A mathematical model has been presented for the case of NOx absorption in aqueous solution of NaOH in a plate column. The model was developed for calculating the overall rate of reaction, it was further optimised for selectivity towards the nitrite formation and the overall height of column. The effects of temperature, pressure and NOx composition have been examined. Optimum design strategy has been suggested by dividing the gas inlet stream into two parts: where one part is introduced directly into column and the other part is introduced into oxidation section, were the gas is oxidised to the desired extent. The gas of appropriate composition from the outlet of oxidiser is introduced at entry of each plate, so that the composition to the inlet of each plate is as desired.