Recent paper on reaction of HFOs and HCFOs with ozone
The paper by Garavagno et al. “Atmospheric Oxidation of Hydrofluoroolefins and Hydrochlorofluoroolefins by Ozone Produces HFC-23, PFC-14, and CFC-13” [1] reports laboratory measurements and quantum-chemical calculations, to explore the degradation mechanisms and quantify the yields of GHG and ODS products from ozonolysis of four HFOs and one HCFO. The paper then uses atmospheric models to estimate the yields of degradation products from the HFOs and HCFOs and provides estimates of indirect GWPs. It then estimates the quantities of degradation products generated due to arbitrary potential emissions of the HFOs and HCFOs. The paper states that “Ozonolysis contributed <1% to the atmospheric removal of all HFO and HCFO compounds studied, with only a small fraction of this loss pathway leading to HFC-23, PFC-14, or CFC-13.”
Table 1 summarises the reported degradation product yields due to reaction with ozone and the indirect GWPs (and ODP) calculated from atmospheric models. The indirect GWPs are extremely small and the indirect ODP of HCFO-1233xf is negligible.
Table1. Degradation product yields from reaction with ozone and estimated indirect GWPs
| The yields are fractional and not percentages | Yields from reaction with ozone | Indirect GWP | Indirect ODP | |||
| Substance | Structure | CF4
(PFC-14) |
CF3Cl
(CFC-13) |
CF3H
(HFC-23) |
100 year | |
| HFO-1234yf | CF3CF=CH2 | 0.0012 | 0.03 | |||
| HFO-1234ze(E) | Trans- CF3CH=CFH | 0.079 | 3.3 | |||
| HFO-1225ye(Z) | Cis-CF3CF=CFH | 0.0102 | 0.2 | |||
| HFO-1225ye(E) | Trans- CF3CF=CFH | 0.0104 | 0.6 | |||
| HCFO-1233xf | CF3CCl=CH2 | 0.00034 | 0.04 | 0.0000007 | ||
Table notes: The degradation product yields are averages (without the uncertainties) from Table 1 of Garavagno et al. [1]. The indirect GWPs are taken from Figure 3 of Garavagno et al. [1] for HFO 1234yf and from information reported in the text of Garavagno et al. for HFO-1234ze(E). The indirect ODP for HCFO-1233xf is calculated from the overall modelled weight yield of CF3Cl and its ODP of 0.3. Therefore, some of these indirect GWP values may be approximations.
The paper explains that the experimentally determined percent yield (7.9%) for HFC-23 produced from the ozonolysis of HFO-1234ze(E) are higher than a previously reported value of 3.11 ± 0.05% obtained using the same experimental apparatus [2]. This is attributed to refinements to the experimental procedure but corrected atmospheric model calculations result in a lower indirect GWP. In addition, PFC-14 (CF4) is detected in a very low yield from reaction of HFO-1234yf with ozone. Previously it was reported that PFC-14 was not detected [2].
The estimated indirect GWPs depend on the atmospheric models used. Van Hoomissen et al. [3] uses the yield of CHF3 from reaction with ozone reaction reported by McGillen et al. [2] to calculate indirect GWPs but using a different model to McGillen et al. The indirect GWP of 1.1 for HFO-1234ze(E) reported by Van Hoomissen et al. due to reaction with ozone is lower than the 3.3 value reported by Garavagno et al. [1] even though the experimentally determined yields for HFC-23 reported by Garavagno et al. are higher than those reported by McGillen et al.
Emissions of the HFOs and HCFO
Garavagno et al. [1] arbitrarily assume that the four HFOs and the HCFO will each be emitted as 1/5 of the total estimated HFC-134a emission of 0.21 Tg yr−1 (210,000 tonnes/year) to give a “full-transition” scenario in equal quantities in the future. The paper also notes that HCFO-1233xf has significant industrial demand, as an intermediate in the production of HFO-1234yf, which is widely used in automotive air-conditioning systems and the paper states that the use of HCFO-1233xf in HFO-1234yf production suggests that substantial amounts of this HCFO could have already been released into the troposphere.
However, as HCFO-1233xf is used as a feedstock in one of the routes used to manufacture HFO-1234yf, any emissions relate to its production and use as a feedstock and do not equal the volume produced. The MCTOC most likely emission factor for modern-day, regulated manufacturing from production, supply chain, and use of feedstock is 3.6 weight % [4]. In addition, HFO-1225ye(Z) and HFO-1225ye(E) are not used as refrigerants or foam blowing agents. HFO-1225ye(Z) exhibited toxic effects [5] upon longer exposures at the relatively low levels of 500 to 1,000 ppm, which precludes its use in these applications. Similar toxic effects would be expected for HFO-1225ye(E).
