Tropospheric OH and the lifetimes of hydrochlorofluorocarbons

Hydrochlorofluorocarbons (HCFCs) may be used as alternatives for the chlorofluorocarbons (CFCs). Lifetimes for the HCFCs are predicted here in two ways: integrating their loss with a global model, and scaling to another compound with a better known lifetime. Both approaches are shown here to yield similar results. Three‐dimensional fields of modeled tropospheric OH concentrations are used to calculate lifetimes against destruction by OH for the HCFCs and other hydrogenated halocarbons. The OH fields are taken from a three‐dimensional chemical transport model Spivakovsky et al., 1990a that accurately simulates the global measurements of methyl chloroform (derived lifetime of 5.5 yr). The lifetimes of various hydro‐halocarbons are shown to be insensitive to possible spatial variations and seasonal cycles. It is possible to scale the HCFC lifetimes to that of methyl chloroform or methane by using a ratio of the rate coefficients for reaction with OH at an appropriate temperature, about 277 K.