Backgrounder: 10 most polluted Chinese cities

China's most polluted cities are to be found in the north of the country, according to the Ministry of Environment. This is due to the large concentration of coal-fired power stations.

Northern China's Shijiazhuang was found to be the most polluted city in May this year, and Tangshan, another city in northern China's Hebei Province is the second worst.

China's Ministry of Environment has released figures for air quality in 74 cities. The 10 most polluted cities were Shijiazhuang, Tangshan, Xingtai, Handan Jinan, Baoding, Zhengzhou, Beijing, Hengshui and Tianjin.

Apart from Jinan and Zhengzhou, all the other cities are located at Beijing-Tianjin-Hebei region, where air quality was bad for three quarters of the month of May. Beijing and Tianjin have seen their air quality fall markedly, with concentrations of four pollutants, PM 2.5, PM 10, sulfur dioxide and nitrogen dioxide, increasing.