Role of iodine oxoacids in atmospheric aerosol nucleation

8 pags., 5 figs.
Iodic acid (HIO) is known to form aerosol particles in coastal marine regions, but predicted nucleation and growth rates are lacking. Using the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we find that the nucleation rates of HIOparticles are rapid, even exceeding sulfuric acid-ammonia rates under similar conditions. We also find that ion-induced nucleation involves IOand the sequential addition of HIOand that it proceeds at the kinetic limit below +10°C. In contrast, neutral nucleation involves the repeated sequential addition of iodous acid (HIO) followed by HIO, showing that HIOplays a key stabilizing role. Freshly formed particles are composed almost entirely of HIO, which drives rapid particle growth at the kinetic limit. Our measurements indicate that iodine oxoacid particle formation can compete with sulfuric acid in pristine regions of the atmosphere.
We thank the European Organization for Nuclear Research (CERN) for supporting CLOUD with important technical and financial resources and for providing a particle beam from the CERN Proton Synchrotron. This research has received support from the Academy of Finland (projects 316114, 307331, 310682, 266388, 3282290, 306853, 296628, 229574, 333397, 326948, and 1325656); the European Research Council (projects 692891, 616075, 764991, 316662, 742206, and 714621); CSC – Finnish IT center; the EC Seventh Framework Programme and the EU H2020 programme Marie Skłodowska Curie ITN “CLOUD-TRAIN” (316662) and “CLOUD-MOTION” (764991); Austrian Science Fund (FWF) (J3951-N36 and P27295-N20); the Swiss National Science Foundation (20FI20_159851, 200021_169090, 200020_172602, and 20FI20_172622); the U.S. National Science Foundation (grants AGS1447056, AGS1439551, AGS1801574, AGS1620530, AGS1801897, AGS153128, AGS1649147, AGS1801280, AGS1602086, and AGS1801329); MSCA H2020 COFUND-FP-CERN2014 fellowship (665779); German Federal Ministry of Education and Research: CLOUD-16 (01LK1601A); Portuguese Foundation for Science and Technology (CERN/FIS-COM/0014/2017); Academy of Finland Centre of Excellence in Atmospheric Sciences (grant 272041); European Regional Development Fund (project MOBTT42); Jiangsu Collaborative Innovation Center for Climate Change; Yangtze River Delta Atmosphere and Earth System Science National Observation and Research Station; Estonian Research Council (project PRG714); Hungarian National Research, Development and Innovation Office (K116788 and K132254); NASA Graduate Fellowship (NASA-NNX16AP36H); and ACTRIS 2TNA H2020 OCTAVE (654109).