春季城区道路不同绿地配置模式对大气颗粒物的削减作用

Effects of different roadside urban vegetative models on airborneparticulate matter in Beijing,China

研究城市道路不同绿地类型对大气颗粒物的吸附削减作用,是提高城市绿地大气污染治理功能绿地配置模式优化的重要基础。以位于北京市海淀区的3条典型主干道道路为对象,选取乔木、灌木、草本、乔-灌、乔-草、乔-灌-草6种典型绿地配置模式,在大气颗粒物污染严重以及城市植被发芽、开花、展叶完成的春季(3月中旬至4月上旬),采用Dustmate便携式颗粒物采样器和NK4500手持自动气象仪分1.5m和3m两个高度同步测定距污染源不同位置的大气颗粒物浓度与小气候因子,分析不同绿地配置模式对颗粒物削减能力的差异及其主要影响因素。研究结果表明:复合配置模式比单一配置模式下空气颗粒物浓度稳定程度高,其主要受风速与空气相对湿度的影响;大气颗粒物粒径越大绿地对其削减作用越强;地表覆盖程度是影响不同绿地配置模式对大气颗粒物垂直削减的关键因素,地表覆盖越好垂直削减效果越好,且垂直削减率与温度成正相关关系;草本、灌木对大气颗粒物的垂直削减作用比其他4种配置模式更好;由于受植被郁闭度、疏透度以及配置种类的综合影响,乔-草、灌木绿地配置对大气颗粒物的水平削减作用比其他4种模式更好。

Development of effective roadside vegetative models is important for achieving urban air-pollution-control objectives in metropolitan cities worldwide. However, there are a number of interactive factors contributing to the effectiveness of the removal of particulate matter（ PM） from urban vegetation such as species composition,vegetation alignment,and environmental factors including air temperature,humidity,wind,and sources of PMs. We selected six types of roadside vegetative models including arbor,shrub,herb,arbor-shrub,arbor-herb,and arbor-shrub-herb according to three typical urban streets of Haidian District,Beijing,China to study their effectiveness on PMs. PM samplers（ Dustmate）and a portable weather station（ NK4500） were placed in the central part of a roadside green belt at 10 m and 20 m away from the edge of the outer lane. PM concentration and environmental factors were determined at 1. 5 m and 3 m heights,respectively. The study period was from spring between mid-March and early April in 2014 when PM concentration was usually high and urban vegetation had phenologically recovered. We found that the concentration of airborne PM under a multi life form model was more stable than under a single life form vegetative model because of the effect of wind speed andrelative humidity. In addition,there was a general trend showing that PMs with larger size were removed more efficiently in green belts. Vertical removal rate of airborne particulates was mainly affected by the degree of surface coverage of green belts. However,the vertical removal rate did not increase with higher surface coverage,even though it was positively correlated with air temperature. Herbs and shrubs showed stronger ability in aiding particulate matter diffusion than the other four types. Overall,the vegetative models of arbor-herb and shrubs are preferred for removing airborne PM over the other four models because of the vegetation canopy density,porosity,and species composition.