中文摘要：

随着霾天气的大范围出现,空气污染已成为中国最受关注的区域性环境问题。本文主要基于中国73个城市近5年（2007年6月5日~2012年6月4日）的空气污染指数（API）,利用聚类分析和趋势分析等方法,研究了中国城市空气污染的区域分布和季节变化特征,讨论了天气现象对空气污染指数区域分布的影响。研究表明：（1）根据空气污染指数,中国73个城市可分为6个类群,分别是东北城市群、华北城市群、山东城市群、中西部城市群、华中和东南沿海城市群以及华南城市群;（2）与前期研究相比,降雨依然是影响API时空分布的主要因素,频繁发生的霾天气也成为API变化的重要原因;（3）当API≥100时,霾、沙尘和烟幕等天气现象对API空间分布的影响存在城市群间差异;（4）趋势分析表明,北方大部分城市的API呈降低趋势,而南方约50%城市的API呈上升趋势,PM2.5~10的浓度变化可能是造成这种变化趋势的主要原因。

英文摘要：

With the frequent occurrence of haze in wide areas,air pollution becomes one of the most notable environmental problems in China.Based on the data of Air Pollution Index（API）from 73 cities of China in recent 5years（from 5June 2007 to 4June 2012）,a regional distribution of API and its seasonal variations are studied by using cluster analysis and trend analysis.The impacts of different weather phenomena（i.e.haze,dust,rain,snow and smoke）on API clusters are also discussed.It is shown that：（1）73cities are divided into 6clusters,and they are northeast city cluster,North China city cluster,Shandong city cluster,Middle and west city cluster,Central China and southeast coast city cluster and south China city cluster.（2）Compared with the previous studies（2004~2007）,rainfall seemed to be the major factor to control the spatial and temporal distribution of API,and haze seemed to play a significant role.In addition,dust and smoke also have obvious impacts.（3）While API≥100,the effects of haze,dust and smoke on the spatial distribution of API are different in city clusters.（4）Based on trend analysis,API is descending in most of the northern cities,but ascending in 50%of the southern cities in China.This research may provide scientific reference for the study of Air Quality Index in the future,which had become the index to indicate statues of air pollution instead of API since 2013 in China.