BEIJING - Beijing's air quality was rated "hazardous" on Monday, as dust lingered in the city for a fourth day.

The Beijing Environmental Protection Monitoring Center said that since Sunday the air quality in most parts of the metropolis has been rated "hazardous," meaning inhalable particulate matter (PM) over 500 micrograms was detected in each cubic meter of air.

The PM2.5 data at the Chegongzhuang monitoring station in Xicheng district reached an average of 111 micrograms per cubic meter from 11 am Sunday to 10 am Monday, exceeding the regulated standard of 75 micrograms per cubic meter.

The PM2.5 gauge monitors "fine" particles 2.5 microns or less in diameter.

Dust carried by winds from the Mongolian region started to linger in Beijing from around 7 am on Friday, and experts said the situation would continue, as it will be windy on Monday night and Tuesday.