A three-dimensional numerical model of air pollutant dispersion

The authors propose a model of air pollutant dispersion over Lodz, the city located in Central Poland. In a 3D calculation domain, topographic features were differentiated using an available digital map. Having a topographic map, sub-areas of similar average building heights were selected which allowed the authors to refer to changes in the character of the buildings. Main traffic roads constituting ventilating ducts for the city were specified in the urbanised area. In the calculation process, Navier-Stokes equations and a continuity equation were integrated which enabled determination of an airflow velocity field. Next, the equation for pollutant transport was solved to obtain continuous concentration fields and their evolution in time. In the calculations the finite element method was applied. The model operation was presented using, as an example, the hypothetical point emissions of hazardous substances. The evolution of air pollutant concentration fields can be observed for different meteorological conditions including the strength and direction of air mass flow over the tested area. Moreover, the tested pollutants can get into the environment in any point in the city either from point or surface sources. The proposed model can be used in the testing of the concentration fields of typical urban pollutants, provided the measuring data relevant to the position and intensity of emissions are available. The above method can also be applied in the case of accidental releases that can be a result of terrorist attacks, for example.