城市道路林对细颗粒物(PM2.5)的阻滞作用解析

  目的  分析细颗粒物(PM_2.5)的动态变化格局及城市道路林对其的阻滞作用，并进一步探索何种配置的林带所发挥的防尘抑霾效果最佳。  方法  选取了3种结构共12种配置模式的城市道路林，首先分析了林带内外PM_2.5的日动态、年际动态和水平空间的变化规律；然后通过减尘率评价不同模式林带对PM_2.5的阻滞作用；最后通过减尘率和小气候因子进行Pearson相关性分析，探讨影响植被减尘率的可能因素。  结果  PM_2.5日动态变化呈早晚高中间低的趋势，峰值出现在8:00和18:00，10:00和14:00最低；年动态规律表现为冬季最高，其次是秋季和春季，夏季最低。PM_2.5在林带内水平空间中的变化规律因季节不同而有所差异，春夏季节，林缘至林内呈逐渐递减趋势；秋冬季节，林缘至林内25 m处呈递增趋势，在25~30 m处下降且低于林外林缘处。对PM_2.5减尘率最高的是乔灌草结构，其次是针阔混交乔木结构，单排乔木结构的减尘率最低；春夏季，12种道路林对PM_2.5阻滞率为正值，秋冬季只有A₅(针阔混交乔木)、B₁~B₃(单排乔木)和C₂、C₃(乔灌草)为正值，其余均为负值。小气候因子与PM_2.5关系存在季节差异，PM_2.5浓度在春秋冬季与风速呈显著负相关(P＜0.05)，春夏季与温度呈显著正相关(P＜0.05)，秋冬季与相对湿度呈正相关(P＜0.05)；林地PM_2.5阻滞率在秋季和温度呈显著正相关(P＜0.05)，在秋冬季和相对湿度呈显著正相关(P＜0.05)，林地阻滞率和风速相关性不显著。  结论  在城市道路林建设中合理增加林带宽度及加大常绿针叶乔木和灌草的比例对于降低PM_2.5质量浓度效果显著。图5表6参32

Analysis of blocking effects of urban roadside forests on PM2.5

  Objective  The present study is to analyze the dynamic change patterns of fine particulate matter (PM_2.5) and the blocking effects of urban road forests, and further explore which type of forest belt has the optimal dust and haze control effects.  Method  Three types of urban road forests with a total of 12 configurations were selected. Firstly, the daily dynamics, interannual dynamics and horizontal spatial variations of PM_2.5 in and out of the forest belt were analyzed. Then, the dust reduction rate was used to evaluate the blocking effect of different forest belts on PM_2.5. Finally, the Pearson correlation analysis was carried out between the dust reduction rate and microclimate factors to explore the possible factors affecting the dust reduction rate of vegetation.  Result  The results showed that concentrations of PM_2.5 in roadside forests were highest around 8:00 and 18:00 and lowest at 10:00 and 14:00. The annual dynamic pattern indicated the most obvious change in winter (136.74?194.18 μg·m?3), followed by autumn (63.48?104.96 μg·m?3), spring (28.68?36.31 μg·m?3), and summer (13.30?19.13 μg·m?3). The variation of PM_2.5 in the horizontal space of the forest belt varies with seasons. In the spring and summer, PM_2.5 gradually decreased from the edge of the forest to the interior of the forest, while in the autumn and winter, the dust margin increased at 25 m in the forest, but decreased at 25?30 m and was lower than the outer edge of the forest. The blocking rate of PM_2.5 was highest in arbor-shrub-grass structure, followed by mixed conifer and broadleaved forest structure, and lowest in uniform arbor type. In spring and summer, the blocking rate of 12 kinds of roadside forests on PM_2.5 was positive, while in autumn and winter only A₅ (mixed conifer and broadleaved forest), B₁, B₂, and B₃ (uniform arbor type) and C₂ and C₃ (arbor-shrub-grass structure) were positive, and the rest were negative. There were seasonal differences between microclimate factors and PM_2.5. PM_2.5 concentration was negatively correlated with wind speed in spring, autumn and winter, but positively correlated with relative humidity in autumn and winter, as well as temperature in spring and summer. The block rate of PM_2.5 in roadside forests showed a significant positive correlation with temperature in autumn and relative humidity in autumn and winter, but had no significant correlation with other microclimate factors.  Conclusion  The belt width, the proportion of evergreen coniferous trees and shrubs of urban roadside forests should be reasonably increased to reduce PM_2.5 and improve air quality. [Ch, 5 fig. 6 tab. 32 ref.]