Global CFC-11 emission, reported production and implied release rate from CFC-11 banks. Graphic: Montzka, et al., 2018 / Nature

16 May 2018 (NOAA) – Chlorofluorocarbons, or CFCs, were once considered a triumph of modern chemistry. Stable and versatile, these chemicals were used in hundreds of products, from military systems to the ubiquitous can of hairspray.

Then in 1987, NOAA scientists were part of an international team that proved this family of wonder chemicals was damaging Earth’s protective ozone layer and creating the giant hole in the ozone layer that forms over Antarctica each September. The Montreal Protocol, signed later that year, committed the global community to phasing out their use. Production of the second-most abundant CFC, CFC-11, would end completely by 2010.

Except that maybe it didn’t.

A new analysis of long-term atmospheric measurements by NOAA scientists shows emissions of the chemical CFC-11 are rising again, most likely from new, unreported production from an unidentified source in East Asia. The results are published today in the journal Nature.

“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 of the ozone layer,’” said NOAA scientist Stephen Montzka, the study’s lead author. “Further work is needed to figure out exactly why emissions of CFC-11 are increasing, and if something can be done about it soon.”

The findings of Montzka and his team of researchers from CIRES, the UK, and the Netherlands, represent 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.

CFC-11 is the second-most abundant ozone-depleting gas in the atmosphere because of its long life and continuing emissions from a large reservoir of the chemical in foam building insulation and appliances manufactured before the mid-1990s. A smaller amount of CFC-11 also exists today in older refrigerators and freezers.

The Montreal Protocol has been effective in reducing ozone-depleting gases in the atmosphere because all countries in the world agreed to legally binding controls on the production of most human-produced gases known to destroy ozone. As a result, CFC-11 concentrations have declined by 15 percent from peak levels measured in 1993. 

Though concentrations of CFC-11 in the atmosphere are still declining, they’re declining more slowly than they would if there were no new sources, Montzka said.

The results from the new analysis of NOAA atmospheric measurements explain why. From 2014 to 2016, emissions of CFC-11 increased by 25 percent above the average measured from 2002 to 2012.

Scientists had been predicting that by the mid- to late century, the abundance of ozone-depleting gases would fall to levels last seen before the Antarctic ozone hole began to appear in the early 1980s.

Montzka said the new analysis can't definitively explain why emissions of CFC-11 are increasing, but in the paper, the team discusses potential reasons why.

"In the end, we concluded that it’s most likely that someone may be producing the CFC-11 that’s escaping to the atmosphere," he said. "We don't know why they might be doing that and if it is being made for some specific purpose, or inadvertently as a side product of some other chemical process."

If the source of these new emissions can be identified and controlled soon, the damage to the ozone layer should be minor, Montzka said. If not remedied soon, however, substantial delays in ozone layer recovery could be expected.


Theo Stein, 303-497-6288

Emissions of an ozone-destroying chemical are rising again

Hemispheric differences in CFC-11 mole fractions represented by results from individual sites at comparable latitudes. Graphic: Montzka, et al., 2018 / Nature

ABSTRACT: The Montreal Protocol was designed to protect the stratospheric ozone layer by enabling reductions in the abundance of ozone-depleting substances such as chlorofluorocarbons (CFCs) in the atmosphere1,2,3. The reduction in the atmospheric concentration of trichlorofluoromethane (CFC-11) has made the second-largest contribution to the decline in the total atmospheric concentration of ozone-depleting chlorine since the 1990s1. However, CFC-11 still contributes one-quarter of all chlorine reaching the stratosphere, and a timely recovery of the stratospheric ozone layer depends on a sustained decline in CFC-11 concentrations1. Here we show that the rate of decline of atmospheric CFC-11 concentrations observed at remote measurement sites was constant from 2002 to 2012, and then slowed by about 50 per cent after 2012. The observed slowdown in the decline of CFC-11 concentration was concurrent with a 50 per cent increase in the mean concentration difference observed between the Northern and Southern Hemispheres, and also with the emergence of strong correlations at the Mauna Loa Observatory between concentrations of CFC-11 and other chemicals associated with anthropogenic emissions. A simple model analysis of our findings suggests an increase in CFC-11 emissions of 13 ± 5 gigagrams per year (25 ± 13 per cent) since 2012, despite reported production being close to zero4 since 2006. Our three-dimensional model simulations confirm the increase in CFC-11 emissions, but indicate that this increase may have been as much as 50 per cent smaller as a result of changes in stratospheric processes or dynamics. The increase in emission of CFC-11 appears unrelated to past production; this suggests unreported new production, which is inconsistent with the Montreal Protocol agreement to phase out global CFC production by 2010.

An unexpected and persistent increase in global emissions of ozone-depleting CFC-11



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