Summary: The repair of the Earth’s ozone layer, which shields the planet from the sun’s harmful ultraviolet radiation, has long been touted as a global success story. Since the 1987 Montreal Protocol required the phase-out by 2010 of production of ozone-depleting chlorofluorocarbons (CFCs), nearly every nation in the world has complied, putting the ozone layer on track for a complete healing by midcentury. But a new development threatens to delay that happy ending. Recent studies have indicated that atmospheric concentrations of the second-most abundant chlorofluorocarbon, known as trichlorofluoromethane (CFC-11) and primarily used as foaming agent for building insulation, refrigerators and other consumer products, have significantly increased since 2012—and that some of this increase has come from eastern Asia. But this research did not establish the exact location and extent of this regional source of CFC-11 emissions.

Now a new study appearing in the journal Nature pinpoints the primary source of the rise in CFC-11 emissions as the northeastern Chinese provinces of Shandong and Hebei, with these two provinces accounting for at least 40 to 60 percent of the global rise in CFC-11 emissions. An international team comprised of scientists from MIT, University of Bristol and several other research institutions combined high-frequency atmospheric observations from Gosan, South Korea, and Hateruma, Japan, with global monitoring data (from NOAA and AGAGE) and atmospheric chemical transport model simulations to produce these findings.

The team found no evidence of significant increases in CFC-11 emissions from any other eastern Asian countries or other regions where long-term, high-frequency atmospheric data could be obtained. The researchers also deduced that the recent increase in CFC-11 emissions from eastern mainland China is due to new production and use of the banned chemical compound, rather than from increased rates of escape from pre-phase-out banks of CFC-11 in existing foam or refrigerators.