Dozens of ozone-destroying chemicals may be undermining the recovery of the ozone hole over Antarctica, researchers say.
The chemicals, which are also greenhouse gases, may be leaking from industrial plants or being used illegally, contravening the Montreal protocol which began banning the ozone destroyers in 1987. Scientists said the finding of the chemicals circulating in the atmosphere showed "ozone depletion is not yesterday's story".
Until now, a total of 13 chlorofluorocarbons and hydrochlorofluorocarbons were known to destroy ozone and are controlled by the Montreal protocol, regarded as the world's most successful environmental law. Scientists have now identified and measured four previously unknown compounds and warned of the existence of many more.
"There are definitely more out there," said Dr Johannes Laube of the University of East Anglia. "We have already picked up dozens more. They might well add up to dangerous levels, especially if we keep finding more."
Laube and his colleagues are in the process of analysing the dozens of new compounds.
Laube is concerned that the atmospheric concentrations of two of the new compounds, while low, are rising.
"They are completely unimpressed by the Montreal protocol," Laube said. "There are quite a few loopholes in the protocol and we hope some of these are tightened. But the good news is that we have picked up these [four] early."
The chemicals take decades to break down in the atmosphere, meaning their impact on ozone is long-lived.
"This research highlights that ozone depletion is not yesterday's story," said Piers Forster, a professor at the University of Leeds who was not involved in the study. "The Montreal protocol, the most successful international environmental legislation in history, phased out ozone-depleting substances from 1987 and the ozone layer should recover by 2050. Nevertheless, this paper reminds us we need to be vigilant and continually monitor the atmosphere for even small amounts of these gases creeping up."
The new research, published the journal Nature Geoscience, analysed air samples captured since the mid-1970s in several ways. Air bubbles trapped in snowpack in Greenland, samples taken by scientists in Tasmania, Australia, and others collected by aircraft flying 20 kilometres above Europe were all analysed.
The team found three new CFCs and one HCFC, none of which had been identified before.
"I was surprised no one had picked these up before," said Laube. At least 74,000 tonnes of the four newly discovered chemicals have been emitted, the scientists estimate, although in the 1980s one million tonnes of other CFCs were pumped into the atmosphere every year.
Despite the production of all CFCs having been banned since 2010, the concentration of one, CFC113a, is rising at an accelerating rate. The source of the chemicals is a mystery but Laube suggests that CFC113a may be being used as a feedstock chemical in the production of agricultural pesticides. "But we can't rule out illegal sources," he said.
CFCs and HCFCs were used mainly in refrigeration and aerosol sprays but, in 1985, scientists discovered the Antarctic ozone hole. It grew in size from almost nothing in 1979 to a peak of 26.6 million square kilometres in 2006. As the Montreal protocol has taken effect, it has recovered slowly, shrinking to 21.0 million square kilometres in 2013. Ozone screens out harmful ultraviolet rays from sunlight that can cause cancer in humans, as well as damage crops and animals.
"Although these new emissions [of the four chemicals] are small, for the Montreal protocol to continue to be successful it is necessary to understand whether it is being strictly complied with," said William Collins of the University of Reading, who was not part of the research team.