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Abstract. Biomass burning (BB) and coal combustion (CC) are important sources of browncarbon (BrC) in ambient aerosols. In this study, six biomass materials andfive types of coal were combusted to generate fine smoke particles. The BrCfractions, including water-soluble organic carbon (WSOC), humic-likesubstance carbon (HULIS-C), and methanol-soluble organic carbon (MSOC), weresubsequently fractionated, and their optical properties and chemicalstructures were then comprehensively investigated using UV–visiblespectroscopy, proton nuclear magnetic resonance spectroscopy (1H NMR),and fluorescence excitation–emission matrix (EEM) spectroscopy combined withparallel factor (PARAFAC) analysis. In addition, the oxidative potential(OP) of BB and CC BrC was measured with the dithiothreitol (DTT) method. Theresults showed that WSOC, HULIS-C, and MSOC accounted for 2.3 %–22 %,0.5 %–10 %, and 6.4 %–73 % of the total mass of combustion-derivedsmoke PM2.5, respectively, with MSOC extracting the highestconcentrations of organic compounds. The MSOC fractions had the highestlight absorption capacity (mass absorption efficiency at 365 nm(MAE365): 1.0–2.7 m2/gC) for both BB and CC smoke, indicatingthat MSOC contained more of the strong light-absorbing components.Therefore, MSOC may represent the total BrC better than the water-solublefractions. Some significant differences were observed between the BrCfractions emitted from BB and CC with more water-soluble BrC fractions withhigher MAE365 and lower absorption Ångström exponent valuesdetected in smoke emitted from BB than from CC. EEM-PARAFAC identified fourfluorophores: two protein-like, one humic-like, and one polyphenol-like fluorophores. Theprotein-like substances were the dominant components of WSOC(47 %–80 %), HULIS-C (44 %–87 %), and MSOC (42 %–70 %). The1H-NMR results suggested that BB BrC contained more oxygenatedaliphatic functional groups (H-C-O), whereas CC BrC contained moreunsaturated fractions (H-C-C= and Ar−H). The DTT assays indicated that BBBrC generally had a stronger oxidative potential (DTTm, 2.6–85 pmol/min/µg) than CC BrC (DTTm, 0.4–11 pmol/min/µg), withMSOC having a stronger OP than WSOC and HULIS-C. In addition, HULIS-Ccontributed more than half of the DTT activity of WSOC (63.1 % ± 15.5 %), highlighting that HULIS was a major contributor of reactive oxygen species (ROS) productionin WSOC. Furthermore, the principal component analysis and Pearsoncorrelation coefficients indicated that highly oxygenated humic-likefluorophore C4 may be the important DTT active substances in BrC.

atmospheric chemistry and physics

Chemical composition, optical properties, and oxidative potential of water- and methanol-soluble organic compounds emitted from the combustion of biomass materials and coal