Observations on recent report: Assessment of Available Low Global Warming Potential Alternatives to F-gas Refrigerants
The recent report “Assessment of Available Low Global Warming Potential Alternatives to F-gas Refrigerants” authored by Gabriel Salierno of the Toxics Use Reduction Institute (TURI) [1], examines alternatives to legacy hydrofluorocarbon gases (HFCs) and emerging low-GWP alternatives across fluorinated and non-halogenated options used in vapor compression air conditioning, refrigeration, and heat pumps. Although, the assessment compares the availability, safety, effectiveness, and affordability of alternative refrigerants to HFCs, it is important to understand the sources and basis for some of its conclusions, particularly as they relate to HFO refrigerants and TFA.
As additional background, the Environmental Effects Assessment Panel (EEAP) Update Assessment 2024 [2] provides an update on the atmospheric chemistry of HFCs and HFOs and discusses new measurements of concentrations of trifluoroacetic acid (TFA) in the environment concluding that for HFOs the formation of CF3H (HFC-23) from photolysis of CF3CHO is of negligible importance and that CF3H generated by ozonolysis does not alter EEAP’s previous assessments that HFOs have minimal contributions to the radiative forcing of climate change. EEAP also concludes that the risk to humans from chronic exposures to TFA in surface waters remains de minimis at current concentrations of TFA.
Formation of HFC-23 as a degradation product from HFOs.
Salierno summarises his earlier review paper ‘On the Chemical Pathways Influencing the Effective Global Warming Potential of Commercial Hydrofluoroolefin Gases’ [3] about the formation of HFC-23 from HFOs from the degradation product CF3CHO and TFA (CF3COOH).
HFC-23 from CF3CHO. Salierno still refers to the Campbell et al. [4] paper commenting CF3CHO can undergo a very fast photo-dissociation in the lower atmosphere potentially delivering HFC-23 in up to 17% yield. This result has been shown to be incorrect by the same research team [5] and independently by Van Hoomissen et al. [6], finding HFC-23 yields of 0.12-0.14% at atmospheric pressure [see item in this newsletter 7]. In fact, the Thomson et al. [5] paper was published on December 23, 2024, before the publication date of Salierno’s report (April 2025). Also not referenced by Salierno is a 2022 paper [8], published following the Campbell et al. paper, which reported an upper limit of HFC-23 formation of 0.3% from CF3CHO. Salierno states “This conversion [to HFC-23] potentially contributes a GWP up to 2516 for HFO-1234ze(E)”, whereas the recent Thomson et al. paper by the same research group estimates a course GWP of about 6.
HFC-23 from TFA conjecture. Salierno’s summary of the potential formation of HFC-23 from degradation of TFA, based on his review paper was analysed in detail in the EFCTC September 2024 newsletter item [9] which reflects on the review by Salierno [3]. Salierno proposes that trifluoroacetic acid (TFA) decarboxylation by three different mechanisms can generate HFC-23. These proposed mechanisms are reviewed in the newsletter item, which also has data on emissions of HFC-23 derived from atmospheric monitoring, which is consistent with increasing HCFC-22 production from the 1940s. It also comments on the lack of known degradation pathways for TFA in environmental aqueous phases. Significantly, the Report of the Scientific Assessment Panel (SAP) in response to Decision XXXV/7: Emissions of HFC-23 [10], published September 2024, comments that “The recent Salierno (2024) review proposes additional chemical pathways to the formation of CHF3 through the heterogeneous chemistry of CF3C(O)OH (trifluoroacetic acid, TFA). However, no experimental evidence exists to suggest that this chemistry might actually occur in the atmosphere, making this suggestion speculative.”
HFC-23 from reaction of HFOs with ozone. For completeness although Salierno does not discuss this, very low yields of HFC-23 can be formed from some HFOs by reaction with ozone. See EFCTC newsletter for January 2024 [11] and January 2025 [12] and this newsletter.
In summary, for the HFOs and HCFOs refrigerants, and contrary to the discussion in Salierno report, the formation of HFC-23 from some HFOs and HCFOs does not change the conclusion that they will not make any significant contribution to the radiative forcing of climate change.
Health effects of TFA in the environment. The Salierno report discusses the health effects of TFA, particularly the studies used to derive the UBA (Germany) health guidance value for TFA in drinking water of 60 ug/L, with a target value of 10 ug/L [13]. Salierno also notes that the possibility of TFA-forming fluorinated refrigerants inducing acute hepatitis cannot be dismissed based on the well-known effects of HCFC-123 and the anaesthetic 1,1,1-trifluoro-2-bromo-2 chloroethane (halothane) causing acute hepatitis. The potential health effects of TFA are distinct (see summary below) from the health effect due to the metabolism of for example halothane.
