COMPARISONS OF DISPERSION CALCULATIONS BETWEEN TA LUFT AND A METHOD BASED ON A MORE COMPLEX MODEL COMBINATION (FITNAH LPDM)/

Dispersion calculations for regulatory purposes in Germany have been b ased on a Gaussian-type model for more than 20 years. Within this proc edure nearly 88 000 hourly consecutive meteorological situations are e valuated statistically and put into 1944 classes. For each of these cl asses surface concentrations are calculated and combined to a one-year mean surface concentration field. Another procedure, consisting of th e combination of a nonhydrostatic model for the wind field and a Lagra ngian dispersion model, is used for 150 different meteorological input datasets. These datasets represent classes of meteorological situatio ns, which are compiled from about 8000 consecutive twice-daily situati ons by cluster analysis. The two different methods have been applied t o a source in the Rhine river valley. The results show differences, in both the value and the location, of the maximum of the mean surface c oncentration; the difference in location seems to be more significant than that in the maximum value.