There has been a suspicious rise in emissions of ozone-damaging CFCs, according to a study published in the journal Nature, despite a global ban on the chemicals introduced in 2010.
The amount of trichlorofluoromethane (CFC-11) in the atmosphere has been sinking more slowly since 2012 than should be expected, scientists at the National Oceanic and Atmospheric Administration in Colorado wrote.
The measurements suggested that there was a new, unreported source of CFC-11, which was previously used as a cooling agent in refrigerators and as a propellant in spray cans as well as in the production of styrofoam.
In the 1970s, scientists proved that their use was linked to the release of chlorine into the atmosphere and the depletion of the ozone layer, which absorbs harmful ultraviolet radiation.
Two years after the discovery of the hole in the ozone layer above the Antarctic in 1985, the Montreal Protocol was signed, an international treaty which introduced restrictions on the production of CFCs.
The regulations were initially reflected by the data, with the amounts detected in the atmosphere sinking at a constant rate between 2002 and 2012. CFC can still be leaked when old refrigerators are scrapped, for example.
But in 2012 scientists noted that the rate of decline had slowed by 50 per cent, according to the new study.
The scientists said the deviation coincided with a rise in amounts of two other chemicals, chlorodifluoromethane and dichloromethane, suggesting they were all coming from the same source, though it was not clear exactly where they were being produced.
