A regional numerical sulfur dispersion model using a meteorological model with explicit treatment of clouds

Abstract

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.