The ozone layer was recovering at a good pace, and one of the main reasons for that recovery is that the world agreed 30 years ago to stop producing a compound called CFC-11. Now, a group of scientists has just discovered that someone has decided to cheat.

If the ozone layer is currently in a better state than in the 2000s, it is thanks to the Montreal Protocol. In 1987, the 193 member countries of the United Nations and some states not attached to this organization signed a historic agreement to reduce the pollutants that were literally eating one of the shields that our planet has to defend against ultraviolet radiation.

Among the banned substances was CFC-11, a compound widely used for the production of air conditioning, aerosols and polystyrene foam. In 2010, and thanks to that agreement, production ceased. The concentration of this pollutant has fallen by 15% since its historical peak in 1993, and the forecasts of recovery of the ozone layer were good … until now.

Scientists from the National Oceanic and Atmospheric Administration of the United States (NOAA) have found something surprising. For the first time in 18 years, concentrations of CFC-11 have risen again. Between 2014 and 2016, the emissions of this compound have increased by no less than 25% above the average from 2002 to 2012.

The data was so rare that the chemist Stephen Montzka and his team decided to make simulations to rule out that the measurements had been affected by some capricious current that had accumulated the compound. When they found that this was not the case, they compared the figures with those of accidental emissions of the compound. It is normal, for example, that during the demolition of old buildings, concentrations of CFC-11 trapped in old air conditioning systems are emitted. The problem is that the figures do not match. The only expiation is that someone in a country has returned to manufacture CFC-11 and emit it into the atmosphere despite being banned for decades.

CFC-11 is not the only pollutant emitted. Montzka and his team have detected other compounds equally harmful to our atmosphere. The aim of the study is not to target any specific country, but researchers have tracked the origin of the emissions to somewhere in Asia, probably in China, Mongolia or the two Koreas.

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