Short- and long-term dispersion factors for calculating the environmental burden due to exhaust air streams

At the Juelich Nuclear Research Establishment dispersion experiments are being conducted with tagged exhaust air streams for the purpose of determining the diffusion parameters which are necessary for calculations of the environmental burden. The distribution of ground-level concentration is measured with about 100 sampling stations for various weather conditions and different altitudes of emission (50 and 100 m). The results show that the maxima of the ground-level concentration in comparison to the Pasquill prognostics, depending on the diffusion category, are located closer to the source by a factor of 2 to 5, whereby the absolute value of the concentration at the maximum is underestimated by a factor of 2. This discrepancy may be explained by the fact that, in determining the diffusion categories by the method based on synoptic observations, the differing irregularities of the terrain are not taken into consideration. Therefore at Juelich statistical studies are being made in order to determine the relation between the dispersion parameters measured in experiments as well as stability parameters such as, for example, the Richardson number. In addition, studies are being conducted on the determination of the ground roughness parameters. The results are used in calculating the environmental burden from emitters of harmful substances