BEIJING, May 16 -- A total of 70.6 percent of the 74 Chinese cities monitored for air quality in April met the national air quality standards, the Ministry of Environmental Protection said on Friday.

The Pearl River Delta reported the best air condition with 93 percent of the cities reaching the air quality standards, and there were no days of heavy pollution.

East China's Yangtze River Delta performed slightly worse last month. Twenty-five cities there reported air pollution on 21.8 percent of the days, including heavy pollution on 0.3 percent of the days.

Beijing and its surrounding areas, including Tianjin and cities in north China's Hebei Province, reported the heaviest pollution last month.

Thirteen cities in the region had on average 65.2 percent of days that failed to meet standards.

Among them, ten cities made the top-ten worst polluted city chart. The ten were Xingtai, Tangshan, Shijiazhuang, Jinan, Handan, Baoding, Tianjin, Qinhuangdao, Beijing and Langfang.

Six of the monitored cities reported 100 percent clean air last month, including Shenzhen, Haikou and Zhoushan.

The primary key air pollutant is PM2.5, accounting for 58.4 percent of the days that failed the air quality standards, the ministry said.