The Montreal Protocol banned most uses of ozone-layer-destroying chemicals known as CFCs and called for their global phase out by 2010.

Despite this, researchers found that atmospheric emissions of five CFCs increased between 2010 and 2020, reporting their findings in a new study published in Nature Geoscience, “Global increase of ozone-depleting chlorofluorocarbons from 2010 to 2020.”

The five CFCs targeted are CFC-13, CFC-112a, CFC-113a, CFC-114a and CFC-115.

It is not so much the amount of CFCs detected in the atmosphere (from 1.6 to 4.2 ODP-Gg yr-1 between 2010 and 2020) that worries researchers, but rather the increasing trend. “We expect the opposite trend, we expect them to slowly go down,” said Martin Vollmer, an atmospheric chemist at the Swiss Federal Laboratories for Materials Science and Technology in Dübendorf, in an article on

Some CFCs are used as feedstocks for the production of other chemicals (a use permitted under the Montreal Protocol). According to the study, CFCs’ emissions are highly likely to occur during the production of HFCs, which still serve as substitutes for CFCs in many applications, though HFCs are being phased down under the Kigali Amendment to the Montreal Protocol.

Also, CFC-113a, CFC-114a and CFC-115 are known byproducts of HFC-125 production, and CFC-113a and CFC-114a are a feedstock and intermediary, respectively, in one of the production pathways to HFC-134a.

Emissions of these CFCs may negate some of the ozone-layer-restoring benefits gained under the Montreal Protocol if they continue to rise, the study noted. In addition, the collective annual warming effect of these five chemicals on the planet is equivalent to that of the CO2e emissions produced by a small country like Switzerland.

The next step suggested by the researchers is to trace where these emissions come from and take corrective actions. But to get this, it would be necessary to increase the coverage of CFC monitoring stations around the world, especially in Africa and South America.

It would also be helpful to rethink the use of HFCs and HFOs, the production of which can emit CFCs. Another action that could be taken to stop increasing CFCs emissions trend is to amend the Montreal Protocol to to address the byproduct problem, they said.