Influence of Tree Species and Tree-canopy Size on Pollutant Distribution Characteristics in Street Canyons
The effects of changes in tree canopy size,tree species on the airflow structure and pollutant dispersion within the street canyon were investigated through numerical simulations.The mean dimensionless concentration(K)and air exchange rate(ACH)were used to assess the ventilation capacity and pollution conditions within the street canyon.The results show that changes in tree crown size and tree species pressure loss coefficients affect the airflow structure and pollutant diffusion patterns in the street canyon.Among them,the increase of tree crown size and tree pressure loss coeffi-cient will increase the obstruction effect of tree crown on airflow,which is unfavorable to the ventilation and pollutant diffusion in the street canyon,resulting in a significant increase of pollutant concentration in the street canyon,especially near the leeward wall,and the effect of the change of tree crown size on pollutant diffusion is more significant than the change of tree crown pressure loss coefficient.
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