Effects of roadside trees on thermal environment and pollutant diffusion in street canyon

The effects of roadside trees on outdoor thermal environment and air pollutant diffusion within street canyons in the city centre of Sendai, Japan, are investigated using CFD analyses. The situation with no planted trees was also simulated for comparison. In the results with no planted trees, a large recirculation was found in the street canyon and the air heated by high temperature road surface and contaminated by exhaust gas from automobiles was convected to the area above the sidewalk. Due to the windbreak effects of trees, this large recirculation was not clearly observed in all cases with roadside trees and the regions with high temperature and high concentration were formed only near the surface of the roads.