Measurement report: Changes in light absorption and molecular composition of water-soluble humic-like substances during a winter haze bloom-decay process in Guangzhou, China

[摘要] Water-soluble humic-like substances (HULIS) absorb light in near-UV andvisible wavelengths and exert significant influence on the atmosphericenvironment and climate. However, knowledge on HULIS evolution during hazebloom-decay process is limited. Herein, PM 2.5 samples wereobtained during a winter haze event in Guangzhou, China, and the lightabsorption and molecular composition of HULIS were investigated by UV–Visspectrophotometry and ultrahigh-resolution mass spectrometry. Compared withHULIS on clean days, the absorption coefficients (Abs 365 ) of HULIS onhaze days were significantly higher but the mass absorption efficiencies(MAE 365 ) were relatively low, suggesting diverse and dynamicabsorption properties of HULIS during haze episodes. The CHO and CHONcompounds were the most abundant components in HULIS, followed by CHOS,CHONS, and CHN. Haze HULIS presented comparatively high molecular weight; alower aromaticity index (AI mod ); and higher O / C w , O / N w , and O / S w ratios, indicating that HULIS fractions undergo relatively highoxidation during haze days compared to clean days. Moreover, CHON and CHO compoundswith high AI mod were the major potential chromophores in HULIS andsignificantly contributed to HULIS light absorption. It is worth noting thatthe proportions of these chromophores decreased during haze events,mainly owing to their higher oxidation during haze episodes. Besides,accumulated contribution of organic compounds emitted from vehicles andformed from reactions of biogenic volatile organic compounds (bio-VOCs) also diluted light-absorbing compounds inhaze HULIS. These findings help us to understand HULIS evolution during hazebloom-decay processes in the subtropic region of China.

[学科分类] 医学（综合）