Workers in Xingfu, China, assemble refrigeration equipment.Credit: Gilles Sabrie/The New York Times/eyevine

A mysterious spike in emissions of an ozone-destroying gas has been tracked1 to northeast China, where scientists suspect that the chemical is being produced and used in violation of international law.

The chemical — trichlorofluoromethane, also known as CFC-11 — was once commonly used in spray-foam insulation for refrigerators and buildings. CFC-11 is one of the most potent chemicals responsible for creating the ozone hole in the stratosphere over the Southern Hemisphere. Its production was phased out in 2010 under the 1987 Montreal Protocol, a global treaty to protect the ozone layer.

In May 2018, scientists reported2 new CFC-11 emissions that seemed to come from east Asia, on the basis of air samples collected at monitoring stations in Hawaii. The latest analysis, which draws on air samples from South Korea and Japan, finds that more than half of the surge in CFC-11 emissions — some 7,000 tonnes annually, beginning around 2013 — originates in the Chinese provinces of Shandong and Hebei. The study was published on 22 May in Nature1.

“It’s pretty unequivocal,” says lead author Matthew Rigby, an atmospheric chemist at the University of Bristol, UK. Four independent modelling groups analysed atmospheric circulation patterns to track down the source of the CFC-11 plumes that wafted into South Korea and Japan. Rigby says that all the groups came back with the same answer.

Hide and seek

The findings are the culmination of years of scientific sleuthing, sparked by analyses that showed an unexpectedly slow decline in the amount of CFC-11 in the atmosphere, given the ban on the chemical’s production. Before 2012, the concentration of CFC-11 was dropping by around 0.8% per year, but the rate of decline slowed by half in 2013. Only a new source of emissions could explain the shift.

Researchers aren’t sure how the chemical is being used in northeast China, nor they have they pinned down the origin of the remaining rogue emissions, an estimated 4,000 tonnes. But the latest evidence will nonetheless have political repercussions as nations work to enforce the Montreal Protocol, which so far has functioned largely as designed.

“No one nation had to defend itself before, because no one nation was put on the map,” says David Fahey, an atmospheric chemist with the US National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado. Fahey co-chairs a scientific panel under the Montreal Protocol, and says the latest study will feed into an ongoing analysis of CFC-11 emissions that treaty members commissioned last November.

Chinese officials have reported during meetings organized under the Montreal Protocol that they have already identified some illegal CFC-11 production and prosecuted those involved. But the nature and extent of the unreported CFC-11 production — as well as the Chinese government’s ability to stop it — remains unclear.

Time bomb

Scientists who have searched for the source of the emissions suspect that factories in northeast China have resumed production of a CFC-11-based foam insulator that was commonly used in buildings before the gas was banned. That would mean that the emissions problem could be significantly larger than current estimates suggest, because much of the CFC-11 used is trapped in the foam and leaks out slowly over time, says Stephen Montzka, a NOAA chemist who co-authored the latest study and led the 2018 work that first documented the existence of the unreported CFC-11 emissions.

“What we actually detect in the atmosphere is only a small fraction of what is produced,” Montzka says.

Rigby says scientists still have plenty of work to do before they can identify the source of the remaining 4,000 tonnes of CFC-11 emissions. But the latest study should help Chinese authorities in their search for illegal production, he says, and scientists should be able to determine in the coming years whether China has halted such operations.

“We’re going to have to wait and see,” Rigby says.