How dynamic growth of avenue trees affects particulate matter dispersion: CFD simulations in street canyons

Abstract

This study combined parameterized tree growth model, Reynolds Averaged Navier–Stokes model and revised generalized drift flux model to investigate the effect of dynamic growth of avenue trees on atmospheric particulate pollution dispersion in street canyons. We tested conditions with three street canyon aspect ratios (H/W = 0.45, 0.9 and 1.8) and five common avenue tree species (Gingko biloba, Aesculus chinensis, Acer buergerianum, Liriodendron chinense and Cedrus deodar). Results demonstrated that: 1) Avenue tree age was strongly correlated with their height and crown diameter (R2 ≥ 0.71). 2) PM reduction ratio increased significantly as tree age increased. G. biloba was the most effective at removing the pedestrian-level PM10, while L. chinenses has the greatest capacity to reduce pedestrian-level PM2.5. 3) Pedestrian-level PM on the windward street-side was positively related to H/W ratios. Maximum PM was measured on the leeward street-side at H/W = 0.9. 4) Tree height, crown diameter and crown volume in the street canyons were the primary factors affecting the pedestrian-level PM reduction ratio, while leaf area index and crown base height had less influence. Our results could provide guidelines for selecting avenue trees within street canyons and appropriate biometric characteristics during different plant stages to enhance urban sustainability.