Photosensitization: A novel pathway to SOA generation and property change in tropospheric particles
Final Report Abstract
In the framework of the ANR/DFG funded project PHOTOSOA, the stability of imidazolebased photosensitizers towards hydroxyl radicals (•OH), the photophysical properties as well as the reactivity of excited triplet states of different photosensitizers (PS) towards organic compounds such as carboxylic acids and unsaturated and aromatic compounds as a function of pH were investigated. The product studies on the photosensitized reactions of MVK and MACR by 3PS* are characterized by the formation of addition products, namely oxetanes. The addition reaction takes place either via a nucleophilic addition between the amine group of 2-IC and the α,β-unsaturated C atom of MVK, followed by ring closure, or a Paterno-Büchi cycloaddition. Finally, in agreement with a previous study, we conclude that the atmospheric solar irradiance, similar to the irradiance used in our chamber experiments, is too low to detect a significant effect of the photosensitizer. In summary, from the various model simulations performed, it can be concluded that photosensitizer chemistry is not as important as expected for the formation of aqSOA. Moreover, 3[PS]* are almost certainly not an important tropospheric oxidant due to efficient quenching by water or O2, but may serve as a source of 1O2 in the aqueous phase of the troposphere. Apart from the small expected contribution to SOA formation, to fully assess the role of photosensitizers in SOA aging requires a detailed and comprehensive modeling approach, which is currently underway in our laboratory. All in all, the contributions of photosensitization to atmospheric particle phase oxidation processes appear to much more limited than suggested at times, especially prior to the studies within this project.
Publications
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OH-Initiated Oxidation of Imidazoles in Tropospheric Aqueous-Phase Chemistry. J. Phys. Chem. A, 2019, 123, (8), 1505-1513
Felber, T., Schaefer, T., and Herrmann, H.
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Five-Membered Heterocycles as Potential Photosensitizers in the Tropospheric Aqueous Phase: Photophysical Properties of Imidazole-2-carboxaldehyde, 2-Furaldehyde, and 2-Acetylfuran. J. Phys. Chem. A, 2020, 124, (48), 10029-10039
Felber, T., Schaefer, T., and Herrmann, H.
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Acidity and the multiphase chemistry of atmospheric aqueous particles and clouds. Atmos. Chem. Phys., 2021, 21, 13483–13536
Tilgner, A., Schaefer, T., Alexander, B., Barth, M., Collett Jr., J. L.; Fahey, K. M., Nenes, A., Pye, H.O.T., Herrmann, H., McNeill, V. F.
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Aromatic Carbonyl and Nitro Compounds as Photosensitizers and Their Photophysical Properties in the Tropospheric Aqueous Phase. J. Phys. Chem. A, 2021, 125, 23, 5078-5059
Felber, T., Schaefer, T., He, L., and Herrmann, H.
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Photolytic radical persistence due to anoxia in viscous aerosol particles. Nat. Commun., 2021, 12, 1769
Alpert, P. A., Dou J., Corral Arroyo, P., Schneider, F., Xto, J., Luo, B., Peter, T., Huthwelker, T., Borca, C. N., Henzler, K. D., Schaefer, T., Herrmann, H., Raabe, J., Watts, B., Krieger, U. K., Ammann, M.
