Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Guangdong Technology Research Center for Photocatalytic Technology Integration and Equipment Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China; Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Guangdong-Hong Kong-Macao Joint Laboratory for Contaminants Exposure and Health, School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006, China.
Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Guangdong Technology Research Center for Photocatalytic Technology Integration and Equipment Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China.
Sci Total Environ. 2022 Mar 25;814:152575. doi: 10.1016/j.scitotenv.2021.152575. Epub 2021 Dec 25.
Photochemical oxidation (including photolysis and OH-initiated reactions) of aromatic hydrocarbon produces carbonyls, which are involved in the formation of secondary organic aerosols (SOA). However, the mechanism of this process remains incompletely understood. Herein, the monocarbonyl-dicarbonyl interconversion and its role in SOA production were investigated via a series of photochemical oxidation experiments for m-xylene and representative carbonyls. The results showed that SOA mass concentration peaked at 113.5 ± 3.5 μg m after m-xylene oxidation for 60 min and then decreased. Change in the main oxidation products from dicarbonyl (e.g., glyoxal, methylglyoxal) to monocarbonyl (e.g., formaldehyde) was responsible for this decrease. The photolysis of methylglyoxal or glyoxal produced formaldehyde, favoring SOA formation, while photopolymerization of formaldehyde to glyoxal decreased SOA production. The presence of ·OH altered the balance of photolysis interconversion, resulting in greater production of formaldehyde and SOA from glyoxal than methylglyoxal. Both photolysis and OH-initiated transformations of glyoxal to formaldehyde were suppressed by methylglyoxal, while glyoxal accelerated the reaction of ·OH with methylglyoxal to generate products which reversibly converted to glyoxal and methylglyoxal. These interconversion reactions reduced SOA production. The present study provides a new research perspective for the contribution mechanism of carbonyls in SOA formation and the findings are also helpful to efficiently evaluate the atmospheric fate of aromatic hydrocarbons.
芳香烃的光化学氧化（包括光解和 OH 引发反应）会产生羰基化合物，这些化合物参与了二次有机气溶胶（SOA）的形成。然而，这一过程的机制仍不完全清楚。在此，通过一系列针对间二甲苯和代表性羰基化合物的光化学氧化实验，研究了单羰基-二羰基的相互转化及其在 SOA 生成中的作用。结果表明，间二甲苯氧化 60 分钟后，SOA 质量浓度达到峰值 113.5±3.5μg/m3，随后下降。主要氧化产物中二羰基（如乙二醛、甲基乙二醛）向单羰基（如甲醛）的变化是导致这种下降的原因。甲基乙二醛或乙二醛的光解产生甲醛，有利于 SOA 的形成，而甲醛的光聚合生成乙二醛则会降低 SOA 的生成。·OH 的存在改变了光解相互转化的平衡，导致由乙二醛产生的甲醛和 SOA 比甲基乙二醛多。光解和 OH 引发的乙二醛向甲醛的转化均被甲基乙二醛抑制，而乙二醛加速了·OH 与甲基乙二醛的反应，生成的产物可逆地转化为乙二醛和甲基乙二醛。这些相互转化反应降低了 SOA 的生成。本研究为羰基化合物在 SOA 形成中的贡献机制提供了新的研究视角，研究结果也有助于有效评估芳香烃在大气中的归宿。
