In aqueous atmospheric aerosol, small difunctional carbonyl compounds can react with amines or ammonia to produce brown carbon (BrC). BrC aerosol contributes to positive radiative forcing but is poorly characterized and therefore not sufficiently accounted for in climate modeling. A complex BrC system was investigated through creation of aqueous atmospheric aerosol mimics containing the carbonyl compounds glyoxal (Gly) and glycolaldehyde (GAld) with ammonium sulfate as a nitrogen source. Analysis using supercritical fluid chromatography-mass spectrometry (SFC-MS) revealed that adjusting the molar ratio of Gly to GAld varies the identity and abundance of BrC products that are formed. UV-Vis spectroscopy analysis demonstrated that light absorption in these Gly + GAld + AS systems does not behave as previously understood, which further suggests that the BrC products formed in the Gly + GAld + AS system vary with changing carbonyl ratios. This indicates a lack of understanding of BrC chromophoricity and subsequent contributions to radiative forcing. The use of tandem mass spectrometry and <sup>15</sup>N experiments confirmed proposed BrC product structures and their mechanistic pathways.

Effects of a varying glyoxal/glycolaldehyde ratio on brown carbon chromophoricity

ACS Spring 2022

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