Killen, Beth, Fisher, Jenny A., Hansen, Christopher S., Krummel, Paul B., Vollmer, Martin K., and Kable, Scott H. (2026) Atmospheric fates and global warming potential of HFO-1234ze(E) and its degradation product trifluoroacetaldehyde (CF3CHO). Environmental Science Atmospheres, 6 (6). pp. 913-932.

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Abstract

Hydrofluoroolefins (HFOs) are replacing high-GWP hydrofluorocarbons (HFCs) across multiple applications including foam blowing, refrigeration, and aerosols, but their atmospheric degradation and climate consequences remain uncertain. We use the GEOS-Chem 3-D chemical transport model, supported by AtChem2 box-model simulations, to develop a complete representation of the atmospheric chemistry and fate of HFO-1234ze(E) and its key intermediate product, trifluoroacetaldehyde (CF<inf>3</inf>CHO). We focus on HFO-1234ze(E) as it is the dominant isomer in commercial use. The model includes newly measured CF<inf>3</inf>CHO photolysis quantum yields to form fluoroform (HFC-23), the recently identified chemical pathways of HFO-1234ze(E) ozonolysis and CF<inf>3</inf>CHO reversible reaction with HO<inf>2</inf>, and explicit wet and dry deposition parameterisations. Using observationally constrained global HFO-1234ze(E) emissions of 15 Gg year⁻¹, simulated HFO-1234ze(E) surface mixing ratios agree well with 2020–2024 observations at 8 Advanced Global Atmospheric Gases Experiment (AGAGE) network sites. We find that 99.6% of HFO-1234ze(E) is removed by reaction with OH, with the remaining 0.4% lost to ozonolysis. Sensitivity tests for effective Henry's law constants spanning 10–10⁶ M atm⁻¹ show sensitivity of CF<inf>3</inf>CHO fate to up to 10⁴ M atm⁻¹ and saturation at higher. Using an upper bound of 10⁵ M atm⁻¹, deposition accounts for ≈51% of total CF<inf>3</inf>CHO loss in GEOS-Chem (20% dry, 31% wet), with photolysis contributing ≈33% and OH reaction ≈15%. The reversible reaction with HO<inf>2</inf> contributes around 1% to net CF<inf>3</inf>CHO loss due to rapid conversion of the reaction products back to reactants. We calculate a total (direct + indirect) GWP<inf>100</inf> for HFO-1234ze(E) of 11.4^+3.1<inf>−1.9</inf>, with CF<inf>3</inf>CHO photolysis to HFC-23 contributing 8.2^+3.1<inf>−1.9</inf>. We also estimate a maximum potential formation of 4.5 Gg year⁻¹ of trifluoroacetic acid (TFA) under current emissions assuming complete conversion of wet-deposited CF<inf>3</inf>CHO from HFO-1234ze(E), suggesting a potential unrecognised TFA source from all CF<inf>3</inf>CHO sources.

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