Transport characteristics of PM2.5 inside urban street canyons: The effects of trees and vehicles

Particles emitted from vehicles can threaten human health. Therefore the investigations about the particle dispersion characteristics inside the street canyon are of significance. For the current work, the airflow fields and the particle movement inside an isolated street canyon with three aspect ratios under perpendicular wind direction and two typical wind speeds are studied numerically, for which the particle distributions are obtained by solving the drift-flux model. The conclusions demonstrate that the trees will result in the particles gathering. However, the particle deposition fluxes on the trees are so small which cannot effectively remove the particles from the ambient air. Besides, the vehicles tend to cluster particles around the street axis and slow down the dispersion to the curbside buildings. Therefore, the vehicles should not be ignored in the numerical models, especially for the cases in the wind direction of 90A degrees. Moreover the cases with the aspect ratio of 0.5 are more sensitive to the effects of trees and vehicles. The shop vendors expose to the highest particle concentrations in most of the scenarios.