The Chinese government now issues hourly air quality updates online for more than 70 cities.

"I think there's been a very big change," prominent Beijing environmental campaigner Ma Jun said, adding that the government knows it no longer has a monopoly on information about the environment. "Given the public's ability to spread this information, especially on social media, the government itself has to make adjustments."

Air pollution is a major problem in China due to the country's rapid pace of industrialization, reliance on coal power, explosive growth in vehicle ownership and disregard for environmental laws, with development often taking priority over health. The pollution typically gets worse in the winter because of an increase in coal burning.

"The pollution has affected large areas, lasted for a long time and is of great density. This is rare for Beijing in recent years," Zhang Dawei, director of Beijing's environment monitoring center, told a news conference Monday.

According to the government monitoring, levels of PM2.5 particles were above 700 micrograms per cubic meter on Saturday, and declined by Monday to levels around 350 micrograms â¿¿ but still way above the World Health Organization's safety levels of 25.

In separate monitoring by the U.S. Embassy, levels peaked Saturday at 886 micrograms â¿¿ and the air quality was labeled as "beyond index."

City authorities ordered many factories to scale back emissions and were spraying water at building sites to try to tamp down dust and dirt that worsen the noxious haze.

Schools in several districts were ordered to cancel outdoor flag-raisings and sports classes, and in an unusual public announcement, Beijing authorities advised all residents to "take measures to protect their health."

The Beijing Shijitan Hospital received 20 percent more patients than usual at its respiratory health department, most of them coughing and seeking treatment for bronchitis, asthma and other respiratory ailments, Dr. Huang Aiben said.

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