2023-04-07 カリフォルニア大学校アーバイン校(UCI)
これまで、OHは光化学反応や酸化還元反応によって形成されると考えられてきたが、カリフォルニア大学アーバイン校の化学教授であるセルゲイ・ニズコロドフ氏を含む研究チームが、空気中の水滴表面の強い電界によってOHが生成されることを報告した。
この発見は、OHが反応して除去することができる大気汚染物質や温室効果ガスの除去メカニズムを再考させるものであると考えられている。今後は実際の大気中での実験が求められる。
＜関連情報＞
- https://news.uci.edu/2023/04/07/scientists-discover-a-way-earths-atmosphere-cleans-itself/
- https://www.pnas.org/doi/10.1073/pnas.2220228120
大気中の水滴界面におけるヒドロキシルラジカルの自発的な暗黒生成 Spontaneous dark formation of OH radicals at the interface of aqueous atmospheric droplets
Kangwei Li, Yunlong Guo, Sergey A. Nizkorodov , Yinon Rudich, Maria Angelaki, Xinke Wang, Taicheng An, Sebastien Perrier and Christian George
Proceedings of the National Academy of Sciences Published:April 3, 2023
DOI:https://doi.org/10.1073/pnas.2220228120
Significance
Recent studies suggest that reactions that do not usually occur in bulk solution can occur spontaneously in small water droplets, possibly due to the naturally formed electric field at the air–water interface. We explore the atmospheric significance of this process by demonstrating efficient spontaneous production of interfacial hydroxyl radicals (OH) from aqueous droplets under ambient conditions. This interfacial OH production does not involve precursors or catalysts, such as light or heat, and is likely the largest aqueous OH source in atmospheric droplets at nighttime. The ubiquity of aqueous aerosols and cloud droplets and their possibly strong OH-producing capability suggests that we have to rethink atmospheric multiphase oxidation chemistry.
Abstract
Hydroxyl radical (OH) is a key oxidant that triggers atmospheric oxidation chemistry in both gas and aqueous phases. The current understanding of its aqueous sources is mainly based on known bulk (photo)chemical processes, uptake from gaseous OH, or related to interfacial O3 and NO3 radical-driven chemistry. Here, we present experimental evidence that OH radicals are spontaneously produced at the air–water interface of aqueous droplets in the dark and the absence of known precursors, possibly due to the strong electric field that forms at such interfaces. The measured OH production rates in atmospherically relevant droplets are comparable to or significantly higher than those from known aqueous bulk sources, especially in the dark. As aqueous droplets are ubiquitous in the troposphere, this interfacial source of OH radicals should significantly impact atmospheric multiphase oxidation chemistry, with substantial implications on air quality, climate, and health.
