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BEIJING — An environmental group says it has new evidence showing that China is behind the resurgence of a banned industrial gas that not only destroys the planet’s protective ozone layer but also contributes to global warming.
The gas, trichlorofluoromethane, or CFC-11, is supposed to be phased out worldwide under the Montreal Protocol, the global agreement to protect the ozone layer. In May, however, scientists published research showing that CFC-11 levels in the atmosphere had begun falling more slowly. Their findings suggested significant new emissions of the gas, most likely from East Asia.
Evidence then uncovered by The New York Times and the Environmental Investigation Agency pointed to rogue factories in China as a likely major source.
Now, the E.I.A. has prepared a report that it says bolsters the finding that Chinese factories are behind the return of CFC-11.
Independent laboratory tests “clearly confirm the use of CFC-11 in three enterprises” in China, the agency said in the report. It plans to submit the work this week in Quito, Ecuador, where delegates from nearly 200 countries are attending a Montreal Protocol meeting on the status of efforts to repair the ozone layer.
Avipsa Mahapatra, head of the climate change campaign at the E.I.A., said the Chinese authorities should make thorough regulatory changes that make underground CFC-11 production impossible. “Simply clamping down a few enterprises without systemic changes could mean that similar illegal enterprises pop up in other regions,” she said in an email.
But definitive answers and solutions to the problem of CFC-11 appear to be some way off.
Chinese officials have said they have already acted vigorously to close rogue chemical makers. They have also asserted that the CFC-11 emissions in question are too large to be solely from those operations.
Scientists have said that they need more time and data to pin down the causes of the CFC-11 resurgence.
“When it comes to definitive answers, I think we have to first emphasize that this mystery has yet to be solved,” said Keith Weller, a spokesman for the United Nations Environment Program, which helps organize the ozone layer talks.
The CFC-11 mystery has wide implications. The ozone layer has been healing, but the return of a banned substance is an alarming breach in one of the world’s most effective environmental pacts and could slow the layer’s recovery.
CFC-11 is also a potent greenhouse gas. If it is leaking directly into the atmosphere from factories, even more gas may be held in the products made in those factories — for example, in insulation foam — and may enter the atmosphere when those products are eventually destroyed.
Scientists discovered decades ago that CFC-11 and other manufactured chemicals used as refrigerants and aerosols and in the production of insulating foams were destroying the ozone layer, which shields humans, crops and animals from the most damaging solar rays.
In 1987, countries agreed on the Montreal Protocol to phase out such gases, steadily replacing them with ever safer substitutes. The protocol has been praised as a model environmental initiative.
The Chinese government has said it will investigate and stamp out any illicit production off CFC-11, and Chinese industrial associations have vowed that their businesses will not use the chemical.
Officials announced last month that the police had broken up an illegal CFC-11 plant in Henan, a rural heartland province, and found more 30 metric tons of the chemical on the site, according to an official report.
A spokesman for the Chinese Ministry of Ecology and Environment, Liu Youbin, told a news conference on Wednesday that inspectors had checked 1,172 businesses over recent months and found evidence of CFC-11 in only 10.
“If it was just those small, illegal roaming producers, the volume could not be that much,” Chen Liang, an official with the ministry who oversees international cooperation, including in ozone layer policy, said in an interview.
Mr. Weller also said the estimated new emissions of CFC-11, in the order of roughly 13,000 metric tons per year, appeared to be too great to come from illegal production alone.
Yet Mr. Chen also said there were daunting barriers to regulating China’s vast numbers of chemical and foam-making businesses. By his count, there were about 3,000 businesses in the foam sector. But the numbers of scattered, under-the-radar plants could be much higher.
Furthermore, Mr. Chen said, local inspectors across China can lack the equipment to quickly measure levels of CFC-11 or the chemicals used to make it. Fly-by-night chemical producers were hard to uncover and punish, he added.
“After they finish up production, everyone leaves,” Mr. Chen said. “This is very difficult to attack.”
CFC-11 was also once widely used as a refrigerant for fridges and air-conditioners, and Mr. Chen said that the pickup in CFC-11 might come from leakage when appliances were improperly scrapped. But an expert panel that advises Montreal Protocol member governments has assembled numbers that put into doubt the assertion that leakage can explain the persistent CFC-11, at least on its own.
The panel noted that it would take the destruction of 13 million large fridges a year to account for 13,000 tons of CFC-11 released in the atmosphere. China, where fridges tend to be smaller, disposes of about 1.5 million of them a year, the panel said.
The delegates meeting in Ecuador will receive a new United Nations assessment of the health of the ozone layer that confirms the resurgence of CFC-11 emissions, and some are likely to press China for more answers. But scientists have said it will take longer before they can confidently track down the source or sources of the pollution.
In September, a team of scientists published research confirming that China has been emitting unaccountably high volumes of carbon tetrachloride, an ozone-destroying chemical with uses that include the production of CFC-11. But Mark Lunt, a researcher at the University of Edinburgh who was a co-author of the study, stressed it was too early to identify the precise sources of the carbon tetrachloride and say if there was a link with making CFC-11.
The team of scientists would soon submit a research paper on CFC-11, Mr. Lunt said. Other efforts to study the resurgence of CFC-11 are also afoot.
“There’s a huge variety of questions we need to answer,” Paul A. Newman, chief scientist for earth sciences at NASA’s Goddard Space Flight Center, said in a telephone interview. “I just think there’s a real lack of information at this point.”
Henry Fountain contributed reporting from New York.
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