Emissions of Banned Ozone-Depleting Substance and Greenhouse Gas are Back on the Decline

Global emissions of a potent substance notorious for depleting the Earth’s ozone layer – the protective barrier that absorbs the Sun’s harmful UV rays – have fallen rapidly after an unexpected increase and are now back on the decline, according to new research.

Two studies published today in Nature show emissions of CFC-11, one of the many chlorofluorocarbon (CFC) chemicals once widely used in insulating foams and refrigerator manufacture, are back on the decline less than two years after earlier scientific research and media accounts exposed their resurgence in the wake of suspected rogue production.

Researchers relied on data collected by the Advanced Global Atmospheric Gases Experiment (AGAGE), a NASA-funded international network co-led by researchers at Scripps Institution of Oceanography at UC San Diego, and on data collected by the US National Oceanic and Atmospheric Administration (NOAA).

“As a direct result of these findings, the Parties of the Montreal Protocol are now taking steps to identify, locate, and quantify any future unexpected emissions of controlled substances by expanding the coverage of atmospheric measurements in key regions of the globe,” said Scripps Oceanography geochemist and AGAGE Co-principal Investigator Ray Weiss.

“The findings are very welcome news and hopefully mark an end to a disturbing period of apparent regulatory breaches,” said Luke Western, a researcher at the University of Bristol in the United Kingdom and a co-lead author of one of the studies. “If the emissions had stayed at the significantly elevated levels we found, there could have been a delay, possibly of many years, in ozone layer recovery. On top of that, since CFC-11 is also a potent greenhouse gas, the new emissions were contributing to climate change at levels similar to the carbon dioxide emissions of a mega-city.”

The production of CFC-11 was banned globally in 2010 as part of the Montreal Protocol, an historic international treaty which mandated the phase-out of ozone-depleting substances. Thereafter, CFC-11 emissions should have steadily fallen.

But in 2018 scientists – many of whom were part of today’s Nature studies – found a jump in emissions had begun around 2013, prompting alarm at the time that production of the banned substance had resumed in an apparent violation of the Montreal Protocol.

The first sign of something unexpected was spotted by an international atmospheric monitoring team led by NOAA.

“We noticed the concentration of CFC-11 had declined more slowly since 2013 than predicted, clearly indicating an upturn in emissions,” said NOAA scientist Steve Montzka. “The results suggested that some of the increase was from eastern Asia.”

Montzka led the initial finding of the surge in CFC-11 levels in 2013 and led one of today’s two studies, titled “A decline in global CFC-11 emissions during 2018-2019.”  

“The global data clearly suggested new emissions. The question was where exactly,” said Ron Prinn from Massachusetts Institute of Technology (MIT), an AGAGE principal investigator and co-author of both Nature papers. “The answer lay in the measurements at AGAGE and affiliate monitoring stations that detect polluted air from nearby regions. Using data from Korean and Japanese stations, it appeared around half of the increase in global emissions originated from parts of eastern China.”

Further investigation by media and environmental campaigners exposed usage of CFC-11 in the manufacture of insulating foams in China. Chinese authorities took notice and at meetings of the Montreal Protocol in 2018 and 2019, they confirmed some banned ozone depleting substances were identified during factory inspections, but only in small amounts relative to those inferred from the atmospheric data. According to their reports, arrests, material seizures, and the demolition of production facilities within China ensued.

The scientific teams have continued to closely monitor atmospheric levels, and the latest evidence, reported in the two papers on global CFC-11 emissions and eastern Chinese emissions, indicates that those efforts have likely contributed to dramatic emission declines.

“To quantify how emissions have changed at regional scales, we compared the pollution enhancements observed in the Korean and Japanese measurement data to computer models simulating CFC-11 in the atmosphere,” said Matt Rigby from the University of Bristol, a contributor to both new studies. “With the global data, we used another type of model that estimated the emissions change required to match the observed global CFC-11 concentration trends. 

“At both scales, the findings were striking: Emissions had dropped by thousands of metric tons per year between 2017 and 2019,” he said. “In fact, we estimate this recent decline is comparable or even greater than the original increase, which is a remarkable turnaround.”

While the findings suggest the rapid action in eastern China and other regions of the world has likely prevented a substantial delay in ozone layer recovery, any unreported production will have a lingering environmental impact.

“Even if the new production associated with the emissions from eastern China and other regions of the world has now stopped, it is likely only part of the total CFC-11 produced has been released to the atmosphere so far,” Rigby said. “The rest may still be sitting in foams in buildings and appliances and will seep out into the air over the coming decades.”

Since the estimated eastern Chinese CFC-11 emissions could not fully account for the inferred global emissions, there are calls to enhance international efforts to track and trace any future unexpected emissions of a wide range of potent ozone-depleting substances and greenhouse gases.

–     Adapted from University of Bristol