Evaluation of the role of vegetation on the air quality in high dense Urban areas

Vegetation is generally considered as an essential component for a sustainable city as it helps improve its microclimate environment and reduce greenhouse gases emissions. However, there is some evidence suggesting that negative effects may be imposed by tree-planting in an Urban street canyon. Vegetation may act as an obstacle impairing the air circulation and pollutant removal processes at the pedestrian zone of some shallow Urban canyons. Accordingly, we intend to examine the effect of vegetation on the air quality of two deep canyons (i.e. with aspect ratios H/W = 2 and 4) under the perpendicular approaching wind condition. In addition, we also aim to examine the effects of different tree configurations on air circulation and pollutant removal processes inside these canyons by constructing a Computational Fluid Dynamics (CFD) model. Our findings suggest that tree planting at street levels may not always enhance the pollutant removal process, and therefore the location of the trees should be carefully planned in order to mitigate the potential negative impacts. The findings should be of great significance to Urban planners in planning a sustainable city.