Observational data of SO₂ in the effluent discharged from the chemical works at Dachangzhen in the outskirts of Nanjing are analysed and its annual mean concentration is computed by both the SD and CD models. The results by the two models are in good agreement with linear correlation coefficient as high as 0.94, average ratio being 0.91 and mean relative error 9%. Values computed by the American ATDL model for plane source are superimposed on the ones obtained by both of the above models and the outcome is found to be satisfactory by comparison with the observations from 26 monitoring cites. In a survey of the sensitivity of the model parameters, it is found that the most significant are the effective height of the source and vertical diffusion.