Impacts of tree-planting pattern and trunk height on the airflow and pollutant dispersion inside a street canyon

Urban Vegetation in Air Quality Management: A Review and Policy Framework

“…For example, in a broad street canyon geometry, an overall improvement was obtained for dense trees, suggesting that in such a case, they might serve as a mitigation strategy, while for sparse and tall trees in the same geometric conditions, a pollution trapping effect was observed [95]. Moreover, for the same tree volume and trunk height, it was observed that tree arrangement had very little influence on flow structure and concentration distribution and the trunk height was the most important factor influencing the air flow and pollution dispersion [89]. Finally, the aerodynamic effects of trees in street canyons may depend on the geometry of the canyon itself.…”

“…Computational fluid dynamics (CFD) simulations with established, previously validated models or models validated against data from previous studies or existing databases [9,77,79,[85][86][87][88][89][90][91] CFD simulations and on-site air quality measurements, or measurements of pollution deposition on plant samples using laboratory techniques or wind tunnel experiments [78,92,93] CFD simulations coupled with photochemical equations for NO X , and O 3 transport [94] Coupled CFD-Lagrangian stochastic model (CFD-LSM) simulations [95] Parallelized Large-Eddy Simulation Model (PALM) with embedded Lagrangian stochastic particle model (LPM) simulations [96] In the studies accounting for the aerodynamic effects, the local or neighbourhood scale was applied (see Table 4). At the local scale, street canyons were mainly investigated, using either idealised 2D [78,92] or 3D street canyon geometries [83,85,89,90,95] or more realistic street canyon models based on existing geometries [93]. Idealised urban blocks, consisting of an array of buildings with several street canyons [87,88,94], were also used as a computational domain.…”

“…Although air flow characteristics at the urban micro-scale, for example, in street canyons, are dominated by wind direction and canyon geometry, the effect of vegetation is not negligible [78,[87][88][89]. Some of the studies reported an overall improvement of air quality and reduced air pollution concentration levels due to the effects of vegetation for some wind conditions and vegetation scenarios [83].…”

Effect of Street Canyon Shape and Tree Layout on Pollutant Diffusion under Real Tree Model

“…They found that a terraced building raises pollutant concentration at the windward wall and reduces concentration at the leeward wall at the pedestrian level. Huang et al [9] argued that two factors (including tree layout and the height of tree trunk) impact the flow field and pollutant dispersion in a street canyon. Wang et al [10] proposed a coupled large-eddy simulation-Lagrangian stochastic model to study the pollutant dispersion in urban canopy layers under the influence of trees.…”

“…In recent years, the research on pollutant diffusion in the street canyon under the influence of trees has been extended to the complicated structures of urban buildings [11], dry deposition [12], tree-planting pattern and trunk height [9], air stability [13], etc. There are more and more research methods, including the Monte Carlo method [14] and the Lattice Boltzmann method [15], etc.…”