This study reports a simple reactor modeling utilizing chemical kinetic data of the gas phase reaction between nitrogen dioxide, ammonia and water vapor in order to estimate the influences of several operating variables on the removal of NO2 which is generated from NO by the oxidation process in a non-thermal plasma reactor or an electron-beam irradiation reactor. The operating variables chosen are water vapor content, initial concentration of NO2, reaction temperature and ammonia concentration and the appropriate ranges of such variables were suggested. The gas phase reaction for the removal of NO2 takes place effectively at the water vapor content higher than 4-6%(v/v), but further increase in the water vapor content does not significantly enhance the removal. The residence time required to achieve a desired removal efficiency of NO2 was found to rapidly increase when the initial concentration of NO2 is less than 100 ppm. Since the removal rate of NO2 is in inverse proportion to the reaction temperature, lower temperature is favorable to promote the reactions. The effect of ammonia concentration on the removal of NO2 was estimated to be negligible.