Chemical composition, optical properties, and oxidative potential of water- and methanol-soluble organic compounds emitted from the combustion of biomass materials and coal
- 1State Key Laboratory of Organic Geochemistry and Guangdong Provincial Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
- 2CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China
- 3University of Chinese Academy of Sciences, Beijing 100049, China
- 4College of Resource and Environment, Anhui Science and Technology University, Anhui 233100, China
- 5Guangdong-Hong Kong-Macao Joint Laboratory for Environmental Pollution and Control
Abstract. Biomass burning (BB) and coal combustion (CC) are important sources of brown carbon (BrC) in ambient aerosols. In this study, six biomass materials and five types of coal were combusted to generate fine smoke particles. The BrC fractions, including water-soluble organic compounds (WSOC), humic-like substances (HULIS), and methanol-soluble organic compounds (MSOC), were subsequently fractionated and their optical properties and chemical structures were then comprehensively investigated using UV-visible spectroscopy, proton nuclear magnetic resonance spectroscopy (1H-NMR), and fluorescence extraction-emission matrix spectroscopy (EEM) combined with parallel factor analysis (PARAFAC). In addition, the oxidative potential (OP) of BB and CC BrC was measured with the dithiothreitol (DTT) method. The results showed that WSOC, HULIS, and MSOC accounted for 2.3 %–22 %, 0.5 %–10 %, and 6.4 %–73 % of the total mass of combustion-derived PM2.5, respectively, with MSOC extracting the highest concentrations of organic compounds. The MSOC fractions had the highest light absorption capacity (mass absorption efficiency at 365 nm (MAE365): 1.0–2.7 m2/gC) for both BB and CC smoke, indicating that MSOC contained more of the strong light-absorbing components. Therefore, MSOC may better represent the total BrC than the water-soluble fractions. Some significant differences were observed between the BrC fractions emitted from BB and CC, with more water-soluble BrC fractions with higher MAE365 and lower absorption Ångström exponent values detected in smoke emitted from BB than from CC. The EEM-PARAFAC analysis identified four fluorophores: two protein-like, one humic-like, and one polyphenol-like. The protein-like substance was the dominant component of WSOC (47 %–80 %), HULIS (44 %–87 %), and MSOC (42 %–70 %). The 1H-NMR results suggested that BB BrC contained more oxygenated aliphatic functional groups (H-C-O), whereas CC BrC contained more unsaturated fractions (H-C-C = and Ar-H). The DTT assays indicated that BB BrC generally had a stronger OP (DTTmass, 2.6–85 pmol/min/μg) than CC BrC (DTTmass, 0.4–11 pmol/min/μg), with MSOC having a stronger OP than WSOC and HULIS. Therefore, the BrC fractions from BB had higher OP values than those from CC.
Tao Cao et al.
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Tao Cao et al.
Tao Cao et al.
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