BEIJING — Beijing and other parts of northern China were stung by hazardous air pollution levels Thursday as strong winds blew a sandstorm through the region.

Air in the capital turned a yellowish hue as sand from China's arid northwest blew in, turning the sky into a noxious soup of smog and dust.

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At 6 a.m. local time, the U.S. Embassy's air quality index showed a reading of 516 for particles less than 2.5 micrometers in diameter. Known as PM2.5, such particles are considered particularly dangerous because they can lodge deeply in the lungs. On the American air pollution index, the air at that time and throughout much of the morning was classified as "beyond index."

 

The developers of the U.S Embassy's air monitoring station had planned for an index capped at 500. The World Health Organization suggests that 24-hour exposure to PM2.5 should be limited to levels of 25 on that scale.

Beijing's municipal government issued a yellow-haze warning late Wednesday while state media urged citizens to stay indoors or to take precautions such as donning face masks before venturing outside.

Across northern China in provinces including Hebei, Hubei, Jiangsu and Inner Mongolia, air monitoring stations recorded readings over 500, and visibility across the region was severely curtailed. In some places visibility was below 3,200 feet, leading to highway closures, suspension of high-speed train services and the cancellation of flights from Beijing International Airport.

By mid-afternoon, pollution levels had fallen and strong winds had pushed much of the remaining cloud cover from the capital.

Geographically close to the Gobi Desert, Beijing and other northern cities are particularly susceptible to sandstorms such as Thursday's. Sandstorms are prevalent in late winter and spring as melting frost frees sand and strong winds kick it up and push it eastward.

The start of 2013 has brought chronic bad air to much of China. In January, air pollution readings were so bad that they were compared to living in an airport smoking lounge. That comparison was underscored by record high levels of PM2.5 on Jan. 12, when readings topped out at 755 on the air quality index.

Frustration over China's continued pollution problems popped up across Chinese social media. But irritation over the long-brewing issue was perhaps best summed up by a viral photo originally posted on popular Web portal QQ.com of an unhappy looking Yao Ming, grimacing at the Beijing sky.

Yao, the former NBA All-Star and current member of a Communist Party advisory board known as the China People's Political Consultative Conference, is currently in Beijing in the lead-up to next month's National People's Congress.

The congress will mark the final step in China's once-in-a-decade leadership change as party heads Xi Jinping and Le Keqiang formally take over as China's president and prime minister, respectively.

Since taking over China's ruling Communist Party late last year, the new leaders have spoken repeatedly about improving the mainland's environment.

Many China watchers believe that China's environmental degradation -- underscored by severe air pollution, contaminated soil and dirty waterways -- will be a focal point during the congress.

This story was originally published on Thu Feb 28, 2013 6:46 AM EST

Thick, off-the-scale smog shrouded eastern China for the second time in about two weeks Tuesday, forcing airlines to cancel flights because of poor visibility and prompting Beijing to temporarily shut factories and curtail fleets of government cars.

The capital was a colorless scene. Street lamps and the outlines of buildings receded into a white haze as pedestrians donned face masks to guard against the caustic air. The flight cancellations stranded passengers during the first week of the country's peak, six-week period for travel surrounding the Chinese New Year on Feb. 10.

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The U.S. Embassy reported an hourly peak level of PM2.5 — tiny particulate matter that can penetrate deep into the lungs — at 526 micrograms per cubic meter, or "beyond index," and more than 20 times higher than World Health Organization safety levels over a 24-hour period.

Liu Peng, an employee at a financial institution in Beijing, said he will keep his newborn baby indoors.

"It's really bad for your health, obviously," Liu said. "I bike to work every day and always wear a mask. The pollution in recent years is probably due to the increase in private cars and government cars."

Visibility was less than 100 yards in some areas of eastern China, the official Xinhua News Agency reported. More than 100 flights were canceled in the eastern city of Zhengzhou, 33 in Beijing, 20 in Qingdao and 13 in Jinan.

