The project was initiated by the Swedish Environmental Protection Agency in order to improve the basis for making standards for PM-10 concentrations in urban air. Model development has been made for Norrköping and Gothenburg. Modelling has been necessary of both long-range and local contributions.

The long-range dispersion has been simulated by the MATCH-Europe and MATCH-Sweden models, the former being a conventional dispersion model based on meteorology and emission data and the latter including also results from background air pollution measurements in Sweden and neighbouring countries.

For the local scale, both car exhaust panicles and resuspended particles from a traffic source inventory are dispersed in the city using meteorological data and a Gaussian dispersion mode! and, if needed, a street canyon dispersion submodel. For panicle resuspension, a new model has been developed. The parameters of the resuspension model have been adjusted to two streets/measuring periods in Norrköping.

At street level in Norrköping, the local model showed to contribute to a large part of the total concentration, especially in late winter and early spring due to resuspension. The MATCH mode! gives same underestimate due to the absence of organic compounds and simulation of PM-2.5 instead of PM-10. However, at some episodes in Norrköping and, in general, for a station at roof level in central Gothenburg and at the rural station Aspvreten, the model estimates of regional PM-2.5 concentrations constitute a larger part of the observed PM-10 concentrations. A good covariation in time with measured data occurs for both the MATCH model and the local model.