EVALUATION STUDIES WITH A REGIONAL CHEMICAL-TRANSPORT MODEL (EURAD) USING AIR-QUALITY DATA FROM THE EMEP MONITORING NETWORK

The EURAD model has been applied to simulate the transport and chemica l transformations of atmospheric constituents over central Europe for a 3 week late winter episode in February/March 1982. The TADAP model ( the European version of ADOM) carried out simulations for the same epi sode with the same emission data set but with different meteorological input. The episode is characterized by two typical European meteorolo gical conditions: a relatively quiet blocking situation at the beginni ng of the episode is followed by rather disturbed conditions with fron tal systems passing through central Europe. The evolution of the pollu tant fields is markedly different during these two conditions. Evaluat ion studies with the focus on the sulfur species were performed using air quality data from the EMEP monitoring network for the comparison o f model predictions with observations. The first simulation with predi cted meteorology and the PHOXA emission data set revealed an underpred iction of airborne sulfate and wet deposition, while SO2 was overpredi cted. A simulation with meteorological data created by a so-called nud ging technique corrected the transport of SO2 to remote regions and dr astically improved the predictions of rainfall and subsequently the am ount of wet deposition. However, the ambient sulfate aerosol concentra tions were still underpredicted. As the same bias in sulfate was also observed for TADAP simulations of the same episode a hypothesis for th e underprediction is a very low primary sulfate emission inherent in t he emission database. By artificially increasing the primary sulfate e mission to an obviously too high value, the underprediction of sulfate was changed into a strong overprediction for the major source regions and into a reasonable range as observed for the remote regions. An an alysis of the precipitation amounts, the aqueous concentrations and th e resulting wet depositions showed that during this episode the aqueou s processes were precipitation limited.