Preprints
https://doi.org/10.5194/acp-2020-1223
https://doi.org/10.5194/acp-2020-1223

  08 Dec 2020

08 Dec 2020

Review status: this preprint is currently under review for the journal ACP.

Photo-degradation of atmospheric chromophores: type conversion and changes in photochemical reactivity

Zhen Mu, Qingcai Chen, Lixin Zhang, Dongjie Guan, and Hao Li Zhen Mu et al.
  • School of Environmental Science and Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China

Abstract. Atmospheric chromophoric organic matters (COM) can participate in photochemical reactions because of the photosensitiveness, thus COM have a potential contribution to aerosols aging. The photochemical mechanism of atmospheric COM and the effect of photo-degradation on its photochemical reactivity are not fully understood. To address this knowledge gap, the characteristics of COM photo-degradation and the potential effects of COM photolysis on the photochemical reactivity are illustrated. COM are identified by excitation-emission matrices combined with parallel factor analysis. We confirm that both water-soluble and water-insoluble COM are photo-bleached, and an average 70 % of fluorescence intensities are lost after 7 days of light exposure. Furtherly, it is found that there is a transformation process of low oxidation to high oxidation HULIS. We propose that the high oxidation HULIS could be used to trace the aging degree of aerosols. In terms of photochemical reactivity, compared with before photolysis, the triplet state COM (3COM*) decrease slightly in ambient particle matter (ambient PM) samples and increase in primary organic aerosol (POA). However, the COM induce fewer singlet oxygen after photolysis. The photolysis and conversion of COM are the major cause of the change of photochemical activity. The result also enunciate that the photochemical reaction mechanisms and aerosol aging processes are relatively different in various aerosols. In conclusion, we demonstrated that the photo-degradation of COM not only change the chemical compositions, but also change the roles of the COM in the aerosol aging process.

Zhen Mu et al.

 
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Status: final response (author comments only)
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Zhen Mu et al.

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Short summary
Sunlight affects the life and chemical composition of atmospheric aerosols and thus alter air quality. This study demonstrated that the photo-aging process not only changed the chemical compositions of chromophoric aerosols, but also changed the roles of the chromophoric organic matter in the photo-aging process of aerosol. This study adds to our understanding of how sunlight affects chromophoric aerosol aging.
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