Articles | Volume 17, issue 6
Research article
23 Mar 2017
Research article |  | 23 Mar 2017

A quantification method for heat-decomposable methylglyoxal oligomers and its application on 1,3,5-trimethylbenzene SOA

Maria Rodigast, Anke Mutzel, and Hartmut Herrmann

Abstract. Methylglyoxal forms oligomeric compounds in the atmospheric aqueous particle phase, which could establish a significant contribution to the formation of aqueous secondary organic aerosol (aqSOA). Thus far, no suitable method for the quantification of methylglyoxal oligomers is available despite the great effort spent for structure elucidation. In the present study a simplified method was developed to quantify heat-decomposable methylglyoxal oligomers as a sum parameter. The method is based on the thermal decomposition of oligomers into methylglyoxal monomers. Formed methylglyoxal monomers were detected using PFBHA (o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride) derivatisation and gas chromatography–mass spectrometry (GC/MS) analysis. The method development was focused on the heating time (varied between 15 and 48 h), pH during the heating process (pH  =  1–7), and heating temperature (50, 100 °C). The optimised values of these method parameters are presented.

The developed method was applied to quantify heat-decomposable methylglyoxal oligomers formed during the OH-radical oxidation of 1,3,5-trimethylbenzene (TMB) in the Leipzig aerosol chamber (LEipziger AerosolKammer, LEAK). Oligomer formation was investigated as a function of seed particle acidity and relative humidity. A fraction of heat-decomposable methylglyoxal oligomers of up to 8 % in the produced organic particle mass was found, highlighting the importance of those oligomers formed solely by methylglyoxal for SOA formation. Overall, the present study provides a new and suitable method for quantification of heat-decomposable methylglyoxal oligomers in the aqueous particle phase.

Short summary
The study presents, for the first time, a quantification method for methylglyoxal oligomers and highlights their importance for SOA formation. The method was applied to determine the fraction of methylglyoxal oligomers of 1,3,5-trimethylbenzene SOA dependent on relative humidity and seed particle acidity. An oligomer contribution of up to 8 % was calculated varying with experimental conditions and thus further hints for the dependency of the oligomer formation mechanism on conditions were found.
Final-revised paper