北京9个树种叶片滞尘量及叶面微形态解释

不同树种叶片对PM(颗粒物)的滞留能力存在较大差别,并与其表面特性密切相关. 在北京市选择空气相对清洁的植物园和污染严重的国贸桥2个地点,测定了9个常见绿化树种——白蜡、大叶黄杨、垂柳、国槐、毛白杨、玉兰、紫叶李、元宝枫和银杏的单位叶面积滞尘量及其粒径组成,并观测了各树种叶面微形态结构. 结果表明,国贸桥和北京植物园9个树种PM、PM>10、PM_2.5~10和PM_2.5平均滞留量之比分别为1.64、1.60、1.89和2.50,该比值随PM粒径减小呈增大的趋势. 环境污染会改变树木叶片表面结构与性质,从而改变其滞尘能力. 叶面沟槽深且间距大、润湿性好、气孔密度(>189 N/mm2)(以单位面积气孔数计)较大有利于滞尘；气孔密度(>217 N/mm2)更大的叶片有利于滞留PM_2.5~10. 此外,叶面绒毛数量直接影响PM_2.5滞留量,在不同污染程度下均表现为有绒毛树叶的PM_2.5滞留能力更强. 

Accumulation of Particulate Matter on Leaves of Nine Urban Greening Plant Species with Different Micromorphological Structures in Beijing

Vegetation may be used as a biological filter, with its foliage accumulating particulate matter (PM). The abilities of leaves as PM receptors depend on a number of factors, such as surface geometry, epidermal and cuticular features and leaf pubescence. Thus, study of the abilities and mechanisms of leaf PM accumulation is very important for selecting suitable plant species for PM reduction in urban environments. In a study carried out at two sites with differing pollution levels (a relatively less polluted site, Beijing Botanical Garden, and another heavily polluted site, Guomao Bridge), the ability of nine plant species (Fraxinus chinensis, Euonymus japonicas, Salix babylonica, Sophora japonica, Populus tomentosa, Magnolia denudate, Prunus cerasifera, Acer truncatum and Ginkgo biloba) to accumulate PM and its size constituents (PM>10, PM_2.5-10 and PM_2.5) from the ambient air were investigated using a washing method. The micromorphological structure of the leaves was observed using field emission environmental scanning electron microscopy, and the leaf contact angle was measured using a goniometer. It was found that the ratio of the average amount of PM captured at Guomao Bridge was 1.64 times that of Beijing Botanical Garden for the nine green tree species, among which the ratio of PM>10 was 1.60 times, the ratio of PM_2.5-10 was 1.89 times and the ratio of PM_2.5 was 2.00 times. This result showed an increasing tendency with the decrease of particle size. Atmospheric pollution altered the leaf surface structure and properties of the tested plant species, which led to variation in PM accumulation. Leaves with deep grooves, high wettability and high stomatal density (>189 N/mm2) had a higher PM capturing amount. Meanwhile, stomatal density larger than 217 N/mm2 enhanced the PM_2.5-10 capturing ability of leaves, and trichomes promoted PM_2.5 capturing ability.