New international research by scientists from the UK, US, Switzerland, Australia and Germany has revealed that global emissions of several banned ozone-depleting chemicals are increasing, the authors report in Nature Geoscience.
The study, led by the University of Bristol in the UK and the National Oceanic and Atmospheric Administration (NOAA) in the US, attributes the rise in part to chemicals known as chlorofluorocarbons (CFCs) being used to make other alternatives to CFCs that do not damage the ozone layer. This is an exception allowed by the Montreal Protocol, but contrary to its more general objectives.
The study's lead author, Dr. Luke Western, a researcher at the University of Bristol and NOAA's Global Monitoring Laboratory (GML), explains that they are paying attention to these emissions now because of the success of the Montreal Protocol. "CFC emissions from more widespread uses that are now banned have fallen to such low levels that CFC emissions from previously minor sources are more on our radar and under scrutiny," he adds.
According to the researchers, the emissions of these CFCs do not currently pose a significant threat to ozone recovery, but because they are potent greenhouse gases, they continue to affect the climate.
"Combined, their emissions are equivalent to the 2020 CO2 emissions of a small developed country like Switzerland, Western said. That is about one percent of total US greenhouse gas emissions," Western adds.
CFCs are known to destroy the Earth's protective ozone layer. Once widely used in the manufacture of hundreds of products, including aerosols, as foam agents and packaging materials, solvents, and in refrigeration, the production of CFCs for such uses was banned under the Montreal Protocol in 2010.
However, the international treaty did not eliminate the creation of CFCs during the production of other chemicals, including hydrofluorocarbons (HFCs), which were developed as second-generation substitutes for CFCs.
This study focused on five CFCs with little or no currently known uses -- CFC-13, CFC-112a, CFC-113a, CFC-114a, and CFC-115 -- and whose lifetimes in the atmosphere range from 52 to 640 years. From the point of view of their impact on the ozone layer, these emissions are equivalent to about a quarter of the recently detected increase in emissions of CFC-11, a substance controlled by the Montreal Protocol, which is believed to be due to a new undeclared production.
In this study, the team used measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE), in which the University of Bristol plays a key role, as well as others from the Forschungszentrum Jülich in Germany, the University of East Anglia and the NOAA, in the United States.
These data were combined with an atmospheric transport model to show that the global atmospheric abundance and emissions of these CFCs increased after their production for most uses was phased out in 2010.
The researchers determined that for the three CFCs they studied (CFC-113a, CFC-114a, and CFC-115), the increased emissions may be due in part to their use in the production of two common HFCs used primarily in refrigeration and air conditioning. The causes of the increase in emissions of the other two CFCs, CFC-13 and CFC-112a, are less clear.
Although the team found an increase in emissions around the world, they were unable to pinpoint specific locations.
"Given the continued increase in these chemicals in the atmosphere, it may be time to think about fine-tuning the Montreal Protocol a bit more," says study co-author Dr. Johannes Laube of the Institute for Energy and Climate Research (IEK). ) of the Forschungszentrum Jülich.
If the emissions of these five CFCs continue to increase, the researchers say, their impact could negate some of the benefits gained from the Montreal Protocol. The study notes that these emissions could be reduced or avoided by reducing leakage associated with HFC production and by properly destroying any co-produced CFCs.
Dr Western notes that "the key takeaway is that the production process for some of the CFC replacement chemicals may not be fully ozone friendly, even though the replacement chemicals themselves are."
