The oxidation of α-pinene, the most abundantly emitted monoterpene, is an important source of secondary organic aerosol. Previous work has focused on α-pinene oxidation by hydroxyl (OH) radicals or ozone (O₃), yet the effect of chlorine radicals (Cl) as oxidizing agents has not received much attention. Recent ambient measurements suggest that Cl could substantially affect SOA formation in continental as well as coastal regions. In this work, we conducted environmental chamber experiments on the Cl-initiated photo-oxidation of α-pinene leading to the formation of oxidized products including highly oxygenated organic molecules (HOM) and SOA. We use a Filter Inlet for Gases and Aerosols mounted onto a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) to monitor gas- and particle-phase products and to investigate their gas-particle partitioning. We identify over 600 species including 197 chlorinated and nonchlorinated HOM, which are up to six times more abundant in the particle phase than in the gas phase. We also find that SOA yields are enhanced under low NO_x conditions. Overall, our work suggests that chlorine-initiated oxidation of α-pinene can substantially impact tropospheric SOA formation given the fast chlorine chemistry and the formation of low volatility HOM which contribute to high SOA yields.

中文翻译：

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氯引发的 α-蒎烯氧化：二次有机气溶胶和高度氧化的有机分子的形成

α-蒎烯是释放量最大的单萜，其氧化是二次有机气溶胶的重要来源。以前的工作主要集中在羟基 (OH) 自由基或臭氧 (O ₃)，但氯自由基 (Cl) 作为氧化剂的作用并未受到太多关注。最近的环境测量表明，Cl 可以显着影响大陆和沿海地区的 SOA 形成。在这项工作中，我们对 α-蒎烯的氯引发的光氧化进行了环境室实验，导致形成氧化产物，包括高度氧化的有机分子 (HOM) 和 SOA。我们使用安装在高分辨率飞行时间化学电离质谱仪 (FIGAERO-CIMS) 上的气体和气溶胶过滤器入口来监测气相和颗粒相产品并研究它们的气体-颗粒分配。我们鉴定了 600 多种物质，包括 197 种氯化和非氯化 HOM，它们在颗粒相中的含量是气相中的 6 倍。_x条件。总体而言，我们的工作表明，氯引发的 α-蒎烯氧化可以显着影响对流层 SOA 的形成，因为氯化学反应速度快，并且形成的低挥发性 HOM 有助于高 SOA 产率。