Canopy density effects on particulate matter attenuation coefficients in street canyons during summer in the Wuhan metropolitan area
Canopy density effects on particulate matter attenuation coefficients in street canyons during summer in the Wuhan metropolitan area
复制标题
武汉市区夏季街道峡谷冠层密度对颗粒物衰减系数的影响
DOI：
10.1016/j.atmosenv.2020.117739
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发表时间：
2020
影响因子：
5
通讯作者：
Yang Xiang
中科院分区：
文献类型：
--
作者：
Xiaoshuang Wang;Mingjun Teng;Chunbo Huang;Zhixiang Zhou;Xiaoping Chen;Yang Xiang
植被特性的变化会影响街道峡谷树木的微粒污染缓解效果；然而，目前尚不清楚树冠密度(即被树冠垂直投影覆盖的街道底部的比例)是促进还是减少这种影响。在4个具有代表性的街道峡谷进行了为期12天的田间试验，研究了4种郁闭度处理对PM1、PM2.5、PM4、PM7、PM10和总悬浮颗粒物(TSP)的影响，包括(1)开阔地和(2)稀疏(≤35%)、(3)中等(35-70%)和(4)密集(≥70%)郁闭度处理。颗粒物衰减系数(PMAC)反映了树木降低PM的能力。各粒级的PMAC值与郁闭度呈负相关，其中TSP(<；100μm)的衰减最大。与露天处理相比，30-36%的郁闭度处理对PM10和TSP的降幅最大，分别为26.75%和27.49%。对于PM2.5浓度，郁闭度在24-36%范围内的降幅最大(7.44%)。在PM浓度较高的地区，稀疏郁闭度是树木的最佳郁闭度。中等郁闭度也促进污染物扩散(尤其是PM2.5)，而浓密郁闭度会导致空气质量恶化。这一研究将对街道峡谷大气颗粒物空间弥散对树木覆盖特征的响应以及这种响应的调控机制提供新的见解。通过对不同情景下这一问题的研究，旨在为城市规划中的定量化植树设计做出贡献。
Changes in vegetation traits influence the particulate pollution mitigating effects of trees in street canyons; however, it remains unclear whether tree canopy density (i.e. the proportion of the street floor covered by the vertical projection of the tree canopy) promotes or reduces this effect. A 12-day field experiment was conducted in four representative street canyons to examine the mitigating effects of street trees on particulate matter (PM) for PM1, PM2.5, PM4, PM7, PM10, and total suspended particles (TSP) among four canopy density treatments, including (1) open spaces and areas with (2) sparse (≤35%), (3) medium (35–70%) and (4) dense (≥70%) canopy densities.The results showed that canopy density is the dominant vegetation trait that affects PM dispersion, with peak decreases occurring at a canopy density of ~30%. The particulate matter attenuation coefficient (PMAC) indicates the PM reduction capability of trees. The PMAC of each particle size class correlated negatively with canopy density and TSP (<100 μm) showed the greatest attenuation. In relation to open space treatment, a canopy density range 30–36% showed the largest reductions in the PM10and TSP concentrations of 26.75% and 27.49%, respectively. And for the PM2.5concentration, a canopy density range 24–36% exhibited the largest reduction (7.44%). It was also concluded that sparse canopy density is optimal for trees in areas with high PM concentration. Medium canopy density also promotes pollutant dispersion (especially PM2.5), while dense canopy density causes air quality deterioration. This study will provide new insights into the response of atmospheric PM spatial dispersion to the characteristics of tree cover in street canyons, as well as the regulation mechanism of this response. By investigating this issue under different scenarios, this study aims to contribute to the quantitative tree planting design in urban planning.