Light absorption properties and molecular profiles of HULIS in PM2.5 emitted from biomass burning in traditional Heated Kang in Northwest China

Humic-like substances (HULIS) in PM2.5 emitted from biomass burning (BB), including maize cob, wheat straw, maize straw, wood branch, and wood, in a traditional Heated Kang were investigated. The relative abundances, optical properties, chemical functional groups, and molecular components in HULIS were characterized using total organic carbon (TOC) analyzer, ultraviolet-visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FT-IR), and Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR/MS), respectively. The emission factors (EF) of HULIS-C (in term of carbon weight, EFHULIS-C) from BB were in the range of 0.83 to 5.17 g/kg fuel, with a mean value of 1.93 +/- 1.31 g/kg fuel. The HULIS-C accounted for 15.0-37.8% and 9.1-12.6% of fractions in organic carbon (OC) and PM2.5, respectively, suggesting that BB is an important emission source of atmospheric HULIS. The FT-IR spectra showed BB HULIS mainly contain O-containing, aliphatic C-H, and aromatic C-C functional groups. The presences of carboxyl group and O-H band demonstrated the uniqueness of maize straw and wood burning. Moreover, the higher ratio of CH3 and -CH2 groups could be used to distinguish the wood branches from the maize cob. CHO and CHON were much dominant in BB HULIS, which accounted for 44.6-47.6% and 50.1-54.2%, respectively, to the total molecular mass. The positive correlation between MAE(365) and AAE in term of number concentration of CHNO implied that the CHNO species could greatly influence on the light absorption properties of the BB HULIS. The CHO and S-containing compounds (i.e., CHNOS and CHOS, that is CHNOS+CHOS) showed weak light absorbances of the BB HULIS. The BB HULIS from maize straw had relatively high molecular weight in comparison to that in other BB emissions. The highest and lowest aromaticity were seen on the wood burning and maize cob, respectively. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the properties and components of humic-like substances (HULIS) in PM2.5 emitted from biomass burning, finding high proportions of HULIS in organic carbon and PM2.5, indicating biomass burning as a significant source of atmospheric HULIS. Different sources of HULIS can be distinguished using various analytical techniques.