The RIVM-MNP contribution to the evaluation of the EMEP Unified (Eulerian) model

Evaluation was also carried out by analysing the source-receptor matrices for the Netherlands and the geographical distribution of the emissions, comparing results with both the OPS model and measurements. The picture given of the Netherlands by the EMEP Unified model was found for most acidifying compounds to be a fair one. The source-receptor matrices calculated by the EMEP and OPS models were seen to be in good agreement for oxidised sulphur, and in reasonable agreement for reduced nitrogen. Large discrepancies between the models were found for oxidised nitrogen.

The contribution of the Dutch emissions to local deposition in the Netherlands came to a factor of 4 higher in the OPS model, compared to the EMEP model. The contributions of Belgium and Germany to deposition are also much higher in the OPS model. These differences can be traced back to the lower concentration and dry deposition, along with higher wet deposition, of NO_x in the EMEP model. For oxidised nitrogen, there was a large difference in the influence of the boundary and initial conditions on the source-receptor matrix.

The EMEP model suggests that almost 30% of the deposition is due to sources outside Europe. The SO₂ concentrations in the Netherlands calculated with the EMEP model are close to the measurements, while the NO_x concentrations are about 40% lower and the NH3 concentrations 30% to 40% lower than the measurements.