Determination of atmospheric mercury during the North Sea Experiment

Total gaseous mercury (TGM) and rainwater were collected on board of two research vessels (F. S. ALKOR and R.V. BELGICA) positioned 200 km apart in the center of the North Sea during the North Sea Experiment, September 1991. On the F. S. ALKOR (up-wind ship) TGM concentrations ranged from 0.7 to 2.6 ng · m^-3 with an average of 1.5 ng · m^-3 and on the R. V. BELGICA (down-wind ship) TGM ranged from 0.7 to 1.9 ng · m^-3 with an average of 1.2 ng · m^-3. An average 20% decrease is observed from the up-wind to the downwind ship, which may largely be affected by entrainment into the free troposphere. An overall removal (entrainment) velocity of 0.95 em · s^-1 was calculated for the whole experiment. The average removal velocity was 0.5 cm · s^-1 for dry periods and varied between 1 to 5 cm · s^-1 during rain events. Rainwater concentrations varied between 5 and 25 ng · l^-1. Based on these data an annual wet deposition flux of 1.08 ng Hg cm^-2 yr^1- was estimated for the North Sea.