Authors' Short Summary: Based on atmospheric HFC-23 observations, the first estimate of post-CDM HFC-23 emissions in eastern Asia for 2008–2019 shows that these emissions contribute significantly to the global emissions rise. The observation-derived emissions were much larger than the bottom-up estimates expected to approach zero after 2015 due to national abatement activities. These discrepancies could be attributed to unsuccessful factory-level HFC-23 abatement and inaccurate quantification of emission reductions.

Executive Editor's Summary: The international Montreal Protocol was signed in 1987 in order to protect the atmospheric ozone layer by phasing out the production of halogenated hydrocarbons that deplete stratospheric ozone. The protocol was successfully implemented and, over the years, amendments and adjustments of the protocol were essential to its success. Ultimately, the protocol has resulted in a reduced halogen loading of the atmosphere since the mid-1990s. Trifluoromethane (HFC-23) is one of the substances regulated by the Montreal protocol since the Kigali amendment in 2016. HFC-23 does not deplete stratospheric ozone but is a very potent greenhouse gas. Commitments were made to reduce emissions of HFC-23 during the production of HCFC-22 as part of agreements in the protocol. However, the data presented and analysed in this paper indicate that in China more than the agreed amount of HFC-23 has been emitted since 2015, resulting either from unsuccessful factory-level HFC-23 abatement and/or inaccurate quantification of emission reductions. The analysis provides valuable data of atmospheric HFC-23. The study is also a good example of how compliance with the Montreal Protocol can be monitored.