Ozone reduction began decades before the hole was discovered

The study, published in the journal Proceedings of the National Academy of Sciencesproves that the main agent of this first alteration was not represented by chlorofluorocarbons (CFCs)universally known as responsible for the phenomenon, but rather from carbon tetrachloride, a chemical compound used since the 1930s for dry cleaning and as a degreasing solvent.

The first author of the research, Jian Guan thus underlined the unexpected result: “What we learned from textbooks is that CFCs cause ozone depletion. It turned out that there was another compound that caused ozone depletion long before CFCs. It was a big surprise.”. The analysis also highlighted that the initial reduction occurred not over Antarctica, but in the upper stratosphere of the tropicsa region where the natural variability of the atmosphere is lower and it is therefore easier to distinguish a signal of anthropic origin from the so-called background “noise” of natural phenomena.

Dr. Solomon commented on the outcome of the work with particular amazement: “The fact that ozone depletion occurred as early as the late 1950s, much earlier than I would have ever imagined, left me literally stunned. This study shows how important it really is to continue monitoring so we can fully understand how the atmosphere responds and recovers.”.

Carbon tetrachloride, later restricted by the Montreal Protocol due to its toxicity and environmental impactwas identified thanks also to data from ice cores, which documented an increase in its concentrations already in the 1940s. The research highlights the need to continue atmospheric surveillance activities, despite the progress made towards healing the ozone layer: “We have made a great effort to get rid of these chemicals. Don’t we have an obligation to continue monitoring to make sure the atmosphere is responding the way we think it should?”, concluded Solomon.