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The atmospheric organic aerosol composition is characterized by a greatdiversity of functional groups and chemical species, challenging simpleclassification schemes. Traditional offline chemical methods identifychemical classes based on the retention behaviour on chromatographic columnsand absorbing beds. Such an approach led to the isolation of complex mixturesof compounds such as the humic-like substances (HULIS). More recently,online aerosol mass spectrometry (AMS) was employed to identify chemicalclasses by extracting fragmentation patterns from experimental data seriesusing statistical methods (factor analysis), providing simplified schemes forthe classification of oxygenated organic aerosols (OOAs) on the basis of thedistribution of oxygen-containing functionalities. The analysis of numerousAMS data sets suggested the occurrence of very oxidized OOAs which werepostulated to correspond to HULIS. However, only a few efforts were made totest the correspondence of the AMS classes of OOAs with the traditionalclassifications from the offline methods. In this paper, we consider a casestudy representative of polluted continental regional backgroundenvironments. We examine the AMS factors for OOAs identified by positivematrix factorization (PMF) and compare them to chemical classes of water-solubleorganic carbon (WSOC) analysed offline on a set of filters collected inparallel. WSOC fractionation was performed by means of factor analysisapplied to proton nuclear magnetic resonance (NMR)spectroscopic data, and by applying an ion-exchange chromatographic methodfor direct quantification of HULIS. Results show that the very oxidizedlow-volatility OOAs from AMS correlate with the NMR factor showing HULISfeatures and also with true "chromatographic" HULIS. On the other hand,UV/VIS-absorbing polyacids (or HULIS {sensu stricto}) isolated onion-exchange beds were only a fraction of the AMS and NMR organic carbonfractions showing functional groups attributable to highly substitutedcarboxylic acids, suggesting that unspeciated low-molecular weight organicacids contribute to HULIS in the broad sense

Identification of humic-like substances (HULIS) in oxygenated organic aerosols using NMR and AMS factor analyses and liquid chromatographic techniques