Advancing Urban Street Canyon Dispersion Modeling: A Large-Eddy Simulation Study on Vehicle-Induced Turbulence

Urban street canyons are critical areas for air quality concerns, where interactions among wind flow, traffic, thermodynamics, and pollutant dispersion pose significant challenges for microscale climate modeling. In this study, we use high-resolution large-eddy simulation (LES) to investigate the effects of traffic-induced turbulence and exhaust emissions on pollutant transport within street canyons. The Imposed Velocity Method (IVM) for incorporating vehicle-induced effects was developed, implemented, and validated by extending the PALM model system.
Through a comprehensive parameter study, we examine how traffic, thermodynamics, and varying wind conditions interact to influence local flow dynamics and pollutant dispersion. We systematically vary vehicle speed, wind speed, and thermal boundary conditions to represent a range of realistic traffic and diurnal heating scenarios. This parametric approach allows us to assess how changes in the wind-to-vehicle speed ratio and different heating configurations influence the interplay between vehicle-induced turbulence, thermal effects, and overall flow dynamics in the street canyon. We also investigate the impact of emission source representation by comparing a point and line source approach, revealing how these modeling choices influence the pollutant transport. This comparison underscores the importance of accurately modeling vehicular emissions to avoid under- or over-estimation of local concentrations.
In this presentation, we will share our latest results and discuss key insights into the role of vehicle-induced turbulence (VIT) in influencing urban air quality.