Iodine, a reactive trace element in atmospheric chemistry, destroys ozone and nucleates particles. While iodic acid (HIO3) is widespread and forms particles more efficiently than sulfuric acid, its gas-phase formation mechanism remained unresolved. This study uses CLOUD atmospheric simulation chamber experiments to show that iodooxy hypoiodite (IOIO) efficiently converts to HIO3 via reactions with ozone and water. The derived reaction rate coefficients are supported by theory and explain field observations of daytime HIO3. This mechanism links iodine sources to particle formation and suggests a catalytic role for iodine in aerosol formation due to the readily reduced particulate iodate recycling iodine back into the gas phase.

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