The annual environmental bulletin, unveiled Thursday morning, showed increasing improvement in air and water quality in the capital last year.

The number of days with heavy air pollution last year was only 15, nine less than the previous year, according to the bulletin released Thursday by the Beijing Ecology and Environment Bureau.

In addition, the quality of surface water in rivers and lakes has been improving, with longer sections seeing better quality, according to monitoring data. The quality of drinking water sources has reached the national standard as well.

Beijing has strengthened cooperation with neighboring regions including Hebei and Tianjin in environmental monitoring and pollution controls. Beijing and Hebei province have signed an agreement to jointly protect the Daqing River and Baiyangdian drainage area in the middle-west part of the region.