Estimates of air-sea exchange of mercury in the Baltic Sea

The concentrations of total gaseous mercury (TGM) in air over the southern Baltic Sea and dissolved gaseous mercury (DGM) in the surface seawater were measured during summer and winter. The summer expedition was performed on 02-15 July 1997, and the winter expedition on 02-15 March 1998. Average TGM and DGM values obtained were 1.70 and 17.6 ng m(-3) in the summer and 1.39 and 17.4 ng m(-3) in the winter, respectively. Based on the TGM and DGM da ta, surface water saturation and air-water fluxes were calculated. The resu lts indicate that the seawater was supersaturated with gaseous mercury duri ng both seasons, with the highest values occurring in the summer. Flux esti mates were made using the thin film gas-exchange model. The average Hg flux es obtained for the summer and winter measurements were 38 and 20 ng m(-2)d (-1), respectively. The annual mercury flux from this area was estimated by a combination of the TGM and DGM data with monthly average water temperatu res and wind velocities, resulting in an annual flux of 9.5 mug m(-2) yr(-1 ). This flux is of the same order of magnitude as the average wet depositio n input of mercury in this area. This indicates that reemissions from the w ater surface need to be considered when making mass-balance estimates of me rcury in the Baltic Sea as well as modelling calculations of long-range tra nsboundary transport of mercury in northern Europe. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.