Banned Ozone-depleting chemicals are on the rise again, and scientists aren't sure why

Once widely used as a foaming agent, production of CFC-11 was phased out by the Montreal Protocol in 2010.

Emissions of one of the chemicals that can make a hole in the ozone layer are on the rise, despite an international treaty that required an end to its production in 2010, a new study says.

Representational image. Reuters.

Representational image. Reuters.

What is even more troubling is that scientists are not sure at present why emissions of this gas are increasing. This gas, Trichlorofluoromethane, or CFC-11, is 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 the lead author of the paper Stephen Montzka, a scientist at National Oceanic and Atmospheric Administration (NOAA) in the US.

"Further work is needed to figure out exactly why emissions of CFC-11 are increasing and if something can be done about it soon," Montzka said.

For the study, scientists at NOAA and Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder, in the US made precise measurements of global atmospheric concentrations of CFC-11.

The results showed that CFC-11 concentrations declined at an accelerating rate prior to 2002 as expected. Then, surprisingly, the rate of decline hardly changed over the decade that followed. Even more unexpected was that the rate of decline slowed by 50 percent after 2012.

After considering a number of possible causes, Montzka and his colleagues 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 at the north of the equator.

Measurements from Hawaii indicate the sources of the increasing emissions are likely in eastern Asia, the study said.

More work will be needed to narrow down the locations of these new emissions, Montzka said.

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