New research has revealed that three previously unknown chlorofluorocarbons (CFCs) and one related compound appear to be slowing down the recovery of ozone hole over Antarctica.
Researchers from University of East Anglia in Britain have found that more than about 82,000 tonnes of these four man-made, ozone-destroying chemicals have already been released into the atmosphere.
"While this quantity is far smaller than peak CFC emissions in the 1980s, it is still a significant quantity that could slow the recovery of the ozone hole," co-author Johannes Laube cautioned.
The ozone hole over Antarctica has been gradually healing ever since the Montreal Protocol began limiting the production of ozone-depleting chemicals in 1989.
These CFCs were commonly used in refrigerators, air conditioners and aerosol.
"In 2010, a total ban on CFCs was put in place but certain loopholes still exist. This allows trace amounts of the chemicals to be used in the production of certain products, including insecticides and solvents used to clean electronic equipment," Laube noted.
In research on centuries-old snow samples taken from Greenland, the team did not detect any of the four new compounds in those samples before the 1960s.
It suggests that the compounds were man-made.
"The findings call for a thorough examination of possible sources, and may offer a good opportunity to tighten the loopholes in the treaty," Laube added in a report published in the journal Nature Geoscience.