Experts’ reflections on the Salierno et al. paper titled ‘On the Chemical Pathways Influencing the Effective Global Warming Potential of Commercial Hydrofluoroolefin Gases [1].’

Photolysis of CF₃CHO to produce CF₃H

Salierno concludes that CF₃H is formed in yields of about 7% to 19% from the photolysis of CF₃CHO. This conclusion is stated to be based on a 2021 paper by Campbell et al. [4,5]. However, the Campbell et al. paper neither discusses CF₃H formation, nor does it provide yields of CF₃H from the photolysis of CF₃CHO. Salierno may have referred to the preprint [6] by the same author group claiming the formation of CF₃H in yields of 11.0 ± 5.5 % from the atmospheric photolysis of CF₃CHO. The preprint was posted on ResearchGate in February 2021 and has yet to be published in a peer-reviewed journal. The experiments described in the preprint did not detect the formation of CF₃H by elimination of CO from CF₃CHO, but instead inferred its formation, by this mechanism, based on the detection of CO. In addition, the experiments were performed under collision-less conditions (zero pressure), which are not representative of atmospheric conditions. Therefore, the yield of 7 to 19% 2021 Campbell et. al paper [4] is not the right number to be used as a general.

To reinforce this, our experts note that the Andersen et al. paper [7], which examined the photolysis of CF₃CHO under tropospheric conditions found that no formation of CF₃H, HFC-23, was observed under any of the experimental conditions. It established an upper limit for the yield of HFC-23 of 0.3 %.

There still is a scientific discussion ongoing with Salierno mentioning that for the Andersen paper the methods employed to disprove the formation of HFC-23 from TFE [CF₃CHO] via photolytic decarbonylation are found to be insufficient. Due to the very low characteristic time of Pathway 1 [the elimination of CO to give CF₃H]. He added that it can only be captured by novel ultrafast spectroscopic techniques such as laser induced fluorescence coupled with velocity map ion imaging. With their experimental method set up to detect the actual formation of CF₃H by elimination of CO from CF₃CHO[1], the Andersen et al. paper comments that their results are in contradiction to those published most recently [6], which claimed to have observed HFC-23, and which has created a lot of debate in the scientific community. This is the first study of broadband UV photolysis of CF₃CHO, combined with FTIR detection of CF₃H.

Pathways Involving the trifluoromethyl radical

Salierno et al. mention that there is another possibility involving CF₃·in hydrogen atom abstraction (Pathway 3: CF₃ + RH ® CF₃H) in contact with any hydrogen donors, collectively denominated here as RH. The atmosphere contains a variety of components that can do so, namely water, methane, methanol, dimethyl amine, among others. They postulate that since the CF₃O₂· adduct intermediate [formed from reaction of CF₃ with O_2, reversibly according to Salierno] is the pivotal precursor towards either HFC-23 or mineralization and the presence of liquid water favors CF₃· hydrogen abstraction, Pathway 3 cannot be ruled out entirely.

In relation to the above statement, the EFCTC experts point out the following:

• The established atmospheric chemistry indicates that CF₃ radicals react rapidly with oxygen [9] (lifetime is on the order of 10s of nanoseconds [10]) to produce the CF₃O₂ peroxy radical, which in turn reacts rapidly (lifetime in the order of seconds [10]) with NO, primarily, and also HO₂ and RO₂
• Salierno proposes that reaction of the CF₃ radical with hydrocarbons and H₂O (gas) is significant. In fact, the reaction rates are quite slow, at least 4-5 orders of magnitude slower than reaction with oxygen. For example, the reaction of CF₃ radical with ethane has a lifetime of 10,000s of seconds [11], many orders of magnitude slower than CF₃ + O₂.
• Salierno discusses reaction of the CF₃ radical in liquid water and proposes this can lead to CF₃ However, liquid water is not abundant in the atmosphere, and this chemistry is typically rate-limited by diffusion into the liquid phase, whereas the CF₃ radical lifetime in the atmosphere is in the order of 10s of nanoseconds [10].

TFA as a potential source of HFC-23

Garavagno et al. 2024 [2] note that TFA demonstrates exceptional stability across different environments, which is primarily attributed to its structural characteristics. It is not photochemically activated at the wavelengths of solar radiation that reach the troposphere. In the absence of any abstractable H atoms, it is resistant to chemical degradation by hydrogen abstraction reactions, and the carbon–fluorine bonds are chemically inactive. Consequently, TFA exhibits a slow rate of degradation in the environment.

