Analysis on Spatio-Temporal Distribution of Air Quality of Key Environmental Protection Cities in China

Based on the daily observations of the air pollution index (API), the primary pollutants and the air quality levels of 86 key environmental protection cities issued by the Ministry of Environmental Protection of the People's Republic of China, the spatial and temporal distribution characteristics of the cities' API were analyzed by cluster analysis method. The main results showed that: (1) By classifying these key environmental protection cities firstly by API and secondly by primary pollutants, it was found that the categories of cities are in certain regional distribution rule in term of spatial distribution. (2) The temporal changes of APIs in China's cities show similarity in seasonal change, that is, the API is highest in winter or spring, lowest in summer, and moderate in fall. However, the temporal changes in APIs of different categories of cities are highly different.