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 CH3CF3 (HFC -143a) and CHF2CH2CF3 (HFC-245fa) have been measured using the flash p hotolysis resonance fluorescence technique over the temperature range 273-370 K. A data analysis procedure is presented which should minimiz e rate constant errors introduced by the possible effects of radical d iffusion. The following Arrhenius expressions have been derived for th e reactions of OH with CH3CF3 and CHF2CH2CF3, respectively (in units o f cm(3) molecule(-1) s(-1)): (0.95(-0.17)(+0.21)) x 10(-12) exp{-1979 +/- 65)/T} and (0.632(-0.078)(+0.089)) x 10(-12) exp{-1331 +/- 43)/T}. With these values, the atmospheric lifetimes for the two HFCs have be en estimated to be 51 and 7.4 years, respectively. An error analysis i s presented from which the rate constant uncertainty at any temperatur e can be calculated.