树种及其树冠尺寸对街谷内污染物分布特征的影响

Influence of Tree Species and Tree-canopy Size on Pollutant Distribution Characteristics in Street Canyons

本研究运用数值模拟方法分析了树冠尺寸、树种的变化对街道峡谷内气流结构及污染物扩散的影响。采用平均无量纲浓度(K)和空气交换率(ACH)对街道峡谷内通风能力与污染状况进行评估。结果表明:树冠尺寸和树种压力损失系数的变化均会影响街谷内的气流流动结构和污染物扩散规律。其中,树冠尺寸和树种压力损失系数的增大都会使树冠对气流的阻碍作用增强,不利于街谷内通风及污染物扩散,导致街谷内特别是背风墙附近污染物浓度明显上升,并且树冠尺寸变化对污染物扩散的影响相较于树冠压损系数的变化更为显著。

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 coefficient 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.