Investigation of the oxidation of methyl vinyl ketone (MVK) by OH radicals in the atmospheric simulation chamber SAPHIR
Authors: Fuchs Hendrik , Albrecht Sascha , Acir Ismail–Hakki , Bohn Birger , Breitenlechner Martin , Dorn Hans-Peter , Gkatzelis Georgios I. , Hofzumahaus Andreas , Holland Frank , Kaminski Martin , Keutsch Frank N. , Novelli Anna , Reimer David , Rohrer Franz , Tillmann Ralf , Vereecken Luc , Wegener Robert , Zaytsev Alexander , Kiendler-Scharr Astrid , Wahner Andreas 
Published: June 2018

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
0.003 s−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.