Formation of substances with humic-like fluorescence properties, upon photoinduced oligomerization of typical phenolic compounds emitted by biomass burning.

Abstract The irradiation under simulated sunlight of some phenolic compounds typically emitted in ambient air by biomass burning, namely vanillin and acetosyringone, yielded intermediates with humic-like fluorescence properties that can be assimilated to humic-like substances (HULIS). Evidence was obtained by ultra-high-resolution mass spectrometry of the occurrence of oligomerization processes up to the formation of trimeric species. In contrast, the irradiation of other biomass-burning compounds such as vanillic acid, m-cresol and guaiacol did not yield either HULIS-type fluorescence or oligomers. We suggest that the photolysis of biomass-burning compounds is a potential HULIS source in the atmosphere, if the relevant substrates undergo photoinduced oligomerization reactions. Graphical abstract Image 1 Highlights • Humic-like fluorescence is produced by irradiation of biomass-burning phenols. • Vanillin and acetosyringone are involved in the process. • Evidence of oligomerization, up to formation of trimeric species. • Norrish-type and phenoxyl reactions are reasonable oligomerization pathways. • This is a potential route to atmospheric humic-like substances (HULIS). [ABSTRACT FROM AUTHOR]