Formation of secondary organic aerosol from nitrate radical oxidation of phenolic VOCs: Implications for nitration mechanisms and brown carbon formation
Formation of secondary organic aerosol from nitrate radical oxidation of phenolic VOCs: Implications for nitration mechanisms and brown carbon formation
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DOI：
10.1016/j.atmosenv.2020.117910
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发表时间：
2021-01
影响因子：
5
通讯作者：
Raphael Mayorga;Zixu Zhao;Haofei Zhang
中科院分区：
文献类型：
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作者：
Raphael Mayorga;Zixu Zhao;Haofei Zhang
挥发性酚类衍生物主要由生物质燃烧排放，并由大气芳香族挥发性有机化合物（VOCs）的光化学产生。酚类挥发性有机物在夜间被硝酸根（NO3-）氧化可能是大气中二次有机气溶胶（SOA）和棕色碳（BrC）形成的重要来源。本论文研究了苯酚、邻苯二酚、3-甲基邻苯二酚、4-甲基邻苯二酚和愈创木酚五种酚类衍生物的NO3-氧化反应。使用电喷雾电离离子迁移谱飞行时间质谱法分析了来自NO3-氧化的SOA组分，其允许表征和鉴定氧化产物中的异构体。通过这些分析，除了已知的硝基酚化合物之外，还观察到几类含硝基的产物，包括：（1）具有额外羟基官能团的硝基酚类产物，（2）具有较低双键当量的非芳族/开环硝基产物，（3）来自C7酚类VOC的具有含碳取代的苯酚和邻苯二酚产物，（4）来自C7酚类VOC的具有含碳取代的苯酚和邻苯二酚产物，（5）来自C7酚类VOC的具有含碳取代的非芳族/开环硝基产物。（4）硝化二苯醚二聚体。目前的工作表明，新的产品从以前未被识别的途径形成NO3-氧化过程中的酚类VOCs，并可能有助于SOA的重要组成部分。在生物质燃烧过程中，在环境气溶胶中也观察到了其中一些产物。我们认为，无处不在的硝基酚型产品在SOA中来自酚类VOC + NO3的挥发性有机化合物是负责在这项研究中测得的强光吸收。因此，阐明这些途径将是至关重要的了解夜间氧化和BrC的形成机制。
Volatile phenolic derivatives are substantially emitted from biomass burning and produced from photochemistry of atmospheric aromatic volatile organic compounds (VOCs). Oxidation of phenolic VOCs at night by nitrate radicals (NO3∙) may represent a significant source of secondary organic aerosols (SOA) and brown carbon (BrC) formation in the atmosphere. In this study, NO3∙ oxidation of five phenolic derivatives, including phenol, catechol, 3-methylcatechol, 4-methylcatechol and guaiacol are investigated in laboratory experiments. The SOA constituents from the NO3∙ oxidation were analyzed using electrospray ionization ion mobility spectrometry time-of-flight mass spectrometry, which allows for characterization and identification of isomers in the oxidation products. Through these analyses, several classes of nitro-containing products in addition to the well-known nitrophenol compounds were observed, including: (1) the nitrophenol type of products with additional hydroxyl functional groups; (2) non-aromatic/ring-opening nitro-products with lower double bond equivalence; (3) phenol and catechol products from the C7phenolic VOCs with carbon-containing substitutions; and (4) nitrated diphenyl ether dimers. The present work indicates that new products from previously unrecognized pathways are formed during NO3∙ oxidation of phenolic VOCs and may contribute an important portion of the SOA. Some of these products were also observed in ambient aerosols during biomass burning. We suggest that the ubiquity of the nitrophenol type of products in the SOA derived from phenolic VOC + NO3∙ are responsible for the strong light absorption measured in this study. Therefore, elucidation of these pathways will be critical for understanding the nighttime oxidation and BrC formation mechanisms.