Illegal emissions of an ozone destroying chemical once used in refrigerants and foam insulation have virtually come to a halt, scientists reported this week, nearly three years after the rogue emissions were first documented. Researchers say the result is a major win for the international treaty that protects the ozone layer.
In May 2018, researchers documented a mysterious spike in atmospheric concentrations of trichlorofluoromethane1, or CFC 11, that had begun in around 2013. Production of the chemical had been banned since 2010 under the Montreal Protocol, a legally binding treaty that has been remarkably successful in curbing the use of ozone depleting substances, so scientists surmised that the sudden increase was probably the result of a new source of illegal emissions. By May 2019, scientists had traced the bulk of the emissions to eastern China. In response to significant international pressure, the country committed to rectifying the problem.
In a pair of studies published in Nature on 10 February, scientists report that atmospheric concentrations of CFC 11 have dropped precipitously since 20183,4. Assuming the current trend continues, the damage to the ozone layer from several years of illegal emissions will be negligible, says Stephen Montzka, an atmospheric chemist at the National Oceanic and Atmospheric Administration in Boulder, Colorado, who led one of the studies.
"The treaty did its job," says Durwood Zaelke, president of the Institute for Governance & Sustainable Development, an advocacy group based in Washington DC. "Whoever the offending parties were including most definitely China they got their act together." However, the sources of illegal emissions outside China remain a mystery.
China's Ministry of Ecology and Environment did not reply to several requests for comment in relation to the latest results and the actions it has taken to halt illegal CFC 11 emissions.
CFC 11 survives in the atmosphere for about 50 years, so, if sources were completely eliminated, global emissions should decline by around 2% annually. But the actual rate is slower, owing to continued emissions of the chemical from old refrigeration systems and from insulating foam when buildings are demolished. Between 2002 and 2012, CFC 11 emissions fell by around 0.85% a year. But that rate halved to about 0.4% after 2013, a sign that somebody was pumping around 13,000 tonnes a year of newly produced CFCs into the atmosphere, Montzka's team calculated in 2018. The most likely culprit was the manufacture and use of foam insulation.
The analysis published this week, using data from two independent global air monitoring networks, indicates that concentrations of CFC 11 began to decline more rapidly in 2018. By late 2019, CFC 11 concentrations were dropping by around 1% a year the fastest pace on record3.
In a second paper, Montzka and colleagues used measurements from air monitoring stations in South Korea and Japan, as well as detailed atmospheric transport modelling, to show that the largest source of the rogue emissions in eastern China has been shut down. The study incorporated independent analyses from four different research groups and two models, all of which showed consistent results, says Luke Western, an atmospheric scientist at the University of Bristol, UK, and a co author on the paper.
"Around 60% of the global increase came from that region, and 60% of the recent decrease also came from there," Western says.
The research can't account for some of the decline in emissions, however, which points to gaps in data collection around the world, including in industrially important countries such as India and Brazil. Although 60% of the recent decrease has been accounted for, "we still don't know where the other 40% was coming from", says Martin Vollmer, an atmospheric scientist at the Swiss Federal Laboratories for Materials Science and Technology in Dubendorf. Nonetheless, the episode should send a warning signal to those who might be tempted to break the rules in future.
Montzka says discussions are under way among parties to the Montreal Protocol to expand the network of monitoring stations. But for now, he says, it's encouraging and a bit surprising to see governments respond to the science and take action to halt illegal emissions. "We were there to catch the problem, and now we can be there to announce that they have addressed it," Montzka says. "It's a nice thing."