Industries in northeastern China have spewed large quantities of an ozone-depleting gas into the atmosphere in violation of an international treaty, global scientists say.

And it's slowing down the rate of recovery for the hole in the crucial ozone layer.

The ozone layer is a region of Earth's stratosphere that essentially act as a shield and absorbs most of the sun's ultraviolet (UV) radiation.

On a hazy morning, chimney of chemistry factory emits smoke to sky at the suburb surrounding the residential district of Shandong. Photo / Getty Images
On a hazy morning, chimney of chemistry factory emits smoke to sky at the suburb surrounding the residential district of Shandong. Photo / Getty Images

So when scientists discovered in 1985 that there was a hole in it over Antarctica and Australia, it was very unsettling news. After that, we all got together and banned the use of harmful gases that depleted Earth's protective layer in the 1987 Montreal Protocol and ever since it has more-or-less been on a slow recovery ever since.

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China is a signatory of the Montreal Protocol but it looks as if the country hasn't been keeping up its end of the bargain.

Since 2013 annual emissions from northeastern China of a banned chemical called CFC-11 have increased by about 7000 tonnes, researchers reported overnight in the peer-reviewed journal Nature.

"This increase accounts for a substantial fraction (at least 40 to 60 per cent) of the global rise in CFC-11 emissions," they wrote.

Before it was phased out CFC-11, or Chlorofluorocarbon-11, was widely used in the 1970s and 1980s as a refrigerant and to make foam insulation. The chemical is a major cause of ozone depletion.

Ever since the ban, the concentration of the chemical in the atmosphere has been steadily declining but last year startled scientists discovered that the pace of that slowdown dropped by half from 2013 to 2017. Because the chemical does not occur in nature, the change could only have been produced by new emissions.

Using high-frequency atmospheric observations from Gosan, South Korea, and Hateruma, Japan, together with global monitoring data and atmospheric chemical transport model simulations, researchers investigated the likely culprit and have pointed the finger at eastern China.

Reports last year from the Environmental Investigation Agency fingered Chinese foam factories in the coastal province of Shandong and the inland province of Hebei, which surrounds Beijing.

Suspicions were strengthened when authorities subsequently shut down some of these facilities without explanation.

Paul Fraser, an honorary fellow at Australia's CSIRO Climate Science Centre and co-author of the paper said while eastern China accounts for about half of the rise in CFC-11, global scientists don't have the technology in place to monitor large parts of the rest of the world.

Along with other scientists, he presented the data last year to Chinese authorities and is optimistic action will be taken to reduce the harm done by the emissions.

"They were concerned, it was clear I think ... that they were going to tackle this issue," he told ABC radio this morning.

But as yet, he has not seen or heard any indication that China has begun cracking down on the rogue factories thought to be responsible.

Because scientists have noticed the chemical increase in the atmosphere early, "that gives us a really good chance to make sure they don't do too much damage," he said.

But pouring more CFC-11 into the air could also prevent ozone from returning to normal levels, scientists warn.

"If emissions do not decline, it will delay the recovery of the Antarctic ozone hole, possibly for decades," Mr Fraser said.