Abstract Heterogeneous aging of organic aerosols can significantly alter their physicochemical properties and thus their impacts on the radiative balance of the earth system. In this study, kinetics and mechanisms of heterogeneous reactions between suspended squalane particles and hydroxyl (OH) radicals were investigated using a self-made photooxidation flow tube and a high-resolution long time-of-flight chemical ionization mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-HR-LToF-CIMS). In addition to the measurements of the heterogeneous reaction rate constants for squalane and its multi-generation functionalization products whose carbon backbone are retaining, identification and semi-quantification of functionalization and fragmentation products from OH radical-initiated aging of squalane were carried out, which were utilized to develop a plausible reaction scheme. Our results show that the heterogeneous oxidation mechanism for particulate squalane is similar to those for OH radical initiated-oxidation of gaseous alkanes, but intermolecular hydrogen abstraction, in addition to reactions with O2, isomerization, and decomposition, could be an important heterogeneous reaction pathway for alkoxy radicals, leading to the formation of functionalization products of alcohols. The relative abundances of fragmentation products suggest that OH radicals preferably attack the tertiary carbon. The evolution of products indicates that functionalization plays a leading role in the early stage of the reaction and the fragmentation products become more and more important with increased OH exposure. Our study depicts heterogeneous reaction pathways of organic aerosols with OH radicals at the molecular level, and helps to better understand the chemical evolution of complex organic aerosols in the atmosphere.

中文翻译：

---

羟基自由基引发颗粒角鲨烷老化

摘要 有机气溶胶的非均质老化会显着改变其理化性质，进而影响地球系统的辐射平衡。在这项研究中，使用自制的光氧化流管和配备过滤器入口的高分辨率长飞行时间化学电离质谱仪研究了悬浮角鲨烷颗粒与羟基（OH）自由基之间的多相反应动力学和机制用于气体和气溶胶 (FIGAERO-HR-LToF-CIMS)。除了测量角鲨烷及其碳主链保留的多代官能化产物的多相反应速率常数外，还对 OH 自由基引发的角鲨烷老化的官能化和断裂产物进行了鉴定和半定量，用于开发合理的反应方案。我们的研究结果表明，颗粒角鲨烷的多相氧化机理与 OH 自由基引发的气态烷烃氧化的机理相似，但分子间夺氢除了与 O2 反应、异构化和分解外，还可能是重要的多相反应途径。烷氧基自由基，导致醇的官能化产物的形成。碎片产物的相对丰度表明 OH 自由基优先攻击叔碳。产物的演变表明，官能化在反应的早期阶段起主导作用，随着 OH 暴露的增加，裂解产物变得越来越重要。