Beijing's meteorological authorities issued a yellow alert for smog, 6 a.m. Sunday, forecasting poor visibility and poor air quality from Sunday to Monday afternoon.
In China's four-tier severe weather warning system, red is the most serious alert, followed by orange, yellow and blue.
On Sunday noon, the city air pollution emergency response office issued a blue alert for heavy air pollution.
A blue alert means heavy pollution -- PM2.5 density of higher than 150 micrograms per cubic meter of air -- for 24 hours.
Data from Beijing Municipal Environmental Monitoring Center shows that the average PM2.5 density in the core six districts of Beijing was 190 micrograms per cubic meter around Sunday noon.
The smog is expected to disperse Monday afternoon when a cold front is forecast to hit the city, according to the city's meteorological authorities.
