A regional scale multi-layer model for the calculation of long-term transport and deposition of air pollution in Europe

In this paper, we present a multi-layer Eulerian model aiming at calculating the long-term source-receptor relationships of air pollutants at the European regional scale. As a first approach, results from annual transport and deposition of sulphur dioxide and sulphate is given in this study. The model is however formulated in order to facilitate further studies of other air pollutants in the future. The model takes advantage of new detailed information on meteorology and emissions to the air in a 50 km x 50 km resolution. The model is formulated in a terrain following coordinate system, and a higher order numerical advection scheme is employed in order to reduce numerical diffusion. A simple linear parameterization scheme for sulphur dispersion and deposition is implemented. The wet scavenging is directly coupled to the release of precipitation in each model layer. The model has been employed for a full year simulations for sulphur transport and deposition in Europe. Model comparison with 60-70 measuring stations in Europe show realistic values for SO2 and sulphate in air and wet deposition of sulphate. Averaged of all stations the model deviates by only a few percent from the measured average. However, at individual stations the differences between the model and the measurements are sometimes larger, but seldom more than a factor of two difference is encountered. Further, comparison with a two-dimensional Lagrangian single layer model shows qualitatively good agreements. The most pronounced improvement encountered by use of the multi-level model are the increased wet deposition rates in remote areas, well in accordance with the measurements. This is ascribed to the improved description of the transport and wet scavenging processes by using a multi-layer rather than a single layer approach.