Influence of Building Height Variation on Air Pollution Dispersion in Different Wind Directions: A Numerical Simulation Study

Abstract

Due to the rapid advancement of urbanization, traffic–related pollutants in street canyons have emerged as the primary source of PM2.5, adversely impacting residents’ health. Therefore, it is necessary to reduce PM2.5 concentrations. In this study, a three–dimensional steady–state simulation was conducted using Computational Fluid Dynamics (CFD). Three representative wind directions (θ = 0°, 45°, and 90°, corresponding to parallel, oblique, and perpendicular winds) and five different building height ratios (BHR = 0.25, 0.5, 1, 2, and 4) were used to explore the effect of building height variations on PM2.5 dispersion within street canyons. The results indicated that wind direction significantly influenced PM2.5 dispersion (p < 0.001). As θ increased (θ = 0°, 45°, and 90°), PM2.5 concentration in the canyon increased, reaching the most severe pollution under perpendicular wind. Building height variations had a minor impact compared to wind direction, but differences in PM2.5 concentration were still observed among various BHRs. Specifically, under parallel wind, the influence of BHR on PM2.5 dispersion was relatively small as compared to oblique and perpendicular winds. For oblique wind, PM2.5 concentrations varied based on BHR. Street canyons composed of low–rise or multi–story buildings (BHR = 0.25 or 4) slightly increased PM2.5 concentrations within the canyon, while the lowest PM2.5 concentration was observed at a BHR of 0.5. Under perpendicular wind, symmetrical (BHR = 1) and step–down canyons (BHR = 2 and 4) exhibited comparable peak concentrations of PM2.5, whereas step–up canyons (BHR = 0.25 and 0.5) showed relatively lower concentrations.