Freeman-Gallant Grace, Davis Emily J, Scholer Elizabeth, Alija Onita, Navea Juan G
Chemistry Department, Skidmore College, Saratoga Springs, New York 12866-1632, United States.
J Phys Chem A. 2024 Nov 14;128(45):9792-9803. doi: 10.1021/acs.jpca.4c05608. Epub 2024 Nov 5.
Photochemical aging and photooxidation of atmospheric particles play a crucial role in both the chemical and physical processes occurring in the troposphere. In particular, the presence of organic chromophores within atmospheric aerosols can trigger photosensitized oxidation that drives the atmospheric processes in these interfaces. However, the light-induced oxidation of the surface of atmospheric aerosols, especially those enriched with organic components, remains poorly understood. Herein, we present a gravimetric and vibrational spectroscopy study aimed to investigate the photosensitized oxidation of nonanoic acid (NA), a model system of fatty acids within organic aerosols, in the presence of complex organic photosensitizers and molecular proxies. Specifically, this study shows a comparative analysis of the photosensitized reactions of thin films containing nonanoic acid and four different organic photosensitizers, namely marine dissolved organic matter (m-DOM) and humic acids (HA) as environmental photosensitizers, and 4-imidazolecarboxaldehyde (4IC) and 4-benzoylbenzoic acid (4BBA) as molecular proxies. All reactions show predominant photooxidation of nonanoic acid, with important differences in the rate and yield of product formation depending on the photosensitizer. Limited changes were observed in the organic photosensitizer itself. Results show that, among the photosensitizers examined, 4BBA is the most effective in photooxidizing nonanoic acid. Overall, this work underscores the role of chromophores in the photooxidation of organic thin films and the relevance of such reactions on the surface of aerosols in the marine environment.
大气颗粒物的光化学老化和光氧化在对流层发生的化学和物理过程中都起着关键作用。特别是，大气气溶胶中有机发色团的存在会引发光敏氧化，从而推动这些界面中的大气过程。然而，大气气溶胶表面的光致氧化，尤其是那些富含有机成分的气溶胶，仍然了解甚少。在此，我们进行了一项重量分析和振动光谱研究，旨在研究在复杂有机光敏剂和分子替代物存在下，壬酸（NA）（有机气溶胶中脂肪酸的模型体系）的光敏氧化。具体而言，本研究对含有壬酸和四种不同有机光敏剂的薄膜的光敏反应进行了对比分析，这四种光敏剂分别是作为环境光敏剂的海洋溶解有机物（m-DOM）和腐殖酸（HA），以及作为分子替代物的4-咪唑甲醛（4IC）和4-苯甲酰苯甲酸（4BBA）。所有反应均显示壬酸的主要光氧化，根据光敏剂的不同，产物形成的速率和产率存在重要差异。在有机光敏剂本身观察到有限的变化。结果表明，在所研究的光敏剂中，4BBA在光氧化壬酸方面最有效。总体而言，这项工作强调了发色团在有机薄膜光氧化中的作用以及此类反应在海洋环境气溶胶表面的相关性。
