Humic-like substances (HULIS) in smoke PM<sub>2.5</sub> emitted from the combustion of biomass materials (rice straw, corn straw, and pine branch) and fossil fuels (lignite coal and diesel fuel) were comprehensively studied in this work. The HULIS fractions were first isolated with a one-step solid phase extraction method and were then investigated with a series of analytical techniques: elemental analysis, total organic carbon analysis, UV-vis spectroscopy, excitation–emission matrix (EEM) ﬂuorescence spectroscopy, Fourier transform infrared spectroscopy, and 1H-nuclear magnetic resonance spectroscopy. The results indicated that HULIS accounted for a significant proportion of the particle matter, total carbon (TC), and water soluble organic carbon in smoke PM<sub>2.5</sub> emitted from the combustion of biomass materials and coal. This suggests that biomass burning and coal combustion are both important sources of HULIS in atmospheric aerosols. However, HULIS in diesel soot only accounted for ~ 0.8 % of the soot particles, suggesting that vehicular exhaust may not be a significant primary source of HULIS. Primary HULIS and atmospheric HULIS display many similar chemical characteristics, as indicated by the instrumental analytical characterization, while some distinct features were also apparent. A high spectral absorbance in the UV-vis spectra, a distinct band at λex / λem ≈ 280 / 350 nm in EEM spectra, lower H / C and O / C molar ratios, and a high content of [Ar–H] were observed for primary HULIS. These results suggest that primary HULIS contains more aromatic structures, and a lower content of aliphatic and oxygen-containing groups than atmospheric HULIS. Among the four primary sources of HULIS, HULIS from BB had the highest O / C molar ratios (0.43–0.54) and [H–C–O] content (10 %–50 %), indicating that HULIS from this source mainly consisted of carbohydrate and phenolic like structures. HULIS from coal combustion had a lower O / C molar ratio (0.27), and a higher content of [H–C–C=] (40 %) and [Ar–H] (31 %), suggesting that aromatic compounds were extremely abundant in HULIS from this source.
Fan, X., Wei, S., Zhu, M., Song, J., & Peng, P. (2016). Comprehensive characterization of humic-like substances in smoke PM 2.5 emitted from the combustion of biomass materials and fossil fuels. Atmospheric Chemistry and Physics, 16(20), 13321–13340. https://doi.org/10.5194/acp-16-13321-2016