POTENTIAL CFC REPLACEMENTS - TROPHOSPHERIC LIFETIMES OF C3 HYDROFLUOROCARBONS AND HYDROFLUOROETHERS

Attack by tropospheric hydroxyl radicals results in much shorter residence times for hydrofluorocarbons (HFCs) than for the fully halogenated chlorofluorocarbons (CFCs). Empirical structure-activity relations, previously calibrated for HFCs containing two carbon atoms, are used with semi-empirical and ab initio calculations to provide realistic first estimates of tropospheric lifetimes of various chlorine-free HFCs and hydrofluoroethers (HFEs) containing three carbon atoms. The heavily fluorinated HFEs are of particular interest in that they are likely to possess thermophysical properties which are suited to a range of applications for which CFCs are currently employed. Many of the HFEs are predicted to have shorter lifetimes than HFC-134a (CF3CH2F), which is already in large-scale commercial production as an alternative refrigerant. Factors are identified which appear to favour short lifetimes for HFEs.