Comparisons Of Model Results With ObservationsFor Acid Depositions And Acidifying Air PollutantsOver Flanders

In order to validate model computations that have been carried out to evaluate the impact of acidifying air pollutants in Flanders, model results are compared with ground level observations. The Lagrangian OPS model* has been used to compute concentrations and depositions for primary and secondary acidifying components. For a large number of monitoring stations in Flanders the yearly averaged SOj and NOz concentrations are compared with model results for 1993. Modelled depositions for 1990 could be compared with dry and wet deposition values derived from measurements. Results show a good agreement for the concentrations and for the dry deposition, but an important discrepancy for the wet deposition of SO%. This is probably due to the fact that the OPS model assumes a linear conversion of SOz concentrations to sulphates in the wet phase, leading to an underestimation of the actual wet SO* deposition.