Characteristics and Causes of Air Pollution in Lanzhou, China

Ten of the top 20 polluted cities are in China, while Lanzhou is the most famous one in the ten. Relevant foreign researches show that urban air pollution generated economic losses reached the city of 3% of national income. In this paper, air pollutants, air pollution index (API for short) and meteorological data of 2000-2008 are analyzed using statistical methods and results show that: (1) Air pollution index (API) in Lanzhou shows an obvious seasonal change with high value in winter and low in summer.(2) Its primary air pollutants are particulate pollutants, in total 3113 days during 2000-2008, only 96days of air quality are good and taking 3.08%; there are severe polluted 168 days, moderate polluted 114 days and light polluted 1106 days.(3) Primary pollution particles of 2928 days are inhalable particles, accounting for 94.06%. Second pollution is SO2 and taking 2.97%. (4) Seasonal distribution of pollution, severe pollution and moderate pollution occurs mostly in winter and spring quarters. Seasonal variation shows the number of severe polluted days in the four months of Jan, March, April, and Dec account for 78.6% of total severe polluted days during 2000-2008. The most severe polluted and second polluted days mainly occurred in winter and spring, closely related with winter house heating and spring dust storm. The number of excellent air quality days is more in the rainy days, indicating that deposition of pollutants or the dilution effect precipitation is apparent. (5) There are close relationship between API and meteorological factor such as precipitation, humidity and wind speed.