"We're raising a flag to the global community to say, 'This is what's going on, and it is taking us away from timely recovery from ozone depletion, '" said NOAA scientist Stephen Montzka, lead author of the paper, which has co-authors from CIRES, the United Kingdom, and the Netherlands. A US observatory in Hawaii found CFC-11 mixed in with other gases that were characteristic of a source coming from somewhere in east Asia, but scientists could not narrow the source down any further.
Paul Young, at Lancaster University, UK, said: "The Montreal Protocol has been rightly hailed as our most successful worldwide environmental treaty, so the suggestion that there are possibly continued, unreported emissions of CFCs is certainly troubling and needs further investigation".
A sharp and mysterious rise in emissions of a key ozone-destroying chemical has been detected by scientists, despite its production being banned around the world.
"It is not clear why any country would want to start to produce, and inadvertently release, CFC-11, when cost effective substitutes have been available for a long while", Watson continued.
Thirty years or more ago CFC11 (R11) was commonly used as a refrigerant and insulation propellant.
The 1987 Montreal Protocol banned industrial aerosols such as chlorofluorocarbons (CFCs) that were chemically dissolving ozone, especially above Antarctica.
However, a study recently published in Nature reveals that CFC-11 production may be happening somewhere in the world despite the Montreal Protocol. A smaller amount of CFC-11 also exists today in chillers.
CFC-11 still contributes about a quarter of all chlorine - the chemical that triggers the breakdown of ozone - reaching the stratosphere.
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The researchers said that the less rapid decline of CFC-11 could prevent ozone from returning to normal levels, or at least as quickly as hoped. Even more unexpected was that the rate of decline slowed by 50 percent after 2012.
It is possible that the increased emissions could be due to older buildings being demolished, but that doesn't seem to be the case.
Zaelke said he was surprised by the findings, not just because the chemical has always been banned, but also because alternatives already exist, making it hard to imagine what the market for CFC-11 today would be. More work will be needed to narrow down the locations of these new emissions, Montzka said. CFC-11 concentrations have declined by 15 percent from peak levels measured in 1993 as a result.
But there a growing scientific doubts about the progress of healing in the ozone hole.
To put that in perspective, production of CFC-11, marketed under the trade name Freon, peaked at about 430,000 tons per year in the 1980s.
"This is the first time that emissions of one of the three most abundant, long-lived CFCs have increased for a sustained period since production controls took effect in the late 1980s", they note.
Erik Solheim, head of UN Environment, said: "If these emissions continue unabated, they have the potential to slow down the recovery of the ozone layer".
But Mr. Doniger noted that the Montreal Protocol, which has been signed by almost 200 countries, has a strong track record of compliance, with countries often reporting their own violations. If not remedied soon, however, substantial delays in ozone layer recovery could be expected, Montzka said.