Modeling of sulfur dioxide oxidation in plume using the Monte Carlo method

Abstract

This research succeeds in modeling of sulfur dioxide oxidation in plume using the Monte Carlo method, for a single point source and flat terrain. The physico-chemical mathematical model is capable of simulating the Gaussian dispersions and chemical transformations of sulfur dioxide. The mathematical model was also used to assess sensitivity analysis of Brimblecombe and Spedding (1974)’s reaction rate, Freiberg (1974)’s reaction rate in ammonia-rich environment and in ammonia-deficient environment and Ibusuki, Ohsawa and Takeuchi (1990)’s reaction rate in ammonia-rich environment, which effects sulfate formation by varying parameters such as atmospheric stability class, relative humidity, temperature, iron and ammonia concentrations. In this study, the measured sulfate concentration in Bang Na was compared with the simulated sulfate concentrations calculated from Freiberg (1974)’s reaction rate and Alkezweeny and Powell (1977)’s first order reaction rate. In comparison with yields of three chemical reactions, it is found that no yield occurs for Brimblecombe and Spedding (1974)’s reaction rate. Only at relative humidity or 99% Freiberg (1974)’s reaction rate in both of ammonia-rich environment and ammonia-deficient environment plays a significant role in sulfate formation for every atmospheric stability class, temperature, iron concentration or ammonia concentration variations. Ibusuki et al. (1990)’s reaction rate in ammonia-rich environment does not cause significant yield for each atmospheric stability class, nor as a result of the temperature decrease or the relative humidity increase or the ammonia concentration increase or iron concentration increase. The results of sensitivity analysis of Freiberg(1974)’s reaction rate in ammonia-rich environment and in ammonia- deficient environment indicate that the sulfate formation increases with increasing relative humidity, iron and ammonia concentrations and with decreasing temperature. Between ammonia-rich environment and ammonia-deficient environment, the yield in the first condition much more than that in the latter condition for the same given condition. In the cases of varying atmospheric stability class, the sulfate production is very low in the unstable and neutral atmospheric stabilities, vice versa, the conversion of sulfur dioxide to sulfate IS very high in the stable atmosphere due to the nature of second order reaction rate. The measured yield, during the dry season at the location of Bang Na with wind velocity of 2 m/s and Freiberg (1974)’s yields in some cases provide the comparable yields, which indicate that Freiberg (1974)’s reaction rate may become important if relative humidity, ammonia and iron concentrations are high with low temperature in the environment.