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, who say their precise origin is a mystery.
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 BBC reports. The evidence quickly pointed to CFC gases, which were invented in the 1920s and then 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 Britain's University of East Anglia say the new gases can destroy ozone and are getting into the atmosphere from as yet unidentified sources. Three are CFCs and one is a hydrochlorofluorocarbon (HCFC), which can also damage ozone.
"Our research has shown four gases that were not around in the atmosphere at all until the 1960s, which suggests they are man-made," says lead researcher Dr Johannes Laube.
Speculation about possible sources
The scientists discovered the gases by analysing polar firm, perennial snow pack. Air extracted from this snow is a natural archive of what was in the atmosphere up to 100 years ago. They also looked at modern air samples, collected at Cape Grim in Tasmania.
They estimate that about 74,000 tonnes of these gases have been released into the atmosphere. Two of the gases are accumulating at significant rates.
"The identification of these four new gases is very worrying as they will contribute to the destruction of the ozone layer," says Dr Laube.
"We don't know where the new gases are being emitted from and this should be investigated. Possible sources include feedstock chemicals for insecticide production and solvents for cleaning electronic components."
The research has been published in the journal Nature Geoscience.