Articles | Volume 16, issue 4
Atmos. Chem. Phys., 16, 2689–2702, 2016
Atmos. Chem. Phys., 16, 2689–2702, 2016

Research article 03 Mar 2016

Research article | 03 Mar 2016

A new source of methylglyoxal in the aqueous phase

Maria Rodigast, Anke Mutzel, Janine Schindelka, and Hartmut Herrmann Maria Rodigast et al.
  • Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Dept. (ACD), Permoserstr. 15, 04318 Leipzig, Germany

Abstract. Carbonyl compounds are ubiquitous in atmospheric multiphase system participating in gas, particle, and aqueous-phase chemistry. One important compound is methyl ethyl ketone (MEK), as it is detected in significant amounts in the gas phase as well as in cloud water, ice, and rain. Consequently, it can be expected that MEK influences the liquid-phase chemistry. Therefore, the oxidation of MEK and the formation of corresponding oxidation products were investigated in the aqueous phase. Several oxidation products were identified from the oxidation with OH radicals, including 2,3-butanedione, hydroxyacetone, and methylglyoxal. The molar yields were 29.5 % for 2,3-butanedione, 3.0 % for hydroxyacetone, and 9.5 % for methylglyoxal. Since methylglyoxal is often related to the formation of organics in the aqueous phase, MEK should be considered for the formation of aqueous secondary organic aerosol (aqSOA). Based on the experimentally obtained data, a reaction mechanism for the formation of methylglyoxal has been developed and evaluated with a model study. Besides known rate constants, the model contains measured photolysis rate constants for MEK (kp  =  5  ×  10−5 s−1), 2,3-butanedione (kp  =  9  ×  10−6 s−1), methylglyoxal (kp  =  3  ×  10−5 s−1), and hydroxyacetone (kp  =  2  ×  10−5 s−1). From the model predictions, a branching ratio of 60 /40 for primary/secondary H-atom abstraction at the MEK skeleton was found. This branching ratio reproduces the experiment results very well, especially the methylglyoxal formation, which showed excellent agreement. Overall, this study demonstrates MEK as a methylglyoxal precursor compound for the first time.

Short summary
The study highlights methyl ethyl ketone as a new and unknown source for methylglyoxal in the aqueous phase that is important for aqueous secondary organic aerosol (aqSOA) formation. Besides 2,3-butanedione (29.5 %) and hydroxyacetone (3.0 %), methylglyoxal was formed with a molar yield of 9.5 %. According to the detected products a reaction mechanism was developed and evaluated. The comparison of the model and experimental data showed excellent agreements, in particular for methylglyoxal.
Final-revised paper