Trends in atmospheric mercury concentrations over the Atlantic Ocean and at the Wank summit, and the resulting constraints on the budget of atmospheric mercury

In 1977 - 1980, 1990, and 1994 we measured the latitudinal distribution of atmospheric mercury over the Atlantic Ocean. The results of these measurements show a pronounced concentration gradient between the northern, and southern hemispheres and a rather small variability of mercury concentrations within the hemispheres, especially within the southern, hemisphere. The measurements made during the cruises also suggest globally increasing atmospheric mercury concentrations by 17.5 per cent in the northern and 14.0 per cent in the southern hemispheres between 1977 - 1980 and 1990 to concentrations of 2.25 ng Hg m(-3) in the northern and 1.50 ng Hg m(-3) in the southern hemispheres in 1990 and a global decrease between 1990 and 1994. The decrease between 1990 and 1994 of 20.4 per cent in the northern and 21.2 per cent in the southern hemispheres is consistent with the decrease of 23.3 per cent observed in the same period at the Wank summit (1780 m a.s.l.) in southern Germany. The results o f all these measurements are reviewed. From these results and from measurements reported by others, we derive several constraints on the budget of atmospheric mercury, its atmospheric burden, residence time, sources, and sinks.