Liu Kun, Wang Tao, Zhang Guohua, Sun Wei, Yang Ye, Tang Mingjin, Wang Xinming, Bi Xinhui
State Key Laboratory of Organic Geochemistry and Guangdong Provincial Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou 510640, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Organic Geochemistry and Guangdong Provincial Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou 510640, China; Guangdong-Hong Kong-Macao Joint Laboratory for Environmental Pollution and Control, Guangzhou Institute of Geochemistry, CAS, Guangzhou 510640, China.
J Environ Sci (China). 2025 Dec;158:686-693. doi: 10.1016/j.jes.2025.01.024. Epub 2025 Jan 25.
Aqueous-phase reactions between carbonyls and reduced nitrogen compounds play a considerable role in the formation of secondary organic aerosols and brown carbon in the atmosphere. However, the reported reaction rate constants for these reactions have largely been limited to bulk aqueous-phase simulations, which may not accurately represent the real state of atmospheric cloud droplets. We employed an integration of optical tweezers and Raman spectroscopy to manipulate and analyze simulated cloud droplets (size range 8000-10,000 nm), comprising a mixture of glyoxal and ammonium sulfate. This approach enabled us to delve into the intricate realm of their reaction kinetics at individual droplet level mimicking cloud droplets. Raman spectroscopy provided high temporal resolution (20 s) measurements of the changes in the amount of nitrogen-containing organics (or NOCs as represented by the CN bond) within the droplets. The results indicate that the reaction follows first-order kinetics throughout the monitoring over 80-400 min. The average reaction rate constant for the formation of NOCs within the single droplet was determined to be (6.77 ± 0.98) × 10 s, up to three orders of magnitude higher than those through the bulk aqueous-phase simulations, especially at lower pH levels. Additionally, the reaction rate constant in single droplet increases with increasing pH, consistent with the trend previously reported for the bulk aqueous-phase simulations. The results highlight the difference of the reaction rate constant between bulk aqueous-phase and droplets, which would improve our understanding on the formation and impacts of secondary organic aerosols and brown carbon in atmospheric aqueous phase.
羰基化合物与还原态氮化合物之间的水相反应在大气中二次有机气溶胶和棕碳的形成过程中起着相当重要的作用。然而，这些反应的报道反应速率常数在很大程度上仅限于整体水相模拟，而这可能无法准确反映大气云滴的真实状态。我们采用光镊和拉曼光谱相结合的方法来操控和分析模拟云滴（尺寸范围为8000 - 10000纳米），其由乙二醛和硫酸铵的混合物组成。这种方法使我们能够在模拟云滴的单个液滴层面深入探究其复杂的反应动力学领域。拉曼光谱提供了对液滴内含氮有机物（或由C - N键表示的NOCs）含量变化的高时间分辨率（20秒）测量。结果表明，在80 - 400分钟的监测过程中，该反应遵循一级动力学。单个液滴内NOCs形成的平均反应速率常数被确定为(6.77 ± 0.98) × 10⁻⁵ s⁻¹，比通过整体水相模拟得到的反应速率常数高出多达三个数量级，尤其是在较低pH值水平下。此外，单个液滴中的反应速率常数随pH值升高而增加，这与之前整体水相模拟报道的趋势一致。这些结果突出了整体水相和液滴之间反应速率常数的差异，这将增进我们对大气水相中二次有机气溶胶和棕碳的形成及影响的理解。
