After studying atmospheric data from South Korea and Japan, they estimated CFC-11 emissions from eastern mainland China during the 2014-17 period were around seven million kilograms per year higher than they were from 2008 to 2012.
In 1985, scientists discovered a hole in the ozone layer that protects the earth's surface from harmful ultraviolet radiation above the Antarctic, which led to the Montreal Protocol of 1987.
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 a year ago. "The most likely explanation is that new production has taken place before the end of 2017, which is the period covered in our work", said another lead author, Matt Rigby of the University of Bristol.
China ratified the treaty in 1991 and said a year ago it has already eliminated as much as 280,000 tonnes of annual ODS production capacity and was speeding up efforts to phase out other ozone-damaging chemicals.
The results are also disconcerting because the emissions had been declining substantially since the mid 1990s, until 2012, when climate scientists were surprised by a "sudden, unexpected" upward trend of global emissions of CFC-11. Models of the movement of air masses suggested the source of these emissions was somewhere in east Asia, and a report by an organisation called the Environmental Investigation Agency emerged shortly afterwards that claimed CFC-11 foam was being illegally manufactured in China for use as a blowing agent to make polyurethane insulation.
But a report past year by the London-based Environmental Investigation Agency (EIA) claimed that dozens of Chinese companies were still using the banned CFC-11 in the production of polyurethane foam. "We didn't find evidence of increased emissions from Japan, the Korean peninsula or any other country", added Luke Western, a post-doctoral researcher at the University of Bristol.
But pouring more CFC-11 into the air could also prevent ozone from returning to normal levels, scientists warn. The source of the emissions remained unknown, however, sparking concerns that it could hamper years of worldwide effort to fix the protective ozone layer.