China’s emissions of a banned gas that damages the Earth’s ozone layer have declined sharply after rising for several years, two teams of scientists said Wednesday, a sign that the Beijing government has pledged to stop the illegal production of the industrial chemical.
The findings allay concerns that increased emissions of the gas, CFC-11, would slow progress in the decades-long environmental struggle to restore the ozone layer, which filters ultraviolet rays from the sun that can cause skin cancer and damage crops.
“We’re seeing a huge drop in both global emissions and what’s coming out of eastern China,” said Stephen A. Montzka, a chemist with the National Oceanic and Atmospheric Administration and the lead author of one of the studies. Work of Dr. Montzka and others three years ago first exposed the illegal emissions.
“It seems there has been a substantial response, possibly due to the fact that we raised a flag and say, ‘Hey, something’s not happening the way it should,’” said Dr. Montzka.
Matthew Rigby, an atmospheric chemist at the University of Bristol in England and an author of the second study, said that if emissions had not decreased, “we could see a slowdown in ozone recovery for years.” A full recovery is currently expected by the middle of this century.
Chinese government officials did not immediately respond to requests for comment.
Chemical traders in Shandong, a heavily industrialized province in eastern China where CFC-11 was widely used to make insulating foam, said the trade in the banned gas had largely dried up. “It’s not completely gone, but it’s much more scarce than before,” Gao Shang, a Shandong chemical trader, said in a telephone interview.
CFC-11 was banned a decade ago under the Montreal Protocol, the treaty signed in the 1980s, when research revealed its effects on ozone in the atmosphere, along with the effects of similar commonly used chemicals.
The disclosure in a 2018 study of rogue emissions from China that began five years earlier came as a shock to scientists, policymakers, environmentalists and others overseeing the protocol, which is largely considered the most effective environmental treaty in history.
Meg Seki, acting executive secretary of the ozone secretariat, the United Nations body that administers the treaty, said the organization was pleased to see emissions decreased and that the impact on the ozone layer would likely be limited. “However, it is important to prevent such unexpected emissions in the future through continuous, high-quality monitoring by the scientific community,” she said in a statement.
The 2018 study did not identify the source of most of the emissions, except that they came from East Asia. But investigations that year by the Environmental Investigation Agency, an independent advocacy group based in Washington, DC, and by The New York Times found evidence that the gas was still being produced and used in East China, particularly Shandong.
An atmospheric analysis led by Dr. Rigby in 2019 noted that Shandong, as well as a neighboring province, Hebei, were important sources.
When first confronted with the evidence, the Chinese environmental authorities had covered up and questioned the findings, suggesting that there could be other, unlisted sources of the chemical or that insulating foam manufacturers might not have as much CFC 11 would use.
At the same time, China’s Ministry of Ecology and Environmental Protection swore “zero tolerance” to companies caught illegally making or using CFC-11.
Policy announcements, industry reports and court rulings all indicate that the Chinese government has cracked down on the illegal trade, even though it continued to deny that there was ever a serious problem. Last year, the government released a conviction against a businessman, Qi Erming, as the first case in China of criminal charges for illegal trade in ozone-damaging chemicals.
In addition to prosecutions, the government tightened rules and controls over the chemical and foam manufacturing industries, and pledged to establish a comprehensive data system to track the movement of chemicals that could be used to make CFC-11.
There are legal gases that can replace CFC-11 in foam production. Mr. Gao, the chemical dealer in Shandong, said his company specializes in one of them.
The availability of substitutes may have contributed to China’s efforts to reduce CFC-11 emissions. Zhu Xiuli, a sales manager at another company in Shandong that sells foaming agents, said customers had previously asked if they had CFC-11. But “in recent years there have been fewer and fewer studies,” she said.
CFC-11 has also been used in refrigeration equipment. As the gear ages and foam containing CFC-11 breaks down over time, the gas will slowly be released. Although the exact size of this “bank” of CFC-11 is not known, this is explained by the protocol, and this is one reason why complete ozone recovery will take decades.
The new articles, published in the journal Nature, also do not reflect the full global increase in CFC-11 emissions since 2013. The gas can still be produced or used in other countries or in other parts of China. , but the researchers said there aren’t enough air sampling stations worldwide to know for sure.
“This is a useful lesson that we really need to expand our monitoring capabilities,” said Dr. Rigby.
Avipsa Mahapatra, a climate campaign leader for the Environmental Investigation Agency, said of the new findings that it was “exciting to see atmospheric studies confirming that on-the-ground intelligence and subsequent enforcement have led to spectacular climate gains.” But she said her group had evidence that enforcement had been more successful in some parts of China than others. “Now is not the time for complacency,” she said.
Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology who was not involved in the study, said the work was “a real win for science.”
But the problem is not over, said Dr. Solomon, because in addition to CFC-11, other similar chemicals are being released. “There’s a whole zoo of molecules,” she said, and although the quantities are smaller, they add up.
They are also powerful greenhouse gases, she said, although their contribution to warming is much less than the much more common heat-trapping gases such as carbon dioxide and methane. “The chemical industry around the world is still not being monitored closely enough to be really sure how many greenhouse gases they produce and how many ozone depleting gases they produce,” she said.
Liu Yi contributed research.