LAUSR

Tree planting has the potential to affect local air quality by both aerodynamic and deposition effects. However, most of the previous studies have failed to take deposition effect into account, which may lead to overestimation in pollution level. This study evaluates the aerodynamic and deposition effects of roadside trees on street canyon air quality and assesses the sensitivity of these effects to different tree parameters by CFD approach. The dispersion of traffic released PM10 in an idealized isolated street canyon are investigated. The results show that, for aerodynamic effect, pressure loss coefficient is a major factor on near-wall mean concentrations, up to +54% and −39% at leeward and windward, respectively. For deposition effect, leaf area density and deposition velocity are dominant factors. When compared with cases having the same pressure loss coefficient, the deposition effect of cases with large leaf area density and high deposition velocity reaches as much as −39% at leeward and −89% at windward, while for low deposition velocity, deposition effect is not distinguishable. Overall, the results suggest that both aerodynamic and deposition effects could be major impacts in street canyon air quality, and that vegetation parameters should be carefully handled when assessing street canyon pollution level.