Chlorofluorocarbons global transport

Rigid foams are based primarily on polyfunctional, low molecular weight alcohols and amines. Most global applications conventionally use polymeric isocyanates, TDI, or an undistilled grade of mixed TDI isomers. TDI prepolymers which have hydroxyl and isocyanate groups have been marketed as a low vapor pressure alternative to undistilled TDI. Density reduction is effected via the addition of chlorofluorocarbons, low molecular weight alkanes, or via the in situ generation of carbon dioxide. The resultant closed cell foams find applications as insulators in construction, appliance, transportation, pipeline, and tank end uses. 

The impact of deposition on global distribution has been noted for the CFC replacements hydro-chlorofluorocarbons (HCFCs), the chlorinated solvents tetrachloroethene (PCE), and trichloro-ethene (TCE), as these compounds undergo gas phase oxidation and photochemical degradation, resulting in the formation of carbonyl halides (e.g., CCI2O) and haloacetyl halides (e.g., bromo-, chloro-, and fluoroacetates). As these compounds are polar and water soluble, they are transported via aerosols, rain, and fog, which impacts their tropospheric lifetime and depositional fluxes (Rompp et al., 2001 de Bmyn et al., 1995). It is not clear whether and to what extent there is evidence of latitudinal fractionation of these compounds. 

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