Air pollution model for an urban area

An atmospheric diffusion model for pollutants emitted from multiple area sources in an urban area was developed. The equation of mass continuity and the well-known wind profiles for surface layer were considered. Vertical distribution of pollutants was assumed to be expressed by a polynomial form. The coefficients of the polynom depended on atmospheric stability conditions. The height of the upper boundary of the plume was assumed as a potential function of distance. Normalized concentration estimates were compared with the values obtained from the Gifford-Hanna urban model. There was a good agreement between both models under stable atmospheric conditions. Differences increased with atmospheric unstability. Model sensitivity analysis showed that relative variations in surface roughness had little influence on relative changes in estimated concentrations values. Variations in the exponent of the potential function assumed for the top of the plume became more critical with distance. Surface concentration distributions estimated for Nashville (USA), Bremen (West Germany) and Frankfurt (West Germany) were in good agreement with the observed values. An index of agreement of 0.983 and a mean fractional error of 0.0408 were obtained between the observed and estimated values.