An LES study of aerodynamic effect of trees on traffic pollutant dispersion in an ideal street canyon

Aerodynamic impacts of two tree implant layout with different tree heights on air pollution distribution inside the street canyon, where the walls height and street width are equal, has been investigated using Parallelized Large Eddy simulation model (PALM). A reference tree-free case, six double-row, and center-row planted trees with 5 m, 10 m, and 15 m height cases were studied. The results of the modeling study reveal that the center-row planted trees have direct impacts on air ventilation inside the street canyon. In street canyons with center-row planted trees, taller trees worsen the air quality up to 10%. In street canyons with double-row planted trees, trees higher than roof-top level improve air quality inside the street canyon by about 6%. The highest concentration values were modeled at the pedestrian level about 1.5 m to 2 m near the leeward wall. The center-row tree implant is more favorable for air quality improvement than the double-row tree implant. The trees increase air pollution around the roof level near the leeward wall.