A numerical global meteorological sulfur transport model and its application to Arctic air pollution

The paper describes the construction of a dynamic atmospheric sulfur transport model and addresses the issue of long-range atmospheric sulfur transport to the Arctic as an application of the model. The global model includes the dynamics of meteorologial and tracer fields, thermodynamics, cloud processes, turbulent boundary layer mixing, multiple three-dimensional anthropogenic sulfur emission sources, dry and aqueous-phase chemical processes for sulfur, dry deposition and the precipitation scavenging of sulfur. So far, the incomplete description of clouds and precipitation has been a major limitation to the modeling of wet chemical processes on the global scale. One of the main features of our study is an attempt to a realistic representation of the interaction between clouds and chemical reactions. The model includes a detailed sub-grid scale convective and stratiform condensation scheme which includes cloud liquid water content as a predictive variable. It is shown that the model is able to reproduce important dynamic and physical structures in the atmospheric circulation leading to a realistic simulation of the important aspects of the long-range transport of sulfur to the Arctic. Realistic simulation of seasonal variations in atmospheric flow and cloud related processes provides reliable estimates of the sulfur deposition fluxes and reproduces the characteristic annual cycle of sulfur concentrations over the Arctic. Zonally averaged fields for the source and Arctic regions reveal important differences in the long-range transport mechanisms in different seasons. The model represents a powerful tool for further examining the mechanisms of sulfur transport and its impact on the atmosphere.