Report on the quality of air in 47 major Chinese cities (12:00 Sept. 17 to 12:00 Sept. 18, Beijing Time), released by the China Environmental Monitoring Center:

The center classifies air quality in China's urban areas into five levels: level I or excellent (pollution reading: not exceeding 50), level II or fairly good (pollution reading: 51 to 100), level III or slightly polluted (pollution reading: 101 to 200), level IV or poor (pollution reading: 201 to 300), and level V or hazardous (pollution reading: over 301).

The 47 cities monitored by the center include the four municipalities of Beijing, Tianjin, Shanghai and Chongqing, provincial (or autonomous regional) capitals, and major cities in economically developed coastal areas, and tourist attractions.