Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere

The main nucleating vapor in the atmosphere is thought to be sulfuric acid (H₂SO₄), stabilized by ammonia (NH₃). However, in marine and polar regions, NH₃ is generally low, and H₂SO₄ is frequently found together with iodine oxoacids [HIOₓ, i.e., iodic acid (HIO₃) and iodous acid (HIO₂)]. In experiments performed with the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we investigated the interplay of H₂SO₄and HIOₓ during atmospheric particle nucleation. We found that HIOₓ greatly enhances H₂SO₄(-NH₃) nucleation through two different interactions. First, HIO₃ strongly binds with H₂SO₄ in charged clusters so they drive particle nucleation synergistically. Second, HIO₂ substitutes for NH₃ , forming strongly bound H₂SO₄-HIO₂ acid-base pairs in molecular clusters. Global observations imply that HIO x is enhancing H₂SO₄(-NH₃) nucleation rates 10- to 10,000-fold in marine and polar regions. ; © 2023 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. This is an article distributed under the terms of the Science Journals Default License. ; We thank CERN for supporting CLOUD with important technical and financial resources and for providing a particle beam from the CERN Proton Synchrotron. We thank the CSC IT Center for Science in Espoo, Finland, for computing time. ; This work was supported by Research Council of Finland ACCC Flagship nos. 337549 and 337552; Research Council of Finland professorship (302958); Research Council of Finland Centre of Excellence nos. 346371, 346372, and 346373; Research Council of Finland project nos. 335844, 334514, 345125, 325656, 316114, 314798, 325647, 353836, 341349, 346372, 296628, and 349659; European Research Council (ERC) project nos. 742206, 714621, 616075, and 101002728; Marie Skłodowska-Curie grant agreement nos. 316662, 701647, 895875, and 764991; National Natural Science Foundation of China grant nos. 42175118 and ...