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 Wa nk mountain (1780 m a.s.l.) in the Bavarian Alps since March 1990. A s tatistical 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 year. The seasonal variation sh ows 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 observatio n 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% between 1990 and 1994 was consistent with decreases of 20.4 and 21.2%, respectively, observed b y us over the northern and the southern Atlantic Ocean. This and the o bservation of a decreasing trend in mercury wet deposition in the U.S. A. indicate the global significance of the TGM trends observed in Euro pe. Several causes may add up, but this 45% change in TGM concentratio ns observed over the period of 6 years cannot be plausibly explained w ithout a substantial decrease of anthropogenic mercury emissions on bo th 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 anthropogen ic emission processes. (C) 1998 Elsevier Science Ltd. All rights reser ved.