Emissions of ozone-depleting trichlorofluoromethane have increased in eastern China despite a worldwide ban aimed at preserving the atmospheric shield that protects Earth from the sun’s ultraviolet radiation, an international research team found.

The team, including the National Institute for Environmental Studies in Japan, published its findings in the British scientific journal Nature on May 23.

Since 2013, according to the researchers, emissions of trichlorofluoromethane, which is used as a bloating agent for heat insulating materials, have risen in eastern China.

Trichlorofluoromethane is a type of chlorofluorocarbon (CFC) that is especially damaging to the ozone layer.

The team determined the source of the emissions based on observation data from South Korea’s Jejudo island and Okinawa Prefecture’s Haterumajima island. Those areas have often experienced increases in CFC densities.

Eastern China now accounts for 40 percent to 60 percent of the increase in CFCs released around the world.

The trichlorofluoromethane emission amount from eastern China was too large to be attributed to the volume of existing heat insulating materials reported to the United Nations Environment Program, the team said.

After scientists found that CFCs, which had been used widely as refrigerants and in aerosols, were creating holes in the ozone layer, an international moratorium was signed in 1989 to reduce production of trichlorofluoromethane. In 2010, it was banned internationally.

The density of trichlorofluoromethane in the air has been decreasing since the late 1990s, but the rate of decline has been leveling off since the early 2010s, the researchers said.

The ozone layer was expected to be restored to the 1980 level as early as 2050, but that target may become out of reach, according to the study.