Investigation of the Acid-Mediated Photosensitized Reactions of Amphiphilic α‑Keto Acids at the Air–Water Interface Using Field-Induced Droplet Ionization Mass Spectrometry

• Published in: Journal of the American Society for Mass Spectrometry 2021-09, Vol.32 (9), p.2306-2312
• Main Authors: Gong, Chu, Zhao, Yutao, Zhang, Dongmei, Wang, Jie, Mu, Chaonan, Wang, Wei, Zhu, Shoufei, Zhang, Xinxing
• Format: Article
• Language: English
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1021/jasms.1c00022

The photochemistry of α-keto acids has been of great interest due to its implications in atmospheric and prebiotic chemistries. α-Keto acids with long alkyl chains are amphiphilic in nature, and they tend to partition at the air–water interface of atmospheric water droplets and add to the complexity of the chemistries therein. The air–water interface is a unique environment that plays a vital role in overall atmospheric processes. However, existing studies mostly focus on the photochemistry of α-keto acids in the bulk solution and neglect the reactions that occur at the interface. In this study, using the field-induced droplet ionization mass spectrometry methodology that is capable of selectively sampling amphiphilic molecules that reside at the air–water interface, we show that the acid-mediated photochemistry of 2-oxooctanoic acid and 2-oxoheptoic acid is highly different from those of previously reported reactions in the bulk and contributes to the formation of humic-like substances (HULIS). This work emphasizes the uniqueness of the photochemistry at the air–water interface. We anticipate that studies of atmosphere-relevant photochemistry at the air–water interface will be an avenue rich with opportunities.