A young girl in a pink snowsuit wears a cartoon mask to protect her young lungs. Elsewhere in Beijing, a grandmother tenderly presses an oxygen mask to her grandson’s face because he suffers from a respiratory disease.

Scenes like these played out across China’s capital Tuesday as a thick, white haze of industrial smog suffocated the city for the fourth time in the past month. Residents were urged to stay indoors and more than 100 flights were cancelled in several cities as visibility was reduced to about 100 metres.

The government ordered 103 heavy-polluting factories to suspend production until Thursday, the official state news agency Xinhua reported.

Fine air pollution was at “hazardous” levels, according to the American embassy’s Twitter feed. Peak levels of PM2.5 — microscopic particulate matter that can embed deep into the lungs and pose a serious health risk — were 526 micrograms per cubic metre over a 24-hour period, according to the embassy’s monitoring station in Beijing. The level recommended by the World Health Organization is just 25 micrograms per cubic metre.

Exposure to PM2.5 pollution can lead to cardiovascular and lung disease, and increases the risk of cancer.

In a sign that state authorities are concerned about the impact of pollution and open to more debate, Xinhua quoted critics who called for a car ban and new air-pollution laws. Among the most outspoken was Wang Lifen, a former journalist and blogger who said cars should no longer be allowed.

“Everyone — senior officials and VIPs included — should take buses and subways instead of private cars,” she told Xinhua. The agency also quoted comments from Weibo, the Chinese version of Twitter, where some complained that children should be allowed to stay home from school on high-pollution days.

Major sources of pollution include the chemical factories surrounding Beijing and the coal that is burned for heating and industry, said Bruce Urch, a research associate at the Dalla Lana School of Public Health at the University of Toronto.

“Coal contains sulphur and sulphur is a nasty pollutant,” he said. “The other problem is cars. It is basically a population problem. If you have 20 million people and many have cars, the emissions from that are big.”

Children are at particular risk because their lungs are still developing, Urch said, and the ubiquitous face masks worn in Beijing are of limited help because they cannot filter out harmful ozone.

PM2.5 air pollution may have led to 8,572 premature deaths last year in four major Chinese cities including Beijing, according to a study by Greenpeace and Peking University’s School of Public Health. China began allowing PM2.5 levels to be monitored in 2011, so its impact on health is in the early stages of being assessed, the reported noted.

With the rise of social media, the authorities can no longer ignore the problem, said Lynnette Ong, associate professor of political science at the University of Toronto.

“Traditionally the authorities have tried to cover up and report as little as they could, but now they see they cannot cover up anymore and so there is disclosure of information,” she said. “At one point the authorities reprimanded the U.S. embassy for the air pollution monitor reports, which are increasingly read by Chinese people.”

Beijing’s new mayor Wang Anshun will have to balance citizens’ demand for cleaner air with economic development, an editorial in the China Daily newspaper said.

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“(Beijing) should definitely not be a city that has most of its winter days shrouded in smog and neither should it be a city whose roads are congested most of the time,” the newspaper said.

With files from The Associated Press

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