Measurements of mercury in dew: atmospheric removal of mercury species to a wetted surface

The importance of dew in the mercury cycle was investigated during three sampling periods in the Great Lakes region and one in the Florida Everglades. Mercury concentrations ranged from 1.0 to 22.6 ng/L in dew. Deposition per dew event was, on average, lowest at a remote site on Lake Superior (0.31 ng/m2) and highest in the Florida Everglades (1.4 ng/m2). The estimated mercury deposition to the canopy associated with dew approximately equaled that of precipitation during the wintertime Everglades study. Relative to other trace elements (Mg, Ti, V, Mn, Ni, Cu, As, Sr, Cd, Sb, La, Ce, Pb), mercury was found to be more enriched in rain than dew, suggesting the importance of gas scavenging for precipitation. The fraction of mercury in dew from particulate deposition was estimated to average 40%, with the remaining contribution from reactive gaseous Hg (RGM). RGM, for which little reliable data exists, was measured in the Everglades and was significantly reduced at the start of a dew event, indicating pronounced removal of this soluble mercury species to wetted surfaces. The first estimates of RGM deposition velocities based on mercury flux measurements are reported here and range up to 1.6 cm/s.