Production of Aerosol paRticle orgAnic Matter in ClOUds: chamber and laboratory studies, mechanisms, modelling and iNTegration
Final Report Abstract
The ANR-DFG collaboration project PARAMOUNT yielded (i) novel chemical kinetic and mechanistic data, (ii) further developed CAPRAM mechanisms, (iii) the development of more sophisticated CESAM chamber experiment protocols and tools for chemical cloud investigations, (iv) a huge CESAM dataset and (v) an advanced framework for CESAM chamber model investigations. In detail, the performed kinetic studies focused on the radical-driven oxidation of hydroxylated aldehydes, by the OH, SO4•–, and NO3• radicals. Overall, six T-dependent aqueous-phase rate constants were determined. Associated model simulations revealed that the aqueous-phase oxidation of the hydroxylated aldehydes by OH radicals is important in cloud droplets under remote and wildfire influenced continental conditions. Furthermore, the aqueous-phase photochemistry of different unsaturated organic compounds was investigated. For this purpose, the method of competition kinetics was adapted using the Fenton reaction as an alternative OH radical source. Finally, product studies on the oxidation of crotonaldehyde, hex-2-enal, and muconaldehyde were carried out exhibiting glyoxal and butendial as fragmentation products from the decay of the alkoxyl radicals. In parallel to this laboratory work, a total of three campaigns at the CESAM chamber (France) were performed. For the first time, aerosol and cloud chemistry were measured simultaneously in the chamber. Because some technical issues found during the cloud generation, a dedicated campaign was set up intended to improve the cloud generation procedure leading to an advanced CESAM chamber experiment protocol. The third campaign was focused on the glyoxal chemistry under deliquesced particles, in-cloud, and cloud evaporation conditions. Chamber results demonstrated the feasibility of such experiments for the first time. Under the deliquesced aerosol conditions, the formation of various higher molecular weight compounds was observed by online mass spectrometers. Even if the cloud lifetime remains short, an aqueous-phase processing of organic compounds can be studied. The glyoxal-related experiments showed that the processing is not only restricted to the in-cloud period but can interestingly occur after the droplet evaporation period. Cloud evaporation periods could provide active chemical conditions that can serve as a source of aqSOA. The further developed model framework enabled advanced model studies investigating chemical processing under both deliquesced aerosol and cloud conditions during the Chamber experiments. The aerosol mass concentration patterns measured by the AMS are rather well reproduced by the model. However, model sensitivity studies also demonstrated that the modelled organic mass concentration is very sensitive to the applied kinetic forward and backward rate coefficients of the glyoxal hydration process. The applied model was able to reproduce the microphysical cloud formation and evaporation cycle for adiabatically formed clouds. Excitingly, the simulations reveal that the water evaporation proceeds on a faster timescale than the adjunct repartitioning of dissolved glyoxal back to the gas phase. As a consequence, the kinetically delayed evaporation of glyoxal leads to higher aqueous-phase concentrations after the cloud evaporation fostering the formation of dimers and formic acid during the post-evaporation period. So, the formation and subsequent release of the less volatile organic compound formic acids by a non-radical oxidation process in both deliquesced particles and evaporating droplets was modelled. All in all, the chamber observations were successfully supported by the accompanied CESAM modelling. Finally, the PARAMOUNT studies implicated that more kinetic and mechanistic investigations are necessary to improve current aqSOA mechanisms and combined CESAM-experimentmodel campaigns constitute the optimal tool for such studies.
Publications
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Direct observation of secondary organics aerosol formation from the photooxidation of glyoxal during cloud condensation-vaporization cycles, European Aerosol Conference (EAC), 2020.
J. Wu, A.Monod, M. Cazaunau, S. Mertes, B. Temime-Roussel, E. Pangui, L. Poulain, A. Berge, L. Wen, A. Gratien, T. Otto, N. Brun, A. Tilgner, H. Herrmann & J.-F. Doussin
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Determination of T-dependent OH radical reaction kinetics in the aqueous phase using the Fenton reaction as OH source. 25. Jahrestagung des SETAC GLB unter wissenschaftlicher Beteiligung der GDCh-FG Umweltchemie und Ökotoxikologie - Umwelt 2021, online, 7-8 September 2021
Mekic, M., Schaefer, T. & Herrmann, H.
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A new analytical method, using the dark Fenton reaction as an OH radical source to study oxidations of unsaturated (di)aldehydes in the aqueous phase, D-A-CH Meteorologie Tagung 2022, Leipzig, Germany & online, 21–25 March 2022
Mekic, M., Schaefer, T. & Herrmann, H.
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New method of determining the T-dependent OH radical reaction kinetics in the aqueous phase using the Fenton reaction as a dark OH source. ACS Spring 2022, San Diego, USA & online, 20-24 March 2022
Mekic, M., Schaefer, T. & Herrmann, H.
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Substantial organic impurities at the surface of synthetic ammonium sulfate particles. Atmospheric Measurement Techniques, 15(12), 3859-3874.
Wu, Junteng; Brun, Nicolas; González-Sánchez, Juan Miguel; R.'Mili, Badr; Temime, Roussel Brice; Ravier, Sylvain; Clément, Jean-Louis & Monod, Anne
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T-dependent oxidation of hydroxyaldehydes in the aqueous phase with atmospherically relevant radicals. EGU 2022, Vienna, Austria & online, 23–27 May 2022
Mekic, M., Schaefer, T. & Herrmann, H.
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Temperature-Dependent Oxidation of Hydroxylated Aldehydes by •OH, SO4•–, and NO3• Radicals in the Atmospheric Aqueous Phase. The Journal of Physical Chemistry A, 127(31), 6495-6508.
Mekic, Majda; Schaefer, Thomas; Hoffmann, Erik H.; Aiyuk, Marvel B.E.; Tilgner, Andreas & Herrmann, Hartmut
