Abstract:

Roadside green barriers as a potential solution to reduce the impacts of traffic emission on the surroundings has attracted considerable attention, but their effects on the distribution of particulate matter, either through adsorbing and settling atmospheric particulate matter on the road or hindering the dispersion of particulate matter due to the special three-dimensional structure, are still controversial. This paper reviewed a vast of literature about the mechanism of how green barriers such as hedgerows, shrubs and trees affect roadside particulate matter distribution, as well as related research methods. We found that (1) with strong survivability as well as extremely fast and strong dust retention in target road environment, plant species are effective in blocking and reducing particulate matters and thus a better choice as road barriers. But the plant community structure, street morphology, planting space, etc are critical to determine the particle sedimentation efficiency. Therefore, although the universal solution of road dust retention is difficult to find, it is important to adopt some standard protocols or methods of constructing roadside green barriers. (2) The effects of roadside green barriers are influenced by the air flow and the composition and structure of the built environment such as urban canyon and open roads, and therefore any optimization of the types and structures of roadside green barriers must take these factors into consideration, so that the roadside particulate matter is dispersed away from the protected target space alongside the road. (3) In order to make roadside green barrier strategy more effective, it is essential to simultaneously consider adsorption sedimentation and diffusion mechanisms into the assessment of green barriers to affect the distribution of particulate matter, and assess the micro-meteorological impacts from single or multiple factors coupling together. (4) In terms of research methods, to understand the mechanism of roadside green barriers affecting the dynamics process of particulate matter, more attentions should be given to simulation methods about the finer quantification or characterization of emission inputs from dynamic traffic, vegetation types, composition and structures and micrometeorological variables. Furthermore, there is an urgent need to develop a flexible and reliable stereoscopic observation technology such as unmanned aerial vehicle observation. Future research also needs to prioritize the response of green barriers to the pollution level of particulate matter at the roadside, and quantify the effect of the plant community as well as other artificial road barriers on reducing pollution in surroundings. Another focus is to optimize the greening strategy by taking into account the time- and space-based population exposure assessment along the road.

Key words: road greenbelt, plant community, atmospheric particulate matter, deposition, diffusion, monitoring, simulation

摘要：

植物屏障,一方面可以吸附沉降道路大气颗粒物,另一方面其特殊的立体结构却阻碍了颗粒物的扩散,由此导致人们对其在道路空气质量方面的影响莫衷一是。该文通过文献调研,深入分析树篱、灌木及行道树等植物屏障对路边大气颗粒物污染分布的影响机理及其研究方法,得出以下有实践指导价值的结论：（1）选择对特定环境生存力强、快速且极强滞尘的植物物种,综合考虑植物群落结构、街道形态、栽种空间等确定提高颗粒物沉降效率的绿化参数,并统一参数选择标准或标准化方法,更有利于提出普适的绿化滞尘方案;（2）基于峡谷型和开阔式道路各自流场特征及局部空间格局,同时兼顾污染防控的目标范围,确定改善污染扩散的植物群落配置及结构,才能积极引导大气颗粒物的动力学扩散过程;（3）在植物屏障调控颗粒物分布的效应评估中同时引入吸附沉降和改变扩散两种机制,并考虑微环境气象等单要素主导或多要素耦合的影响,才能使道路绿化降污策略更具实践性;（4）通过精细测算或表征动态交通排放、植物群落配置参数、微气象变量等来改进模拟方法,并发展灵活可靠且适合道路环境的立体观测技术,才能从研究方法上对植物屏障影响道路颗粒物动态过程的认识更趋真实。未来研究也亟需关注路旁植物屏障对周边大气颗粒物污染程度的响应机制,量化植物群落及与其他人工屏障的组合结构对改善周边环境污染的作用,以及考虑基于时间和空间的人群暴露评估来优化绿化配置策略。

关键词: 道路绿带, 植物群落, 大气颗粒物, 沉降, 扩散, 监测, 模拟