The problem was that the industry began to use massively the chemical compounds, actively reacting with ozone and destroying it.
By the way, there is a version that studies on the harm caused by the same freons to the ozone layer were conducted with the massive financial support of commercial companies that created an alternative to chlorofluorocarbons
After the adoption of a number of key decisions to ban the use of chlorofluorocarbons in industry, the question arose as to how the impact of such a ban could be assessed. The fact is that the ozone layer itself is quite dynamic. There are seasonal fluctuations and perennial cycles.
Ozone generation is an extremely slow process. So slow that people who claimed to restore the ozone layer were seen by many as scammers.
The decision was proposed by NASA. The organization launched the satellite "Aurora", which is intended, first of all, to track the chemical composition of the atmosphere. Now two researchers from NASA, the Goddard Space Flight Center, are studying satellite data for a long period of several years. A huge amount of information has already been processed, so you can draw certain conclusions about the dynamics of the ozone layer.
After carrying out all the necessary research, the scientists concluded: All this is a proof of the effectiveness of regulators in the Montreal Protocol - the amount of chlorobutyls in the atmosphere over the Antarctic is decreasing, and the concentration of ozone is increasing.