The formation of clouds and their properties in the central Arctic Ocean are highly sensitive to the availability of cloud condensation nuclei (CCN). This study reveals that all observed new particle formation (NPF) events during the Arctic Ocean 2018 expedition were driven by iodic acid (HIO3), with minimal contribution from sulfuric acid. HIO3 primarily explains the growth of ultrafine particles (UFP), and its concentration significantly increases from summer to autumn, potentially linked to ocean freeze-up and rising ozone levels. This results in a tenfold increase in UFP concentration in autumn. Measurements suggest that particles smaller than 30 nm can activate as CCN, indicating iodine NPF's potential impact on Arctic Ocean cloud properties.

Andrea Baccarini, Linn Karlsson, Josef Dommen, Patrick Duplessis, Jutta Vüllers, Ian M. Brooks, Alfonso Saiz-Lopez, Matthew Salter, Michael Tjernström, Urs Baltensperger, Paul Zieger, Julia Schmale