Beijing saw improvement in air quality during the first half of the year, with the concentration of PM2.5 lower by more than 15 percent from the same period last year, an environmental watchdog said.

PM2.5 - airborne particles smaller than 2.5 microns in diameter - fell to 77.7 micrograms per cubic meter, a cut of 15.2 percent year-on-year, the Beijing Municipal Environmental Protection Bureau said on Thursday.

Levels of the three other major airborne pollutants have also been reduced. Sulfur dioxide was lower by 41.3 percent than that recorded in the first six months of 2014; nitrogen oxides fell by 14.5 percent and PM10 was down by 12.7 percent.

Residents experienced nine more days with air quality better than national standards between January and June, the bureau said.