In contrast, Salierno proposes that trifluoroacetic acid (TFA) decarboxylation by three different mechanisms can generate HFC-23. He adds that HFO-1234yf and other sources of TFA would, if this were correct, contribute to this unexpected HFC-23 surge. These three proposed degradation mechanisms are reviewed, plus some data on emissions of HFC-23 derived from atmospheric monitoring and the lack of known degradation pathways in environmental aqueous phases:

• Proposed mechanism 1: hydrothermal TFA Decarboxylation:

Salierno proposes that the decarboxylation of TFA, or its sodium salt, in water at > 100^oC and 275 bar pressure (hydrothermal conditions) in the presence of a catalytic surface can be used to derive indirect GWPs due to HFC-23 formation from TFA in water at room temperature. A paper referenced by Salierno (Auerbach et al. [12]) reports that sodium trifluoroacetate and TFA do not decompose in water at temperatures below the boiling point of water. Salierno references decarboxylation rates in water at 275 bar pressure at temperatures > 100°C (hydrothermal conditions) and then uses the rate constants to derive half- life data for TFA in water at nearly room temperature and its effective GWP100 contribution. However, the data reported by Salierno has a wide range of results and show surface effects from the reaction vessel: In addition, the reactor surface might play a role in the rate of reactions [including for TFA and TFA acetate] at hydrothermal conditions [13]. For example, with the same reaction conditions Salierno derives, at 17°C an indirect GWP of 0 from a reaction carried out in stainless steel-316 compared to an indirect GWP of 111 from reaction at 17^oC in a titanium vessel [14]. Other data from similar experiments reported by Salierno, resulted in derived GWPs of 0 at 17°C. In his summary table 10, Salierno selects the derived indirect GWPs in the titanium vessel (111-8169 indirect GWP for temperature range 17°C to 45°C) and not the much lower derived GWPs in stainless steel 316 (0-44 indirect GWP, 17°C to 45°C), or the 0-34 GWP (17°C to 45°C) derived from data in a different referenced paper [15].

TFA in precipitation, due to the degradation of fluorocarbons in the atmosphere, will subsequently be transferred to the oceans, where there is already a large TFA burden, thought to be from a natural source (see discussion below on emissions of HFC-23 derived from atmospheric monitoring). The sea surface temperature is about 21°C averaged over the extra-polar global ocean (60°S–60°N) [16] and the sea water temperature generally decreases with depth [17], so it is unclear why Salierno has selected data up to 45°C, derived from experiments at high temperature, 275 bar, in the presence of a titanium surface, which appears to have a catalytic effect promoting the decarboxylation of TFA.

• Proposed mechanism 2: direct Overtone Photodissociation (DOP) of TFA:

Salierno uses the tropospheric lifetime for HF elimination from TFA by DOP and applies it to the decarboxylation of TFA. DOP involving vibrational overtone excitation in the visible light bandwidth is followed by intramolecular energy transfer to a weaker bond, which may cause a molecule to dissociate. Salierno references a paper by Reynard and Donaldson “Overtone-Induced Chemistry of Trifluoroacetic Acid: An Experimental and Theoretical Study” [18]. This paper quotes a tropospheric lifetime of between 8 and 127 years for the elimination of HF from CF₃COOH and states that this reaction has the lowest activation energy:

CF₃COOH ® CF₂CO₂ + HF

The paper by Reynard and Donaldson does not derive tropospheric lifetimes for the decarboxylation of TFA to give HFC-23, and finds that the decarboxylation pathway has a higher activation energy (72.5 kcal/mol) than the pathway involving elimination of HF (50.3 kcal/mol). It is mentioned that according to the MP2 ab initio calculations, the lowest energy barrier is for HF elimination at 50.3 kcal mol^-1, corresponding to a wavelength <569 nm. This is accessible following excitation to the V_OH= 6 overtone, which is predicted to lie at 525 nm. Salierno uses the tropospheric lifetimes for HF elimination from TFA in the atmosphere and applies these to decarboxylation of trifluoroacetic acid in surface waters: it is plausible that the reinforcement of HFC-23 formation from TFA via DOP could contribute more than 3500 and up to 14800 to the effective GWP of HFOs that degrade into TFA. A further point not discussed by Salierno is that TFA will be in the form of hydrated trifluoroacetate ions in surface waters and not TFA in the atmosphere, which was the subject of the Reynard and Donaldson paper.