Halothane. The detection of metabolically generated TFA in mammals has been reported and TFA has a reported urinary elimination half-life in humans of 16 hours [14]. Halothane was extensively used as an anaesthetic in the past and jaundice and hepatic necrosis are rare toxic reactions which follow halothane anaesthesia. However, TFA produced by metabolism of halothane does not result in these toxic effects. It is important not to confuse the metabolic formation of TFA with the formation of reactive intermediates (e.g., trifluoroacetyl chloride) [15]. Once inhaled, some halogenated anaesthetic agents are biotransformed (i.e., metabolized) in the liver with the halothane biotransformation shown to occur via trifluoroacetyl chloride and not via TFA [16]. The biotransformation products include reactive intermediates along both oxidative (trifluoroacetyl chloride) and reductive (free radical) pathways that ultimately generate the metabolites trifluoroacetic acid and fluoride, respectively [17]. The chemically reactive trifluoroacetyl chloride forms non-protein thiol adducts as well as adducts with nucleophilic tissue macromolecules (e.g., proteins, unsaturated lipids) and leads to hepatic injury and potentially fatal hepatitis-like reaction that is characterized by severe hepatocellular necrosis. The free radicals that are formed have been shown to affect lipid peroxidation.
TFA health effects. The unreactive nature of TFA in the environment translates into an inertness in organisms, thereby limiting its toxic effects. TFA has been detected in a wide range of organisms, therefore a primary concern relates to its potential toxicity in humans and other mammals. A full review of the question of mammalian toxicity in 2023 can be found in Dekant et al. [18] and was subsequently summarized by Garavagno et al. [19], “A full review of the question of mammalian toxicity can be found in Dekant et al. [18], but can be summarized with the following: at the time of writing, the potential of TFA to induce toxicity in living organisms is considered to be very low. Additionally, TFA is reported to be easily excreted by mammals and so is unlikely to bioaccumulate.”
The Federal Office for Chemicals (BfC) at the Federal Institute for Occupational Safety and Health (BAuA) serves as the designated competent authority in Germany for implementation and enforcement of the European Chemicals Regulation (REACH) and the Classification, Labelling and Packaging (CLP) Regulation. In 2024, in a coordinated effort with the Federal Environment Agency (UBA) and the Federal Institute for Risk Assessment (BfR), the BfC has submitted a dossier to the European Chemicals Agency (ECHA) proposing a harmonized hazard classification for trifluoroacetic acid (TFA) pursuant to the CLP Regulation.
German authorities have identified TFA as exhibiting reproductive toxicity (Category 1B) proposing a corresponding harmonized classification and labelling. The CLH dossiers for TFA and its inorganic salts have been published on the ECHA website [20].
The harmonization process is currently in the consultation phase. The outcome of this process will determine the final classification and labelling requirements for TFA.
There is now an opportunity to review and submit public comments. As long as the CLH process is ongoing, no conclusion on the proposed TFA classification can be drawn. There has not been any evidence for risk from environmental TFA exposure for human health or the environment to date. Stakeholders with information regarding the identity or hazard properties of a substance are encouraged to share this information between 26 May and 25 July 2025.
LINK: https://echa.europa.eu/harmonised-classification-and-labelling-consultation/-/substance-rev/80001/term.
Flammability of HFOs. According to the Salierno report, the flammability of HFOs is only slightly lower than that of HCs. However, there are distinct differences that result in the classification of HFOs as ASHRAE 2L flammability compared to HCs as 3 flammability. The three flammability properties used for classification are compared in the table below for HFO-1234yf and HC-290 and confirm that there are significant differences [21].
Average GWP for HFC/HFO blends. The Salierno report states “The concept of “average GWP”, when the components are weighted by mass percentage of their GWPs, can be misleading as it downplays the fact that some gases in a blend may have a much higher GWP than others, and it does not avoid the release of high-GWP gases into the atmosphere, even if the overall GWP of the blend is relatively low.” In fact, with a phase down of HFCs (in the USA and the EU and globally under the Kigali Amendment) the quantity of HFCs as CO2e is capped and the lower GWP blends do not change the allowable quantity. Improved leak tightness and monitoring will contribute to an overall reduction in emissions.
