Seven cities from Hebei province filled spots in a list of 10 with severe air pollution during September, the national environment watchdog said.

The Ministry of Environmental Protection released its monthly report on the air quality of 74 major cities on Wednesday, among which seven in Hebei including Hengshui, Tangshan and Shijiazhuang, were listed as having heavy air pollution.

Jinan in Shandong province ranked as the worst with Zhengzhou from Henan province second worst, the report said.

Although residents of the seven cities in Hebei witnessed heavy smog last month, the air quality in the Beijing-Tianjin-Hebei region has seen an improvement.

In the trilateral zone, the concentration of PM2.5 – particulate matter with a diameter smaller than 2.5 microns – has been lowered by 26.2 percent year-on-year, said Luo Yi, head of environment supervision of the ministry.