Back in 1987, the global community signed an agreement known as The Montreal Protocol, which called for all countries to phase out the production of ozone-layer-depleting chlorofluorocarbons (CFCs). According to a new study, however, one of the most abundant CFCs is likely still being made.

Included in The Montreal Protocol was a chemical called CFC-11 (aka trichlorofluoromethane), production of which was supposed to end by 2010. It was already known that some CFC-11 gas would subsequently continue to be released by sources such as foam building insulation and appliances manufactured prior to the mid-1990s.

That's why CFC-11 is still the second-most abundant CFC in the atmosphere, although levels have dropped by 15 percent since their peak in 1993.

However, based on an analysis of remote-site readings conducted by the US National Oceanic and Atmospheric Administration (NOAA), those levels are declining more slowly than they would if there were no new sources of CFC-11. In fact, levels recorded between 2014 and 2016 were 25 percent higher than the average from 2002 to 2012.

The source of the emissions is thought to be somewhere in East Asia.

"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,'" says NOAA scientist Stephen Montzka, lead author of a paper on the study. "We concluded that it's most likely that someone may be producing the CFC-11 that's escaping to the atmosphere. 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."

The paper was published this week in the journal Nature.

Source: NOAA