An investigation of source–receptor relationships for mercury in south Florida using event precipitation data

A recent pilot study suggested that local anthropogenic sources may play an important role in the atmospheric deposition of mercury (Hg) in South Florida. To examine the potential impacts of these local anthropogenic sources of Hg, the South Florida Atmospheric Mercury Monitoring Study (SoFAMMS) was conducted from 6 August to 6 September 1995. The major goals of the SoFAMMS were to investigate potential source–receptor relationships between anthropogenic point-source emissions in south-east Florida (Dade and Broward Counties) and the atmospheric deposition of Hg and other trace elements across this region, which includes the Florida Everglades. As part of SoFAMMS, daily event precipitation samples were collected concurrently at 17 sites across the study domain during the 1-month period. All samples were analyzed for Hg and other trace elements. The volume-weighted mean concentrations of Hg measured at the 17 sites during the study ranged from 13 to 31 ng l−1. While these monthly means indicated a significant site-to-site variation in Hg concentration, even greater differences between sites were observed on an event basis. Concentrations of Hg in individual daily event precipitation samples ranged from 5 to 113 ng l−1. Similar spatial and temporal variations in precipitation concentrations were observed for other trace elements as well. These variations could not be accounted for by rainfall amounts alone. The spatial and temporal patterns observed suggest that local sources strongly influence atmospheric wet deposition across this region. Extensive elemental composition and meteorological precipitation data (including WSR-88D radar data from Miami, FL) were combined in an effort to look at the history of precipitation storm cells impacting the sampling sites and their spatial relationships to potential anthropogenic sources. Two sample periods are presented which demonstrate not only the impacts of local anthropogenic sources, but that these impacts fluctuate as a function of the mesoscale meteorological transport conditions. These preliminary findings indicate that local sources of Hg to South Florida and the Everglades may be more substantial than previous estimates.