A REGIONAL NUMERICAL SULFUR DISPERSION MODEL USING A METEOROLOGICAL MODEL WITH EXPLICIT TREATMENT OF CLOUDS

A regional numerical short-term (hours to days) sulfur dispersion model, interacting with a NWP-model with a detailed treatment of clouds and condensation, is formulated and tested. The model has 10 layers in the vertical, 50 km horizontal resolution and covers NW-Europe. It is initialized with model-simulated fields of sulfur dioxide and sulfate in air, based on realistic sulfur SO2 emission fields. A simple parameterization scheme for dry deposition, oxidation, uptake by clouds and deposition by precipitation is applied. The numerical treatment ensures positive-definite and mass-conserving solutions. A comparison between a 36-h integration on a real synoptic situation and surface measurements, suggests that the wet deposition of sulfate and the sulfate in air is underestimated over Scandinavia. SO2 in air is overestimated close to the sources. The simulations indicate that both the oxidation rate and the vertical transport by eddy diffusion are too low.