Change Characteristics of API of Several Typical Cities within Three Urban Agglomerations in China from 2001 to 2010
2001年至2010年中国三大城市群中几个典型城市的API变化特征

Due to the enormous differences in economic development level, climate, geography and other natural conditions, the atmospheric pollution and change characteristics of air quality present diverse trends in different regions. Air pollution index (API) is released daily for some important cities and it serves as a useful reference for public atmospheric environment researches. Beijing-Tianjin-Hebei region, Yangtze River Delta and Pearl River Delta are the most important and most developed urban agglomerations in China. Therefore, studying their air quality characteristics and clarifying the API similarities as well as differences among different cities and urban agglomerations will play an active role in amending environmental protection policies and technical standards and in providing policy reference for other cities. API data used in this study come from the announced results of State Department of Environmental Protection. In this paper, daily API data of nine typical cities within the above three urban agglomerations in the last decade were used to research API’s annual and seasonal change characteristics and to calculate days with low pollution level or above every year. In addition, the reasons leading to pollution change were analyzed and discussed. The results show that API had declined clearly in typical cities of three urban agglomerations in the last decade as a whole; API of Beijing-Tianjin-Hebei urban agglomeration is the highest and presents the most obviously decline trend, while the Pearl River Delta urban agglomeration has the lowest API and the least prominent decline; annual and seasonal API for all cities decrease from north to south with latitude, and the API of a city near the sea is lower than other cities; the API of three urban agglomerations are high in winter and spring and lowe in summer; the pollution days in Beijing and Shijiazhuang are the most, while in Zhuhai are the least; the pollution days have large gaps among three urban agglomerations during 2001-2008, but the gaps narrow significantly after 2008; the API of all typical cities have the trend of synchronous development and atmospheric pollution presents regional homogeneous characteristics in a certain extent. Analyzing the API change trend and characteristics of three urban agglomerations in the last decade systemically can provide certain reference for scientific evaluation and comparison of two indices in the future.