Impacting factors of a heavy air pollution process in autumn over Beijing

Air pollution has been one of the major urban environmental problems in Beijing recently. A heavy air pollution process happens on October 8-13, 2002 in Beijing. Weather conditions and pollutant transport trajectory of this process were analyzed by MICAPS system and HYSPLT model. The results indicate that three disadvantageous conditions lead to this heavy air pollution. One is the weather conditions, namely, the strong high pressure and equal pressure at sea level make vertical atmospheric stratification stable over Beijing, which is not benefit to horizontal diffusion of air pollutants. Another is the terrain, namely, it is surrounded by mountains in the west and the north as well as the northeast, which become barriers to horizontal diffusion of air pollutants when the breeze comes from the south. The last is transport pathway, namely, lots of air pollutants are taken from Jiangsu province, Shandong province, Hebei province and Tianjin region by the southward breeze into Beijing region.