• Proposed mechanism 3: Biodegradation of TFA:

A summary in a report [19] for the German Environment Agency (UBA) concludes that the tests consistently report a negligible degradability of TFA. Salierno references a paper by Visscher et al., mentioning that HFC-23 biogenic production competes with TFA reductive dehydrofluorination by methanogenic bacteria from freshwater sediments and sea beds [20]. These results could not be repeated, however, as reported by Boutonnet et al. [21]. The latter explain that the phenomenon has only been observed in certain field samples by the one laboratory and that reinvestigation of samples from the same field sites (by the same laboratory) failed to confirm the initial results (Matheson et al. [22]). Boutonnet refers to Emptage et al. [23] noting that another laboratory reported that marine sediments from the sites that had previously been shown to be active by Visscher et al. (San Francisco Bay) for methanogenic TFA biodegradation were unable to degrade TFA.

A 2021 UBA report [19] summarises TFA biodegradability by stating that different degradation results from standard tests with (extended) closed bottle tests (OECD 301 D) or the SCAS test (OECD 302 A) are available, and that the tests consistently report a negligible degradability of TFA. UBA notes that there is evidence that trifluoroacetic acid is degraded in both oxic (oxygen-containing) and anoxic (oxygen-free) marine sediments (Visscher et al. 1994 [20], Oremland et al. 1995 [24]). The results could not be reproduced and are therefore questioned by Boutonnet et al. (1999, [21]). During bank filtration (26 meters in 8 days) TFA showed a conservative behaviour (Berg et al., 2000, [25]). Scheurer et al. (2017, [26]) confirm that TFA is neither degraded in sewage treatment plants nor in soil filters. Franco et al. (2014, [27]) describe that the mycorrhizal fungus Pisolithus tinctorius tolerates and is able to degrade TFA. Ellis et al. (2001a, [28]) observed in a field study no degradation of TFA even after one year. Kim et al (2000, [29]) report anaerobic TFA degradation via co-metabolism by reductive dehalogenation in a 90-week study.

• Evidence from emissions monitoring

The Salierno paper proposes that these pathways for the formation of HFC-23 may contribute to the increasing atmospheric levels of HFC-23 and explain the difference between reported inventory based estimates and atmospheric monitoring derived emission estimates for the year 2017: There is a gap in the understanding of current atmospheric HFC-23 concentration trends that motivates the present review as a comprehensive global warming hazard assessment of HFOs to find its significance in this context. Moreover, the mechanisms and intermediates addressed in this work could bring a fresh revision of processes taken from granted, such as the fate of CF₃ radical, common with other HFCs, and would help explain this unexpected HFC-23 surge.
However, in determining the potential contribution, if any, of HFOs to the mentioned unexpected HFC-23 surge, these factors should be considered:

• HFO emissions estimates
• Historical HFC-23 emissions and HCFC-22 production trends from 1950; and
• Trifluoroacetic Acid (TFA) burden in surface waters,

The Stanley et al. paper [30] referenced by Salierno, discusses an unexpected increase HFC-23 emissions until 2017. It concludes that, given the magnitude of the discrepancy between expected and observation-inferred emissions, it is likely that the reported reductions have not fully materialized or there may be substantial unreported production of HCFC-22, resulting in unaccounted-for HFC-23 by-product emissions. Stanley et al. add that their integrated difference between the inferred top-down emissions and the bottom-up estimate that considers reported emission reductions, was 24.4 Gg [24,400 tonnes] between 2015 and 2017.

• HFO emission estimates

The Scientific Assessment of Ozone Depletion: 2022 (SAP 2022) [31] estimates 30,000 tonnes of TFA emissions in 2020 from 30,000 tonnes of HFO-1234yf emissions to atmosphere. Emissions of HFO-1234yf would be much lower in the years to 2017. Although SAP 2022 does not estimate emissions for the other HFOs, these are expected to be significantly lower due to their production volumes and applications. It is likely that global emissions of HFO-1234ze, HFO-1366mzz and HCFO-1233zd were negligible before 2015. The EU was an early adopter of HFOs and estimates of emissions for 2018 are available in a UBA report [32]. Based on this, it is unlikely that global emissions of HFO-1234ze, HFO-1366mzz and HCFO-1233zd were significantly larger in 2016 and 2017.

	2018 EU-28 Emissions Metric Tonnes
HFO-1234yf	2,926
HFO-1234ze	4
HFO-1336mzz	8
HCFO-1233zd	159

Table 1. Extract from Table 24 of UBA report [32]: Overview of the demand and emission quantities of the individual HCFCs, HFCs, u-HFCs [HFOs] and u-HCFCs [HCFOs] in Europe (EU-28) in metric tons in the years 2018, 2020, 2030 and 2050 for the “u-HFC and u-HCFC maximum scenario”.

