title: Study of traffic-related pollutant removal from street canyon with trees: dispersion and deposition perspective.
abstract: Numerical experiments involving street canyons of varying aspect ratio with traffic-induced pollutants (PM2.5) and implanted trees of varying aspect ratio, leaf area index, leaf area density distribution, trunk height, tree-covered area, and tree planting pattern under different wind conditions were conducted using a computational fluid dynamics (CFD) model, ENVI-met. Various aspects of dispersion and deposition were investigated, which include the influence of various tree configurations and wind condition on dispersion within the street canyon, pollutant mass at the free stream layer and street canyon, and comparison between mass removal by surface (leaf) deposition and mass enhancement due to the presence of trees. Results revealed that concentration level was enhanced especially within pedestrian level in street canyons with trees relative to their tree-free counterparts. Additionally, we found a dependence of the magnitude of concentration increase (within pedestrian level) and decrease (above pedestrian level) due to tree configuration and wind condition. Furthermore, we realized that only ∼0.1-3 % of PM2.5was dispersed to the free stream layer while a larger percentage (∼97 %) remained in the canyon, regardless of its aspect ratio, prevailing wind condition, and either tree-free or with tree (of various configuration). Lastly, results indicate that pollutant removal due to deposition on leaf surfaces is potentially sufficient to counterbalance the enhancement of PM2.5by such trees under some tree planting scenarios and wind conditions.
authors: School of Energy and Environment, City University of Hong Kong, Hong Kong, SAR, China.
authors: Tobi Eniolu
authors: TE
authors: Morakinyo
authors: School of Energy and Environment, City University of Hong Kong, Hong Kong, SAR, China. yunflam@cityu.edu.hk.|Guy Carpenter Asia-Pacific Climate Impact Centre, City University of Hong Kong, Hong Kong, SAR, China. yunflam@cityu.edu.hk.
authors: Yun Fat
authors: http://orcid.org/0000-0002-5917-0907
authors: YF
authors: Lam
mesh_terms: D000393:Air Pollutants; D000397:Air Pollution / Q000517:prevention & control*; D004784:Environmental Monitoring; D008962:Models, Theoretical; D052638:Particulate Matter / Q000302:isolation & purification*; D014197:Trees; D001335:Vehicle Emissions; D014919:Wind
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D001335:Vehicle Emissions
keywords: Deposition; Dispersion; Near-road; Removal capacity; Street canyon; Street-trees; Traffic pollution