Atmospheric degradation of HFCs and HCFCs: chemistry and noxiousness.

Hydrohaloalkanes are potential alternatives to the fully halogenated compounds (CFCs) that are believed to be responsible for depletion of the stratospheric ozone. In order to establish whether hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) are actually more environmentally acceptable, it is extremely important to know, in addition to ODP and HGWP, their atmospheric degradation mechanism, tropospheric lifetime, and toxicity and noxiousness of their atmospheric degradation products. The primary atmospheric sink for hydrohaloalkanes is the reaction with hydroxyl radicals (OH), so that laboratory measurements or a reliable estimation of the rate constants (kOH) of these reactions is essential in order to assess their atmospheric lifetimes. The previsional models for kOH developed in our laboratory allow the estimation of the atmospheric lifetimes of as many as 449 halocarbons (i.e., all the halocarbons containing F and/or Cl with one, two, and three carbon atoms). The harmful character of some degradation products halogenated and oxygenated is also discussed.