• Some more information on degradation via CF₃CHO:

HFO-1234ze, HFO-1366mzz and HCFO-1233zd all degrade in the atmosphere via CF₃CHO. Salierno suggests HFC-23 yields of 7 to 19% [33] from CF₃CHO. Assuming global emissions of HFO-1234ze, HFO-1366mzz and HCFO-1233zd in the period 2015 to 2017 are 500 tonnes in total, then, according to Salierno, HFC-23 emissions would be about 20 to 70 tonnes [34]. Stanley et al. identified a 24,400 tonne gap in inventory and atmospheric monitoring derived HFC-23 emissions between 2015 and 2017. This means that degradation of these HFOs can be discounted as contributing significantly to the HFC-23 emissions gap. In fact, Andersen et al. [7] reported that for HFC-23 from CF₃CHO in the troposphere no formation of CF₃H, HFC-23, was observed under any of the experimental conditions and an estimated upper limit for the yield of HFC-23 of 0.3 % was established.

• HFC-23 emissions and HCFC-22 production

Emissions of HFC-23 derived from atmospheric monitoring do not support Salierno’s theories about production of HFC-23 from TFA. Stanley et al. [30] explain that, in common with previous studies, their bottom-up HFC-23 estimate, based on HCFC-22 production and UNFCCC reports, was in good agreement with emissions inferred from atmospheric observations prior to the CDM period (2006). They also noted that, during the CDM period, the measurement-derived emissions showed a decline to a minimum in 2009, as expected from CDM reports. Between 2009 and 2012, both top-down and bottom up (with developing country abatement) HFC-23 emissions estimates increased and were in good agreement, within the uncertainty of the top-down estimate.

Salierno proposes that TFA present in surface water can degrade to HFC-23. If this was a significant degradation route to HFC-23, then HFC-23 emissions might be expected to result from the large quantity of TFA in the Atlantic Ocean and its surface waters, which is thought to have accumulated over possibly millions of years [35, 36]. However, according to Simmonds et al. [37], the top-down (atmospheric monitoring) annual mean emissions of HFC-23 in 1950 were effectively zero. Reported production of HCFC-22 for non-feedstock use was 100 tonnes in 1943, increasing to 800 tonnes in 1950 [38]. Although only HCFC-22 non-feedstock production data is available (AFEAS), its use as a feedstock, for the production of PTFE, can be approximately estimated from available PTFE production data [36]. Simmonds et al. in the supplementary material provide tabulated data for HFC-23 emissions until 1978 [39]. The chart below shows the correlation between estimated HCFC-22 production (feedstock and non-feedstock) and HFC-23 emissions in the period until 1978.

Figure 1: HCFC-22 estimated production is reported non-feedstock production and estimated production for feedstock use.

References and Notes

[1] 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

[2] 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

[3] Luecken, D.J.; Waterland, R.L.; Papasavva, S.; Taddonio, K.N.; Hutzell, W.T.; Rugh, J.P.; Andersen, S.O. Ozone and TFA Impacts in North America from Degradation of 2,3,3,3-Tetrafluoropropene (HFO-1234yf), A Potential Greenhouse Gas Replacement. Environ. Sci. Technol. 2010, 44, 343–348

[4] Photodissociation Dynamics of CF₃CHO: C-C Bond Cleavage, J. S. Campbell, K. Nauta, S. H. Kable, et al., J. Chem. Phys. (in press) (2021); https://doi.org/10.1063/5.0073974

[5] Cited as reference 43 in the Salierno paper

[6] https://assets.researchsquare.com/files/rs-199769/v1_covered.pdf?c=1631852903

[7] Tropospheric photolysis of CF₃CHO, M. P. Andersen and O. J. Nielsen, Atmos. Environ., 2022, 272, 118935. Tropospheric photolysis of CF3CHO - ScienceDirect

[8] The photoreactor used in the work consists of a 101-liter quartz reactor connected to a Bruker IFS 66v/s FTIR spectrometer. The compounds, including CF₃H were monitored using absorption features at several wavenumbers.

[9] Chapter 5: Atmospheric Chemistry of Halogenated Organic Compounds, T. J. Wallington, M. P. Andersen , and O. J. Nielsen, in Advances in Atmospheric Chemistry, pp. 305-402 (2017).

