AN UPDATE ON FLUOROCARBONS

Dear subscribers,

This Newsletter in an update of the document sent on the 10th September.
We have encountered some technical issues, which are now resolved. We would like to thank you for your patience and understanding

In the January 2024 Newsletter, EFCTC elaborated on the 2023 McGillen et al. paper [1], indicating the formation of small yields of HFC-23 (CF3H) from some HFOs (not HFO-1234yf) by reaction with ozone. In 2022, Andersen et al. [2] had already reported experimental work demonstrating that HFC‑23 (CF3H) was not formed through the degradation of TFA (CF3CHO), an intermediate in the degradation of some HFOs and HCFOs. More details can be found in ourJanuary 2022 Newsletter.

Recently, two papers have reported the potential for significant HFC-23 generation from the atmospheric degradation of HFOs/HCFOs:

• The Salierno et al. 2024 paper [3], titled ‘On the Chemical Pathways Influencing the Effective Global Warming Potential of Commercial Hydrofluoroolefin Gases’, proposes significant yields of HFC-23 from the degradation of trifluoroacetic acid (TFA). These yields were unexpected, as TFA demonstrates exceptional stability across different environments, which is primarily attributed to its structural characteristics [4]. When analysing the paper in detail, our experts found some statements that were in disagreement with existing publications. You will find their comments in the more detailed section of this Newsletter.
• In their 2024 paper titled ‘Assessing the atmospheric fate of trifluoroacetaldehyde (CF3CHO) and its potential as a new source of fluoroform (HFC-23)’, Perez-Peña et al. [5] applied model simulations to determine how TFA is lost in the atmosphere and how much HFC-23 can be produced from its photolysis under realistic atmospheric conditions. Based on their model they conclude that the HFC-23 photolysis channel accounted for between 1.3% and 4.4% of the CF3CHO atmospheric removal globally.
  Obtained numbers are significantly higher than the ones reported by McGillen et al. and Andersen et al. Our experts assessed the details of the quantum yields and the emission scenarios used by Perez-Peña et al. and formulated a set of remarks.
  Full details on the recent papers on HFC-23 generation from HFOs can be found in the detailed section of this Newsletter.

Enjoy the reading!

References and Notes

[1] Ozonolysis can produce long-lived greenhouse gases from commercial refrigerants, Max R. McGillen, Zachary T. P. Fried, M. Anwar H. Khan, Keith T. Kuwata, Connor M. Martin, Simon O’Doherty , Francesco Pecere, Dudley E. Shallcross, Kieran M. Stanley , and Kexin Zhang, PNAS 2023 Vol. 120 No. 51 e2312714120, https://doi.org/10.1073/pnas.2312714120.

[2] 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

[3] Assessing the atmospheric fate of trifluoroacetaldehyde (CF3CHO) and its potential as a new source of fluoroform (HFC-23) using the AtChem2 box model, Maria Paula Perez-Peña, Jenny A. Fisher, Christopher Hansen and Scott H. Kable, Environ. Sci.: Atmos., 2023, 3, 1767, https://doi.org/10.1039/D3EA00120B

[4] 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

[5] Emissions, degradation and impact of HFO-1234ze from China PU foam industry, Y. Wang, Z. Wang, M. Sun, J. Guo and J. Zhang, Sci. Total Environ., 2021, 780, 146631.

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

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.

Click "Read More" to read the full article.

Experts' reflections on the Perez-Peña et al. paper titled "Assessing the atmospheric fate of trifluoroacetaldehyde (CF3CHO) and its potential as a new source of fluoroform (HFC-23)"

The output from any atmospheric model depends on the input data. In this paper the use of 0.3% and 1% HFC-23 quantum yields directly results in the conclusion that HFC-23 yields are significant. the values were selected as Perez-Peña et al. tested two quantum yields for the HFC-23 channel, 0.3% was chosen to reflect the values in the Andersen paper [2] reported as an upper limit at 1 bar. 1% was the extrapolated value by Campbell [4] and chosen to reflect a realistic upper bound.” The following sections go into more detail on these choices.

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UBA report "Analysis of current seawater samples for trifluoroacetic acid"

The UBA report “Analysis of current seawater samples for trifluoroacetic acid” is an important new study on current concentrations of TFA in the Atlantic Ocean [1]. 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, with the exception of one, showed a slight decrease in TFA concentration with increasing ocean depth.

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Do the UBA results indicate a significant TFA content in the Atlantic Ocean and imply a natural source? Detailed Discussion

Do the results in the UBA report “Analysis of current seawater samples for trifluoroacetic acid” [1] indicate a significant TFA content in the Atlantic Ocean, and if there is a significant TFA content in the Atlantic Ocean, can it all result from industrial sources or does it imply there must be a natural source?

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Are the differences in concentration measurements (1998/2002) and (UBA: 2022/2023) due to a significant increase in the TFA oceanic content? Detailed Discussion

The UBA report “Analysis of current seawater samples for trifluoroacetic acid” [1] comments that “However, a comparison of the recent and historical data was only possible to a limited extent. This was mainly due the uncertain quality and robustness of the TFA data determined in previous studies and the differences in the sampling sites.” Even so, it is worth exploring if the apparent increase in TFA oceanic concentrations could be a result of anthropogenic TFA.

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Comment on Guardian Article ‘Air and rain samples in Detroit show high levels of TFA ‘forever chemical’

Recognising that the UK Guardian newspaper makes some valid observations in its article Air and rain samples in Detroit show high levels of TFA ‘forever chemical’, the EFCTC experts would like to point out some inaccuracies about TFA (trifluoroacetic acid) that have slipped in.

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