The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source
Henning Finkenzeller, Siddharth Iyer, Xu‐Cheng He, Mario Simon, Theodore K. Koenig, Christopher F. Lee, Rashid R. Valiev, Victoria Hofbauer, A. Amorim, Rima Baalbaki, Andrea Baccarini, Lisa Beck, David M. Bell, Lucía Caudillo, Dexian Chen, Randall Chiu, Biwu Chu, Lubna Dada, Jonathan Duplissy, Martin Heinritzi, Deniz Kemppainen, Changhyuk Kim, Jordan Krechmer, Andreas Kürten, А. Н. Квашнин, Houssni Lamkaddam, Chuan Ping Lee, Katrianne Lehtipalo, Zijun Li, В. С. Махмутов, 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 Wang, Mingyi Wang, Yonghong Wang, Stefan K. Weber, Wei Nie, Yusheng Wu, Mao Xiao, Qing Ye, Marcel Zauner-Wieczorek, Armin Hansel, Urs Baltensperger, J. Brioude, Joachim Curtius, Neil M. Donahue, Imad El Haddad, Richard C. Flagan, Markku Kulmala, J. Kirkby, Mikko Sipilä, Douglas R. Worsnop, Theo Kurtén, Matti Rissanen, Rainer Volkamer
Abstract
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 O 3 surface concentrations. Although iodic acid (HIO 3 ) 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 HIO 3 via reactions (R1) IOIO + O 3 → IOIO 4 and (R2) IOIO 4 + H 2 O → HIO 3 + HOI + (1) O 2 . The laboratory-derived reaction rate coefficients are corroborated by theory and shown to explain field observations of daytime HIO 3 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.