Abstract

The global distributions of elemental mercury (Hg0) and divalent mercury compounds (HgII) were estimated with a climatological transport model (MOGUNTIA). Natural and man-made sources, including re-emission of previously deposited mercury (of man-made origin), oxidation of Hg0 to HgII and wet and dry deposition of HgII were explicitly treated. Comparisons with observations of Hg0 in surface air, HgII in precipitation and trends in mercury deposited in lake sediments and peat bogs show a reasonable agreement if the oxidation rate of Hg0 was chosen to be 1,0/yr. An oxidation time scale outside the range 0.5-1.5 yr is difficult to reconcile with observations. A recently measured large decrease in the concentrations of Hg0 over the Atlantic is difficult to explain only by a decrease in man-made emissions in Europe and North America. This latter difficulty indicates either that the man-made emissions have been underestimated or that there are large temporal variations in natural emissions (or re-emissions). We conclude that direct global man-made mercury emissions are likely to be at least 30% as large as the natural emissions, implying that the deposition rate, averaged over the globe, has increased by at least 50% since pre-industrial times. To the extent that re-emission of previously deposited mercury of man-made origin is important, the average deposition rate may well have tripled. In and around the most industrial regions (Europe, North America, Southeastern China) the deposition rate has increased by a factor 2-10 during the past two hundred years.