Scientists at the Massachusetts Institute of Technology believe they have found the source of mysterious emissions of ozone-destroying chemicals that have popped up even after they were completely banned in 2010.
In 1987, 197 countries signed the Montreal Protocol, an agreement to phase out the production and consumption of substances that deplete the ozone layer of the atmosphere, which absorbs most of the ultraviolet radiation reaching the Earth from the sun.
The treaty mandated the complete stop of chlorofluorocarbon, or CFC, production by 2010.
CFCs were developed in the 1930s as chemicals for refrigeration and as spray can propellants. The chemicals are most commonly known by the brand name Freon.
CFCs drift up into the stratosphere, where they are broken up by ultraviolet radiation, releasing chlorine. Chlorine is able to destroy ozone molecules.
The Montreal Protocol was supposed to have stopped their production and use.
In 2012, scientists started detecting levels of CFC in the atmosphere, attributing it mostly to unauthorized production of the chemicals in China.
But the production was not enough to account for the levels the researchers were finding.
Finally, in 2020, they put the pieces together.
They found that equipment and materials produced before CFCs were fully banned were still in use today and contain large amounts of the chemicals.
The scientists said the equipment and materials are decaying, leading to enough CFC emissions to slow down the complete healing of the ozone layer by at least six years.
You can read the research here.