Using a monitoring network that includes the Jungfrau research station in Switzerland, researchers detected an alarming rise in CFC levels between 2010 and 2020. Image credit: Shutterstock

The Montreal Protocol bans most of the ozone-depleting chemicals known as chlorofluorocarbons (CFCs) and calls for their global phase-out by 2010. The protocol has been a huge success: the Earth's ozone layer is expected to recover by the 2060s.

However, atmospheric chemists have found a disturbing signal in recent monitoring data -- five CFCs have risen rapidly in the atmosphere between 2010 and 2020. These five chemicals contribute to the global greenhouse effect equivalent to Switzerland's annual greenhouse gas emissions. Related research results were published in Nature-Earth Science on April 3.

"This shouldn't be happening," says Martin Vollmer, an atmospheric chemist at the Swiss Federal Laboratory for Materials Science and Technology. He helped analyze data from the international CFC monitoring network, and "we expect the opposite trend - they will slowly decline".

On March 30, Luke Western, a chemist at the University of Bristol in the United Kingdom, said at an online news conference that at current levels, these CFCs do not pose much threat to the recovery of the ozone layer. CFCs have been used as refrigerants and aerosols and can persist in the atmosphere for hundreds of years. Given that they are potent greenhouse gases, eliminating emissions of CFCs would have a positive impact on the Earth's climate.

The researchers said it is likely that factories accidentally released three chemicals -- CFC-113a, CFC-114a and CFC-115 -- in the production of CFC substitutes. When CFCs were phased out, HFCs were introduced as replacements. But in the production of HFCs, CFCs may be produced as by-products. The Montreal Protocol discourages such "accidental" production, but does not prohibit it.

"A lot of it comes down to the plant level." Vollmer noted that HFC production is on the rise.

The rise in levels of two other CFCs remains 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 Institute who was not involved in the study.

The researchers speculate that levels of CFC-112a may be on the rise due to its use as a solvent or chemical feedstock. However, further discussions with chemical engineers are needed to confirm this speculation, they said.

But the emergence of CFC-13 is even more confusing. "We really don't know where the emissions are coming from, or what chemical processes are producing this substance as a by-product," Vollmer said. Also, it is difficult to identify sources of emissions of CFC-13 and other CFCs because there are not enough monitoring stations around the world.

Still, the study shows that the global monitoring system is working, says Andreas Engel, an atmospheric scientist at the University of Frankfurt in Germany. Scientists are keeping a close eye on Earth's atmosphere and spotting problems. "We just have to find out where it's coming from, and there will be a willingness and an obligation to address it," Engel said.

If most of the emissions from the five recently detected CFCs come from the production of CFC substitutes, the world may need to rethink HFCs, and even the next generation of refrigerant chemicals — HFOs, because HFOs Olefin production also emits CFCs.

Vollmer added that if the problem persists, then an amendment to the Montreal Protocol may be needed to address the by-product problem head-on.

"This really shows that we need to keep our eyes open." Engel said, "The story is not over."

Related paper information:

https://doi.org/10.1038/s41561-023-01147-w