The Montreal Protocol, which banned most uses of ozone depleting chemicals known as chlorofluorocarbons (CFCs) and called for their global phase-out by 2010, was a major success: Earth’s ozone layer is estimated to have recovered by the 1960s.
So atmospheric chemists were surprised to see a troubling signal in the recent data. They found that atmospheric levels of five CFCs rose rapidly from 2010 to 2020.
“This shouldn’t happen,” says Martin Vollmer, an atmospheric chemist at the Swiss Federal Laboratories for Materials Science and Technology in Dübendorf, who helped analyze data from the International CFC Monitor Network. “We expect the opposite trend, we expect them to slowly decline.”
At current levels, these CFCs do not pose a major threat to the healing of the ozone layer, Luke Western, a chemist at the University of Bristol in the United Kingdom, said at an online news conference on the 30th. CFCs, once used as refrigerants and aerosols, can persist in the atmosphere for hundreds of years.
Since they are potent greenhouse gases, eliminating emissions of these CFCs will also have a positive impact on the Earth’s climate. The collective annual warming effect of these five chemicals on the planet is equivalent to the emissions produced by a small country like Switzerland.
It is highly likely that manufacturing plants are accidentally releasing three chemicals CFC-113a, CFC-114a, and CFC-115 in the production of CFC substitutes. When CFCs were phased out, hydrofluorocarbons (HFCs) were introduced as replacements. But CFCs can appear as unintended byproducts during the production of HFCs. This accidental production is discouraged but not prohibited by the Montreal Protocol.
“A lot of it probably boils down to the factory level,” Vollmer says, noting that HFC production is on the rise. “A factory can be run relatively clean or relatively dirty.”
Eyes in the sky
The rise in levels of two other CFCs is a mystery. “CFC-13 and CFC-112a should not be used or produced at this time,” says Rona Thompson, an atmospheric scientist at the Norwegian Air Research Institute in Kjeller, who was not involved in the analysis.
Scientists speculate that levels of CFC-112a could be rising due to its use as a solvent or as a chemical feedstock. However, he says he needs to discuss the idea further with chemical engineers to confirm this assessment.
But the appearance of CFC-13 is much more confusing. “We really have no idea” where the emissions are coming from, Vollmer says. “We don’t know of any chemical process where this would show up as a byproduct.” And because there aren’t enough monitoring stations around the world, it’s difficult to pinpoint where these and other CFC emissions are coming from, Thompson says.
However, Andreas Engel, an atmospheric scientist at Goethe University Frankfurt in Germany, says this research shows that the global monitoring system is largely working. Scientists keep a close eye on the planet’s atmosphere and observe problems. “We just need to figure out where it’s coming from, and then people will be willing and able to fix it,” says Engel.
This happened several years ago when researchers detected high levels of CFC-11 in the atmosphere2 and traced it to eastern China3. They inferred the source based on data from monitoring stations in South Korea and Japan that reported in May 2019, after which levels began to decline. Scientists had a bit of luck with CFC-11: the monitoring stations equipped to detect this particular chemical happened to be relatively close to the source.
Engel says this would help increase coverage of CFC monitoring stations the continents of Africa and South America, for example, have little, if any, coverage.
If the majority of emissions from the five recently identified CFCs come from the production of CFC-replacing chemicals, the world may have to think differently about HFCs and perhaps even the next generation of refrigerant chemicals hydrofluoroolefins (HFOs), Vollmer says. HFO production can also release CFCs, he says.
And if the problem persists, Vollmer adds, the Montreal Protocol may need to be modified to address this byproduct issue directly. “This shows that we have to keep our eyes open,” says Engel. “The story doesn’t end.”
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