Air–sea exchange of mercury vapour over the Gulf of Gda sk and southern Baltic Sea

The total gaseous mercury (TGM) in air over the coastal station at Hel and over the southern Baltic Sea was measured during the summer and winter conditions. Recorded 30-min resolution TGM data showed both higher concentrations and variability during the summer compared to the winter conditions. The summer TGM data ranged from 1.1 to 7.5 ng m−3, while the winter data ranged from 0.8 to 4.4 ng m−3. The TGM content in air over the southern Baltic Sea indicated that, in general, during the summer conditions, the sea-to-air transport of gaseous mercury dominated, while during the winter season, a tendency of gaseous mercury to sink into the water has been found. The evidences of enhanced water-to-air transfer of mercury vapour were noted, in particular, over the shallow waters of the Gulf of Gda sk under the strong water-to-air temperature gradients. Obtained results indicate that under such conditions, the coastal waters could act as a significant source of mercury vapour that may contribute to the overall budget of atmospheric mercury over the Baltic proper.