Atmospheric Lifetimes of HFC-143a and HFC-245fa:  Flash Photolysis Resonance Fluorescence Measurements of the OH Reaction Rate Constants

Rate constants for the reactions of hydroxyl radicals with CH 3 CF 3 (HFC-143a) and CHF 2 CH 2 CF 3 (HFC-245fa) have been measured using the flash photolysis resonance fluorescence technique over the temperature range 273−370 K. A data analysis procedure is presented which should minimize rate constant errors introduced by the possible effects of radical diffusion. The following Arrhenius expressions have been derived for the reactions of OH with CH 3 CF 3 and CHF 2 CH 2 CF 3, respectively (in units of cm 3 molecule -1 s -1 ): × 10 -12 exp{−(1979 ± 65)/ T } and × 10 -12 exp{−(1331 ± 43)/ T }. With these values, the atmospheric lifetimes for the two HFCs have been estimated to be 51 and 7.4 years, respectively. An error analysis is presented from which the rate constant uncertainty at any temperature can be calculated.