Abstract:  The Beijing Olympic Games requires high air quality.The emissions from Beijing and its surroundings have significant impacts on Beijing air quality in summer.Ozone evolution and transportation are simulated over Beijing and its surroundings in August 2006 with the nested air quality prediction modeling system(NAQPMS)and estimates the contribution ratio from these regions to Beijing with a new tagged method of mass trajectory.The results show that the model can well represent the evolution of ozone and transportation over Beijing and the surroundings.The regional transportation of pollutants from the surroundings has significant impacts on the ozone levels in Beijing.These source regions include Tianjin city,Baoding city,and the Langfang area.The maximum contribution is Baoding city,from which the pollutants are distributed to the Beijing urban and suburban areas in proportions of 28.1% and 59.5%,respectively.Southwesterly winds are the dominant meteorological parameter for this transpo