Naturally occurring TFA. The Salierno report states that “The consensus among most experts is that TFA is not naturally occurring”. The report does not reference the 2024 UBA report “Analysis of current seawater samples for trifluoroacetic acid” is an important new study on current concentrations of TFA in the Atlantic Ocean [22]. A validated analytical method was applied to surface water and deep-sea water samples of the Atlantic Ocean collected in 2022 and 2023 during two independent sampling campaigns. During the expeditions, a total of 33 surface water samples were taken in the Atlantic Ocean at 31 measuring points between latitudes 47° south to 50° north. The surface water samples had TFA concentrations between 260 ng/L and 306 ng/L. A total of seven depth profiles of the Atlantic Ocean were obtained, at maximum extraction depths of 3800 m and 4590 m. The TFA concentrations of samples from seven depth profiles ranged from 237 ng/L to 294 ng/L. All depth profiles, except for one, showed a slight decrease in TFA concentration with increasing ocean depth. In the current UBA measurement campaign, no significant difference could be determined in the mean TFA contents of samples from the northern and southern hemisphere. According to EFCTC Newsletter of September 2024, these concentrations would imply that there is a large natural content of TFA in the Atlantic Ocean [23].
The Salierno report has a US focus and references an EPA report “The Social Costs of Hydrofluorocarbons and the Large Climate Benefits from their Expedited Phasedown” [24] which comments that “Whilst a full phase-out of HFCs may be difficult to realize in the short-term, the existence of HFC substitutes (such as HFOs) and low-GWP refrigerants (such as ammonia and CO2) may enable a more aggressive and accelerated phasedown schedule than that outlined under Kigali”. The Salierno report also references the EPA Regulatory Impact Analysis [25] which states “One breakdown byproduct of certain HFOs that has been studied as a potential source of adverse health and environmental impact is trifluoroacetic acid (TFA). TFA is also a breakdown product of the most widely used HFC, HFC-134a. HFO-1234yf produces about three times as much TFA per molecule as HFC-134a, and the TFA produced is more contained in the local area near the release of the HFO, so a transition from HFC-134a to HFO-1234yf may lead to increased environmental concentrations of TFA in some areas. EPA’s SNAP program considered the potential risk associated with increased concentrations of TFA when HFO-1234yf was first listed as acceptable subject to use conditions in motor vehicle air conditioners. It cited myriad studies that concluded that the additional TFA from HFO-1234yf did not pose a significant additional risk, even if it were assumed to be used as the only refrigerant in all refrigeration and air conditioning equipment (76 FR 17492-17493; March 29, 2011). More recently, the World Meteorological Organization concluded that “[t]here is increased confidence that [TFA] produced from degradation of HFCs, HCFCs, and HFOs will not harm the environment over the next few decades” while also calling for periodic re-evaluation of this conclusion [26].
References
[1] Toxics Use Reduction Institute (TURI) University of Massachusetts Lowell and commissioned by the Natural Resources Defense Council (NRDC). https://www.turi.org/wp-content/uploads/2025/04/2025-Refrigerant-Report-041025-FINAL.pdf
[2] United Nations Environment Programme (UNEP), Environmental consequences of interacting effects of changes in stratospheric ozone, ultraviolet radiation and climate: UNEP Environmental Effects Assessment Panel, Update 2024, UNEP: This document is available online at the following location: https://ozone.unep.org/sites/default/files/2025-03/EEAP%20Update%20Assessment%202024.pdf
[3] On the Chemical Pathways Influencing the Effective Global Warming Potential of Commercial Hydrofluoroolefin Gases, Gabriel Salierno, ChemSusChem, 2024, e202400280 , Review doi.org/10.1002/cssc.202400280
[4] Campbell, Jyoti S., Scott H. Kable, and Christopher S. Hansen. "Photodissociation of CF3CHO provides a new source of CHF3 (HFC-23) in the atmosphere: implications for new refrigerants." Preprint Publication (2021).
[5] Thomson, Joshua D., Jyoti S. Campbell, Ethan B. Edwards, Christopher Medcraft, Klaas Nauta, Maria Paula Pérez-Peña, Jenny A. Fisher, David L. Osborn, Scott H. Kable, and Christopher S. Hansen. "Fluoroform (CHF3) Production from CF3CHO Photolysis and Implications for the Decomposition of Hydrofluoroolefins and Hydrochlorofluoroolefins in the Atmosphere." Journal of the American Chemical Society (2024).
[6] D. Van Hoomissen, A. Chattopadhyay, S. A. Montzka, and J. B. Burkholder, 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
[7] EFCTC Newsletter Very low yields of HFC-23 from some HFOs and some HCFOs: Summary of recent publications
[8] Andersen, Mads Peter Sulbaek, and Ole John Nielsen. "Tropospheric photolysis of CF3CHO." Atmospheric Environment 272 (2022): 118935.
