The atmospheric fate of potentially toxic/hazardous chemicals currently undergoing assessment by EPA was evaluated. Both chemical and physical removal processes are discussed. Mathematical descriptions of physical removal mechanisms were developed and applied to specific chemicals, i.e., acrylonitrile, ethylene dichloride, perchloroethylene, vinylidene chloride and benzo(a)pyrene. Estimates of physical removal by rainfall suggest half-lives of 300 days or longer for these compounds. Calculations based on reported photo-decomposition rates of halomethanes in contact with silica surfaces (e.g., desert sands) suggest half-lives on the order of 25 years for such halogenated chemicals, and dry deposition of the other compounds of interest is probably equally slow. Adsorption on aerosol particles is a reasonable removal mechanism only for benzo(a)pyrene, and all physical removal processes are generally demonstrated to be rather inefficient. Forty-six individual materials were evaluated relative to their probable fates and tropospheric lifetimes. Known or theoretical rate constants are listed for reaction with hydroxyl radicals and ozone. The probability of photolysis and of physical removal was assessed, and residence lifetimes assigned. Probable products of tropospheric oxidation processes were also tabulated.