The dispersion of pollution released from near building sources is of considerable interest and importance with regard to health and safety and air quality concerns. It is also a very complicated problem being dependant not only upon the meteorological and source conditions but also on the building shape, source to building separation/relative position and the angle of incidence between the mean wind and building. This level of complication also means that fully resolved computational 'solutions' are simply not practical for emergency response, environmental impact and risk assessment studies. The atmospheric dispersion group of the Met Office (UK) has undertaken to develop, as part its next generation of their lagrangian stochastic model (NAME), the capability for simulating the flow field in the vicinity of an isolated cubical building and hence the resulting dispersion.

The model consists of three parts, the first is the formulation of the mean flow field, the second part is the calculation of turbulent velocity statistics and the third is the use of a Langevin equation to simulate the particle trajectory. The mean flow field is divided further by distinguishing between the bluff body wake deficit flow and the induced vortex flow, the latter being present for non-normal building to mean wind orientations. Numerically the flow fields are also divided spatially enabling the application of the derived physical parameterisations to their respective regions. The physical parameterisation is largely based on the body of research that has been carried out in this field. In addition, due to significant gaps in these data, new approaches have also been derived, evaluated and implemented; inparticular the explicit inclusion of the trailing vortex pair for non-normal building to mean wind alignment.

Detailed comparison with experimental data has been conducted as part of the model development and evaluation. This includes comparison with both ground level and elevated concentration measurements for cuboid buildings of height to width aspect ratios ranging from 3:1 to 1:2, for passive emissions at heights ranging from 1 to 1.5 building heights and for differing building orientations. The model has been found to capture very well both the magnitude and the three dimensional spatial distribution of the concentration fields. Results comparing the numerical and experimental data for these numerous cases will be presented.