Iodine, an unexpected great destroyer of ozone in the Arctic

The destruction of ozone in the stratosphere (between 15 and 50 km altitude) is well known. The main causes are the chlorofluorocarbons emitted by human activities. These are chemical substances associated with the use of refrigeration systems, insulating foams or air conditioners, among others, that weaken the mantle of the stratosphere, where 90% of the ozone present in the atmosphere is concentrated.

However, short periods of time have also been observed in which the destruction of ozone reduces its concentration to a minimum in the troposphere, located between 0 and 10 kilometers above the earth’s surface, in the part located above the regions poles, and where 10% of atmospheric ozone is concentrated. “Until now, it was assumed that these episodes of surface ozone destruction were mainly caused by chemical reactions of a single type of halogen compound, bromine, which is emitted into the atmosphere from the ice surface of the polar regions,” explains Alfonso. Saiz-López, from the Rocasolano Institute of Physical Chemistry (IQFR), dependent on the Higher Council for Scientific Research (CSIC) in Spain, and coordinator of a study in which researchers from various countries have participated.

Aboard the Polarsten icebreaker, which was stranded in the Arctic Ocean ice for a year, 600 researchers from 19 countries rotated to analyze environmental changes related to global warming, as part of the Mosaic mission (Multidisciplinary drifting observatory for the study of Arctic climate), the largest scientific expedition to the Arctic in history. Researchers from the Rocasolano Physical Chemistry Institute took part in this mission,

Unlike bromine, the effect of another halogen, iodine, is often not included in environmental models due to uncertainty about its presence in the arctic atmosphere. However, observations made on the Mosaic expedition during 2020 revealed the presence of iodine in a wide region of the Arctic Ocean. Using an atmospheric model, researchers have shown that catalytic reactions with iodine represent the second leading cause of ozone destruction. It would be ahead of that caused by the reaction of ozone with bromine and behind the main cause of ozone reduction in the troposphere: photolysis, that is, the destruction of an ozone molecule by ultraviolet-visible radiation. The results presented by the researchers question decades of the established paradigm about the causes of the destruction of surface ozone in the Arctic region.

The Polarsten ship. (Photo: Alfred-Wegener-Institut / Mario Hoppmann. CC BY 4.0)

The study also highlights that ocean emissions of iodine are increasing due to anthropogenic pollution and the retreat of the Arctic ice pack, as a result of global warming. Nuria Benavent, IQFR researcher and first author of the work, underlines: “Our results indicate that iodine chemistry could play a gradually more important role in the destruction of Arctic ozone throughout this century, and should be considered in models of the Arctic. climate for a correct quantification of the concentration of ozone in the Arctic atmosphere”.

The study is titled “Substantial contribution of iodine to Arctic ozone destruction.” And it has been published in the academic journal Nature Geoscience. (Source: Alejandro Parrilla García / CSIC)