Emissions of a banned chemical most responsible for the giant Antarctic ozone hole are on the rise, according to a study which suggests that an international treaty that required an end to its production in 2010 is being violated.
Trichlorofluoromethane, or CFC-11, is the second-most abundant ozone-depleting gas in the atmosphere and a member of the family of chemicals most responsible for the giant hole in the ozone layer that forms over Antarctica each September.
Once widely used as a foaming agent, production of CFC-11 was phased out by the Montreal Protocol in 2010.
The new study, published in the journal Nature, documents an unexpected increase in emissions of this gas, likely from new, unreported production.
"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 Stephen Montzka, scientist at the US National Oceanic and Atmospheric Administration (NOAA).
"Further work is needed to figure out exactly why emissions of CFC-11 are increasing and if something can be done about it soon," said Montzka.
CFCs were once widely used in the manufacture of aerosol sprays, as blowing agents for foams and packing materials, as solvents, and as refrigerants.
Though production of CFCs was phased out by the Montreal Protocol, a large reservoir of CFC-11 exists today primarily contained in foam insulation in buildings, and appliances manufactured before the mid-1990s. A smaller amount of CFC-11 also exists today in chillers.
Since CFC-11 still accounts for one-quarter of all chlorine present in today's stratosphere, expectations for the ozone hole to heal by mid-century depend on an accelerating decline of CFC-11 in the atmosphere as its emissions diminish - which should happen with no new CFC-11 production.
Despite the increase in CFC-11 emissions, its concentration in the atmosphere continues to decrease, but only about half as fast as the decline observed a few years ago, and at a substantially slower rate than expected.
This means that the total concentration of ozone-depleting chemicals, overall, is still decreasing in the atmosphere. However, that decrease is significantly slower than it would be without the new CFC emissions.
Precise measurements of global atmospheric concentrations of CFC-11 made by scientists at 12 remote sites around the globe show that CFC-11 concentrations declined at an accelerating rate prior to 2002 as expected.
Then the rate of decline hardly changed over the decade that followed. Even more unexpected was that the rate of decline slowed by 50 per cent after 2012.
After considering a number of possible causes, researchers concluded that CFC emissions must have increased after 2012.
This conclusion was confirmed by other changes recorded in NOAA's measurements during the same period, such as a widening difference between CFC-11 concentrations in the northern and southern hemispheres - evidence that the new source was somewhere north of the equator.
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