Photochemical evolution of the molecular composition of dissolved organic carbon and dissolved brown carbon from wood smoldering

Ranran Zhao; Weixiong Zhao; Yong Dai; Jiacheng Zhou; Xuezhe Xu; Feng Wang; Qixing Zhang; Yongming Zhang; Weijun Zhang

Environment International (Apr 2024)

Photochemical evolution of the molecular composition of dissolved organic carbon and dissolved brown carbon from wood smoldering

Ranran Zhao,
Weixiong Zhao,
Yong Dai,
Jiacheng Zhou,
Xuezhe Xu,
Feng Wang,
Qixing Zhang,
Yongming Zhang,
Weijun Zhang

Affiliations

Ranran Zhao: School of Chemistry and Chemical Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu, China; School of Emergency Management and Safety Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu, China; Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China; Corresponding authors at: School of Chemistry and Chemical Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu, China (R. Zhao).
Weixiong Zhao: Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China; School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, Anhui, China
Yong Dai: School of Chemistry and Chemical Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu, China; School of Emergency Management and Safety Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu, China
Jiacheng Zhou: Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China
Xuezhe Xu: Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China
Feng Wang: School of Environmental Science and Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu, China
Qixing Zhang: State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, Anhui, China; Corresponding authors at: School of Chemistry and Chemical Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu, China (R. Zhao).
Yongming Zhang: State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, Anhui, China
Weijun Zhang: Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei 230031, Anhui, China; School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, Anhui, China

Journal volume & issue: Vol. 186
p. 108629

Abstract

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Recently, extreme wildfires occur frequently around the world and emit substantial brown carbon (BrC) into the atmosphere, whereas the molecular compositions and photochemical evolution of BrC remain poorly understood. In this work, primary smoke aerosols were generated from wood smoldering, and secondary smoke aerosols were formed by the OH radical photooxidation in an oxidation flow reactor, where both primary and secondary smoke samples were collected on filters. After solvent extraction of filter samples, the molecular composition of dissolved organic carbon (DOC) was determined by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). The molecular composition of dissolved BrC was obtained based on the constraints of DOC formulae. The proportion of dissolved BrC fractions accounted for approximately 1/3–1/2 molecular formulae of DOC. The molecular characteristics of dissolved BrC showed higher levels of carbon oxidation state, double bond equivalents, and modified aromaticity index than those of DOC, indicating that dissolved BrC fractions were a class of organic structures with relatively higher oxidation state, unsaturated and aromatic degree in DOC fractions. The comparative analysis suggested that aliphatic and olefinic structures dominated DOC fractions (contributing to 70.1%-76.9%), while olefinic, aromatic, and condensed aromatic structures dominated dissolved BrC fractions (contributing to 97.5%-99.9%). It is worth noting that dissolved BrC fractions only contained carboxylic-rich alicyclic molecules (CRAMs)-like structures, unsaturated hydrocarbons, aromatic structures, and highly oxygenated compounds. CRAMs-like structures were the most abundant species in both DOC and dissolved BrC fractions. Nevertheless, the specific molecular characteristics for DOC and dissolved BrC fractions varied with subgroups after aging. The results highlight the similarities and differences in the molecular compositions and characteristics of DOC and dissolved BrC fractions with aging. This work will provide insights into understanding the molecular composition of DOC and dissolved BrC in smoke.

Published in Environment International

ISSN: 0160-4120 (Print)
Publisher: Elsevier
Country of publisher: United Kingdom
LCC subjects: Geography. Anthropology. Recreation: Environmental sciences
Website: https://www.journals.elsevier.com/environment-international

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