Abstract

HFC-1345fz (3,3,4,4,4-pentafluoro-1-butene, CF₃CF₂CH=CH₂) is currently considered as an acceptable alternative to high global warming potential (GWP) HFCs as foam blowing agents. The tropospheric photooxidation of HFC-1345fz initiated by hydroxyl (OH) radicals is expected to be faster than the saturated HFCs because of the presence of the C-C double bond. To evaluate the tropospheric persistence of HFC-1345fz it is necessary to determine the rate coefficients of the main removal pathway in the gas-phase, i.e. its reaction with OH (k_OH). In this paper, we present the first absolute measurement of k_OH at 298 K as a function of total pressure (31 - 624 Torr of He). The determination of k_OH has been performed by the pulsed laser photolysis – laser induced fluorescence technique using H₂O₂ and HNO₃ as OHprecursor. A global tropospheric lifetime of HFC-1345fz due to the reaction with OH radicals (τ_OH) of around 9 days was estimated from k_OH and assuming a 24-h averaged OH concentration of 1×10⁶ cm^-3. Degradation route of HFC-1345fz initiated by OH radicals is compared with other atmospheric removal processes. The IR absorption cross sections, σ_v , of HFC-1345fz are also determined in the wavenumber range of 500-4000 cm^-1 to quantify its radiative properties, such as the radiative efficiency (RE). The lifetime corrected RE for HFC-1345fz is calculated to be 0.022 W m^-2 ppbv^-1, which implies a negligible global warming potential. Therefore, from the kinetic and atmospheric degradation points of view, the studied hydrofluoroolefin seems to be suitable for replacing saturated HFCs as foam blowing agents, since they are shortlived species that do not contribute to the Earth’s global warming.

Keywords: CFC replacement, GWP, hydrofluoroolefin, lifetimes, OH radicals, rate coefficients, radiative efficiency.