The CFC measurements used in this study were made by multiple organisations from air sampled at sites around the world, including at NOAA's American Samoa Baseline Observatory. Credit: NOAA
A loophole in the extremely successful Montreal Protocol is, at least in part, causing an increase in ozone-depleting chlorofluorocarbons (CFCs). While it’s not enough to threaten ozone recovery, the chemicals are still potent greenhouse gases so they have a negative effect on global warming.
The original Montreal Protocol, signed in 1987 by 197 international parties, phased out CFCs like freon, but made one allowance. The treaty says CFCs can be used to make other ozone-friendly alternatives.
“We’re paying attention to these emissions now because of the success of the Montreal Protocol,” said Luke Western, a research fellow at the University of Bristol and researcher at the NOAA’s Global Monitoring Laboratory. “CFC emissions from more widespread uses that are now banned have dropped to such low levels that emissions of CFCs from previously minor sources are more on our radar and under scrutiny.”
For the study, published in Nature Geoscience, the international team of researchers—from the UK, U.S., Switzerland, Australia and Germany—focused their analyses on five CFCs with few or no known current uses. FC-13, CFC-112a, CFC-113a, CFC-114a, and CFC-115 all have atmospheric lifetimes ranging from 52 to 640 years. In terms of their impact on the ozone layer, these emissions were equivalent to around one quarter of a recently detected rise in emissions of CFC-11, a substance controlled under the Montreal Protocol, thought to be due to unreported new production.
The team used measurements from the Advanced Global Atmospheric Gases Experiment and the University of East Anglia in the UK, as well as other data from Forschungszentrum Jülich in Germany and the NOAA. These were combined with an atmospheric transport model to show that global atmospheric abundances and emissions of these CFCs increased after their production for most uses was phased out in 2010.
For three of the CFCs studied—CFC-113a, CFC-114a and CFC-115—the researchers determined that increased emissions may be partly due to their use in the production of two common hydrofluorocarbons (HFCs) used primarily in refrigeration and air conditioning. HFCs were developed as second-generation replacements for CFCs, especially given the loss of popular freon for AC applications.
According to the study results, the drivers behind increasing emissions of the other two CFCs—CFC-13 and CFC-112a—were less certain.
“Combined, the [newly detected] emissions are equal to the CO2 emissions in 2020 for a smaller developed country like Switzerland,” said Western. “That’s equivalent to about 1% of the total greenhouse gas emissions in the United States.”
Still, according to the researchers, if emissions of the five CFCs continue to rise, their impact may negate some of the benefits gained under the Montreal Protocol. The study noted these emissions might be reduced or avoided by reducing leakages associated with HFC production and by properly destroying any co-produced CFCs.
“The key takeaway is that the production process for some of the CFC-replacement chemicals may not be entirely ozone-friendly, even if the replacement chemicals themselves are,” concluded Western.