It's back: Wave of smog hits Beijing

Most urban districts of Beijing began seeing moderate air pollution early Sunday owing to weather conditions that are "not favorable for dispersing pollutants", Beijing Youth Daily reported on Sunday evening, citing the Beijing Environmental Monitoring Center.

The pollution is expected to reach its peak on Monday, and some parts of southeast Beijing will see heavy air pollution, the environmental watchdog told the newspaper.

This pollution will clear on Tuesday, the watchdog said.

China has a six-level air quality rating system. Excellent air requires index levels below 50, and from 151 to 200 or from 201 to 300 are respectively classified as moderately polluted and heavily polluted. Days when the index rises over 300 are considered severely polluted.

According to the center's official Weibo account, the index in southeast Beijing reached 141 by 8 am on Sunday. Northwest and northeast Beijing reached almost 130.

Ma Jun, director of the Institute for Public and Environmental Affairs, said this is the first time in three months that Beijing has been hit by large-scale air pollution.

"The smog won't dissolve until Tuesday, and Beijing residents should use protection, such as masks and air purifiers," he said.