BEIJING - The air in Beijing, as well as its surrounding areas, was heavily polluted in June, the Ministry of Environmental Protection (MEP) said Wednesday.

Up to 21.2 percent of the days in June saw air quality in Beijing, as well as neighboring Tianjin municipality and Hebei province, heavily polluted, according to MEP air quality readings for 74 cities and three city agglomerations.

Combined average air quality readings for the 74 cities met standards for over half the days in June. The Pearl River Delta, a city agglomeration in South China, had good air quality for nearly 90 percent of the days in June.

The air in Beijing, Tianjin and Hebei was heavily polluted for about one-quarter of the first half of the year, the worst of the three city agglomerations monitored by the MEP.

An unidentified official with the MEP said the major pollutant in Beijing is PM2.5, or dangerous airborne particles measuring less than 2.5 microns in diameter.

The average reading for PM2.5, or dangerous airborne particles measuring less than 2.5 microns in diameter, in the 74 cities in the first half was 76 micrograms per cubic meter.

But in Beijing and its surrounding areas, the average reading was 115 micrograms per cubic meter.

An MEP official who requested anonymity cited coal-burning, automobile emissions, construction projects and industry as the major causes of the heavy pollution.

Environment Minister Zhou Shengxian said last week that the government is making an action plan to improve air quality during the 2013-2017 period. The plan is expected to be released before early August.