Beijing's average PM2.5 density in 2014 dropped by four percent compared with 2013, but some pollutants rebounded, said the municipal environmental protection bureau.

The average density of PM2.5, airborne particles smaller than 2.5 microns in diameter, was 85.9 micrograms per cubic meter in 2014, compared with 89.5 micrograms per cubic meter in 2013, the bureau said in a statement Sunday.

The reading was still 1.5 times higher than the national standard of 35, which was set by the State Council in 2012.

The city witnessed 93 days of "excellent air quality" in 2014, or 22 days more than in 2013. The number of heavily polluted days dropped by 13 to reach 45.

Air concentrations of sulfur dioxide fell 17.7 percent. But nitrogen dioxide and PM10, or particles under 10 microns in diameter, grew 1.3 percent and 7.1 percent respectively, said Zhang Dawei, director of the Beijing Municipal Environmental Monitoring Center.

As part of efforts to curb pollution, Beijing reduced coal use by 2.6 million tonnes to keep it below 19 million tonnes. The capital also removed 476,000 outdated vehicles from roads and shut down about 375 factories in 2014.

In 2015, Beijing aims to cut PM2.5 index by around five percent and reduce the emission of sulfur dioxide and nitrogen oxides by six percent.

The city will try to keep its coal consumption under 15 million tonnes and further phase out 200,000 vehicles as well as more than 300 polluting factories, according to Yu Jianhua, an official of the bureau.

Beijing will cut its cement capacity to 5 million tonnes, Yu added.

With a population of more than 20 million, Beijing has been plagued by smog in the past few years due to industrial pollution and vehicle exhaust.

In Beijing and surrounding areas, PM 2.5 should fall by about 25 percent from 2012 levels by 2017, according to government plans. Endi