Freezing point depression (FDP) modeling was performed for selected aqueous nitrate and sulfate salt solutions to evaluate Pitzer ion interaction parameter values at 273.15 K. 1-1 and 1-2 electrolyte solutions of NaNO3, KNO3, NH4 NO3, Na2SO4, K2SO4, and (NH4)(2)SO4 were studied. New Pitzer parameter values of beta(0), beta(1), and C-phi were obtained for the studied electrolyte solutions. FDP modeling was also used to determine temperature derivatives of interaction parameters for the Pitzer model for selected salt solutions. Osmotic and activity coefficients using the new parameter values are also presented.