Observations in the central Arctic indicate that iodine chemistry plays a major role in controlling tropospheric ozone over the pan-Arctic region.

This study reports halogen oxide measurements in the central Arctic Ocean carried out during the ship-based Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The observations were made by the IQFR MAX-DOAS instrument as part of an international collaboration during the MOSAiC expedition, the largest scientific expedition to the Arctic in history, conducted on the German research icebreaker Polarsten, which set sail from Norway, to spend a year drifting through the Arctic Ocean - trapped in the ice. The goal of the MOSAic expedition was to take the closest look ever at the Arctic as the epicenter of global warming and to gain fundamental insights that are key to better understand global climate change. Hundreds of researchers from 20 countries were involved in this expedition. Surface ozone depletion events in the Arctic, when ozone concentrations drop to nearly zero, have been reported for decades. Until now, these surface depletion events were thought to occur mainly because of catalytic depletion by bromine while the effect of iodine was not understood or poorly constrained. The observations now show the ubiquitous presence of active iodine in large areas of the central Arctic during the sunlit period. An atmospheric model constrained with the observations show that the reactions between iodine and ozone substantially enhance surface ozone depletion in the Arctic. Indeed, we calculate that iodine is the second highest contributor to ozone loss over the sunlit period, after photolysis-initiated loss and ahead of bromine. This collective effort during MOSAiC sheds new light on the drivers of Arctic ozone destruction. Nuria Benavent, Anoop S. Mahajan, Qinyi Li, Carlos A. Cuevas, Julia Schmale, Hélène Angot, Tuija Jokinen, Lauriane L. J. Quéléver, Anne-Marlene Blechschmidt, Bianca Zilker, Andreas Richter, Jesús A. Serna, David Garcia-Nieto, Rafael P. Fernandez, Henrik Skov, Adela Dumitrascu, Patric Simões Pereira, Katarina Abrahamsson, Silvia Bucci, Marina Duetsch, Andreas Stohl, Ivo Beck, Tiia Laurila, Byron Blomquist, Dean Howard, Stephen Archer, Ludovic Bariteau, Detlev Helmig, Jacques Hueber, Hans-Werner Jacobi, Kevin Posman, Lubna Dada, Kaspar R. Daellenbach and Alfonso Saiz-Lopez. Substantial contribution of iodine to Arctic ozone destruction. Nature Geoscience. DOI: 10.1038/s41561-022-01018-w Photo credit: Michael Gutsch