Numerical modeling of the effects of motor vehicle lanes layout on the transport and dispersion of exhaust pollutants in urban street canyons.

To reveal the impacts of motor vehicle lane layout on street-canyon air quality, we used computational fluid dynamics (CFD) numerical simulations to construct models for the transport and diffusion of traffic exhaust pollutants in urban street canyons under different lane layouts, and investigated the effects of the lane number and location on the distribution and diffusion of traffic exhaust pollutants in urban street canyons. The results showed that the number and location of motor vehicle lanes significantly affected the distribution and dispersion of pollutants in urban street canyons, but such impacts depended on the in-canyon airflow structure. Air quality within shallow street canyons was generally better than that of deep street canyons. Furthermore, air quality on the leeward side of shallow canyons was poorer than that on the windward side, whereas the spatial heterogeneity of air pollutant distribution in deep canyons differed due to the location of motor vehicle lanes. The configuration of motor vehicle lanes could change the spatial homogeneity of pollutant distribution within urban street canyons and promote the diffusion and removal of traffic exhaust pollutants, and consequently improve the in-canyon air quality. Controlling the number of lanes and placing them closer to the upstream building facilitated the improvement of air quality at the pedestrian level and on the windward side in shallow street canyons. Increasing the number of lanes and locating them nearer to the downstream building could reduce pedestrian-level air pollution risks at the leeward side in deep street canyons. Our findings could provide a scientific reference for numerical modeling of pollutant dispersion in street canyons and help develop urban design strategies for enhancing in-canyon air quality.