A study of air pollution of city clusters

In this study, the Daily Air Pollution Index (DAPI) of 81 cities in China from June 2004 to June 2007 was used to study the air pollution of city clusters. The cluster analysis results show that the DAPI of 71 cities in central and eastern China is divided into two regimes, the north regime and the south regime along the Qinling Mountain and its eastern extension to Huaihe River. The demarcation line between the two DAPI regimes duplicates the demarcation line of the watersheds of the northern and southern climate regions and the DAPI were statistically negatively correlated to the amount of rainfall, suggesting that precipitation could play an important role in determining the two regimes. The two DAPI regimes are further divided into seven city clusters mainly associated with emissions of air pollutants and geographical distributions, supported by remote sensing data of aerosol optical depth (AOD), NO2 and emission inventories of air pollutants in China in 2006 reported in the literature. DAPI of three city clusters in the north regime exhibited a similar seasonal trend, which was different from the four city clusters in the south regime. Outbreak of dust storms in spring and an increase in emissions due to space-heating impacted the DAPI of the northern city clusters. Although the consumption of electricity decreased in the southern city clusters in the fall and winter, the reported high DAPI were the result of less rainfall and poor dispersion. Seven cities in western China were classified into two groups associated with their unique nature environments. Three cities were not allocated to any of the city clusters.