Water-soluble organic matter with various polarities in PM2.5 over Xi'an, China: Abundance, functional groups, and light absorption--颗粒学报PARTICUOLOGY

Xueting Yang^a, Shasha Huang^a, Dan Li^a, Hongmei Xu^a *, Yaling Zeng^b, Liu Yang^a, Diwei Wang^a, Ningning Zhang^c, Junji Cao^c, Zhenxing Shen^{a c *}

a Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an, 710049, China
b School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China
c State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710049, China

10.1016/j.partic.2023.07.005

Volume 84, January 2024, Pages 281-289

Received 29 May 2023, Revised 5 July 2023, Accepted 8 July 2023, Available online 22 July 2023, Version of Record 29 July 2023.

E-mail: xuhongmei@xjtu.edu.cn; zxshen@mail.xjtu.edu.cn

Highlights

• HULIS-n is the main component in winter in contrast to HULIS-a in summer.

• Neutral HULIS plays a major role in light absorption of WSOC.

• Aromatic content has a crucial effect on light absorption of WSOC.

• Winter HULIS has higher molecular weight and light absorption than summer.

Abstract

Humic-like substances (HULIS) are a major component of brown carbon and consequently play a major role in climate change. In this study, 70 PM_2.5 samples were collected from Xi'an in winter 2019 and summer 2020. Neutral HULIS (HULIS-n), acidic HULIS (HULIS-a), and high-polarity water-soluble organic compounds (HP–WSOC) were analyzed to determine their carbon concentrations and measure their ultraviolet–visible absorption and infrared spectra. Of the three components, HULIS-n had the highest carbon content in both winter (3.29 ± 1.45 μg m⁻³) and in summer (1.38 ± 1.10 μg m⁻³). The semiquantitative results for the functional groups revealed that HP-WSOC was rich in carboxylic acids and had high aromaticity in winter, whereas HULIS-n was rich in carboxylic acids in summer. Moreover, HULIS-a was richer in nitrate esters and saturated aliphatic hydrocarbons in summer than in winter. The results for specific ultraviolet absorbance (SUVA) and E₂₅₀/E₃₆₅ revealed that HULIS had higher molecular weight and aromaticity in winter than in summer. HULIS-n dominated in the total light absorption of HULIS + HP-WSOC in both winter (73.08%) and summer (48.57%). Overall, the results on the carbon content, optical properties, and functional groups of WSOCs with differing polarity can improve understanding of environmental and climatic effects.

Graphical abstract

Keywords

Humic-like substances (HULIS); Aromaticity; Fourier-transform infrared (FTIR) spectroscopy; Light absorbance

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