Measurements in the central Arctic show that iodine forms particles that grow to cloud condensation nuclei.

New atmospheric particle formation is one is the largest uncertainties in climate simulations. The source of new particles in the central Arctic has remained elusive since the first aerosol measurements in the Arctic in 1991.

In this study, we report observation that show iodine to be the main source of new particles in the central Arctic. The observations were made during an expedition to the central Arctic in 2018 (Microbiology-Ocean-Cloud-Coupling in the High Arctic, MOCCHA) onboard the Swedish icebreaker Oden. The results not only highlight the remarkable capacity that iodine oxides have to form new particles but also show that these new particles grow to cloud condensation nuclei (CCN) sizes, thereby establishing a direct link between iodine emissions and CCN in the remote region.

This new mechanism is climatically relevant since the global iodine emissions have tripled in the last 70 years following the increase in anthropogenic ozone pollution (, and it is expected that this increase will continue in the future (

Andrea Baccarini, Linn Karlsson, Josef Dommen, Patrick Duplessis, Jutta Vüllers, Ian M. Brooks, Alfonso Saiz-Lopez, Matthew Salter, Michael Tjernström, Urs Baltensperger, Paul Zieger, and Julia Schmale. Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions. Nature Communications. DOI: