Tropospheric degradation of Fourth-Generation halocarbons by O3: Formation of long-lived greenhouse gases and ozone-depleting substances

Hydrofluoroolefins (HFOs) and hydrochlorofluoroolefins (HCFOs) are widely adopted as next-generation substitutes for ozone-depleting substances (ODSs) and long-lived greenhouse gases (GHGs) in refrigeration, foam-blowing, and propellant applications. In the troposphere, these compounds are primarily removed by reaction with hydroxyl radicals, resulting in short atmospheric lifetimes and low global warming potentials (GWPs) compared with their predecessors, hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), and chlorofluorocarbons (CFCs).¹˒² However, their secondary chemistry, particularly the formation of the potent GHG trifluoromethane (HFC-23) during the ozonolysis of HFOs and HCFOs,³˒⁴ has raised increasing concern and remains incompletely understood.In this work, we examine the ozonolysis of selected HFOs and HCFOs in the 123 L EXTreme RAnge (EXTRA) chamber, a Teflon®-coated stainless-steel reactor,⁵ under atmospheric conditions (25 °C, 1 atm). Studies of four HFOs demonstrate that ozonolysis can produce either the GHG HFC-23 or carbon tetrafluoride (PFC-14). HFC-23 is formed from HFO-1234ze(E) in a yield of Figure 1. Experimentally determined ozonolysis product yields at 298 K and 1 atm pressure of: Left panel: HFC-23 from HFO-1234ze(E); Middle panel: PFC-14 from HFO-1225ye(E), HFO-1225ye(Z), and HFO-1234yf; Right panel: CFC-13 from HFCO-1233xf. Different symbols distinguish separate experiments. The panels show the ratio of products to initial HFO or HCFO concentrations plotted against the fractional change in the HFO or HCFO concentration. 1 B. Burkholder, R. A. Cox, A. R. Ravishankara, Chem. Rev., 2015, 115, 3704.2 J. Wallington, M. P. Sulbæk Andersen, O. J. Nielsen, Chemosphere, 2015, 129, 135.3 R. McGillen, Z. T. P. Fried, M. A. H. Khan, K. T. Kuwata, C. M. Martin, S. O’Doherty, F. Pecere, D. E. Shallcross, K. M. Stanley, K. Zhang, Proc. Natl. Acad. Sci. USA, 2023, 120, e23127141204.4 J. Nielsen, M. P. Sulbaek Andersen, T. J. Wallington, Atmos. Environ., 2025, 343, 120953.5 E. Leather, M. R. McGillen, C. J. Percival, Phys. Chem. Chem. Phys.,2010, 12, 2935.6 M.d.l.A. Garavagno, A. Wenger, R. E. T. Holland, B. R. Fena, S. D. Goldstein, D. E. Hicks, F. Liu, J. B. Madell, S. J. Solomon, K. T. Kuwata, M. R. McGillen, M. A. H. Khan, D. E. Shallcross, K. M. Stanley, A. J. Orr-Ewing, Environ. Sci. Technol., 2025, 59, 26031.