摘要/Abstract

芳香烃作为城市大气臭氧(O₃)和二次有机气溶胶(SOA)的重要前体物, 由于其对大气二次污染、气候变化及人体健康具有重要影响, 因此芳香烃氧化机理研究成为当前大气环境化学领域最具挑战的热点研究之一. 本文综述了芳香烃氧化机理的研究成果, 详细讨论了它们与OH自由基在高低氮氧化物条件下的各反应通道和影响因素, 重点关注近年来芳香烃氧化反应研究中的新发现和新理论. 芳香烃的大气氧化反应起始由OH自由基主导, 根据其反应产物主要分为醛通道、酚通道、双环RO₂通道和环氧化物通道. 随着形成多羟基化合物、烷氧自由基环氧化、双环过氧自由基分子内氢转移、醛类化合物氢转移、CO-loss生成低碳产物等新理论的提出, 对芳香烃氧化的理解虽然有所提高, 但反应过程仍存在碳质量不守恒和自由基不闭合的问题, 导致对后续O₃和SOA形成机制的认识还十分有限. 理论计算和实验室模拟是目前芳香烃氧化机理研究的主要手段. 质谱法和光谱法是芳香烃氧化产物最常用的测量技术, 在线质谱技术尝试从分子水平上捕捉示踪性中间产物的转化, 对揭示芳烃氧化机理具有重要作用. 随着示踪物测量技术的发展, 特别是色谱-质谱联用技术为中间产物的精准测量和芳香烃氧化机制的完善开拓了新方向. 在此基础上, 厘清芳烃氧化中的碳平衡和自由基收支等关键科学问题、探究实际大气中芳香烃的环境效应有望成为未来该领域的重点研究方向.
关键词: 芳香烃, 醛途径, 酚途径, 双环RO₂途径, 氢转移反应
Aromatic hydrocarbons are important precursors of ozone and secondary organic aerosols in the urban atmosphere, which have important impact on air pollution, climate change and human health. Thus the research on the oxidation mechanism of aromatic hydrocarbons has become one of the most challenging hotspots topics in atmospheric environmental chemistry. This paper reviews the recent studies of aromatic hydrocarbons oxidation mechanism, discusses the reaction channels and influencing factors during the oxidation process under high/low NO_x conditions, and focuses on new discoveries and new theories in the studies of aromatic hydrocarbon oxidation reactions. In the atmosphere, the initiation of aromatic hydrocarbons is dominated by the reaction with the OH radicals. According to the different reaction products, the oxidation reaction of aromatic hydrocarbon is mainly divided into aldehyde pathway, phenolic pathway, bicyclic RO₂ pathway and epoxide pathway. With the development of new theories such as the formation of polyhydroxy compounds by aldehyde pathway, alkoxy radical epoxidation reaction, intramolecular H-migration reaction of bicyclic peroxy radicals, 1,5-aldehydic H-shift reaction, and the generation of low-carbon products by CO-loss reaction, the understanding of aromatic hydrocarbons oxidation mechanisms has improved. However, due to the carbon missing and radical budgets imbalance problems in the existing oxidation mechanism, our understanding about the subsequent O₃ and secondary organic aerosols formation mechanisms are very limited. Theoretical calculation and experiment are the main methods to study the oxidation mechanism of aromatic hydrocarbons. Mass spectrometry and spectroscopy are the dominant measurement techniques for the oxidation intermediates of aromatic hydrocarbons. Online mass spectrometry can capture the tracer intermediates at the molecular level, which plays an important role in revealing the oxidation mechanism of aromatic hydrocarbons. In recent years, tracer measurement technology, especially chromatography-mass spectrometry technology has developed rapidly. This open up a new direction for the accurate measurement of intermediates and the improvement of aromatic hydrocarbon oxidation mechanism. On this basis, improving aromatic hydrocarbons oxidation mechanism, paying attention to the carbon missing and radical budgets imbalance in the oxidation reaction, and exploring the environmental implication of aromatic hydrocarbons oxidation in the real atmospheric conditions are expected to become the important directions of aromatic hydrocarbon oxidation study in the future.
Key words: aromatic hydrocarbon, aldehyde pathway, phenolic pathway, bicyclic RO₂ pathway, H-migration


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