Numerical prediction of traffic-related air pollution in urban street canyons of asymmetrical layout

In this work, an investigation was carried out to reveal the impact of urban street layout, especially an asymmetrically distribution on local atmospheric environment using computational fluid dynamics (CFD) technique. Several cases of modeling the airflow and pollutant dispersion from vehicle emissions were implemented for different height-to-height ratios between windward side of building and leeward side of building, which vary from 2.0 to 0.33. A finding was obtained that higher concentration may appear on the windward face than on the leeward face when the specific ratio is a small value because of the different flow and vortex structure from the previous studies for those of symmetrical street canyons. It was shown that the local atmospheric environment close to the lower building is always poorer than the higher building when the ratio is satisfied a specific range.