CFD analysis on traffic-induced air pollutant dispersion under non-isothermal condition in a complex urban area in winter

There is a higher concentration of traffic-induced air pollution alongside roads in winter than in summer due to the relatively stable atmospheric conditions. In this study, a three-dimensional computational fluid dynamics (CFD) simulation coupled with radiation and conduction analysis was carried out to analyze the pollutant dispersion under non-isothermal conditions within an objective area in Kawasaki city, Japan, in winter. The temporal variations of wind speed and pollutant concentrations were analyzed at the pedestrian level (1.5 m above the ground level). The average wind velocity in the high-density building area is very low. The pollutant accumulates around the fencings on the road due to the weak winds and vortices around them. The surface and air temperature were also discussed. The results show a systematic variation of the differences from 9:00 to 17:00. Numerical predictions demonstrate reasonably good agreement with measurements. The concentration is a little lower under non-isothermal condition than under isothermal condition.