Science papers about fluorocarbon environmental effects are not always perfect

In recent months EFCTC has reported on two academic papers, one about trifluoromethane formation and another questioning the natural occurrence of TFA (see below). Another recent paper by Xiao et al. [1] challenged numerous past studies and the well-established HCFC atmospheric degradation. Xiao et al. claimed that HCFCs could react in the atmosphere to form CFCs through self-reactions of CFC radicals formed from HCFCs by H abstraction with OH radical. The first step of H abstraction by OH radical is well established. The self-reaction is proposed to compete with the reactions of the CFC radicals with O₂ molecules and increase the risk of ozone layer depletion. This surprising conclusion is in error according to published comments submitted by eminent atmospheric scientists [2]. Three points raised are:

1. Computational analysis by Xiao et al. of the addition of CFC-radicals to molecular oxygen led to excessively high reaction barriers (which would result in low reaction rates with O₂).
2. The CFC-radical + O₂ reactions are shown to be much faster than proposed and represent the predominant atmospheric CFC-radical loss process.
3. The low steady-state concentration of the CFC radicals makes their self-reaction a negligible atmospheric loss process.

EFCTC published an in-depth position paper disagreeing with a review paper “Insufficient evidence for the existence of natural trifluoroacetic acid”. EFCTC also published a news article “A new study demonstrates that HFC-23 (CF₃H) is not formed during the decomposition of HFOs and HCFOs in the troposphere.”

EFCTC will continue to monitor the peer-reviewed scientific literature, report on recent developments and support science-based facts related to fluorocarbon science.

 

References

[1] Extremely rapid self-reactions of hydrochlorofluoromethanes and hydrochlorofluoroethanes and implications in destruction of ozone, Y. Xiao, J. Wang, X. Ma, Y. Jia, Y. Ji, Chemical Physics Letters Volume 779, 16 September 2021, 138867, https://doi.org/10.1016/j.cplett.2021.138867

[2] Comment on ‘Extremely rapid self-reactions of hydrochlorofluoromethanes and hydrochlorofluoroethanes and implications in destruction of ozone’, P. Marshall and J. B. Burkholder, Chemical Physics Letters Available online 29 January 2022, 139411, https://doi.org/10.1016/j.cplett.2022.139411