Brown Carbon Formation by Aqueous-Phase Reactions of Glycolaldehyde and Methylamine

Brown carbon in aerosol remains a significant source of error in global climate modeling due to its complex nature and limited product characterization. Though significant efforts have been made to identify the major light-absorbing brown carbon chromophores formed through the reactions of small difunctional carbonyl-containing compounds with ammonium, substantial work is still required to identify the main absorbing species resulting from reactions of carbonyls with more complex amines. Using tandem mass spectrometry and isotopic substitution experiments to confirm proposed structures and support their mechanistic pathways, evidence is provided for the formation of N-containing oligomers and heterocycles in glycolaldehyde + methylamine reaction systems. Decomposed time-resolved UV-visible absorbance spectra infer multiple parallel reactions occurring at different rates. Surface tension measurements identify potential amphiphilicity in reaction products. Theoretical time-dependent density-functional theory calculations provide insight into the light absorption properties of individual molecules within the complex reaction mixture. These products may contribute to brown carbon light absorption, thus holding significant relevance toward accurately predicting their effects on global climate.