BEIJING - Beijing will extend its air quality monitoring network with more stations and focus on vehicles with high emission, confirmed the city environmental authority Friday.

These stations will be along the fifth and sixth ring roads and other ?highways heading into the urban areas, the main routes of heavy diesel vehicles, said Zhang Dawei, director of the Beijing Municipal Environmental Monitoring Center.

Heavy diesel vehicles only comprise about five percent of Beijing's traffic but spew out about fifty percent of the city's nitric oxide.

The new stations will help environmental authorities understand high emission vehicle pollution, said Zhang.

Beijing has 35 air monitoring stations measuring the city's six main pollutants, including sulfur dioxide, PM10 and PM2.5.

Beijing reported 58 days of heavy pollution last year, compared with 176 days of excellent or fairly good air.