华北平原冬季常见灰霾中有机气溶胶单颗粒的研究

发布时间：2018-08-07 14:56

【摘要】：有机气溶胶能够影响大气颗粒物的物理化学特性,如粒径、光学特性和吸湿性等,进而通过对太阳光的散射和吸收影响大气能见度和气候变化。当前大量的研究主要集中针对中国华北地区重度灰霾大气中气溶胶的物理化学特性,却忽略了发生最频繁的轻及中度霾中气溶胶颗粒的物理化学特性。近20年,中国华北平原频繁发生轻及中度霾,这些颗粒物中占比最大的有机物气溶胶的形貌和混合状态目前还未知。基于此,了解轻及中度霾中大气气溶胶的物理化学特性,对进一步评估它们对气候和人体健康的影响具有重要的科学意义。本研究于2014年12月13至23日进行了一次大规模区域性气溶胶外场观测实验,采样地点选择在城市点-济南(S1)、高山站点-泰山(S2)和区域性污染的大气背景点-长岛(S3)。本研究采集了气溶胶单颗粒样品和PM2.5样品,应用离子色谱分析仪和OCEC分析仪分析了各采样点灰霾天及清洁天的无机水溶性离子组分和OC、EC浓度。针对单颗粒样品分析,本研究使用带能谱的透射电子显微镜(TEM-EDX)、原子力显微镜(AFM)和纳米二次离子质谱分析仪(NanoSIMS)等微观分析仪器,分析了华北平原轻及中度灰霾中有机物气溶胶单颗粒的粒径、形貌和混合状态。该研究还进一步结合气流后向轨迹(HYSPLIT)模型获得华北平原轻及中度霾中有机气溶胶来源及老化过程,并对不同采样点有机物的特性进行对比分析。此外,本研究初步探索了华北平原冬季轻及中度霾大气中几种典型有机气溶胶颗粒物的耐热特性。透射电镜分析结果显示,在灰霾期间颗粒物的主要类型有六种:硫酸盐(包括钾盐和硫酸铵)、金属、飞灰、矿物颗粒、烟尘和有机物。其中,含有机物的颗粒物在所有灰霾样品(共5090个单颗粒)中最为丰富,占比约为70%。基于有机颗粒的形貌特征,将其分为六种类型:圆形(类型1)、近圆形(类型2)、不规则状(类型3)、半透明穹顶状(类型4)、溅射状(类型5)和有机包裹物(类型6)。华北平原轻及中度霾大气中类型1-3的有机物占比最大,并且大部分是内部混合于非有机气溶胶。基于透射电镜的较高分辨率,本研究发现华北平原冬季区域性灰霾中约86%的有机物内部混合于非有机气溶胶,如烟尘、矿物、金属、飞灰和硫酸盐颗粒。根据混合组分的不同,将有机物内混颗粒分为四类:有机物-烟尘颗粒混合颗粒、有机物-飞灰/金属混合颗粒、有机物-硫酸盐混合颗粒和有机物-矿物混合颗粒。研究结果显示,约83%的类型1-4有机物与烟尘颗粒、矿物、金属和硫酸盐颗粒发生内混,只有17%的类型1-4有机物是外部混合,而类型5-6有机物都是与无机盐以内混形式存在。S2和S3采样点采集的含有机物的单颗粒粒径分析显示二者颗粒物的粒径峰值一致,约400nm,而S1站点则是在600nm。此结果表明本地源直接排放的含有机物颗粒粒径比长距离传输后的颗粒粒径大。本研究中,进一步获得三个采样点采集的类型1-3有机物的粒径分布,结果显示在同一灰霾事件中类型1-3有机物的粒径峰值是一致的(约350nm)。本研究发现华北平原同一灰霾事件中不同采样点的有机物来源具有很大相似性。本研究讨论了华北平原区域性轻及中度霾中有机气溶胶颗粒物的来源。结果显示冬季华北平原大量存在的类型1-3有机物是由缺乏控制措施的家用燃炉或小型锅炉燃煤或燃烧秸秆所排放,尤其是具有高圆度和低长宽比的近圆形有机物占比较大,它们是在燃煤或秸秆燃烧排放出来的污染烟气的冷却过程中形成。本研究中为了评估有机物的来源,与室内实验进行结合,采集实验室燃煤和秸秆燃烧排放出来的新鲜颗粒物,对比分析了灰霾大气、燃煤及秸秆燃烧产生的有机物中Si、O、C的比值。结果发现71%的类型1-3有机物与燃煤排放的有机物相符。本研究结果显示在华北平原,缺乏控制措施的家用燃炉或小型锅炉的燃煤污染物排放是个从城市至农村广泛存在的污染源。此外,本研究分析了华北平原有机气溶胶的老化过程,发现有机包裹物的平均厚度从S1至S2至S3显示出微弱的增长,或间接表明低湿度条件下轻及中度霾大气中气溶胶和气体之间的非均相反应和光化学反应的程度较弱。这与本研究中发现的一次有机物(类型1-3)占比较高,二次有机物(类型6)占比较小的结果相一致。本研究对华北平原冬季轻及中度霾大气中几种典型有机气溶胶单颗粒的耐热特性做了研究,结果发现经过300摄氏度及500摄氏度的加热过程之后,类型1圆形有机物的形貌相对稳定,类型6有机包裹物的厚度变薄。有机物-烟尘混合颗粒在温度为300度至500度的加热过程中粒径缩小。类型4穹顶状有机物含有300度下挥发和不挥发的有机物,类型5溅射状有机物含有在500度下挥发和不挥发的有机物。对于类型5溅射状有机物和类型6有机包裹物中混合的无机盐则在加热至300摄氏度的过程中挥发完全。本论文研究了华北平原冬季常见灰霾中有机气溶胶单颗粒的物理化学特性,通过分析灰霾大气中有机物与室内燃煤及秸秆燃烧排放出的有机物中C-O-Si含量的比值,得出结论:缺乏控制措施的家用燃炉和小型锅炉的直接排放对华北平原冬季区域性轻及中度霾有重要影响。这个发现为华北平原地区进一步治霾提供重要的事实依据,对探究不同灰霾事件形成及评估它们对气候变化和人类健康的影响提供重要参考。
[Abstract]:Organic aerosols can affect the physical and chemical properties of atmospheric particles, such as particle size, optical properties and hygroscopicity, and then influence the atmospheric visibility and climate change through the scattering and absorption of solar light. A large number of current studies focus on the physical and chemical properties of the aerosol in the heavy haze atmosphere in North China, but ignore the physical and chemical properties of the aerosol. The physical and chemical properties of aerosol particles in the most frequent light and moderate haze occurred. In recent 20 years, light and moderate haze occurred frequently in the North China Plain. The morphology and mixing state of the largest organic aerosols in these particles were unknown. Based on this, the physical and chemical properties of atmospheric aerosols in light and medium haze were understood. One step to assess their impact on climate and human health is of great scientific significance. In this study, a large-scale regional aerosol outfield observation experiment was conducted on 13 to 23 December 2014. The sampling sites were selected at the