【作者】 龙时磊；

【导师】 李燕；

【作者基本信息】 中国科学院研究生院（上海应用物理研究所） ， 粒子物理与原子核物理， 2014， 博士

【摘要】 灰霾是一次颗粒物以及这些颗粒物与污染气体反应生成的二次颗粒物在有限的大气容量下发生积聚导致能见度下降而引起的。灰霾天气的增多不仅影响了交通安全、公共健康和农业生产，甚至影响着全球的气候变化，大气的灰霾污染已经引起全球的普遍关注。同步辐射X射线吸收谱（XAFS）技术以其检测限低、精度高和能进行原位测量等优点成为颗粒物成分分析的最有效手段之一。本论文基于实际大气颗粒物采样与模拟箱模拟实验，结合同步辐射XAFS、离子色谱（IC）与X射线荧光谱（XRF）技术，从两个角度（颗粒物的积聚效应和二次颗粒物生成）系统研究了上海地区灰霾形成过程中的主要物理（逆温层、相对湿度、气团轨迹等）和化学问题（颗粒物中硫酸盐、硝酸盐和铵盐（SNA）的粒径分布特征、硫酸盐的生成机制等）。地处长江入海口的上海，其周边是坦荡低平的长江三角洲平原，属于较利于大气颗粒物扩散的地形和地理位置，但是灰霾事件却频繁发生。上海地区灰霾期间各粒径段颗粒物的质量浓度均比非灰霾天高，差别最大的是0.49-0.95以及0.95-1.5μm粒径段。灰霾期间细粒径段（<1.5μm)中水溶性离子中SO42-、NO3-和NH4+的浓度较非灰霾期间高，细颗粒物中的硫酸盐主要以硫酸铵的形式存在。论文通过气团后向轨迹的聚类分析研究区域污染对上海地区颗粒物浓度及其成分的影响，得到六条平均后向轨迹，其中来自长三角地区（全年所占比例为8%）的长度较短的后向轨迹期间上海地区容易发生较严重的颗粒物污染。长度较短的后向轨迹为上海带来大量周边地域的颗粒物污染，研究上海地区灰霾污染必须考虑长江三角洲区域大量污染源的影响。结合后向轨迹以及区域污染源排放可为上海地区的灰霾预测提供一定的科学依据。气象条件决定了一个城市大气污染非常重要的指标，即大气环境容量，超过当时环境容量的颗粒物排放量将引起颗粒物污染。上海地区逆温层底高与颗粒物浓度有着一定的反比例关系，可以用公式Y=15000/(H-16)+36表达二者之间的关系，其中Y和H分别为PM10浓度（μg/m3）与逆温层底高（m）；在逆温层底的高度比较低时，城市大气中的颗粒物浓度会因逆温层下方空间容量减小发生积聚增长。上海市作为中纬度沿海城市，冬季经常出现近地逆温层，这可能是上海冬季灰霾污染严重的主要原因之一。同时，高相对湿度、低风速以及较低温度均会降低大气环境容量，加速上海地区大气颗粒物的积聚，导致颗粒物浓度升高。二次无机气溶胶的主要成分SNA被认为是能见度降低的最重要的贡献者之一，上海地区颗粒物中的SNA倾向于在气团静滞时期的细粒径段上大量生成。论文建立基于S的XANES技术综合分析大气颗粒物中S的价态和硫酸盐存在形式的方法。使用所建立的分析方法得到上海地区灰霾期间和非灰霾期间大气颗粒物中的S元素分布特征。颗粒物中S主要以硫酸盐的形式存在（70%以上），细粒径段（<3μm）颗粒物中硫酸盐的比例更高（90%左右）。而颗粒物中的硫酸盐主要以硫酸钙和硫酸铵的形式存在，灰霾期间细颗粒中硫酸铵浓度非常高。颗粒物中高浓度的硫酸铵将会促进二次颗粒物的生成，降低大气能见度，促进灰霾发生。基于同步辐射Fe的X射线吸收谱（XAFS）技术，论文对灰霾条件下含Fe颗粒物催化氧化SO2生成硫酸盐的异相化学反应过程进行了模拟和原位检测。结果证实了灰霾条件下Fe离子催化氧化SO2的异相化学反应过程的确在颗粒物表面上发生，而且该异相化学反应与颗粒物表面的水环境有关，实际大气中的相对湿度则是形成颗粒物表面水环境的非常重要的条件，因此较高相对湿度一定程度上会促进二次颗粒物的生成。这些结果表明大气中金属元素催化氧化SO2生成硫酸盐的异相化学反应的确在颗粒物上发生，一定程度上解释了灰霾天颗粒物中部分硫酸盐成分的来源，为评估硫酸盐对灰霾形成的影响提供了科学依据。本文研究结果为全面评估上海地区灰霾产生的条件和机制提供相关理论和实验依据。更多还原

【Abstract】 Haze was caused by visibility reduction which was closely related to theaccumulation of not only primary particles but also secondary particles under alimited atmosphere capacity. The increase of haze not only affects traffic safety,public health and agricultural production, but also affects the global climate change.Atmospheric haze pollution has attracted global attention. Synchrotron radiationX-ray absorption fine structure (XAFS) is a very powerful technology in analysis ofPM with its low detection limit, high accuracy and the ability of in-situ detection. Inthis thesis, based on the actual atmospheric particulate matter (PM) sampling andsmog chamber experiments, the main physical (temperature inversion layer (TIL),relative humidity (RH), air mass trajectories) and chemical problems (sulfates, nitratesand ammonium (SNA) in PM, the formation of sulfates) during haze formation inShanghai were studied by combining XAFS, ion chromatography (IC) and X-rayfluorescence (XRF).Located on the Yangtze River estuary, the main terrain of Shanghai is plain. Thegeographical location of Shanghai could favor the diffusion of PM, but haze event hasoccurred frequently in Shanghai. The mass concentrations of all size-fractionated PMwere higher in haze days than in non-haze days and even higher in the size of0.49-0.95and0.95-1.5μm in Shanghai. High concentrations of SNA and(NH4)2SO4were oberseved in fine (<1.5μm) PM during haze episodes. Clusteranalysis of air mass backward trajectories was calculated in this thesis to evaluate theimpact of regional pollution on PM concentration and characteristics in Shanghai.Results revealed that there are six clusters of average air mass trajectories in Shanghai.Air masses with short backward trajectories from the Yangtze River delta (YRD)region (8%in a whole year) brought serious PM pollution for Shanghai. The study ofhaze pollution in Shanghai must consider the impact of pollution sources in the YRDregion. The analysis with backward trajectory and area pollution emissions sourcescan provide some scientific basis for the prediction of haze in Shanghai.Meteorological conditions determine an important indicator of air pollution, environmental capacity. The particulate emissions that exceed the environmentalcapacity will cause PM pollution. The inversely proportional relationship between thebase heights of TIL and PM concentrations in Shanghai was found in this thesis. Therelationship can be signified as Y=15000/(H-16)+36, where Y and H refers PM10concentration (μg/m3) and the base heights of TIL (m), respectively. As a mid-latitudecoastal city, TIL with low height often appears during winter in Shanghai, whichmight be an important reason why haze occur frequently in winter of Shanghai.Similarly, high RH, low wind velocity and low temperature would also lowerenvironmental capacity, accelerate the accumlation of PM and cause PMconcentration rise.As the main components of secondary inorganic aerosol, SNA are considered asone of the most important contributors to visibility impairment. Combined with airmass back-trajectories, the highest concentration of SNA in fine PM of Shanghai wasobserved during the periods of air mass stagnations. The method for speciation of theoxidation state of sulfur and different sulfate species in PM by sulfur K-edge x-rayabsorption near edge structure (XANES) were established. The PM samples duringhaze and non-haze episodes in Shanghai were analyzed by this method. Resultsrevealed that sulfur mainly existed as sulfate with a proportion (atomic basis) morethan73%in all size of PM and even higher as90%in fine particles. Sulfate mainlyexisted as (NH4)2SO4and CaSO42H2O in PM of Shanghai. Compared to non-hazedays, a dramatic increase of (NH4)2SO4content was found in fine particles on hazedays only, which suggested the promoting impact of (NH4)2SO4on haze formation. Inorder to study the formation mechanism of sulfate in PM during haze episodes, theheterogeneous chemical process of sulfate formation catalyzed by Fe-containingparticles under haze conditions was simulated and measured in-situ with synchrotronradiation XAFS techniques. Results indicated that the water content on the surface ofPM was very important, which suggested that high RH favored the secondary PMformation. Results also confirmed that this heterogeneous chemical process actuallytake place on the surface of PM. This result explained part of sulfate component source in PM during haze episodes.The results of this thesis can provide relevant theoretical and experimental basisfor the comprehensive assessment of haze formation in Shanghai.更多还原