Climate Metrics for C3-C4 Hydrofluorocarbons (HFCs) Lacking Fundamental Experimental Measurements

The vast majority of C3 and C4 (linear and branched) hydrofluorocarbons (HFCs) do not have fundamental laboratory measurements of their infrared absorption spectra and reactivity available in the literature. Availability of climate metrics for these molecules is desirable for potential future policy decisions. In this work, theoretical methods were used to calculate optimized geometries and infrared absorption spectra for all C3 and C4 hydrofluorocarbons (HFCs). Radiative efficiencies (REs) were calculated using the estimation method of Hodnebrog et al. and are consistent with values reported in the WMO ozone assessment. Atmospheric lifetimes for these molecules were estimated using their OH radical reactivity based on the structure activity relationship (SAR) developed by DeMore and estimates of stratospheric loss processes. The REs and lifetimes were used to derive global warming potentials (GWPs) and global temperature potentials (GTPs) for each of these molecules. The derived GWPs are roughly estimated to be accurate to within a factor of 2. The results from this study only provide a guide to the HFC climate metrics and fundamental laboratory measurements are needed for compounds considered for commercial applications.