Every year, China's transport system bursts at the seams as tens of millions of people travel for the Lunar New Year holiday, in the world's largest seasonal migration of people.

Ren Haiqiang, a bank worker in his early 30s, said he had booked tickets to fly out of Beijing on Thursday to visit family in the coastal city of Dalian, but now worried about flight cancellations.

"Traveling over the holiday is already a huge hassle, along with all the gift-giving and family visits. We thought flying would be the best way to avoid the crush, but if the weather continues like this we'll be in real trouble," Ren said as he waited in line at a bakery in downtown Beijing.

Beijing's city government ordered 103 heavily polluting factories to suspend production and told government departments and state-owned enterprises to reduce their use of cars by a third, Xinhua said. The measures last until Thursday.

Beijing's official readings for PM2.5 were lower than the embassy's — 433 micrograms per cubic meter at one point in the afternoon— but even that level is considered "severe" and prompted the city government to advise residents to stay indoors as much as possible. The government said that because there was no wind, the smog probably would not dissipate quickly.

Patients seeking treatment for respiratory ailments rose by about 30 percent over the past month at the Jiangong Hospital in downtown Beijing, Emergency Department chief Cui Qifeng said.

"People tend to catch colds or suffer from lung infections during the days with heavily polluted air," he said.

Air pollution has long been a problem in Beijing, but the country has been more open about releasing statistics on PM2.5 — considered a more accurate reflection of air quality than other pollutants — only since early last year. The city hit its highest readings on Jan. 12, when U.S. Embassy readings of PM2.5 reached as high as 886 micrograms per cubic meter.

Celebrity real estate developer Pan Shiyi, who has previously pushed for cities to publish more detailed air quality data and who is a delegate to Beijing's legislature, called Tuesday morning for a "Clean Air Act." By late afternoon, his online poll had received more than 29,000 votes, with 99 percent in favor.

On Monday, Wang Anshun was elected Beijing's mayor after telling lawmakers the municipal government should make more efforts to fight air pollution, according to Xinhua.

Last week, he announced plans to remove 180,000 older vehicles from the city's roads and promote government cars and heating systems that use clean energy.

BEIJING — Air quality in Beijing was the "worst on record" on Saturday and Sunday, according to environmentalists, with pollution 30-45 times above the recommended safety levels.

With a thick smog wrapping the Chinese capital since Friday, the city's pollution monitoring center warned the city's 20 million residents to stay indoors.

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Data posted on Sunday by the monitoring center showed particulate matter measuring less than 2.5 micrometers in diameter (PM2.5) had reached more than 600 micrograms per square metre at some monitoring stations in Beijing, and was as high as 900 on Saturday evening.

The recommended daily level for PM2.5 is 20, according to the World Health Organisation. Such pollution has been identified as a major cause of asthma and respiratory diseases.

"This is really the worst on record not only from the official data but also from the monitoring data from the U.S. embassy — some areas in (neighboring) Hebei province are even worst than Beijing," said Zhou Rong, climate and energy campaigner at Greenpeace.

The Beijing Municipal Environmental Monitoring Center said heavy pollution had been trapped by an area of low pressure, making it harder to disperse, and the conditions were likely to last another two days.

Related: Beijing's pollution could cut 5 years off life span

Pollution has been identified as one of the biggest challenges facing China's leaders, with outgoing president Hu Jintao saying during his address to the Communist Party Congress last November that the country needed to "reverse the trend of ecological deterioration and build a beautiful China."

China said at the end of last year that it would begin releasing hourly pollution data for its biggest cities.

Beijing has already committed to a timetable to improve air quality in the city, and has relocated most of its heavy industry, but surrounding regions have not made the same commitments, said Zhou.

"For Beijing, cleaning up will take a whole generation but other regions don't even have any targets to cut coal burning. I bet the pollution here is mainly from those surrounding regions."