Tropospheric degradation chemistry of HCFC-123 (CF3CHCl2): A proposed replacement chlorofluorocarbon

Article abstract of DOI:10.1016/1352-2310(94)90121-X

HCFC-123 has been proposed as a replacement for some of the fully halogenated chlorofluorocarbons and other chlorinated hydrocarbons, which are being phased out under the Montreal Protocol. This paper reports laboratory studies which were undertaken to determine kinetic and mechanistic parameters of reactions involved in the atmospheric degradation of HCFC-123 and the use of these parameters in a 2D global model of the troposphere to evaluate the yields of products formed in the degradation. The experimental studies have made use of the laser flash photolysis technique with time-resolved ultra-violet absorption spectroscopy for the kinetic measurements and broad-band ultra-violet absorption spectroscopy for product characterization. Rate coefficients have been determined for the self-reaction of CF₃CCl₂O₂ as (3.6 ± 0.5) x 10^-12 cm³ mol^-1 s^-1 and for its reactions with HO₂ and NO as (1.9 ± 0.7) x 10^-12 cm³ mol^-1 s^-1 and (1.5-2.0) x 10^-11 cm³ mol^-1 s^-1, respectively, at room temperature. Kinetic data have also been obtained for the reaction of CF₃CCl₂O₂ with C₂H₅O₂ and two channels have been identified; CF₃CCl₂O₂ + C₂H₅O₂ → CF₃CCl₂O + C₂H₅O + O₂ k = (9 (_-5⁺⁹) x 10^-13 cm³ mol^-1 s^-1 and CF₃CCl₂O₂ + C₂H₅O₂ → CF₃CCl₂OH + CH₃CHO + O₂, k = (3.6 ± 0.5) x 10^-12 cm³ mol^-1 s^-1. Studies undertaken using the Cl-initiated oxidation of HCFC-123 suggest that trifluoroacetyl chloride, CF₃COCl, is the major product of the gas-phase degradation. The kinetic and mechanistic data have been used to formulate a chemical module of the degradation of HCFC-123 in the troposphere. The module has been incorporated into a 2D model of the global troposphere so that the potential atmospheric impact of using HCFC-123 can be assessed. HCFC-123 has been proposed as a replacement for some of the fully halogenated chlorofluorocarbons and other chlorinated hydrocarbons, which are being phased out under the Montreal Protocol. This paper reports laboratory studies which were undertaken to determine kinetic and mechanistic parameters of reactions involved in the atmospheric degradation of HCFC-123 and the use of these parameters in a 2D global model of the troposphere to evaluate the yields of products formed in the degradation. The experimental studies have made use of the laser flash photolysis technique with time-resolved ultra-violet absorption spectroscopy for the kinetic measurements and broad-band ultra-violet absorption spectroscopy for product characterization. Rate coefficients have been determined for the self-reaction of CF₃CCl₂O₂ as (3.6±0.5)×10^-12 cm³ mol^-1 s^-1 and for its reactions with HO₂ and NO as (1.9±0.7)×10^-12 cm³ mol^-1 s^-1 and (1.5-2.0)×10^-11 cm³ mol^-1 s^-1, respectively, at room temperature. Kinetic data have also been obtained for the reaction of CF₃CCl₂O₂ with C₂H₅O₂ and two channels have been identified; CF₃CCl₂O₂+C₂H₅O₂→CF₃CCl$ -2$/O+C₂ H₅O+O₂, k = (9_-5⁺⁹)×10^-13 cm³ mol^-1 s^-1 and CF₃CCl₂O₂+C₂H₅O₂→CF₃CCl$ -2$/OH+CH₃ CHO+O₂, k = (3.6±0.5)×10^-12 cm³ mol^-1 s^-1. Studies undertaken using the Cl-initiated oxidation of HCFC-123 suggest that trifluoroacetyl chloride, CF₃COCl, is the major product of the gas-phase degradation. The kinetic and mechanistic data have been used to formulate a chemical module of the degradation of HCFC-123 in the troposphere. The module has been incorporated into a 2D model of the global troposphere so that the potential atmospheric impact of using HCFC-123 can be assessed.