1. Seasonal and diurnal variation of PM2.5 HULIS over Xi'an in Northwest China: Optical properties, chemical functional group, and relationship with reactive oxygen species (ROS).
- Author
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Zhang, Tian, Huang, Shasha, Wang, Diwei, Sun, Jian, Zhang, Qian, Xu, Hongmei, Hang Ho, Steven Sai, Cao, Junji, and Shen, Zhenxing
- Subjects
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SEASONS , *REACTIVE oxygen species , *OPTICAL properties , *FUNCTIONAL groups , *CARBOXYLIC acids , *LIGHT absorbance - Abstract
Humic-like substances (HULIS) in particulate matter (PM) play critical roles in the atmospheric changes in our environment. In this study, high time resolution PM 2.5 samples were collected to insight the abundances, spectroscopic characters, chemical groups, and oxidative potential of HULIS in Xi'an, China. The average mass concentrations of HULIS in term of carbon (HULIS-C) was 11.55 ± 5.85 and 8.28 ± 2.23 μg C m−3 in winter and summer, respectively. The diurnal variations of HULIS displayed three peaks (03:00–07:00, 10:00–14:00, and 18:00–21:00 LT) in winter, but a single peak (08:00–12:00 LT) in summer. The optical parameters show obvious difference between winter and summer. Fourier Transform infrared (FT-IR) spectra revealed that the HULIS mainly consisted of aliphatic chains, aromatic rings, and carboxylic groups. The FT-IR spectra proved that the aromatic compounds and carboxylic acids dominated the diurnal variation in winter, while carboxylic acids were responsible for that in summer. The normalized oxidative potential of HULIS exhibited an inverse trend with the HULIS-C concentration measured by the DCFH assay. The diurnal reactive oxygen species (ROS) productions from HULIS presents three valleys (03:00–07:00, 10:00–14:00, and 18:00–21:00 LT) in winter but only a single valley (08:00–12:00 LT) in summer. In addition, a positive correlation (R2 ≈ 0.6, p ＜0.01) between the oxidative potential and specific ultraviolet absorbance at a wavelength of 254 nm (SUVA 254) in winter suggested that the oxidative power of HULIS could be more related to the compounds with high light absorbance, high aromaticity, and molecular weight. The results of this study offer more solid knowledge on the spectral and chemical characteristics and oxidative potential of the HULIS in PM 2.5 of the typical city in northwest China. [Display omitted] • Oxidative potential of HULIS decreased with the increase of HULIS-C concentration. • Aromatic compounds and carboxylic acids dominated the diurnal variation in winter. • Carboxylic acids were responsible for the diurnal variation in summer. • The oxidative power of winter HULIS was related to high light-absorbance and high-aromaticity compounds. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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