[9] EFCTC Newsletter September 2024 Experts’ reflections on the Salierno et al. paper titled ‘On the Chemical Pathways Influencing the Effective Global Warming Potential of Commercial Hydrofluoroolefin Gases
[10] Report of the Scientific Assessment Panel in response to Decision XXXV/7: Emissions of HFC-23, 15 September 2024, Lead Authors: S. A. Montzka, NOAA Global Monitoring Laboratory, USA; J. B. Burkholder, NOAA Chemical Sciences Laboratory, USA, available here, or from or from Scientific Assessment Panel (SAP) | Ozone Secretariat (unep.org).
[11] EFCTC Newsletter January 2024 Reaction of Ozone with HFOs and HCFOs
[12] EFCTC Newsletter January 2025 Reaction of Ozone with HCFO-1233zd(E)
[13] Trifluoressigsäure (TFA)–Gewässerschutz im Spannungsfeld von toxikologischem Leitwert, Trinkwasserhygiene und Eintragsminimierung. Erläuterungen zur Einordnung des neuen Trinkwasserleitwerts von 60 μg/L.
- Oktober 2020. Umweltbundesamt www.umweltbundesamt.de
[14] Absorption, Biotransformation, and Storage of Halothane, D. A. Holaday, Environmental Health Perspectives, Vol. 21, pp. 165-169, 1977
[15] Biotransformation of Halothane, Enflurane, Isoflurane, and Desflurane to Trifluoroacetylated liver Proteins: Association Between Protein Acylation and Hepatic Injury, Njoku, D. et al, Anesth Analg 1997; 84: 173-8
[16] Atkinson J., et al., (2012). Biochemical Mechanisms of Drug Toxicity. Principles of Clinical Pharmacology (Third Edition).
[17] Covalent binding of oxidative biotransformation reactive intermediates to protein influences halothane-associated hepatotoxicity in guinea pigs, Lind, R.C., and Gandolfi, A.J. (1991). Adv. Exp Med. Biol. 283:763-6. DOI: 10.1007/978-1-4684-5877-0_102
[18] Mammalian toxicity of trifluoroacetate and assessment of human health risks due to environmental exposures, Dekant, W.; Dekant, R. Arch. Toxicol. 2023, 97, 1069–1077.
[19] Trifluoroacetic Acid: Toxicity, Sources, Sinks and Future Prospects, M. de los Angeles Garavagno, R. Holland, M. A. H. Khan, A. J. Orr-Ewing and D. E. Shallcross, Sustainability 2024, 16(6), 2382; https://doi.org/10.3390/su16062382
[20 ] Two CLH dossiers are available at ECHA: Trifluoroacetic acid https://echa.europa.eu/harmonised-classification-and-labelling-consultation/-/substance-rev/80001/term Sodium trifluoroacetate; [1] and other inorganic salts of trifluoroacetic acid [2] https://echa.europa.eu/harmonised-classification-and-labelling-consultation/-/substance-rev/80002/term
[21] Journal of Loss Prevention in the Process Industries 49 (2017) 662 – 674, Flammability and explosion characteristics of mildly flammable
Refrigerants, S.G. Davis, J.L. Pagliaro T.F. Debold, M. van Wingerden, K. van Wingerden. Note, some of the flammability data in this reference is different to that usually quoted for refrigerants, but different test methods can result in different results although with the same trends
[22] ] Examination of current seawater samples for trifluoroacetic acid | Federal Environment Agency (umweltbundesamt.de), Texte 35/2024, F. Freeling, and A Mangels
[23] EFCTC September 2025 Newsletter “UBA report “Analysis of current seawater samples for trifluoroacetic acid”, “Do the UBA results indicate a significant TFA content in the Atlantic Ocean and imply a natural source? Detailed Discussion”, and
[24] US EPA, O. The Social Costs of Hydrofluorocarbons and the Large Climate Benefi ts from their Expedited Phasedown.
[25] US EPA. Regulatory Impact Analysis for Phasing Down Production and Consumption of Hydrofluorocarbons (HFCs), 2022.
[26] World Meteorological Organization (WMO), Executive Summary: Scientific Assessment of Ozone Depletion: 2018, World Meteorological Organization, Global Ozone Research and Monitoring Project – Report No. 58, 67 pp., Geneva, Switzerland, 2018. Available at https://ozone.unep.org/sites/default/files/2019-04/SAP-2018-Assessment-report-ES-rev%20%281%29.pdf.