Light absorption properties and molecular compositions of water-soluble and methanol-soluble organic carbon emitted from wood pyrolysis and combustion

Ranran Zhao; Qixing Zhang; Xuezhe Xu; Wenjia Wang; Weixiong Zhao; Weijun Zhang; Yongming Zhang

doi:10.1016/j.scitotenv.2021.151136

Light absorption properties and molecular compositions of water-soluble and methanol-soluble organic carbon emitted from wood pyrolysis and combustion

Sci Total Environ. 2022 Feb 25:809:151136. doi: 10.1016/j.scitotenv.2021.151136. Epub 2021 Oct 22.

Authors

Ranran Zhao¹, Qixing Zhang², Xuezhe Xu³, Wenjia Wang¹, Weixiong Zhao⁴, Weijun Zhang⁵, Yongming Zhang¹

Affiliations

¹ State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, Anhui, China.
² State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, Anhui, China. Electronic address: qixing@ustc.edu.cn.
³ Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, Anhui, China. Electronic address: xzxu@aiofm.cac.cn.
⁴ Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, Anhui, China.
⁵ Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, Anhui, China; University of Science and Technology of China, Hefei 230026, Anhui, China.

PMID: 34695472
DOI: 10.1016/j.scitotenv.2021.151136

Abstract

Organic carbon (OC) emitted from biomass burning (BB) plays an important role in the global radiation budget. In this work, primary OC emitted from wood pyrolysis and combustion under nitrogen (N₂) and air conditions in a tube furnace was investigated. The absorption spectra, chemical functional groups, and molecular compositions of OC were analyzed using UV-Vis-NIR spectrophotometer, Fourier transform infrared spectroscopy (FTIR), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), respectively. The light absorption properties showed that the mass absorption efficiency at 365 nm (MAE₃₆₅) of methanol-soluble OC (MSOC) is 3.1-3.8 times higher than that of water-soluble OC (WSOC). Moreover, the MAE₃₆₅ values derived from the N₂ pyrolysis atmosphere are higher than that from the air atmosphere for both MSOC and WSOC. These results indicated that OC extracted by methanol has higher light absorption, especially for the OC emitted from the N₂ pyrolysis atmosphere. Although the FTIR spectra showed identical functional groups for the OC from the air and N₂ conditions, molecular compositions from the FT-ICR MS analysis presented significant differences. The molecular weight (MW), double bonds equivalent (DBE), DBE/C, and modified aromaticity index (AI_mod) of extracted OC showed higher values in MSOC than those in WSOC, and higher values under the N₂ atmosphere than those under the air atmosphere. In addition, MAE₃₆₅ showed positive correlations with MW (r = 0.94), DBE (r = 0.88), DBE/C (r = 0.96), and AI_mod (r = 0.97), whereas negative correlations with H/C (r = -0.97), O/C (r = -0.90), N/C (r = -0.88), and S/C (r = -0.93). These results indicated that molecules with larger MW and a high level of unsaturation and aromaticity present higher light absorption, while molecules with high elemental ratios of H/C, O/C, N/C, and S/C are adverse to light absorption.

Keywords: Light absorption; Molecular compositions; Wood pyrolysis and combustion.

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Carbon* / analysis
Environmental Monitoring
Methanol
Particulate Matter / analysis
Pyrolysis
Water
Wood / chemistry

Substances

Aerosols
Air Pollutants
Particulate Matter
Water
Carbon
Methanol