Old equipment such as building insulation foam, refrigerators, cooling systems and foam insulation are still leaking ozone-destroying gases into the atmosphere, scientists have said.
Researchers have found "unexpectedly high" levels of man-made chemicals known as CFC-11 and CFC-12, which belong to a group compounds responsible for creating a hole in Earth's ozone layer known as chlorofluorocarbons (CFCs), despite a worldwide ban on the production of these gases.
The team from the Massachusetts Institute of Technology in the US traced the source of these CFCs to "large banks" of old equipment which were manufactured before the global phase-out, which began in 2000. They said their findings contradict previous analysis that these would be too small to cause significant damage to the ozone layer.
High in the atmosphere, the ozone shields the planet from harmful ultraviolet rays that can cause problems such as skin cancer and crop damage.
In 1987, countries around the world agreed in the Montreal Protocol to phase out CFCs. The effect was observed in 2016, when scientists noticed signs of healing in the Antarctic ozone layer.