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

摘要

Methylglyoxal forms oligomeric compounds in the atmospheric aqueous particlephase, which could establish a significant contribution to the formation ofaqueous secondary organic aerosol (aqSOA). Thus far, no suitable method forthe quantification of methylglyoxal oligomers is available despite the greateffort spent for structure elucidation. In the present study a simplifiedmethod was developed to quantify heat-decomposable methylglyoxal oligomersas a sum parameter. The method is based on the thermal decomposition ofoligomers into methylglyoxal monomers. Formed methylglyoxal monomers weredetected using PFBHA (-(2,3,4,5,6-pentafluorobenzyl)hydroxylaminehydrochloride) 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 thesemethod parameters are presented.The developed method was applied to quantify heat-decomposable methylglyoxaloligomers 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 ofthose oligomers formed solely by methylglyoxal for SOA formation. Overall,the present study provides a new and suitable method for quantification ofheat-decomposable methylglyoxal oligomers in the aqueous particle phase.