Semi-empirical models as a combination of wind tunnel and numerical dispersion modelling

Semi-empirical models predict the dispersion of releases within built-up areas by a combination of wind tunnel and calculated data, for instance from simple Gaussian plume models. An example of such a semi-empirical model for point sources and releases of neutral density is described. It includes influences of the building arrangement on the dispersion like the lateral shift of a dispersion plume. The parameters of that model, such as the so-called radius of homogenization or the lateral shift of the dispersion plume, were determined by wind tunnel experiments using some typical urban arrangements of buildings. Comparing the results of the semi-empirical model with other wind tunnel results and on-site data, a better forecast of the concentration than that with unmodified Gaussian plume models can be discovered.