Mysterious source of ozone depleting substances sent to eastern China

The mysterious source of a chemical depleting the ozone layer has been identified in eastern China. Scientists have discovered "large and continuous" emissions of carbon tetrachloride from Shandong Province.

The discovery raises questions about the source of the substance. In 2010, carbon tetrachloride production was banned under the Montreal Protocol. It is therefore extremely important to determine how and why it occurs in the atmosphere.

The Montreal Protocol is an international agreement concluded in 1987 to protect the ozone layer by progressively phasing out the production of substances that deplete the ozone layer. By the early 1980s, scientists had discovered evidence of a huge hole in the ozone layer, a layer of the Earth's stratosphere located at an altitude of about 6.2 km, which was filtering the harmful ultraviolet rays of the Sun. Researchers have discovered that synthetic CFCs (chlorofluorocarbons) are the cause: these compounds are deposited in the stratosphere and destroy the ozone molecules.

Earlier this year, NASA issued the first direct evidence that the hole in the ozone layer had decreased thanks to the ban on CFCs. "We are very clear that chlorine from CFCs is being depleted in the ozone hole and that this is causing less destruction of the ozone layer," said Susan Strahan, a scientist specializing in ozone depletion. atmosphere at NASA's Goddard Space Flight Center.

But the problem of CFCs remains. In recent years, scientists have started looking for traces of carbon tetrachloride in the atmosphere. About 40,000 tonnes are still emitted each year, but the origin of these emissions is a mystery.

Now in the research published in the journal Letters of geophysical researchScientists led by Mark Lunt of the British University of Bristol have discovered the origin of carbon tetrachloride. "Despite the controls on production set up, [carbon tetrachloride] Emissions from the eastern part of China have not declined between 2009 and 2016, "says the study.

Representative image The ozone layer protects the Earth from harmful UV rays. iStock

"This finding contrasts with a recent bottom-up estimate, which predicts a significant decrease in emissions after production controls are put in place."

The team used ground and air atmospheric concentrations to create two models simulating the transport of gases into the atmosphere. Their findings showed that over the eight-year study period, significant carbon tetrachloride emissions from eastern China were ongoing. They also found evidence suggesting that a new source of emissions would have appeared in Shandong Province after 2012.

The team notes that carbon tetrachloride is not necessarily produced voluntarily. "Our work shows the location of carbon tetrachloride emissions," said Matt Rigby, co-author of the study, in a statement. "However, we do not yet know the responsible processes or industries. This is important because we do not know if it is produced intentionally or inadvertently.

"There are parts of the world such as India, South America and other parts of Asia, where ozone-depleting gas emissions can be in progress, but detailed atmospheric measurements are lacking. "

Lunt said Newsweek for the moment, they can only speculate on the source of the emissions: "One possible explanation is that these fugitive emissions in China are more important than previously supposed," he said. "Alternatively, the source could be linked to some other unknown processes.

"Under the Montreal Protocol, each party provides information on carbon tetrachloride production, imports, exports, the use of the raw material and the quantity destroyed, but this does not include emissions by inadvertence resulting from the production of other substances (such as chloromethanes), which could be one of the main processes behind these emissions.As long as we will not be sure of the process behind the emissions we find, it is difficult to what are the implications for the Montreal Protocol. "

He added that the recovery of ozone had been delayed because of these emissions. "I think the delay will be relatively small because of the" extra "emissions we have had so far," he said. "[But] if they continue in the future, I imagine we could see relatively large delays. "

This story has been updated to include quotes from Mark Lunt.