2018 SCIENTIFIC ASSESSMENT OF OZONE DEPLETION UPDATE ON TFA

There is increased confidence that trifluoroacetic acid (TFA) produced from degradation of HFCs, HCFCs, and HFOs will not harm the environment over the next few decades. This assessment is based on the current estimates of future use of hydrofluorocarbons, HCFCs, and HFOs. It is noteworthy that HFCs and HCFCs have atmospheric lifetimes long enough to globally distribute any TFA emissions, while HFOs have atmospheric lifetimes so short that TFA emissions are deposited near the point of emission. Periodic re-evaluation is prudent, given the uncertainties in the sources and sinks of TFA and because of its persistence in the environment.

TFA is a stable compound that can accumulate in lakes and the ocean. As an acid or as a salt, TFA is of low to moderate toxicity to a range of organisms. The salts of TFA are inert and not of toxicological or environmental concern in the small concentrations (~200 ng L−1) that are present in the ocean. The contribution of most sources to the total TFA budget is uncertain, although the source strength from atmospheric oxidation of HCFCs and HFCs is now better quantified.

Solomon et al estimated TFA added to the oceans as a result of unregulated use of HCFCs and HFCs (including HFOs) up to 2050. Under an upper range scenario of global HFC use, it was estimated that by 2050 the total additional contribution of TFA to the oceans would be less than 7.5% of the approximately 200 ng acid equivalents L−1 estimated to be present at the start of the millennium.

The effects of TFA on human and ecosystem health resulting from the use of compounds regulated under the Montreal Protocol have been assessed. Mammals are insensitive to TFA, and plants and other animals have a high tolerance to TFA. ……The large body of published field measurements, toxicological studies, modelling studies, and environmental assessments point to a clear conclusion: The current and estimated future concentrations of TFA and its salts resulting from degradation of HCFCs, HFCs, and HFOs do not pose any known significant risk to human or ecosystem health.

It has been shown recently that the reaction of Criegee intermediates (see explanatory note) with TFA in the gas phase is extremely rapid. Criegee intermediates are present in the atmosphere as a result of the reaction of ozone with alkenes and play an important role in atmospheric chemistry over landmasses with vegetation, where biogenic emissions of alkenes (e.g., isoprene and terpenes) are significant and ozone is available. Reactive loss of TFA via reaction with Criegee intermediates could be an important loss mechanism for TFA, and it has not been accounted for in atmospheric models of TFA deposition. Inclusion of this new gas-phase chemistry in atmospheric models could decrease the projected deposition of TFA over landmasses (by as much as a factor of two).

Note these are extracts as written (without the embedded references). See the 2018 Scientific Assessment of Ozone Depletion Chapters 2 (HFCs) and 6 (Scenarios and information for policy makers) for the complete information.
Explanatory Note: Criegee intermediates are named after the chemist Rudolf Criegee, who first postulated their formation in the 1950s. They are very reactive.