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The relationship of air pollution with meteorological factors and weather systems for 10 typical cases in summer (July to September) from 2005 to 2007 in Hebei Province is analyzed by using the conventional observation data and NECP sixhour reanalysis data. It is concluded that the main weather patterns related to the typical processes of air pollution are longitudinal, frontal low trough, peripheral subtropical high patterns, etc. Air pollution occurs usually in fog and haze days, with minimum visibility between 05:00 and 20:00, and the dewpoint deficit less than 3 ℃. There is no significant vertical motion or weak systematic downwelling at upper air. Because the weak pressure and wind fields near the surface are not conducive to the diffusion of contamination and the temperature inversion of the surface layer, the air pollutants are easily kept in the stable layer. When cold air invades,precipitation can make air pollution weaken or disappeared.