The 20 most polluted cities (PM10) in China in the first half of year 2011 are:
- Lanzhou, Gansu
- Urmqi, Xinjiang
- Xi'an, Shannxi
- Chifeng, Inner Mongolia
- Hefi, Anhui
- Yan'an, Shannxi
- Xining, Qinghai
- Beijing
- Yangzhou, Jiangsu
- Lianyungang, Jiangsu
- Nanjing, Jiangsu
- Jinan, Shandong
- Chengdu, Sichuan
- Harbin, Heilongjiang
- Wenzhou, Zhejiang
- Huzhou, Zhejiang
- Jining, Shandong
- Zhengzhou, Henan
- Ningbo, Zhejiang
- Yinchuan, Ningxia
As any numbers coming out of mainland China, the number should be swallowed with a grain of salt. Economically developed eastern provinces such as Jiangsu and Zhejiang probably are more confident in releasing more realistic data; and cities within a same province are likely peer-pressured to fix its data to the positive direction.
PM10 is considered an old, obsoleted method of measuring air quality because it ignores small particles in the air, which are the major health concerns. However, the Chinese government did not provide and pragmatically forbid study of smaller pollutants.
The US Embassy in Beijing set up an instrument in its back yard, and release data automatically through Twitter. The reading often went off roof, with 'crazy' (quoted literally from Embassy brief) numbers such as 570. At this time of writing, the figure is 257 and 307 'Hazardous', read from two sensors MetOne BAM 1020 and Echotech EC9810, according to the Twitter account. One interesting observation after studying the Embassy Twitter data is that the worst readings usually came around 1:00 am after midnight, where there were fewest cars on the road. Residents believe it was caused by factories who secretly release chemical waste in the middle of night.
