DETERMINATION OF ATMOSPHERIC MERCURY DURING THE NORTH-SEA EXPERIMENT

Total gaseous mercury (TGM) and rainwater were collected on board of t wo research vessels (F. S. ALKOR and R.V. BELGICA) positioned 200 km a part in the center of the North Sea during the North Sea Experiment, S eptember 1991. On the F. S. ALKOR (up-wind ship) TGM concentrations ra nged from 0.7 to 2.6 ng.m(-3) with an average of 1.5 ng.m(-3) and on t he 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 f rom the up-wind to the downwind ship. which may largely be affected by entrainment into the free troposphere. An overall removal (entrainmen t) velocity of 0.95 cm.s(-1) was calculated for the whole experiment. The average removal velocity was 0.5 cm.s(-1) for dry periods and vari ed between 1 to 5 cm.s(-1) during rain events. Rainwater concentration s 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 Nort h Sea.