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

Abstract

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

Theoretical and experimental study of peroxy and alkoxy radicals in the NO3-initiated oxidation of isoprene

“…The rate coefficients for O 2 elimination from NO 3 -isoprene-O 2 radicals are then obtained from the forward O 2 -addition reaction rates and theory-derived equilibrium constants, similar to the approach by Peeters et al 13 More details, the temperature-dependent rate coefficients, and the equilibrium constants are provided in the ESI. † [70][71][72][73] and can be neglected. Ring closure reactions should be divided into three categories: formation of 5-membered peroxide rings with an endo-cyclic alkyl radical site, formation of 5-membered rings with an exo-cyclic radical site, and formation of 6-membered rings (here always with an endo-cyclic radical site).…”

Radical chemistry in the Pearl River Delta: observations and modeling of OH and HO2 radicals in Shenzhen in 2018

“…Additionally, prior studies also reported that OH regeneration might be achieved from the oxidation of MACR and MVK, which are the major first-generated products of isoprene (Fuchs et al, 2018(Fuchs et al, , 2014. As a potential explanation for the high OH concentration, the impacts of MACR and MVK oxidation were evaluated here.…”

Experimental and theoretical study on the impact of a nitrate group on the chemistry of alkoxy radicals

“…The large majority of the alkoxy radicals formed will either decompose or isomerize 13,[58][59][60] and their detectability will be determined by their yield of HO 2 radicals. A recent study on methyl vinyl ketone (MVK), 61 one of the main products from the OH-initiated oxidation of isoprene, showed that only a partial detection of the RO 2 radicals generated was achieved due to the ''slow'' formation of HO 2 radicals.…”