The transport of air pollutants from several big cities in the north of China and theneighboring countries is researched by using the isentropic trajectory model. The trajectories arecalculated twice daily for the cities in January, April. July and October for the period of 1992-1994. The statistical method has been used to deal with trajectory dots at intervals of 30 min forthe forward and backward trajectories during 0-24 h and 24-48 h. The probability distributiondiagrams of trajectory show clearly the ensemble properties of isentropic trajectories for each cityand the dominant transport directions of pollutants. They possess notable seasonal variations. Theforward trajectory areas of the Ulaan Baatar in Mongolia can spread over North China. and thoseof the Chita in Russia can influence Northeast China except in summer. In July the forwardtrajectory of Pyongyang and Seoul can extend northward to the boundaries of China.
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