Impact of urbanization level on urban air quality: a case of fine particles (PM(2.5)) in Chinese cities.

We examined and compared PM2.5 concentrations in urban and the surrounding regions, and further investigated the impact of urbanization on urban PM2.5 concentrations at the Chinese prefectures. Annual PM2.5 concentrations in most prefectures were greater than 10 μg/m(3), the air quality guideline of the World Health Organization. Those prefectures were mainly distributed along the east coast and southeast of Sichuan province; The urban PM2.5 concentrations ( [Formula: see text] ) in 85 cities were greater than (>10 μg/m(3)) those in the surrounding area. Those cities were mainly located in the Beijing-Sichuan and Shanghai-Guangxi belts. In addition, [Formula: see text] was less than (<0 μg/m(3)) that in surrounding areas in only 41 prefectures, which were located in western China or nearby mega cities; Significant positive correlations were found between [Formula: see text] and urban population (R(2) = 0.99, P < 0.05), and between [Formula: see text] and urban second industry fraction (R(2) = 0.71, P < 0.05), suggesting that urbanization had considerable impact on PM2.5 concentrations.