Direct field evidence of autocatalytic iodine release from atmospheric aerosol

Yee Jun Tham, Xu-Cheng He, Qinyi Li, Carlos A. Cuevas, Jiali Shen, Joni Kalliokoski, Chao Yan, Siddharth Iyer, Tuuli Lehmusjärvi, Sehyun Jang, Roseline C. Thakur, Lisa Beck, Deniz Kemppainen, Miska Olin, Nina Sarnela, Jyri Mikkilä, Jani Hakala, Marjan Marbouti, Lei Yao, Haiyan LiWei Huang, Yonghong Wang, Daniela Wimmer, Qiaozhi Zha, Juhani Virkanen, T. Gerard Spain, Simon O'Doherty, Tuija Jokinen, Federico Bianchi, Tuukka Petäjä, Douglas R. Worsnop, III Roy L. Mauldin, Jurgita Ovadnevaite, Darius Ceburnis, Norbert M. Maier, Markku Kulmala, Colin O’Dowd, Miikka Dal Maso, Alfonso Saiz-Lopez, Mikko Sipilä

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Reactive iodine plays a key role in determining the oxidation capacity, or cleansing capacity, of the atmosphere in addition to being implicated in the formation of new particles in the marine boundary layer. The postulation that heterogeneous cycling of reactive iodine on aerosols may significantly influence the lifetime of ozone in the troposphere not only remains poorly understood but also heretofore has never been observed or quantified in the field. Here, we report direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of interhalogen product species (i.e., iodine monochloride [ICl] and iodine monobromide [IBr]) in a midlatitude coastal environment. Significant levels of ICl and IBr with mean daily maxima of 4.3 and 3.0 parts per trillion by volume (1-min average), respectively, have been observed throughout the campaign. We show that the heterogeneous reaction of HOI on marine aerosol and subsequent production of iodine interhalogens are much faster than previously thought. These results indicate that the fast formation of iodine interhalogens, together with their rapid photolysis, results in more efficient recycling of atomic iodine than currently considered in models. Photolysis of the observed ICl and IBr leads to a 32% increase in the daytime average of atomic iodine production rate, thereby enhancing the average daytime iodine-catalyzed ozone loss rate by 10 to 20%. Our findings provide direct field evidence that the autocatalytic mechanism of iodine release from marine aerosol is important in the atmosphere and can have significant impacts on atmospheric oxidation capacity.
Original languageEnglish
Article numbere2009951118
Number of pages8
JournalProceedings of the National Academy of Sciences
Issue number4
Publication statusPublished - 26 Jan 2021
Publication typeA1 Journal article-refereed

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