Key message
According to results of model calculations the atmospheric depositions of Cd and Pb to the Baltic Sea slightly decreased during the period 1996-2000, whereas atmospheric depositions of mercury increased by 14%. However, no significant temporal pattern in depositions of Cd, Hg, and Pb to the Baltic Sea and its sub-basins in period 1996-2000 can be detected.
Assessment
The document present the calculated total depositions of Cd, Hg, and Pb on the Baltic Sea for 1996-2000. Atmospheric depositions of heavy metals were obtained using the latest version of MSCE-HM model developed at MSC-E of EMEP. The latest available emission data for the HELCOM countries have been used in the model calculations. Calculated annual total depositions of Cd, Hg, and Pb to the entire Baltic Sea basin in the period 1996 – 2000 are shown in Figure 1. Time-series of annual total depositions of Cd, Hg, and Pb to the six sub-basins of the Baltic Sea are presented in Figures 2-3.
Results
Figures for atmospheric deposition rates are also only rough estimates, since they are dependent on either uncertain emission inventories or measurement series taken at just a few coastal stations whose data is difficult to extrapolate to cover the whole sea.
Lead deposition evidently decreased by more than 50% during the 1990s, mostly due to the increased use of unleaded gasoline.
It is estimated that about 9 tonnes of cadmium was deposited in the Baltic Sea during the year 2000. The mean cadmium deposition rates for the period 1996-2000 are on average 30% lower for all the sub-basins of the Baltic Sea in comparison with the preceding period 1991-1995.
Figure 1: Atmospheric depositions of Cd, Hg, Pb to the Baltic Sea for the period 1996-2000, t/year.
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Figure 2: Atmospheric deposition of Cd to six main sub-basins of the Baltic Sea for the period 1996-2000, t/year.
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Figure 3: Atmospheric deposition of Hg to six main sub-basins of the Baltic Sea for the period 1996-2000, t/year.
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Figure 4: Atmospheric deposition of Pb to six main sub-basins of the Baltic Sea for the period 1996-2000, t/year.
Further information
Atmospheric Supply of Nitrogen, Lead, Cadmium, Mercury and Lindane to the Baltic Sea in the period 1996 - 2000
Helsinki Commission