Processes influencing rainfall deposition of mercury in Florida

The primary goal of the Florida Atmospheric Mercury Study (FAMS) was to qua ntify the atmospheric deposition of Hg throughout Florida. Monthly integrat ed precipitation and weekly integrated particulate samples were collected a t 10 sites in. Florida for periods ranging from 2 to 5 yr. The monthly rain fall across the state and the concentrations of Hg in wet-only and bulk dep osition increased by a factor of 2-3 during the summertime "wet season" (Ma y-October). These parallel increases in rainfall amount and. Hg concentrati on resulted in 5-8-fold increases in rainfall Hg deposition during the wet season. The annual volume-weighted Hg concentrations ranged from 14 +/- 2 t o 16 +/- 2 ng/L across southern Florida, and the annual rainfall Hg fluxes ranged from 20 +/- 3 to 23 +/- 3 mug m(-2) yr(-1). The weekly integrated pa rticulate Hg concentrations in southern Florida were low (4.9-9.3 pg/m(3)) and did not exhibit strong seasonal variability. Considering the pronounced seasonal pattern in rainfall Hg deposition, the relatively uniform summert ime rainfall Hg concentrations, and the law concentrations of particulate H g,we conclude that processes other than,particulate Hg transport and scaven ging govern rainfall Hg deposition in southern Florida; We hypothesize that long-range transport of reactive gaseous Hg (RGM) species coupled with str ong convective thunderstorm activity during the summertime represents >50% of the Hg deposition in southern Florida. Model calculations indicate that local anthropogenic particulate Hg and RGM emissions account for 30-46% of the summertime rainfall Hg deposition across the southern Florida peninsula .