Solvent effects on chemical composition and optical properties of extracted secondary brown carbon constituents
Solvent effects on chemical composition and optical properties of extracted secondary brown carbon constituents
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DOI：
10.1080/02786826.2022.2100734
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发表时间：
2022-07-17
影响因子：
5.2
通讯作者：
Lin, Ying-Hsuan
中科院分区：
文献类型：
--
作者：
Chen, Kunpeng;Raeofy, Nilofar;Lin, Ying-Hsuan
棕色碳（BrC）气溶胶是地球上正辐射强迫的重要贡献者，但由于目前用于表征其光学和化学性质的分析方法的局限性，其对全球辐射收支的影响仍然不确定。虽然在线光学仪器提供了BrC光吸收特性的原位表征，但由于光学仪器的光源，波长通常受到限制。离线测量可以覆盖整个UV-Vis波长范围，但溶剂的使用可能会引入伪影。在这项研究中，我们比较了由杂环挥发性有机前体夜间氧化产生的气溶胶样品的在线和离线仪器测量的375 nm的质量吸收系数（MAC(375)）。用乙腈（ACN）和甲醇（MeOH）对离线样品进行萃取，考察溶剂对样品的埃-埃-埃吸收指数和BrC发色团的影响。我们的研究结果表明，meoh提取的样品和acn提取的样品之间存在相当大的差异，其中吡咯SOA特别容易受到溶剂效应的影响。多仪器分析证实，MeOH可以通过与共轭羰基发色团（邻苯二甲酸酐、马来酸酐和马来酰亚胺）反应诱导溶剂伪影，从而改变BrC组分的光吸收性能。我们的研究结果强调了甲醇分解在人工产物形成中的重要性，而惰性溶剂如ACN对于BrC发色团的适当表征是理想的。因此，使用甲醇作为溶剂的脱机分析结果应谨慎解释。Copyright (c) 2022美国气溶胶研究协会
Brown carbon (BrC) aerosol is an important contributor to positive radiative forcing on Earth, but its influence on the global radiative budget remains uncertain due to the limitations of current analytical methods used to characterize its optical and chemical properties. While online optical instruments provide in situ characterization of BrC light-absorption properties, the wavelengths are often limited due to the light source of optical instruments. Offline measurements can cover the entire UV-Vis wavelength range, but the use of solvents may introduce artifacts. In this study, we compared the mass absorption coefficients at 375 nm (MAC(375)) measured by online and offline instruments for aerosol samples generated from the nighttime oxidation of heterocyclic volatile organic precursors. Offline samples were extracted with both acetonitrile (ACN) and methanol (MeOH) to investigate the potential solvent effects on the angstrom ngstrom absorption exponent and BrC chromophores. Our results indicated considerable variations between MeOH-extracted samples and ACN-extracted samples, with pyrrole SOA being especially susceptible to solvent effects. Multi-instrumental analysis confirmed that MeOH could induce solvent artifacts by reacting with conjugated carbonyl chromophores, such as phthalic anhydride, maleic anhydride and maleimide, and subsequently modify the light absorption properties of BrC constituents. Our findings highlight the importance of methanolysis in the formation of artifacts, whereas an inert solvent such as ACN would be ideal for proper characterization of BrC chromophores. Consequently, the results from offline analysis using MeOH as the solvent should be interpreted with caution. Copyright (c) 2022 American Association for Aerosol Research