西北典型城市交通污染生物磁学诊断及其影响因素研究

Emissions from road traffic are known as one of the major sources of particulate matter (PM) in urban areas with fast urbanization and increases in automobiles. Magnetic biomonitoring of traffic pollutants using roadside tree leaves as proxy is potentially efficient, as samples are wide-spread providing a high density of sampling points, and magnetic techniques are sensitive, rapid and relatively cheap. Previous studies mostly focus on the relationship between magnetic parameters and heavy metals or PAH. In contrast, this study will select Lanzhou as the target city, which is an important transportation hub in northwestern China, and investigate the validity of magnetic biomonitoring approach and its influence factors in a complex environment of arid and semi-arid climate zones..First, a systematic investigation of the ratio of between the detaining dust and that fixed by leaf epidermis is needed to select dominant tree species..Second, a comparative analysis between magnetic properties and elements through correlation analysis, clustering analysis and factor analysis will be carried out to select the ideal proxy which can distinguish traffic and natural sources..Third, the sensitivity and effectivity of using magnetic properties of leaves as indicators of PM10 and PM2.5 from vehicles emissions will be investigated and preliminary quantitative evaluation model which is applicable to the study area will be established..This work will provide theory and evidence on using magnetism for high resolution biomonitoring traffic pollution in a large-scale area in northwestern China.

随着城市化进程加速和机动车保有量增加，交通污染倍受关注。生物磁学在监测交通源粉尘方面具有独特优势。与前人研究主要着眼于考察交通过程排放颗粒物化学性质与磁学参数之间的内在联系不同，本研究拟选取我国西北地区重要交通枢纽城市——兰州为研究对象，重点考察干旱、半干旱气候区交通污染生物磁学诊断的有效性及影响因素。首先，以树叶表面长期滞尘和总滞尘的比值为标准，选取适合生物磁学研究的优势树种。然后，对比分析交通源与自然源磁性特征和重金属元素特征，结合地统计学方法，提取可有效区分交通源和自然源的磁参数组合。最后，根据磁学分析方法提取树叶中交通源粉尘磁参数信号和相应高度大气中交通过程排放的PM10和PM2.5浓度，通过二者的相关性分析建立适用于研究区的交通污染生物磁学诊断标准。本研究的开展有助于提高环境磁学在监测交通污染中的有效性，为实现大范围高分辨率的西北城市交通污染生物磁学监测提供可靠理论依据。

随着经济的快速发展和城市化水平的不断提高，我国城市交通污染问题日益凸显，已引起科学界、政府部门和大众的关注。本研究通过兰州市不同树种滞尘量分析，选取了小叶黄杨、刺柏为最优滞尘树种；通过不同功能区树种叶片滞尘量和磁参数分析，表明了植物叶片表面滞尘量和磁性矿物含量均随距离地面高度的增加而减小，其值在交通区明显高于公园和生活区，且二者之间显著相关，叶表粉尘饱和等温剩磁可作为有效指示植物叶表颗粒物污染程度的磁学参数。通过冬夏季刺柏叶片颗粒物磁性特征对比，掌握叶面滞尘磁性特征的时间变化规律，判断叶面颗粒物中磁性矿物种类、含量随时间的变化特征，区分人为污染源和自然污染源在不同季节对叶面尘的贡献率，结合不同季节的气象条件，分析外在环境对叶面滞尘的影响。通过选取主干道单株和成排刺柏叶片为研究对象，综合环境磁学和地球化学方法，采用富集因子法对叶表颗粒物中元素来源进行识别，探寻磁性特征与元素之间的内在联系，通过对叶表颗粒物中主要的磁性矿物种类和粒径进行判别，结合常见的主要地壳类元素和交通相关的元素浓度以及元素富集因子的变化，通过多指标性相关性分析判定和识别在不同采样方位和采样高度上叶表颗粒物的主要来源。通过对比分析叶表污染物在面对道路一侧和背对道路一侧的差异，在车辆驶来的方向和驶去的方向的差异，探究成排树和单棵树这两种不同的行道树栽种模式对道路污染物扩散进程的影响，以及两种不同的行道树栽种模式在垂直和水平方向上道路污染物拦截作用的差异，力求为合理的城市绿化规划寻找更有力的科学依据。