BEIJING, Dec. 1 (Xinhua) -- Beijing Municipality on Thursday issued an orange alert for air pollution in the next three days.
The orange alert, the second highest in a four-tier warning system, will be effective from midnight Thursday, according to the city air pollution emergency response office.
An orange alert means heavy pollution -- PM2.5 density of higher than 150 micrograms per cubic meter of air -- for three consecutive days.
When the alert is in force, outdoor activities in schools are to be canceled, and construction projects suspended.
The smog is expected to disperse Sunday evening when a cold front is forecast to hit the city, according to the city's meteorological authorities.