Photochemical reactions are important for the diurnal variation of the concentrations of air pollutants in the urban atmosphere. A photochemical reaction model was developed, which includes in terms of the effective chemical reaction. Various experimental results were introduced to the construction of model. To verify the applicability of the model, the simulated results were compared with those observed. By comparing the simulated results with those observed, it was shown that those two are in good agreement qualitatively. As a result, the photochemical reaction model which has been developed in this study is found to be useful for the prediction of concentrations of air pollutants in the atmosphere.