Beijing has been suffering this year's most severe smog since Friday, with pollution readings off the charts that have forced schools to close and caused traffic chaos.

Tourists visit Tian'anmen Square on Tuesday as the city experiences its most severe smog this year.[Photo/China Daily]

However, with a westerly wind due to reach the capital at midnight on Tuesday, good air quality was being forecast for Wednesday, said Zhang Dawei, director of the Beijing Municipal Environmental Monitoring Center.

He said the air quality is expected to remain good from Wednesday to Friday.

The capital's orange pollution alert was due to be lifted from midnight on Tuesday.

Beijing had issued its first orange pollution alert of the year on Sunday, restricting production at more than 2,100 companies and suspending all work on construction sites that could generate dust.

Thick, choking smog has enveloped the capital for five days, with the air quality index in many monitoring stations soaring to 500, the highest possible reading. The municipal government encourages people to stay indoors when the reading is higher than 300.

The concentration of PM2.5－particulate matter with a diameter less than 2.5 microns that poses health risks－was 689 at 5 pm on Tuesday in some southern Beijing monitoring stations, down from the peak reading of 945 on Monday.

Students at some kindergartens, and primary and middle schools had their classes canceled so they could stay indoors.

The capital has also seen more road accidents due to the poor visibility, and traffic congestion was bad around the city through most of Monday. Many expressways linking Beijing and neighboring cities in Hebei province were closed for hours.

The municipal environmental watchdog sent inspection teams to supervise measures to restrict emissions on Tuesday. Of 545 companies they inspected, 12 had violated orange alert restrictions, the capital's environmental protection bureau said.

For example, a Dongfeng Nissan factory failed to suspend work on Tuesday. And a construction site at the China University of Political Science and Law left piles of building materials uncovered which could release dust into the air.

All companies and construction sites violating the regulations would be severely punished, the bureau said.

The smog covering a vast area across northern China has been caused by unfavorable weather, with no wind and high humidity, and an increased consumption of coal in the heating season, the Ministry of Environmental Protection said.

Humor provides light relief from heavy smog

Some of the Chinese capital's 22.5 million residents have turned to humor to cope with persistent toxic air that once again soared above hazardous levels on Tuesday.

A joke circulating among Chinese journalists told of a reporter approaching an old woman on the street to ask about the impact of the smog. "The impact is huge," the woman replies. "First of all, I'm your uncle."

Some users of social media traced the shapes of famous Beijing landmarks on photographs in which the buildings were nearly obscured by the smog and posted them online.

One said living in Beijing was like working on the crew of a zombie apocalypse movie.

"As a friend finished eating lunch, he slapped on his face mask and said he had to return to the set. They were filming Resident Evil in the afternoon," one micro-blogger joked, invoking the horror film.

Another online joke said a Beijing radio broadcaster received a call from a member of the audience who was worried about his traffic violations. "I cannot see the red light until it's too late," he cried, saying he had run through eight lights.

"Don't worry," the broadcaster said. "The heavy smog has also protected you from the traffic cameras."