Abstract

The global distributions of elemental mercury (Hg-0) 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 Hg-0 to HgII and wet and dry deposition of HgII were explicitly treated. Comparisons with observations of Hg-0 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 Hg-0 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 Hg-0 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. (C) 1999 Elsevier Science Ltd. All rights reserved.