Based on the hydrodynamics and chemical thermodynamics of acidic fogs,a two-dimensional physico-chemical numerical model of advection-radiation fog has been developed to investigate the formation and evolution of fog and the acidification process of fog water,and to estimate regional distribution of sulfur dioxide and PH of fog water in Qingdao in summer. Turbulence, advection, radiation, gravitational settling and SO2 (g) transformation are included in the model. The calculated results show good agreements with measured concentrations of fog and pH of fog water, and may be account for the presence of very acid fogs in Qingdao or along the Shandong coast and may be important for the understanding of acid rain.