More than half of the number of days in the first three months of the year saw clean air, according to results from 74 Chinese cities that were monitored.

Forty-eight days out of 90, or 53.1 percent, had clean air, up 5.1 percent year on year, the Ministry of Environmental Protection revealed on April 25.

The 10 cities with the most serious air pollution were Xingtai, Shijiazhuang, Baoding, Tangshan, Handan, Hengshui, Jinan, Xi'an, Langfang and Chengdu—most of which are in the country's north—the ministry said in a report.

Air pollution in the region surrounding Beijing was worse than other parts of the country during the three months, and the 13 monitored cities in the region experienced days that failed to meet standards 69.4 percent of the time, while the national average stood at around 47 percent.

There was a slight drop in the density of PM2.5 and PM10 (airborne particles less than 2.5 micrometers and 10 micrometers, respectively) in March compared with the same period of last year, the report added.