[10] IUPAC recommendations https://iupac.aeris-data.fr/catalogue/#/catalogue/categories/oFOx

[11] See https://kinetics.nist.gov/kinetics/Detail?id=1986ARI/ART437:2

[12] Kinetic Studies on the Decarboxylation of Sodium Trifluoroacetate in Ethylene Glycol, I. Auerbach, F. H. Verhoek, and A. L. Henne, J. Am. Chem. Soc. 1950, 72, 1, 299–300, https://doi.org/10.1021/ja01157a079

[13] Spectroscopy of Hydrothermal Reactions 13. Kinetics and Mechanisms of Decarboxylation of Acetic Acid Derivatives at 100-260 °C under 275 bar, A. J. Belsky, P. G. Maiella, and T. B. Brill, J. Phys. Chem. A 1999, 103, 4253-4260

[14] The reaction cells, used by Belsky et al. have a relatively high surface to volume ratio of 20-50 cm^-1. The paper states “The choice of the two reactor types (316 SS and Ti) was made, in part, to test the role of surface catalysis on the reaction rate. The half-life for decarboxylation of CH₃CO₂H differs by about 10⁷ at 100 °C on SS and Ti surfaces,11 and, therefore, these cell materials should give an indication of the importance of surface effects on the decarboxylation of the derivatives of acetic acid. We recognize that a preferred method of testing the role of surface catalysis is to vary the surface-to-volume ratio. This method is not practical in the precision spectroscopy flow reactors used in this work. We also recognize that the present study is not a decisive surface study particularly because the cell surfaces are machined and also undoubtedly possess an undefined degree of oxidation.”

[15] Spectroscopy of Hydrothermal Reactions 22. The Effects of Cations on the Decarboxylation Kinetics of Trifluoroacetate, Cyanoacetate, Propiolate, and Malonate Ions, D. Miksa, J. Li, and T. B. Brill, J. Phys. Chem. A 2002, 106, 46, 11107–11114, https://doi.org/10.1021/jp020941t

[16] Copernicus: February 2024 was globally the warmest on record – Global Sea Surface Temperatures at record high | Copernicus

[17] World Ocean Atlas 2023 Figures (noaa.gov)

[18] Overtone-Induced Chemistry of Trifluoroacetic Acid:  An Experimental and Theoretical Study, L. M. Reynard and D. J. Donaldson, J. Phys. Chem. A 2002, 106, 37, 8651–8657, https://doi.org/10.1021/jp021084w

[19] Persistent degradation products of halogenated refrigerants and blowing agents in the environment: type, environmental concentrations, and fate with particular regard to new halogenated substitutes with low global warming potential, D. Behringer, F.Heydel, B. Gschrey, S. Osterheld, W. Schwarz, K. Warncke, F. Freeling, K. Nödler, S. Henne, S. Reimann, M. Blepp, W. Jörß, R. Liu, S. Ludig, I. Rüdenauer, S. Gartiser, On behalf of the German Environment Agency TEXTE 73/2021, See Section 2.10.2.1 Biodegradability

[20] Degradation of trifluoroacetate in oxic and anoxic sediments, P.T. Visscher, C. W. Culbertson & R. S. Oremland, Nature 369, 729–731 (1994). https://doi.org/10.1038/369729a0

[21] Environmental Risk Assessment of Trifluoroacetic Acid, J. C. Boutonnet et al. Article in Human and Ecological Risk Assessment · February 1999, https://doi.org/10.1080/10807039991289644

[22] Summary of research results on bacterial degradation of trifluoroacetate (TFA). Matheson, L.J., Guidetti, J.R., Visscher, P.T., Schaefer, J.K., and Oremland, R.S. 1996. USGS Open File Report 96–219. Prepared in cooperation with the Alternative Fluorocarbons Environmental Assessment Study (AFEAS). Published by U.S. Geological Survey, Information Services, Box 25286, Mail Stop 417, Denver Federal Center, Denver, CO 80225–0046.

[23] The effect of fluoroacetates on methanogenesis in samples from selected methanogenic environments Emptage, M., Tabinowski, J.A., and Odom, J.M. 1997. Environ. Sci.Technol. 31, 732–734.

[24] Oremland, R. S., L. Matheson & J. Guidetti (1995): Summary of research results on bacterial degradation of trifluoroacetate (TFA), November, 1994 - May, 1995. Open File Report 95-OF 95-0422; USGS: Denver, CO:15.

