Scientists have identified four new man-made gases that are contributing to the depletion of the ozone layer.
Two of the gases are accumulating at a rate that is causing concern among researchers.
Worries over the growing ozone hole have seen the production of chlorofluorocarbon (CFC) gases restricted since the mid 1980s.
But the precise origin of these new, similar substances remains a mystery, say scientists.
Lying in the atmosphere, between 15 and 30km above the surface of the Earth, the ozone layer plays a critical role in blocking harmful UV rays, which cause cancers in humans and reproductive problems in animals.
Scientists from the British Antarctic Survey were the first to discover a huge "hole" in the ozone over Antarctica in 1985.
The evidence quickly pointed to CFC gases, which were invented in the 1920s, and were widely used in refrigeration and as aerosol propellants in products like hairsprays and deodorants.
Remarkably, global action was rapidly agreed to tackle CFCs and the Montreal Protocol to limit these substances came into being in 1987.
A total global ban on production came into force in 2010.
Now, researchers from the University of East Anglia have discovered evidence of four new gases that can destroy ozone and are getting into the atmosphere from as yet unidentified sources.
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