Laboratory experiments show the transition between iodine precursor gas phase molecules and molecular clusters of growing size.

New atmospheric particle formation is one is the largest uncertainties in climate simulations. Although it is known for the last two decades that iodine oxides form new particles in the lower atmosphere, its inclusion in atmospheric models is hindered by a lack of understanding of the first steps of the photochemical gas-to-particle conversion mechanism.

In this study, we combine laboratory experiments, theory and modelling to reveal the mechanism that connects oceanic iodine emissions and atmospheric particle formation. The results show that the gas to particle conversion proceed primarily via clustering of iodine oxides and that the composition of nanometric particles (iodic acid) is due to the processing of these clusters in the presence of atmospheric humidity. This study highlights the remarkable capacity that iodine oxides have to form new particles.

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, thereby pointing to a more prominent role of iodine particle formation in the future atmosphere.

Juan Carlos Gómez Martín, Thomas R. Lewis, Mark A. Blitz, John M.C. Plane, Manoj Kumar, Joseph S. Francisco and Alfonso Saiz-Lopez. A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxidesNature Communications.  DOI: 10.1038/s41467-020-18252-8