city point Ji'nan (S1), the alpine site Taishan (S2) and the regional pollution atmospheric background - Long Island (S3). The aerosol single particle samples and PM2.5 samples were collected. The inorganic water-soluble ionic components and OC, EC concentration of the haze days and cleaning days were analyzed by ion chromatography and OCEC analyzer. For single particle sample analysis, this study used transmission electron microscopy (TEM-EDX) with energy spectrum, atomic force microscopy (AFM) and two nanoscale times. The particle size, morphology and mixing state of organic aerosol particles in light and moderate haze in North China Plain were analyzed by microanalysis instruments such as ion mass spectrometry (NanoSIMS), and the source and aging process of organic aerosols in light and medium haze in North China Plain were further combined with the HYSPLIT model. In addition, the heat resistance of several typical organic aerosol particles in the light and moderate haze atmosphere in the North China Plain was preliminarily investigated. The transmission electron microscope analysis showed that there were six main types of particulate matter during the haze: sulphate (including potassium and ammonium sulfate), metal, and fly. Ash, mineral particles, smoke and organic matter. Among them, the particles containing the machine are the most abundant in all the haze samples (5090 single particles). The proportion is about 70%. based on the morphology of organic particles. It is divided into six types: round (type 1), near circular (type 2), irregular (type 3), translucent dome like (type 4), sputtering (Class 4). Type 5) and organic inclusions (type 6). The type 1-3 organic matter in the light and moderate haze atmosphere of the North China Plain is the largest, and most of them are mixed in the non organic aerosol. Based on the high resolution of transmission electron microscopy, this study found that about 86% of the organic matter in the regional haze in the North China Plain is mixed with non organic aerosols in winter. Smoke, minerals, metals, fly ash and sulphate particles. According to the difference of the mixed components, the mixed particles in the organic matter are divided into four types: organic matter - dust particles, organic matter - fly ash / metal mixed particles, organic matter sulfate mixed particles and organic matter - mineral mixture particles. The results show that about 83% of the 1-4 organic compounds and tobacco Dust particles, minerals, metals and sulphate particles have internal mixing. Only 17% of the type 1-4 organic compounds are external mixed, and type 5-6 organic matter is the single particle size analysis of the organic matter in the form of.S2 and S3 sampling in the form of inorganic salts, which shows that the particle size peak of the two particles is the same, about 400nm, while the S1 site is in 600nm. The results show that the particle size of the local source has a larger particle size than the long distance transmission. In this study, the particle size distribution of the type 1-3 organic matter collected at three sampling points is further obtained. The results show that the peak diameter of type 1-3 organic matter in the same haze event is the same (about 350nm). The sources of organic matter from different sampling points in the same haze event