As a result of the cluster rule for the control of the hazardous air pollutants, pulp and paper mills are in the process of further substituting chlorine with aqueous chlorine dioxide for their bleaching operations. In addition, ammonia aqueous solutions are applied by paper mills in various processes. An evaporation model including both heat and mass transfer for aqueous solutions has been developed to quantify chemical evaporation rates. Chemical and physical properties for chlorine dioxide and ammonia aqueous solutions have been analyzed to allow plants to perform a dynamic analysis for various accidental release scenarios. This paper provides a detailed discussion of the methodologies for quantifying source parameters and modeling downwind concentrations from liquid spills of chlorine dioxide and ammonia aqueous solutions.