Atmospheric lifetime and global warming potential of HFC-245fa

We describe the method used to compute the global warming potential of hydrofluorocarbon (HFC) 245fa (CHF2CH2CF3). The Atmospheric and Environmental Research (AER) two‐dimensional (latitude‐height) chemistry‐transport model was used to calculate the atmospheric lifetime and atmospheric scale height of HFC‐245fa. Assuming that reaction with OH is the only removal mechanism, the recommended rate constant from Jet Propulsion Laboratory [1997] (6.1 × 10−13 exp (−1330/T) cm3 s−1) implies a lifetime of 7.6 years and an average atmospheric scale height of 35 km in the stratosphere. Using the IR absorption cross sections for HFC‐245fa and CFC‐11 determined in the laboratory, the AER one‐dimensional radiative‐convective model was used to calculate the radiative forcing. The value for HFC‐245fa is 1.14 times larger than that for CFC‐11 on a mass basis and 1.11 larger on a per molecule basis. The global warming potentials for HFC‐245fa (relative to carbon dioxide) are 2400, 760, and 240 (based on the values for absolute global warming potential for carbon dioxide reported by Intergovernmental Panel on Climate Change [1996]) at integration time horizons of 20, 100, and 500 years, respectively.