Long-term behaviour of Chernobyl fallout in air and precipitation

The long-term behaviour of Chernobyl fallout at Munich-Neuherberg has been studied and compared with those at other locations in the Federal Republic of Germany. Between August 1986 and the end of 1988, air concentrations and ground depositions of 134Cs and 137Cs at the Neuherberg site decreased exponentially, with a half-time of about 250 days; airborne activity of 106Ru decreased with a half-time of about 150 days. A similar decrease in airborne 137Cs was observed at other locations in the FRG. The deposition rates of 137Cs at five sites in the FRG are significantly associated with the total Chernobyl 137Cs deposits at each location. Since the end of 1986, local resuspension has exerted a dominant influence on both airborne activities and ground depositions at any given station in the FRG. A resuspension factor of (3 ± 1) x 10-9 m-1 is calculated for the Cs isotopes in the uppermost soil layer, a value which is very similar to that found in 1985 at Neuherberg for global fallout 137Cs. The 137Cs activities in air and precipitation show significant correlations with local wind speeds. The total deposition velocities of 137Cs and 106Ru are found to be distinctly higher than that of cosmic-ray-produced 7Be. (author)