Radical mechanisms of methyl vinyl ketone oligomerization through aqueous phase OH-oxidation: on the paradoxical role of dissolved molecular oxygen 1Aix-Marseille Université, CNRS, LCE FRE3416, 13331, Marseille, France
08 Jul 2013
2Aix Marseille Université, CNRS, ICR UMR7273, 13397, Marseille, France
3Université Joseph Fourier, Grenoble 1/CNRS-INSU, Laboratoire de Glaciologie et Géophysique de l'Environnement, 54 rue Molière, 38402 Saint-Martin-d'Hères, France
4Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) UMR5274, UJF-Grenoble1/CNRS-INSU, Grenoble, 38041, France
5Clermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, 63000 Clermont-Ferrand, France
6CNRS, UMR6296, ICCF, BP 80026, 63171 Aubière, France
Received: 17 Dec 2012 – Published in Atmos. Chem. Phys. Discuss.: 28 Jan 2013 Abstract. It is now accepted that one of the important pathways of secondary organic
aerosol (SOA) formation occurs through aqueous phase chemistry in the
atmosphere. However, the chemical mechanisms leading to macromolecules are
still not well understood. It was recently shown that oligomer production by
OH radical oxidation in the aerosol aqueous phase from α-dicarbonyl
precursors, such as methylglyoxal and glyoxal, is irreversible and fast.
Revised: 03 Jun 2013 – Accepted: 04 Jun 2013 – Published: 08 Jul 2013
Methyl vinyl ketone (MVK) was chosen in the present study as it is an
α,β-unsaturated carbonyl that can undergo radical
oligomerization in the aerosol aqueous phase. We present here experiments on
the aqueous phase OH-oxidation of MVK, performed under various conditions.
Using NMR and UV absorption spectroscopy, high and ultra-high resolution
mass spectrometry, we show that the fast formation of oligomers up to 1800 Da
is due to radical oligomerization of MVK, and 13 series of oligomers (out
of a total of 26 series) are identified. The influence of atmospherically
relevant parameters such as temperature, initial concentrations of MVK and
dissolved oxygen are presented and discussed. In agreement with the
experimental observations, we propose a chemical mechanism of OH-oxidation
of MVK in the aqueous phase that proceeds via radical oligomerization of MVK on
the olefin part of the molecule. This mechanism highlights in our
experiments the paradoxical role of dissolved O2: while it inhibits
oligomerization reactions, it contributes to produce oligomerization
initiator radicals, which rapidly consume O2, thus leading to the
dominance of oligomerization reactions after several minutes of reaction.
These processes, together with the large range of initial concentrations
investigated show the fundamental role that radical oligomerization
processes likely play in polluted fogs and atmospheric aerosol.
Citation: Renard, P., Siekmann, F., Gandolfo, A., Socorro, J., Salque, G., Ravier, S., Quivet, E., Clément, J.-L., Traikia, M., Delort, A.-M., Voisin, D., Vuitton, V., Thissen, R., and Monod, A.: Radical mechanisms of methyl vinyl ketone oligomerization through aqueous phase OH-oxidation: on the paradoxical role of dissolved molecular oxygen, Atmos. Chem. Phys., 13, 6473-6491, doi:10.5194/acp-13-6473-2013, 2013.