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Volume 18, issue 11 | Copyright
Atmos. Chem. Phys., 18, 8001-8016, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Jun 2018

Research article | 07 Jun 2018

Investigation of the oxidation of methyl vinyl ketone (MVK) by OH radicals in the atmospheric simulation chamber SAPHIR

Hendrik Fuchs1, Sascha Albrecht1, Ismail–Hakki Acir1,a, Birger Bohn1, Martin Breitenlechner2, Hans-Peter Dorn1, Georgios I. Gkatzelis1, Andreas Hofzumahaus1, Frank Holland1, Martin Kaminski1,b, Frank N. Keutsch2, Anna Novelli1, David Reimer1, Franz Rohrer1, Ralf Tillmann1, Luc Vereecken1, Robert Wegener1, Alexander Zaytsev2, Astrid Kiendler-Scharr1, and Andreas Wahner1 Hendrik Fuchs et al.
  • 1Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
  • 2School of Engineering and Applied Sciences and Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
  • anow at: Institute of Nutrition and Food Sciences, Food Chemistry, University of Bonn, Germany
  • bnow at: Bundesamt für Verbraucherschutz, Abteilung 5 – Methodenstandardisierung, Berlin, Germany

Abstract. The photooxidation of methyl vinyl ketone (MVK) was investigated in the atmospheric simulation chamber SAPHIR for conditions at which organic peroxy radicals (RO2) mainly reacted with NO (high NO case) and for conditions at which other reaction channels could compete (low NO case). Measurements of trace gas concentrations were compared to calculated concentration time series applying the Master Chemical Mechanism (MCM version 3.3.1). Product yields of methylglyoxal and glycolaldehyde were determined from measurements. For the high NO case, the methylglyoxal yield was (19±3)% and the glycolaldehyde yield was (65±14)%, consistent with recent literature studies. For the low NO case, the methylglyoxal yield reduced to (5±2)% because other RO2 reaction channels that do not form methylglyoxal became important. Consistent with literature data, the glycolaldehyde yield of (37±9)% determined in the experiment was not reduced as much as implemented in the MCM, suggesting additional reaction channels producing glycolaldehyde. At the same time, direct quantification of OH radicals in the experiments shows the need for an enhanced OH radical production at low NO conditions similar to previous studies investigating the oxidation of the parent VOC isoprene and methacrolein, the second major oxidation product of isoprene. For MVK the model–measurement discrepancy was up to a factor of 2. Product yields and OH observations were consistent with assumptions of additional RO2 plus HO2 reaction channels as proposed in literature for the major RO2 species formed from the reaction of MVK with OH. However, this study shows that also HO2 radical concentrations are underestimated by the model, suggesting that additional OH is not directly produced from RO2 radical reactions, but indirectly via increased HO2. Quantum chemical calculations show that HO2 could be produced from a fast 1,4-H shift of the second most important MVK derived RO2 species (reaction rate constant 0.003s−1). However, additional HO2 from this reaction was not sufficiently large to bring modelled HO2 radical concentrations into agreement with measurements due to the small yield of this RO2 species. An additional reaction channel of the major RO2 species with a reaction rate constant of (0.006±0.004)s−1 would be required that produces concurrently HO2 radicals and glycolaldehyde to achieve model–measurement agreement. A unimolecular reaction similar to the 1,5-H shift reaction that was proposed in literature for RO2 radicals from MVK would not explain product yields for conditions of experiments in this study. A set of H-migration reactions for the main RO2 radicals were investigated by quantum chemical and theoretical kinetic methodologies, but did not reveal a contributing route to HO2 radicals or glycolaldehyde.

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Short summary
The photooxidation of methyl vinyl ketone MVK, one of the most important products of isoprene that is emitted by plants, was investigated in the atmospheric simulation chamber SAPHIR for conditions found in forested areas. The comparison of measured trace gas time series with model calculations shows a gap in the understanding of radical chemistry in the MVK oxidation scheme. The possibility of unimolecular isomerization reactions were investigated by means of quantum-chemical calculations.
The photooxidation of methyl vinyl ketone MVK, one of the most important products of isoprene...