"CFCs are the main culprit in depletion of the stratospheric ozone layer, which protects us from the Sun's ultra-violet radiation", said lead author Matt Rigby, an atmospheric chemist at the University of Bristol.
Any production and use of CFC-11 is a violation of the Montreal Protocol, a 1987 agreement that phased out chlorofluorocarbons that cause damage to the ozone layer. It is assumed that CFCs have been used illegally in the manufacture of new products.
A new study finds that annual CFC emissions from eastern China have jumped by 7,000 tonnes since 2013, when global emissions began to rise again - although the increase was only discovered previous year.
There were indications that some region in eastern Asia was still emitting thousands of tonnes of CFC-11, but the exact location was not known.
"This research identifies the major source region for new CFC-11 emissions as eastern mainland China, likely due to the new production of insulating foams used in buildings, which is not permitted under the Montreal Protocol", said Paul Fraser, one of the paper's authors.
Reports a year ago from the Environmental Investigation Agency blamed Chinese foam factories in the coastal province of Shandong and the inland province of Hebei, which surrounds Beijing.
Industries in northeastern China have spewed large quantities of an ozone-depleting gas into the atmosphere in violation of an worldwide treaty, global scientists say.
The researchers acknowledged that China produces a substantial fraction of the emissions, but they said it is possible that other countries have seen smaller increases, as well.
The work provides further evidence that CFC-11 has been produced in China in the last few years, but doesn't account for the total estimated increase in emissions.
The findings also have implications for the fight against climate change. But since 2012, air samples had shown a troubling amount of CFC-11 present in them.
CFC-11 persists in the atmosphere for about half a century, and still contributes about a quarter of all chlorine - the chemical that triggers the breakdown of ozone - reaching the stratosphere.