Speciation and distribution of atmospheric mercury over the northern Chesapeake Bay

Baltimore's urban air is a potentially important source of mercury (Hg) to the northern Chesapeake Bay. Elevated total atmospheric Hg (THg) concentrations were detected at a sampling site in downtown Baltimore (4.4±2.7 ng/m³), as compared to a rural site (1.7±0.5 ng/m³). The urban air was also enriched with reactive gaseous Hg (RGHg) and particulate-bound Hg (Hg-P). The annual dry depositional fluxes of RGHg and Hg-P at sites around the northern Chesapeake Bay have been determined, with the fluxes of RGHg ranging from 7 to 121 μg/m² and the fluxes of Hg-P from 1 to 34 ng/m². These values were the same magnitude as the wet depositional fluxes of Hg measured at the same sites. Local wind direction influenced the concentration of atmospheric Hg detected at the urban sampling site. When air came from the SE, S and SW directions, the urban sampling site tended to be impacted by the local emission sources, with higher THg and Hg-P concentrations detected.