A mathematical model has been developed for the absorption of NOx gases in aqueous solutions of NaOH. The present model is for adiabatic operation, which is an extension of the previous isothermal model of Pradhan and Joshi (Chem. Eng. Sci. 55(7) (2000) 1269). Heat effects have been considered for gas phase reactions such as the oxidation of NOx dimerisation of NO2, and formation of N2O3, HNO2 and HNO3. Absorption of NO2, N2O3, HNO2(g), RNO3(g), into NaOH solutions is accompanied by large heat effects which have been incorporated in the model. Evaporation/condensation of water has also been considered. A comparison between isothermal and adiabatic operation has been presented. The model was validated using data from an operating small-scale plant which uses the process of absorption of NOx in NaOH and a good match between plant and simulation results was obtained. Minor modifications were suggested in the existing plant which would improve the selectivity of the product NaNO2.