![]() Studies were evaluated that discussed personal exposure to local sources of air pollution under the presence of vegetation in open road and built-up street canyon environments. This review examined published literature on neighbourhood air quality modifications by green interventions. Intensifying the proportion of urban green infrastructure has been considered as one of the remedies for air pollution levels in cities, yet the impact of numerous vegetation types deployed in different built environments has to be fully synthesised and quantified. This paper shows that the relationship vegetation-microclimate-air quality should be analyzed taking into account not only the total area covered by vegetation but also its layout and degree of aggregation. In conjunction with a low landscaping plot ratio, a high landscaping isolation index (which means a distributed structure of vegetation) enhances the capability of local cooling and the general thermal comfort, decreasing the average temperature up to about 0.5 ☌ and the average predicted mean vote (PMV) up to about 20% compared with the non-green scenario. ![]() When trees are present, a low ecological landscaping plot ratio (which expresses the weight of carbon dioxide absorption and is larger in the presence of trees) is preferable due to a lower blocking effect on wind and pollutant dispersion. Results show that under the same green cover ratio (i.e., the same quantity of all types of vegetation), the reduction of grass and shrub cover ratio (i.e., the quantity of grass and shrubs), replaced by trees, has an impact, even though small, on thermal comfort, wind speed and air pollution, and increases the leisure space for occupants. Four green indices, i.e., the green cover ratio, the grass and shrub cover ratio, the ecological landscaping plot ratio and the landscaping isolation index, were combined to evaluate thermal and wind fields, as well as air quality in district models. Simulations were performed using Computational Fluid Dynamics and the microclimate model ENVI-met. This study numerically investigates the influence of different vegetation types and layouts on microclimate and air quality in residential districts based on the morphology and green layout of Nanjing, China. The findings of this study showed great opportunities for supporting decision-makers in improving the urban thermal environment through street greenery. (3) Over-dense tree canopy may reduce the vertical air circulation, which leads to the heated air block in the pedestrian spaces. (2) Street trees performed differently by influencing the thermal environment in streets in different directions. The results revealed: (1) the microclimate in the streets planted with deciduous trees can create a better thermal environment than conifers. The human thermal comfort was evaluated by Universal Thermal Climate Index (UTCI), which can be calculated in the model. Furthermore, the ENVI-met model was used to analyze the optimal strategies for improving the thermal environment. We analyzed the microclimate variations by on-site meteorological measurement. The research objective is to investigate how the street tree species affect microcli-mate and pedestrian comfort. Therefore, this study took two typical "three boards and four belts" type streets in Nanjing as a study site. However, the specific relationship between street tree species and microclimate has not been sufficiently studied in diverse urban settings. In addition, urban microclimate analyses are becoming more and more to address the planning decision process to create liveable and healthy public spaces. ![]() The shade from the tree cover can create a more comfortable pedestrian space in a city with hot summer. Street trees are important components of urban green spaces, and their ecosystem services improve the urban thermal environment.
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