BEIJING, July 22 -- Beijing and its surrounding regions saw a year-on-year decline in PM2.5 density in the first half of 2015, the Beijing Municipal Environmental Protection Bureau announced on Wednesday.

Concentration of PM2.5, airborne particles measuring less than 2.5 microns, in Beijing has reduced by 15.2 percent in the first half while the PM2.5 density in the capital and its surrounding areas including Tianjin Municipality, Inner Mongolia Autonomous Region, and the provinces of Hebei, Shanxi, Shandong and Henan, dropped by 15.4 percent in the same period, said Yu Jianhua, chief engineer of the bureau.

The Beijing-Tianjin-Hebei region's average PM 2.5 density in the first half stood at 78 micrograms per cubic meter, a decline of 22.1 percent.

Other air pollutants have also been reduced. The density of sulfur dioxide, nitrogen dioxide and PM10 dropped by 41.3, 14.5, and 12.7 percent, respectively, according to Yu.

The capital saw 88 days of sound air quality in the first half, nine days more than in the same period last year. Air pollution was registered on 16 days, a decrease of nine days compared with the first half of last year.

Yu attributed the improved air quality to limits to emissions, favorable weather conditions and clean production in Beijing and its surrounding areas.

The city imposed strict emissions limits for its coal-fired boilers, crematoriums, printing houses, wooden furniture manufacturers and refineries in the first half.

It closed three of its four coal power plants and scrapped 178,000 old vehicles in the six months, and it has banned heavy-duty diesel vehicles since June if they cannot meet the national fifth phase emissions standard, which is equal to the Euro V emissions cap.

The Beijing Municipal Commission of Housing and Urban-Rural Development also fined 511 construction sites 10.33 million yuan (1.66 million U.S. dollars) for failing to control their dust pollution, Yu said.

Beijing environmental protection departments dealt with 1,424 cases of environmental crimes and issued fines of 43 million yuan January-June.