighted mean (VWM) concentrations of Hg in precipitation with easterly cell paths (26 ng/l, from the local urban source area) than those with westerly paths (13 ng/l, from the Everglades) for storms arriving at Everglades sites. This also coincided with significantly higher VWM concentrations of the known anthropogenic elements V and Ni (oil combustion), and Pb and Sb (waste incineration). A multivariate receptor modeling approach found municipal waste incineration and oil combustion sources to account for 71% $\pm$ 8% of the Hg wet-deposited during the study at five sites in the Everglades. Similarly, analysis of additional event precipitation samples collected over a one-year period (6/22/95 to 6/21/96) at a site in Davie, FL found 73% $\pm$ 6% of the Hg wet-deposited at this site over the entire one-year period to be accounted for by local anthropogenic sources. Receptor modeling results closely agreed with the stack measurements made at local point sources during the study, as well as with the Florida Hg emissions inventory compiled by USEPA. An emissions reconciliation found local medical waste incineration sources to account for 30% $\pm$ 16% of Hg wet deposition at the Everglades sites. Therefore, 100% $\pm$ 18% of the Hg wet-deposited at these sites could be accounted for by the combined local emissions of medical waste incineration, municipal waste incineration, and oil combustion sources. Finally, it was calculated that locally emitted anthropogenic Hg, which was measured during the study in a soluble Hg(II) form, can account for the Hg wet-deposited on an annual basis to the entire Florida Everglades. The above findings suggest that emissions from local urban point sources have played the dominant role in the wet deposition of Hg to south Florida and the Everglades.