The Development Of A Fast Urban Air Pollutant Dispersion Model For Emergency Response

Buildings obviously influence flow field and pollutant dispersion in urban areas. An accurate description of the urban local three-dimensional flow structure is the basis to study the problems of urban pollutant dispersion. Efficient modeling simulation method is the main means to deal with air pollution in urban sudden environmental issues.Based on the existing wind field parameterized interpolation methods and mass conservation wind field adjustment schemes, from the building scale, the street canyon scale to the urban residential scale, this paper describes the establishment of a Wind Field Fast Analysis model, called NJU-WiFFA, in urban areas. The model can explicitly resolve the urban buildings, and greatly reduce the computing time with the diagnostic method. Including the NJU-WiFFA model and the Random Walk Model (RWM), the Fast Urban Air Dispersion Model (FUADM) can be used to rapidly simulate urban small-scale wind field structure and pollutant distribution. FUADM model may basically meet urban environmental emergency response needs.Using wind tunnel experimental data to evaluate and validate the FUADM modeling capability of wind field and pollutant dispersion. The results show that the model simulates the flow field structure and speed distribution of single building, street canyon and urban residential area very well; characteristics of vortex and flow around the buildings are accurately revealed; modeling wind speed and direction is consistent with wind tunnel observations, and modeling error is within reasonable limits; the model can reflect the accumulation of pollutants in the building vortex and near the vicinity of walls, the diffusion trends and concentration of pollutants is close to the wind tunnel measurements, the maximum value of the concentration is modeled relatively well.Evaluation of FUADM model shows that the simulation results are of good accuracy. Then, the FUADM model is run in an urban residential pollutant dispersion case. The modeling results show that:the layout and the height of the buildings near the source region have a significant effect on pollutant diffusion; pollutants accumulate obviously and form high concentration regions at the windward side of the building, in the middle of the street canyon and near building concave; below the building canopy, because pollutants are affected by dynamic obstruction and reflection of building obstacles, the lateral diffusion is relatively slow and the vertical mixing is sufficient; above the building canopy, rapid transport and dispersion of pollutants result in low concentration phenomenon. These distribution characteristics indicate that the model can simulate pollutants dispersion around urban buildings.