Effects of Nitrate Radical Levels and Pre-Existing Particles on Secondary Brown Carbon Formation from Nighttime Oxidation of Furan
Effects of Nitrate Radical Levels and Pre-Existing Particles on Secondary Brown Carbon Formation from Nighttime Oxidation of Furan
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DOI：
10.1021/acsearthspacechem.2c00244
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发表时间：
2022-10-18
影响因子：
3.4
通讯作者：
Lin, Ying-Hsuan
中科院分区：
文献类型：
--
作者：
Chen, Kunpeng;Mayorga, Raphael;Lin, Ying-Hsuan
呋喃是大气中主要的杂环挥发性有机化合物，来源包括一次和二次来源，例如野火的直接排放和二烯的大气氧化。已报道了由呋喃氧化形成二次有机气溶胶（SOAs）。先前的研究表明，呋喃SOA产生的夜间氧化有助于棕色碳（BrC）的形成;然而，如何夜间氧化剂水平[代表硝酸根（NO3）水平]和预先存在的颗粒影响SOA的化学组成和BrC的光学性能没有得到很好的约束。在这项研究中，我们进行了室内实验，系统地研究了这两个环境因素在夜间呋喃衍生的二次BrC形成的作用。我们的研究结果表明，通过气溶胶质谱仪测量的离子碎片家庭的SOA的散装组合物不受NO3水平的变化，但可以通过预先存在的硫酸铵颗粒的存在下的影响。基于在不同的实验条件下产生的SOA的质量吸收系数的配置文件，BrC光吸收增强由更高的NO3水平和减少预先存在的硫酸铵种子颗粒的存在下，这表明NO3引发的呋喃氧化可以促进光吸收产物的形成，而预先存在的颗粒可能有利于非吸收性有机物在气溶胶相中的分区。此外，分子水平的组成分析揭示了在各种研究的环境条件下发色团的类似模式，其中高度氧化的单体（例如，C4 H4 O 6和C4 H3 NO 7）、二聚体和低聚体都可以贡献于BrC发色团。总之，NO3水平和预先存在的颗粒可以通过改变SOA组合物来影响二次BrC的形成，这对于评估复杂环境中BrC的光学特性至关重要。
Furans are predominant heterocyclic volatile organic compounds in the atmosphere from both primary and secondary sources, such as direct emissions from wildfires and atmospheric oxidation of dienes. The formation of secondary organic aerosols (SOAs) from the oxidation of furans has been reported. Previous research has shown that furan SOA generated from nighttime oxidation contributes to brown carbon (BrC) formation; however, how nighttime oxidant levels [represented by nitrate radical (NO3) levels] and pre-existing particles influence the SOA chemical composition and BrC optical properties is not well constrained. In this study, we conducted chamber experiments to systematically investigate the role of these two environmental factors in furan-derived secondary BrC formation during the nighttime. Our results suggest that the bulk compositions of SOA measured as ion fragment families by an aerosol mass spectrometer are unaffected by changes in NO3 levels but can be influenced by the presence of pre-existing ammonium sulfate particles. Based on the mass absorption coefficient profiles of SOA produced under different experimental conditions, BrC light absorption was enhanced by higher NO3 levels and reduced by the presence of pre-existing ammonium sulfate seed particles, suggesting that NO3- initiated oxidation of furan can promote the formation of light-absorbing products, while pre-existing particles may facilitate the partitioning of nonabsorbing organics in the aerosol phase. Furthermore, molecular-level compositional analysis reveals a similar pattern of chromophores under various studied environmental conditions, in which highly oxygenated monomers (e.g., C4H4O6 and C4H3NO7), dimers, and oligomers can all contribute to BrC chromophores. Taken together, the NO3 levels and pre-existing particles can influence secondary BrC formation by altering SOA compositions, which is critical for assessing BrC optical properties in a complex environment.