The effect of mercury speciation and meteorological processing on concentrations, transport and deposition of atmospheric mercury

The toxic trace element mercury can be transported locally, regionally or globally within the atmosphere before deposition to a watershed. The fate of atmospheric mercury is dependent on its chemical and physical form, which determine its deposition rate under different environmental conditions. The importance of these influences on atmospheric mercury was investigated in dew, clouds and the coastal atmosphere.; Measurements of mercury in dew were made at locations in Michigan and Florida. The mercury in dew was accounted for by deposition of particulate mercury and reactive gaseous mercury (RGM). RGM concentrations were significantly reduced at the onset of dew with RGM deposition velocities ranging from 0.2 to 1.3 cm/s. In areas with frequent dew formation and low precipitation, dew appears to be an important contribution to mercury deposition.; Measurements of mercury in non-precipitating cloud water were made at Mt. Mansfield, VT. Concentrations of mercury and other trace elements with predominately anthropogenic, but not crustal origin, were higher in cloud water than in precipitation. This is hypothesized to be caused by (1) greater in-cloud scavenging of crustal aerosol in precipitating than non-precipitating clouds and (2) more efficient below-cloud scavenging of crustal than anthropogenic aerosol by rain. Concentrations of mercury in cloud water were explained by transport history, with the highest concentrations from the Mid-Atlantic and Ohio River Valley.; Atmospheric mercury measurements along the Atlantic Coast of Florida revealed low concentrations of Hg0_(g) and RGM in the marine boundary layer. This indicated that the ocean is not a large net source of mercury to the Eastern Florida shoreline. Higher daytime peaks in diurnal cycles of RGM were observed under anthropogenic influence, possibly produced by reaction with a photochemical oxidant. Particulate mercury concentrations could not be explained by sea spray alone, suggesting that gaseous Hg diffused into the aerosol. Deposition of aerosol elevated in Hg via this process may constitute an important global mercury flux to the oceans.; A sampling artifact was observed in which mercury was lost from aerosols as sampling duration increased. The cause of this artifact is hypothesized to be reduction of Hg2+_(aq) to Hg0 _(aq) that volatilizes off the filter.