MECHANISM OF ATMOSPHERIC OXIDATION OF 1,1,1,2-TETRAFLUOROETHANE (HFC-134A)

The chlorine-initiated photooxidation of hydrofluorocarbon 134a (CF3CH 2F) has been studied in the temperature range 235-318 K and at 1 atm t otal pressure using UV absorption. Trifluoroacetyl fluoride [CF3C(O)F] and formyl fluoride [HC(O)F] were observed as the major products. IR analysis of the reaction mixture also showed carbonyl fluoride [C(O)F2 ] as a product. By measurement of the yields of HC(O)F from the photoo xidation as a function of [O2] and temperature, the rate of the unimol ecular decomposition of the oxy radical, CF3CHFO, reaction (5), was de termined relative to its reaction with O2, reaction (4): CF3CHFO + O2 --> CF3C(O)F + HO2 (4) CF3CHFO --> CF3 + HO(O))F (5). The results were treated using both an arithmetic derivation and numerical integration with a detailed reaction scheme. Inclusion of other recently publishe d kinetic data leads to the following recommended rate expression for reaction (5) at 1 atm k5 = 7.4 x 10(11) exp[(-4720 +/- 220)/T] s-1. Th e errors are 1sigma. The observation of enhanced product yields in the present work is attributed to the reaction of the CF3O radical with H FC 134a leading to further peroxy radical formation. The results have been incorporated into a 2D atmospheric model to assess the environmen tal implications of HFC 134a release in the troposphere.