|Alternative Title||Formation Mechanism and Pollution Characteristics of Environmentally Persistent Free Radicals|
|Thesis Advisor||郑明辉 ; 刘国瑞|
|Place of Conferral||北京|
|Keyword||环境持久性自由基（Epfrs）,二恶英,生成机理,金属氧化物,大气颗粒物 Environmentally Persistent Free Radicals (Epfrs), Dioxins, Formation Mechanism, Metal Oxide, Airborne Particulate Matter|
环境持久性自由基（Environmentally persistent free radicals, EPFRs）是相对于传统关注的短寿命自由基提出的、具有环境持久性和潜在毒性的一类新污染物。目前国内外对于EPFRs的生成和稳定化机制及环境污染特征的研究还处于起步阶段，热过程中多氯代二苯并-对-二恶英和多氯代二苯并呋喃（Polychlorinated dibenzo-p-dioxins and dibenzofurans, PCDD/Fs）等典型持久性有机污染物与EPFRs的相关关系尚不明确。
本研究在利用电子顺磁共振（Electron paramagnetic resonance, EPR）波谱技术研究典型前驱物氯酚生成PCDD/Fs的过程中发现EPFRs的产生，提出了PCDD/Fs生成的自由基机制，进一步研究了金属氧化物种类和形貌对EPFRs生成和稳定化的作用。对我国大气颗粒物中EPFRs的污染特征和来源进行了研究，发现燃煤和金属冶炼等工业排放是EPFRs的重要来源。有机自由基是典型持久性有机污染物（Persistent organic pollutants, POPs）生成的重要中间体，我们对实际冶炼工厂排放烟气中的典型POPs和EPFRs进行了分析，揭示了PCDD/Fs等典型POPs的排放特征，对EPFRs和PCDD/Fs的相关性进行了初步探索。所获得的主要研究结果如下：
3、建立了大气颗粒物中EPFRs的检测方法，系统研究了EPFRs在大气细颗粒物中的污染特征。研究表明北京雾霾天大气颗粒物中EPFRs的平均浓度为2.18×1020 spins/g。EPFRs主要存在于细颗粒物上，在PM<1.0 μm颗粒物上的浓度最高。对不同来源的颗粒物中EPFRs分析发现，煤燃烧、生物质燃烧、汽车尾气等是环境中EPFRs的重要来源。
Environmentally persistent free radicals (EPFRs) is a kind of emerging persistent organic pollutants, which are of potential toxity and can be stable in the environment. Currently, studies on the formation and stablization mechaniam and the characteristics of EPFRs are still at an early stage. It is not clear that if EPFRs can be formed along with the traditional persistent organic pollutants such as Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during the thermal processes. The relationship between EPFRs and PCDD/Fs is also unknown currently.
In this study, laboratory simulation experiment combined with in situ detection of electron paramagnetic resonance (EPR) spectroscopy were conducted to clarify the radical intermediate of PCDD/F formation. During the thermal processes of PCDD/F formation, EPFRs were found. Therefore, in this study, the formation mechanism of PCDD/Fs from the radicals was proposed. Considering the importance of metal oxides during EPFR formation, the pivotal roles of different kinds of metal oxides on the formation and stablization of EPFRs were systematically studied. The pollution characteristics and potential sources of EPFRs in the atmosphere were also studied. Results were shown as follows:
1. In situ EPR spectroscopy indicated the 2,3,6-trichlophenoxy radical (TCPradical) formed during PCDD/F formation from 2,3,6-chlorophenol (2,3,6-TCP) as precursor. Five elementary processes including dimerization of TCPradical, orthochloride abstraction, Smiles rearrangement, ring closure, and intra-annular elimination of Cl were proposed as the main formation mechanism of PCDDs. The proposed mechanism was further confirmed by gas chromatography/quadrupole time-of-flight mass spectrometry and gas chromatography/high resolution mass spectrometry. The in situ detection method by EPR during PCDD/F formation can provide direct and sufficient evidence for the proposed mechanism.
2. The effect of the metal oxide on the EPFR formation and stablization were clarified. The abilities of metal oxides to promote EPFR formation were related to the oxidizing strengths of the metal cations. The radical yields were dependent on the concentration and particle size of the metal oxide. Metal oxide nanoparticles increased the EPFR concentrations more than micrometer-sized particles.
3. During the formation of PCDD/Fs, EPFRs (phenoxy radicals) were also found. These EPFRs can be emitted to the atmosphere along with the stack gas. The detection method of EPFRs in atmospheric particles were established in this study. The levels and pollution characteristics of EPFRs in particles of different diameters were systematically studied. The results showed that the average concentration of EPFRs in the atmospheric particles were 2.18×1020 spins/g. EPFRs mainly attached in the fine particles (PM<1.0 μm). Significant occurrence of EPFRs in particles collected from coal burning activities, biomass burning activities, vehicle exhaust, and so on, indicating the potential primary sources of EPFRs in the atmosphere. The results in this study may help to understand the potential risks of EPFRs in the atmospheric particles.
|杨莉莉. 环境持久性自由基的生成机理与污染特征研究[D]. 北京. 中国科学院生态环境研究中心,2018.|
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