Mercury in the air and precipitation.

Total mercury in the air and rain water has been measured in order to study the residence time of mercury in the atmosphere. The mercury concentration in air directly affected by terrestrial sources varies by a factor of 7 whereas in ocean air it shows a constant value, 1 ng/m3 throughout the seasons. On the other hand, mercury in rain water shows also a constant value, 1 ng/l for any rainfall and for any phase of it. These observations suggest that mercury in the atmosphere behaves as a vapour, and the rate of its elimination from the atmosphere is slow. From both data, the residence time of mercury in the atmosphere is estimated to be 5.7 years.