Analysis on Typical Atmospheric Pollution Process in Nanjing Area

General characteristics of air pollution process in Nanjing area were analyzed.Three different types of typical air pollution processes occurred in 2009-2011 were selected to analyze the characteristics and influence factors respectively.It was found mat 91%pollution process in Nanjing lasted for less than 4 days according to assessment indexes of API,and air pollution occurred in autumn and winter lasted longer.Pollution caused by dust event was mainly controlled by the sand source and long range transport meteorological condition,with wide affected area.The ratio of PM_(205)/PM_(10) reached up to 70% from the pollution of crop residue burning combined with high PM_(2.5) concentration.The wind direction is main factor influencing the pollution area,and the pollution decreased quickly with precipitation or strong wind,as well as disappearance of pollution source.Long duration air pollution in autumn and winter is related to the unfavorable weather condition,such as relative uniform pressure pattern,along with local circulation at the bottom boundary layer,resulting in the pollution accumulation.