According to two recently published peer-reviewed articles emissions of trichlorofluoromethane (CFC-11), a potent ozone depleting substance banned under the Montreal Protocol since 2010, have since 2018 started to decline at a rate closer to the one expected if the Protocol was fully adhered to. These findings indicate a reversal from previously documented higher than expected emissions between 2013 to 2018 that indicated illegal production of the chemical. Scientists had traced a majority of these illegal emissions to eastern China sparking international pressure to rectify the problem. This seems to have resulted in action not only by the Chinese government and industry, but also other still unaccounted for CFC-11 emitters leaving scientists positive that any substantial delay in ozone layer recovery has been avoided.
Before being phased out, CFC-11 was used as a refrigerant, as a propellant gas and in the manufacturing of foams for building and domestic appliances. Thus, even though its production has been halted, substantial CFC-11 ‘banks’ persist which are expected to continue emitting the gas for several decades although at a declining rate. However, while CFC-111 emissions fell around 0.85% a year for the period 2002 to 2012, this rate dropped to 0.4% after 2013 indicating around 13,000 tons of newly produced CFCs being emitted annually. The research teams were able to attribute between 40-60% of these excess emissions to eastern mainland China based on air-monitoring stations in South Korea and Japan. As the most likely source for newly produced CFC-11 the manufacturing of closed-cell foams has been identified.
In 2018 and 2019 China embarked upon a broad plan to curb any illicit CFC production and use including internal inspections and enhanced inspection measures. These initiatives seem to have been successful given the effective and rapid mitigation of the renewed emissions. The new study concludes that around 60% of the recent decrease of illegal emissions can be attributed to eastern China. Importantly, the return to pre-2013 emission values occurred before the end of 2019 precluding an attribution to the reduced economic activity in the wake of SARS-CoV-2.
Nevertheless, 40% of the decrease remain unaccounted for pointing to data gaps, particularly in global air-monitoring stations, around the world. Yet it seems that parties to the Montreal Protocol have responded to the science and halted illegal emissions even when they could not be identified as a source of CFC-11. The study authors are confident that if the downward trajectory of global CFC-11 emissions is sustained – which in 2020 experienced the strongest decrease ever recorded – the substantial delays in ozone layer recovery projected based on the 2013-2018 CFC trends will have been avoided.