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Effects of atmospheric degradation products from ultra-low GWP refrigerants

27 July 2023

Ultra-low GWP (< 30) [1] refrigerants include HFOs, HCFOs and hydrocarbons. The atmospheric breakdown and environmental effects of their intermediate and final breakdown products are summarised, including the most recent data in the Environmental Effects Assessment Panel 2022 Report [2] and Scientific Assessment of Ozone Depletion: 2022 [3].  For all these refrigerants their environmental effects depend on their atmospheric chemistry and their emissions. The atmospheric degradation of the HFOs, HCFOs and hydrocarbons determine their indirect global warming contributions, if any. The atmospheric degradation of HFOs and HCFOs is described in detail in the Environmental Effects Assessment Panel 2022 Report and the yields of TFA are reported in EEAP 2022: TFA yields from HFCs and HFOs - Fluorocarbons.

HFCs, HFOs and HCFOs degradation products: The widely used fluorinated refrigerants should not affect the oxidative capacity as much as hydrocarbon refrigerants based on their lower Photochemical Ozone Creation Potential (POCP) values, compared to propane (see newsletter item about POCP values for these refrigerants). The degradation of fluorocarbon refrigerants has extensively studied and the effects, if any, determined for the intermediate and final fluorinated degradation products.  These are summarised in Table 1.  From this data it can be concluded that the contribution to global warming for intermediate and final breakdown products is of no significance.

Hydrocarbon refrigerants indirect GWPs reported: For the non-methane hydrocarbons (NMHCs) the main contributors to indirect GWPs are through tropospheric chemistry interactions, e.g. methane concentrations increase when the hydroxyl radicals are consumed by the more reactive organic compounds emitted during anthropogenic activities. The photochemical production of ozone, also a greenhouse gas, is also enhanced by an increased burden of NMHCs [4]. The hydrocarbon GWPs [5] have an indirect GWP component accounting for virtually all of their the total GWP.  The indirect GWP of propane is reported as 9.5 due to indirect effects for CH4 lifetime (contributing 5.5 to the indirect GWP) and as an O3 precursor (contributing 4.0 to the indirect GWP), and the direct GWP of propane is reported as 0.018 [Hodnebrog 2018]. The net or total GWP of propane, the sum of the direct and indirect GWPs, is hence 9.5. Similar effects are reported for butane. Reported direct, indirect, and total GWPs are shown in Table 2.

Table References

  1. Montreal Protocol On Substances that Deplete the Ozone Layer UNEP 2022 Assessment Report of the Environmental Effects Assessment Panel (EEAP 2022), Chapter 6, Appendix
  2. SAP 2022: World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022. Annex Table 5A special compounds. Available at https://ozone.unep.org/science/assessment/sap
  3. Tropospheric photolysis of CF3CHO, Mads P. Sulbaek Andersen Ole J. Nielsen, Atmospheric Environment Volume 272, 2022, 118935, https://doi.org/10.1016/j.atmosenv.2021.118935
  4. WMO (World Meteorological Organization), Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project–Report No. 52, 2010. Section 5.4.3.2
  5. Jubb, A.M., McGillen, M. R., Portmann, R. W., Daniel, J. S., Burkholder, J. B.: An atmospheric photochemical source of the persistent greenhouse gas CF4, Geophys. Res. Lett., Volume 42, 2015, Pages 9505-9511, DOI: 10.1002/2015GL066193.
  6. SAP 2022: World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022. Section 7.2.5.2. Available at https://ozone.unep.org/science/assessment/sap

 

Table References

Lifetimes, direct and indirect radiative forcing, and global warming potentials of ethane (C2H6), propane (C3H8), and butane (C4H10), Atmos. Sci. Lett. 2018;19:e804. wileyonlinelibrary.com/journal/asl2 https://doi.org/10.1002/asl.804  Øivind Hodnebrog, Stig B. Dalsøren, Gunnar Myhre, Center for International Climate and Environmental Research-Oslo (CICERO), Oslo, Norway

AR4: Climate Chang 2007: The Physical science Basis, Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.

F-Gas 517.2014, Annex IV

WMO SAP 2022: SAP 2022:  World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022. Annex Table 5A

 

References

[1] Montreal Protocol on Substances that Deplete the Ozone Layer, UNEP 2022 Report of the Refrigeration, Air-conditioning and Heat Pumps Technical Options Committee 2022 Assessment Table 3-1: Classification of 100-year GWP levels

[2] Montreal Protocol On Substances that Deplete the Ozone Layer UNEP 2022 Assessment Report of the Environmental Effects Assessment Panel (EEAP 2022), Chapter 6

[3] SAP 2022:  World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022.

[4] IPCC/TEAP Special Report: Safeguarding the Ozone Layer and the Global Climate System page 163

[5] Lifetimes, direct and indirect radiative forcing, and global warming potentials of ethane (C2H6), propane (C3H8), and butane (C4H10), Atmos. Sci. Lett. 2018;19:e804. wileyonlinelibrary.com/journal/asl2 https://doi.org/10.1002/asl.804  Øivind Hodnebrog, Stig B. Dalsøren, Gunnar Myhre, Center for International Climate and Environmental Research-Oslo (CICERO), Oslo, Norway

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