Evolution of the chromophore aerosols and its driving factors in summertime Xi'an, Northwest China

• Published in: Chemosphere (Oxford) 2021-10, Vol.281, p.130838-130838, Article 130838
• Main Authors: Chen, Qingcai, Hua, Xiaoyu, Dyussenova, Ainur
• Format: Article
• Language: English
• Subjects: Aerosols; Atmospheric chromophores; Atmospheric photochemical reactions; Excitation-emission matrix (EEM) fluorescence
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.130838

Atmospheric chromophores have photo-sensitiveness that can participate in photochemical reactions, so they may have the potential to make an important contribution in organic aerosols aging. This study attempts to explain the effects of oxidation reaction and photochemical reaction on atmospheric chromophores. For this study, the summer period (higher sunshine intensity) was selected to observe the mechanisms by the online excitation emission matrix (EEM) fluorescence. The results showed that a lot of secondary organic aerosols were produced in the afternoon, but a large portion of them is non-chromophore. We observed that the secondary chromophores of highly-oxygenated humic-like substances (HULIS) were produced, which suggests a degradation product of less-oxygenated HULIS. The photochemical reaction and oxidation reaction were the important reactions that occur in the afternoon, which drives the oxidation state evolution of the atmospheric chromophores. Atmospheric oxidation processes are the mainly driving reaction for the transformation of atmospheric chromophore. The aged aerosol has a lower fluorescence index and a high degree of humification. It is speculated that the aerosol from night to morning is in the accumulation process dominated by local sources, and then it is mainly in the process of being gradually aged at noon and afternoon. This study will guide to better understand the atmospheric chemical processes of chromophore aerosols and provide guidance for the EEM approach to trace the aerosol aging in the atmosphere. [Display omitted] •The hourly variation of the chromophore compositions was studied in summertime.•The secondary chromophores of highly-oxygenated HULIS were produced.•A large portion of secondary organic aerosols is non-chromophore.•The changes of the chromophore compositions mainly come from the oxidation process.•The aged aerosol has a lower fluorescence index and a high degree of humification.