美国科罗拉多大学博尔德分校Kirkby, Jasper团队报道了碘酸作为大气气溶胶源的气相形成机理。相关研究成果发布在2022年11月14日出版的《自然—化学》。

碘是大气化学中的一种活性微量元素，可破坏臭氧并使粒子成核。自1950年以来，碘排放量增加了三倍，预计随着O₃表面浓度的升高，碘排放将继续增加。尽管碘酸（HIO₃）广泛存在并且比硫酸更有效地形成颗粒，但其气相形成机制仍未解决。

该文中，在以大气相关速率产生碘自由基的CLOUD大气模拟室实验中，研究表明碘氧基次碘酸盐IOIO通过反应（R1）IOIO+O₃有效转化为HIO₃→IOIO₄和

（R2）IOIO₄+H₂O→HIO₃+HOI+（1）O₂。实验室导出的反应速率系数得到了理论的证实，并证明可以解释在遥远的自由对流层较低的地区白天HIO₃的现场观测。该机制提供了碘源和颗粒形成之间缺失的联系。由于微粒碘酸盐很容易被还原，使碘再循环回气相中，结果表明碘在气溶胶形成中起催化作用。

附：英文原文

Title: The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source

Author: Finkenzeller, Henning, Iyer, Siddharth, He, Xu-Cheng, Simon, Mario, Koenig, Theodore K., Lee, Christopher F., Valiev, Rashid, Hofbauer, Victoria, Amorim, Antonio, Baalbaki, Rima, Baccarini, Andrea, Beck, Lisa, Bell, David M., Caudillo, Luca, Chen, Dexian, Chiu, Randall, Chu, Biwu, Dada, Lubna, Duplissy, Jonathan, Heinritzi, Martin, Kemppainen, Deniz, Kim, Changhyuk, Krechmer, Jordan, Krten, Andreas, Kvashnin, Alexandr, Lamkaddam, Houssni, Lee, Chuan Ping, Lehtipalo, Katrianne, Li, Zijun, Makhmutov, Vladimir, Manninen, Hanna E., Marie, Guillaume, Marten, Ruby, Mauldin, Roy L., Mentler, Bernhard, Mller, Tatjana, Petj, Tuukka, Philippov, Maxim, Ranjithkumar, Ananth, Rrup, Birte, Shen, Jiali, Stolzenburg, Dominik, Tauber, Christian, Tham, Yee Jun, Tom, Antnio, Vazquez-Pufleau, Miguel, Wagner, Andrea C., Wang, Dongyu S., Wang, Mingyi, Wang, Yonghong, Weber, Stefan K., Nie, Wei, Wu, Yusheng, Xiao, Mao, Ye, Qing, Zauner-Wieczorek, Marcel, Hansel, Armin, Baltensperger, Urs, Brioude, Jrome, Curtius, Joachim, Donahue, Neil M., Haddad, Imad El, Flagan, Richard C., Kulmala, Markku, Kirkby, Jasper

Issue&Volume: 2022-11-14

Abstract: Iodine is a reactive trace element in atmospheric chemistry that destroys ozone and nucleates particles. Iodine emissions have tripled since 1950 and are projected to keep increasing with rising O3 surface concentrations. Although iodic acid (HIO3) is widespread and forms particles more efficiently than sulfuric acid, its gas-phase formation mechanism remains unresolved. Here, in CLOUD atmospheric simulation chamber experiments that generate iodine radicals at atmospherically relevant rates, we show that iodooxy hypoiodite, IOIO, is efficiently converted into HIO3 via reactions (R1) IOIO+O3→IOIO4 and (R2) IOIO4+H2O→HIO3+HOI+(1)O2. The laboratory-derived reaction rate coefficients are corroborated by theory and shown to explain field observations of daytime HIO3 in the remote lower free troposphere. The mechanism provides a missing link between iodine sources and particle formation. Because particulate iodate is readily reduced, recycling iodine back into the gas phase, our results suggest a catalytic role of iodine in aerosol formation.

DOI: 10.1038/s41557-022-01067-z

Source: https://www.nature.com/articles/s41557-022-01067-z