Table 2 has estimates of the four HFO and HCFO emissions and the generated degradation products in the period until 2020. It is assumed, as an upper limit, that all HFO-1234yf production uses HCFO-1233xf as feedstock with an emission factor of 3.6%, although there are other commercial routes that do not use HCFO-1233xf. There are no published data on HFO and HCFO global production, but one paper [6] comments that HFO-1234yf is the dominant HFO refrigerant in the period until 2020, with significant production of other HFOs and HCFOs occurring from 2015. It estimated 105,000 tonnes of HFO-1234yf production by 2020 and as global emissions of HFOs and HCFOs are not well characterized, the paper estimated total emissions of HFO-1234yf by 2020 at 30,000 tonnes and assumes that global emissions of HFO-1234ze(E), HFO-1336mzz isomers, and HCFO-1233zd(E) together are similar to HFO-1234yf emissions up to 2020. In Table 2 it is assumed that HFO-1234ze(E) emissions account for 50% of the 30,000 tonnes for these HFOs and HCFO. Table 2 also has the reported global emissions of HFC-23, PFC-14 and CFC-13 in 2020 [7]. Clearly, the estimated degradation product generation is currently insignificant compared to reported global emissions from atmospheric monitoring.
Table 2. Estimated generation of degradation products up to 2020 compared to global emissions
| Degradation products generated up to 2020 (tonnes) | ||||
| Substance | Emissions by 2020 (tonnes) | CF4 (PFC-14) |
CF3Cl (CFC-13) |
CF3H (HFC-23) |
| HFO-1234yf | 30,000 | 0.12 | ||
| HFO-1234ze(E) | 15,000 | 3.7 | ||
| HFO-1225ye(Z) | 0 | |||
| HFO-1225ye(E) | 0 | |||
| HCFO-1233xf | 4500 | 0.01 | ||
| Global emissions in 2020 [7] | 15,000 | 600 | 16,500 | |
EFCTC conclusion. The extremely small indirect GWPs mean that they do not change the conclusion that these substances will not make any significant contribution to the radiative forcing of climate change. The EFCTC newsletter of May 2025, discussed yields of HFC-23 from the intermediate degradation product CF3CHO “Very low yields of HFC-23 from some HFOs and some HCFOs: Summary of recent publications”
References
[1] Garavagno, M. d. l. A., Wenger. A., Holland, R. E. T., Fena, B. R., Goldstein, S. D., Hicks, D. E., et al., Atmospheric Oxidation of Hydrofluoroolefins and Hydrochlorofluoroolefins by Ozone Produces HFC-23, PFC-14, and CFC-13. Environmental Science & Technology 2025 59 (48), 26031-26040. https://doi.org/10.1021/acs.est.5c11383
[2] McGillen, M. R., Fried, Z. T. P., Khan, M. A. H., Kuwata, K. T., Martin, C. M., O’Doherty, S., et al., Ozonolysis can produce long-lived greenhouse gases from commercial refrigerants. Proceedings of the National Academy of Sciences 120, no. 51 (2023): e2312714120., https://doi.org/10.1073/pnas.2312714120
[3] Van Hoomissen, D. Chattopadhyay, A., Montzka, S. A. and Burkholder, J. B., CHF3 (HFC-23) and CF3CHO Quantum Yields in the Pulsed Laser Photolysis of CF3CHO at 248, 266, 281, and 308 nm, ACS Earth and Space Chemistry 2025 9 (3), 589-602, DOI: 10.1021/acsearthspacechem.4c00316
[4] TEAP (2024). Technology and Economic Assessment Panel Progress Report, Volume 1, Table 5-9. Available at Technology and Economic Assessment Panel (TEAP) | Ozone Secretariat
[5] Schuster, P. X., Biotransformation of Trans-1,1,1,3-tetrafluoropropene, 2,3,3,3-Tetrafluoropropene and 1,2,3,3,3-Pentafluoropropene (Bayerischen Julius-Maximilians-Universita¨t Wurzburg, 2009).
[6] Lindley, A. A., An Updated Inventory of Fluorspar CaF2 Production, Industrial Use, and Emissions of Trifluoroacetic Acid (TFA) from 1930, Including the Period from 2000 to 2020 https://doi.org/10.4236/gep.2025.1311008
[7] Scientific Assessment of Ozone Depletion (2022), World Meteorological Organization (WMO). GAW Report No. 278, 509 pp.; WMO. Scientific Assessment Panel (SAP) | Ozone Secretariat