| With the rapid development of the national economy, the continuous expansion of the cities, some of the air quality in large and medium-sized cities have been gradually worsening, the air pollution problems, in which SO2, NOx, PM10 as the major pollutants, has become increasingly serious. At the same time, the improvement of living standards makes it increasingly concerned about the air quality in urban living. Air quality will have a direct impact on people's physical and mental health, thus, deeper research on air pollution is of great significance.API (Air Pollution Index, the API) is a method in reflection and evaluation of air quality, in which the several monitored pollutant concentration is implified into single conceptual number and classified to represent the air condition and pollution. This can present us a more consise report on the air quality and suitabel for representing cites'short-term air quality condition and variety trend.In this study, the daily air quality report data between June 5th, 2004 to Jun 5th,2007 of 84 key environmental protection cities in China is adopted and analyzed by cluster and wavelet methods. By integrating meteorologic data of some cities into the analysis of API, the temporal and spatial distribution characteristics of API in China is obtained and shown in follows:1,There exist three API peak regions,which are Northwest, the North part of NorthChina, Shanxi and Henan.API decreases eastward and southward from the three regions and displays the lowest in southern coastal cities, like Haikou, Zhuhai, and Zhanjiang and so on. In general, API features hign value in the North and low in the South. When it comes to four different seasons each year, API shows an order of winter>spring>autumn>summer, with similar distribution pattern. In spring, summer and autumn, there is no significant difference between southern and northern API, while the difference enlarges in winter, with a sharply increase in the North part of China and much larger than the South.2,Inhalable particles accounts the majority of city pollutant in most cities,while it occurs less frequently in southern coastal cities. Sulphur dioxide is more likely occurred in Inner Mongolia, Hebei, northern and southern Yunnan, Guizhou, Guangxi region, while nitrogen dioxide mainly massed in Guangdong and Southeastern cities.3,The cluster analysis results show that cities in the eastern and middle china are clustered into two regions by the qinling mountain and huahe river ,one is the north and ther other is the south, which are further divided into 11 regions: North East, North China, North West, Shandong Pennisula, Shanxi-Henan, Yangtze river delta, Hubei-Hunan, Sichuan-Guizhou, South China, South part, and Yunnan. The spatial distribution of API presents a feature of region difference and region synchronization covers a strip of hundreds of kilometres and shows no apperant changes in the three years. In this study, representative city of each region is obtained after composing a complex index which will reflect the API similarity between individual city and the region.4,Low-frequency signal is obtaind by wavelet analysis. The annual varitey characteristics of each region are discussed by analysing the low-frequency signal. By analyzing the variety of each region, we found that the pollution is much more serious in the North during heating period, and SO2 occurred more frequently.5,The climatic conditions infuencing API in the southern part of China are discussed. Heating, inversion weather, spring heavy wind and dust storm will worsen the pollution in the north, while the maritime climate and plenty precipitation will improve the air quality in the south. By analyzing five meterological factors'relationship with air pollution, which are wind speed, tempreture, humidity, air pressure, precipitation, we found a result of negative corelation with wind speed, tempreture, precipitation, while positive corelation with humidity, air pressure.6,By analyzing the imfluence of sand storm on cities'air quality, we found that the influence shares some geological features. In the North, especially in NW, NC, air quality is heavily affected by dust storm.While the sand storm also affect air quality in the central and southern and eastern coastal cities.
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