[25] Berg, M., S. R. Müller, J. Mühlemann, A. Wiedmer & R. P. Schwarzenbach (2000): Concentrations and Mass Fluxes of Chloroacetic Acids and Trifluoroacetic Acid in Rain and Natural Waters in Switzerland. Environmental Science & Technology 34:2675–2683.

[26] Scheurer, M., K. Nödler, F. Freeling, J. Janda, O. Happel, M. Riegel, U. Müller, F. R. Storck, M. Fleig, F. T. Lange, A. Brunsch & H.-J. Brauch (2017): Small, mobile, persistent: Trifluoroacetate in the water cycle – Overlooked sources, pathways, and consequences for drinking water supply. Water Research 126:460–471.

[27] Franco, A. R., M. A. Ramos, S. Cravo, C. Afonso & P. M. L. Castro (2014): Potential of ectomycorrhizal fungus Pisolithus tinctorius to tolerate and to degrade trifluoroacetate into fluoroform.

[28] Ellis, D. A., M. L. Hanson, P. K. Sibley, T. Shahid, N. A. Fineberg, K. R. Solomon, D. C. G. Muir & S. A. Mabury (2001a): The fate and persistence of trifluoroacetic and chloroacetic acids in pond waters. Chemosphere 42:309–318.

[29] Kim, B. R., M. T. Suidan, T. J. Wallington & X. Du (2000): Biodegradability of Trifluoroacetic Acid. Environmental Engineering Science 17:337–342.[30] Increase in global emissions of HFC-23 despite near-total expected reductions, K. M. Stanley, D. Say, J. Mühle, C. M. Harth, P. B. Krummel, D. Young, S. J. O’Doherty, P. K. Salameh, P. G. Simmonds, R. F. Weiss, R. G. Prinn, P. J. Fraser, M. Rigby, Nat. Commun. 2020, 11, 397.

[31] World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022. Available at: https://ozone.unep.org/science/assessment/sap 7.2.5.1 Trifluoroacetic Acid (TFA) page 408

[32] Persistent degradation products of halogenated refrigerants and blowing agents in the environment: type, environmental concentrations, and fate with particular regard to new halogenated substitutes with low global warming potential, TEXTE 73/2021 Ressortforschungsplan of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Project No. (FKZ) 3717 41 305 0 Report No. FB000452/ENG, Section 3.4.1 Demand and emission quantities of HCFCs, HFCs, u-HFCs and u-HCFCs in the EU-28 until the year 2050, Table 24 page 147

[33] Salierno paper, Table 10: TFE (CF₃CHO) decarbonylation by UVB radiation

[34] Salierno paper, Table 10: TFE dissociation to CF₃· radical formation suggested by Salierno as low environmental likelihood with a maximum suggested HFC-23 yield of about 10%. Overall proposed yield by Salierno from CF₃CHO is a maximum of about 30% from this low likelihood route and the photolysis decarbonylation route

[35] TEXTE 35/2024Projektnummer 172963FB001431 Untersuchung von aktuellen Meerwasserproben auf Trifluoressigsäure. Finnian Freeling, Anna Mangels Im Auftrag des Umweltbundesamtes, TEXTE 35/2024 Examination of current seawater samples for trifluoroacetic acid | Federal Environment Agency (umweltbundesamt.de)

[36] An Inventory of Fluorspar Production, Industrial Use, and Emissions of Trifluoroacetic Acid (TFA) in the Period 1930 to 1999, A.A. Lindley, Journal of Geoscience and Environment Protection > Vol.11 No.3, March 2023, https://doi.org/10.4236/gep.2023.113001

[37] Recent increases in the atmospheric growth rate and emissions of HFC-23 (CHF₃) and the link to HCFC-22 (CHClF₂) production, P. G. Simmonds et al. Atmos. Chem. Phys., 18, 4153–4169, 2018, https://doi.org/10.5194/acp-18-4153-2018 see Figure 3

[38] AFEAS (2003). Data is available at https://agage.mit.edu/sites/default/files/documents/em-hcfc-22.pdf

[39] Recent increases in the atmospheric growth rate and emissions of HFC-23 (CHF₃) and the link to HCFC-22 (CHClF₂) production, P. G. Simmonds et al. Atmos. Chem. Phys., 18, 4153–4169, 2018, https://doi.org/10.5194/acp-18-4153-2018 see Supplementary Material (6): Additional HFC-23 emissions

 

 

[1]    The photoreactor used in the work consists of a 101-liter quartz reactor connected to a Bruker IFS 66v/s FTIR spectrometer. The compounds, including CF₃H were monitored using absorption features at several wavenumbers