A girl takes photos in front of Tiananmen Square as the sky clears when PM 2.5 density decreased to 5 micrograms per cubic meter in Beijing on Aug 30, 2013. [Photo by Zou Hong / Asianewsphoto]

BEIJING -- The Beijing municipal government on Monday pledged to reduce PM 2.5 density by 25 percent or more by 2017 with the implementation of a five-year action plan.

According to the plan, air quality will improve significantly by 2017, with PM 2.5 density controlled to around 60 micrograms per cubic meter.

PM 2.5 are airborne particles measuring less than 2.5 microns in diameter which can pose health risks.