植物叶面微观结构与化学对其吸附大气颗粒物的作用机理

Plants can play an important role in the reduction of particulate matter pollution. The properties of leaf surfaces are the most crucial factors in controlling the removal of airborne particles by plants. The mature leaves of 24 common plants selected and their replicas will be continuously gathered during the sampling period under the urban atmospheric background pollution in Beijing. The replication of leaf surfaces is a two-step molding process, in which a negative replica of a template is generated using a polyvinylsiloxane dental wax and a positive replica is made with a liquid epoxy resin. Physicochemical characteristics of particles on leaf surfaces and on replica surfaces and their dynamic changes, characterization parameters of the microstructures of leaf surfaces, adhesion and surface energy of leaf surfaces, chemical composition and crystal structures of epicuticular waxes can be obtained using the advanced instruments, including field emission scanning electron microscopy, white light scanning interferometry, atomic force microscope, optical contact angle measuring device, gas chromatography - mass spectrometry, X-ray diffraction, transmission electron microscopy and scanning tunneling microscope. The key characterization parameters of the microstructures of leaf surfaces for the adsorption of leaf surfaces to airborne particles and the mode of acting forces between leaf surfaces and particles will be determined, and then the mechanisms of the coupled effects of microstructures and chemistry of leaf surfaces on airborne particles collection by plant leaves will be expounded. The replicas of leaf surfaces from different plants have the same chemical properties, so the adsorption of replicas surfaces to airborne particles only maps the effect of the microstructures of leaf surfaces to airborne particles collection by plants. The research results have important significances to reveal the mechanism of the removal of airborne particles by plants and the micro-mechanism of action of deposit surfaces in the theory of dry deposition, to improve a variety of application models and to provide the foundation for the selection of green plants.

植物在降低大气颗粒物污染方面发挥着重要作用。叶面特性是植物去除大气颗粒物最重要的内在控制因素。本项目拟在北京市城市大气污染背景下，以24种常见植物为对象，利用扫描电子显微镜、表面形貌仪、原子力显微镜、接触角测量仪、气相色谱-质谱联用仪、X射线衍射仪、透射电子显微镜、扫描探针显微镜等仪器分析手段，获取叶面和叶面复制品附着颗粒物理化特征及其动态变化、叶面微观结构的表征参数、叶面粘附力与表面能数据和叶表皮蜡质化学组成与晶体结构信息，以确定叶面微观结构对其吸附大气颗粒物作用的关键表征参数和叶面与附着颗粒物之间的作用力模式，进而阐明叶面微观结构与化学对其吸附大气颗粒物的耦合作用机理。不同植物叶面复制品具有相同的化学特性，其表面吸附特征的差异仅映射叶面微观结构的作用。研究结果对揭示植物去除大气颗粒物机理和干沉降机制中沉积表面微观作用机理有重要意义，且有助于改进各种应用模型，亦为绿化植物种选取提供依据。

植物在降低大气颗粒物污染方面发挥着重要作用。叶面特性是植物去除大气颗粒物最重要的内在控制因素。然而，植物叶面吸附大气颗粒物的机理仍不清楚。本项目对24种测试植物叶面微观结构的形貌进行了表征，并利用ArcGIS软件对其三维数据进行了分析，结合叶面附着颗粒物的动态监测结果，确定1~2µm尺度微观结构的密度是叶面吸附大气颗粒物能力的关键表征参数。分析了测试植物叶面蜡质化学成分。选择碳黑、石墨、还原石墨烯、氧化石墨烯等四种元素碳颗粒物和两种代表叶面蜡质的化合物，利用光谱学（红外光谱和拉曼光谱）和X射线衍射的方法，开展碳颗粒物与叶面蜡质相互作用的模式研究，结果揭示，元素碳颗粒物与蜡质分子之间能够形成C-H…π型氢键，并且在与伦敦色散力的耦合作用下，两者之间存在较大的相互吸引力。此外，这种相互作用能够导致蜡质晶体结构向水分能够通过的无定形结构转变，因此，在现实中，碳黑颗粒物能够导致植物失去更多水分。本研究在研究思路和方法上能够为研究其它类型大气颗粒物与叶面蜡质相互作用提供重要借鉴，同时，为园林绿化树种选择和城市大气颗粒物污染防治提供重要的科学依据。

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