Trends in atmospheric mercury concentrations at the summit of the Wank Mountain, Southern Germany
Total gaseous mercury (TGM) has been monitored at the summit of the Wank mountain (1780 m a.s.l.) in the Bavarian Alps since March 1990. A statistical analysis of the data set until May 1996 consisting of 1670 individual TGM measurements shows a linear decrease of 0.169 +/- 0.009 ng Hg m(-3) yr(-1), i.e. about 7 per cent per year. The seasonal variation shows maximum TGM concentrations in March and minima in October-December. The frequency of occurrence of extremely high TGM concentrations and the amplitude of the seasonal variation decreased over the observation time. The observed decrease of the TGM concentration is in agreement with measurements in Scandinavia, indicating that the measurements at Wank are representative for the region of central and northern Europe. The decrease in TGM concentration of 23.3 per cent between 1990 and 1994 was consistent with decreases of 20.4 and 21.2 per cent, respectively, observed by us over the northern and the southern Atlantic Ocean. This and t he observation of a decreasing trend in mercury wet deposition in the U.S.A. indicate the global significance of the TGM trends observed in Europe. Several causes may add up, but this 45 per cent change in TGM concentrations observed over the period of 6 years cannot be plausibly explained without a substantial decrease of anthropogenic mercury emissions on both regional and global scales. Such decrease, however, is difficult to reconcile with most of the current anthropogenic emission inventories. This points to possible gaps in our understanding of the anthropogenic emission processes.