A review of current understanding of HFC-23 emissions and contributing source processes

A side event (5th July 2023) at the Montreal Protocol 45^th OEWG meeting in Bangkok presented new data on the atmospheric measurements of HFC-23 and sources of HFC-23 by-production and emissions.  The presentation by Steve Montzka, for the Scientific Assessment Panel (SAP) included recent data, available since the SAP 2022 Assessment Report.  The presentation summary stated:

• Surface measurements of HFC-23 provide accurate quantification of global emissions and trends.
• HFC-23 emissions during 2016 to 2020 were larger than any other time in the measurement record and are substantially larger than expected given reports of mitigation (17.2 ± 0.8 vs 2.2 kt/yr in 2019).
• The high value of global HFC-23 emissions and their increasing trend is “inconsistent with new information suggesting a substantial rise in abatement independent of Kigali Amendment controls.”
• The effective global ratio Emission HFC-23/Production HCFC-22 has not decreased in recent years.
• Updated surface data show a hint of slightly lower global emission in 2021 compared to 2020.
• HFC-23 emissions from eastern China:
  • have increased since 2015-16 despite reporting of substantial mitigation during that time.

Notes:

1. In China, from 15^th September 2021, the Regulation “Circular on Controlling the Emissions of HFC-23 By-products” prohibits direct emissions of hydrofluorocarbon-23 (HFC-23) from production processes for hydrochlorofluorocarbon-22 (HCFC-22) and hydrofluorocarbons (HFCs) as of its effective date. It also provides that, except for feedstock and controlled usages, HFC-23 shall be destroyed to the extent practicable using technology approved by the Parties to the Montreal Protocol. This is consistent with language from the Kigali Amendment. This means that emissions of HFC-23 from China from September 2021 might be expected to be greatly reduced. See China Takes Steps to Address HFC-23 Emissions in Advance of International Ozone Day - IGSD.
2. The EU reports a very minor contribution to global emissions of HFC-23. In its National Inventory Report submission in 2023 (available at European Union. 2023 National Inventory Report (NIR). | UNFCCC). In 2021, the reported emissions of HFC-23, according to the Common Reporting Format Table 2(II)BHs-1, are 17.81 tonnes as a by-product from HCFC-22 production and 8.05 tonnes fugitive emissions from chemical production. The SAP 2022 Assessment Report also notes that up until 2013, global bottom-up emissions track (within ± 2 Gg yr–1) the global emissions derived from atmospheric measurements.
3. According to SAP 2022, the contribution to the global atmospheric HFC-23 budget from the photolysis of trifluoroacetaldehyde (CF₃CHO), a minor degradation product of some fluorinated compounds, is assessed to be negligible.

Slide 3 reproduced from the presentation by Steve Montzka

The side event second presentation “HFC-23 By-production and Emissions” by Helen Tope and Nick Campbell, for the Technical and Economic Assessment Panel (TEAP), discussed sources of HFC-23 emissions, and their relative importance to total HFC-23 emissions. Information presented is from the 2023 TEAP Progress Report and the 2022 MCTOC Assessment Report. While HCFC-22 production is the main pathway generating HFC-23 by-product (2-4% generation rate), for other processes, very low generation rates are possible. The presentation noted that fluorochemical plants with integral destruction facility to treat gaseous fluorocarbon containing vents will emit only a fraction of total generated HFC-23.

The 2023 TEAP Progress Report in Section 5.3 Response to Decision XXXIV/5: Identification of gaps in the global coverage of atmospheric monitoring of controlled substances and options for enhancing such monitoring provides detailed information on:

1. Chemical pathways in which substantial emissions of controlled substances are likely.
2. Best practices available to control these emissions.
3. Gaps in understanding the sources of emissions referred to in point (a) above.