Report of the Scientific Assessment Panel: Emissions of HFC-23

Emissions of HFC-23 derived from atmospheric measurements continue to be substantially higher than reported emissions according to the September 2025 Report of the Scientific Assessment Panel to the Montreal Protocol in response to Decision XXXVI/3: Emissions of HFC-23 [1].  With the small changes from 2022 to 2023 in emissions derived from global atmospheric abundance changes and available reported emissions, the gap in our understanding of HFC-23 emissions in 2023 of 11.4 – 12.8 kt/year is similar to the gap estimated for 2022 in the previous HFC-23 report [2] of 10.5 – 12.5 kt/year. The gap between reported HFC-23 emissions and those inferred from atmospheric abundances is not reconciled by considering all known sources beyond HCFC-22 production. An updated assessment by the Technology and Economic Assessment Panel (TEAP) [3] estimates HFC-23 emissions from all known sources and reported abatements after 2020 to be in the range of 1.6 – 3.7 kt/year, which is substantially smaller than the atmospherically-derived emission of 14.2 ± 0.7 kt/year during 2023.

China HFC-23 emissions. Emissions from eastern China in 2023 were 4.7 ± 0.7 kt greater than the 0.9 kt reported to the Ozone Secretariat for all of China in that year, and this emission accounts for 40 ± 10% of the global emission gap in 2023.

Europe HFC-23 emissions. From continued atmospheric measurements at a network of sites in Europe, HFC-23 emissions in 2023 were estimated to be 0.15 ± 0.04 kt/year from the sum of countries in the north-western Europe including Ireland, the United Kingdom (UK), France, the Netherlands, Belgium, Luxembourg, and Germany. This emission was 0.13 ± 0.04 kt greater than reporting to the UNFCCC in 2022 (latest available year), and this region accounts for 0.7 to 1.5% of the global emission gap.

Photochemical production of HFC-23 in the atmosphere. HFC-23 is produced in the atmosphere during the oxidation of certain fluorocarbons (some HFCs, some HFOs and some HCFOs) by the hydroxyl radical and by ozone. Based on new studies, the contribution of fluorocarbon oxidation reactions to HFC-23 in the atmosphere is estimated to be less than 0.215 kt/year, which is a factor of 2 smaller than the estimate in the earlier SAP report [2]. This value is a conservative upper limit, meaning that the actual value is likely smaller.

Explanatory note: The EFCTC newsletter of January 2025 in ‘Estimate of HFC-23 production from HFO and HCFO emissions’ discusses the SAP report [2] estimate of HFC-23 derived from HFO and HCFO emissions and explained why HFC-23 generation from these sources is considerably lower, estimated at less than 17 tonnes in 2022.

References

[1] Report of the Scientific Assessment Panel in response to Decision XXXVI/3: Emissions of HFC-23, September 2025. Lead Authors: S. A. Montzka, NOAA Global Monitoring Laboratory, USA; J. B. Burkholder, NOAA Chemical Sciences Laboratory, USA. Available here, or from Scientific Assessment Panel (SAP) | Ozone Secretariat (unep.org).