in the North China Plain are very similar. The source of organic aerosol particles in the light and moderate haze in the North China Plain is discussed. The results show that a large number of 1-3 organic compounds in the North China Plain in winter are burned by a household burning furnace or a small boiler which is not controlled. Coal or burning stalks, especially the near circular organic compounds with high roundness and low width and width ratio, are relatively large, they are formed during the cooling process of the polluted flue gas emitted by coal or straw combustion. In this study, in order to evaluate the source of organic matter, combined with laboratory experiments, the emission of coal and straw combustion in the laboratory is collected. The ratio of Si, O and C in the organic matter produced by the haze atmosphere, coal and straw combustion was compared and analyzed. The results showed that 71% of the type 1-3 organic matter was in accordance with the coal fired organic matter. The results of this study showed that the emission of coal combustion in the household combustion furnace or small boiler which was not controlled in the North China Plain was from the North China Plain. In addition, this study analyzed the aging process of organic aerosols in the North China Plain, and found that the average thickness of organic inclusions showed a weak increase from S1 to S2 to S3, or indirectly showed the heterogeneous reaction and photochemical reaction between gas soluble gas and gas in light and moderate haze atmosphere under low humidity. The degree of stress is weak. This is higher than the one found in this study (type 1-3), and the two organic matter (type 6) accounts for a relatively small result. This study has studied the heat resistance of several typical organic aerosol particles in the light and moderate haze atmosphere in the North China Plain in winter. The results were found to be 300 degrees centigrade and 500 subjects. After the heating process, the morphology of type 1 circular organic matter is relatively stable, and the thickness of type 6 organic inclusions is thinner. The mixture particles of organic matter and dust are reduced in the heating process of 300 degrees to 500 degrees. Type 4 dome contains 300 degrees of volatilization and non volatilization organic matter, type 5 sputter organic matter contains The volatilization and non volatilization of organic compounds at 500 degrees. The inorganic salts mixed in type 5 sputter organics and type 6 organic inclusions are volatilized completely during heating to 300 degrees centigrade. The physical and chemical properties of organic aerosol particles in common haze in winter in the North China Plain are studied in this paper. The ratio of C-O-Si content in organic matter and organic matter discharged from coal and straw combustion shows that the direct emission of household burning furnace and small boiler which lacks control measures has important influence on regional light and moderate haze in North China Plain in winter. This discovery provides an important basis for further haze treatment in the North China Plain. It is important to explore the formation and assessment of different haze events and their impact on climate change and human health.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513

【相似文献】