Lungs weren't the problem, says Ding Rongjing, the hospital's deputy head of cardiology. Five people were admitted for heart attacks from Dec. 4 to Dec. 6, compared with one or two a week typically. One 60-year-old male patient died.

The illnesses are an unwanted consequence of the economic growth that helped spur a 32 percent jump in China's car sales last year. Outdoor air pollution kills 1.3 million people globally each year, the World Health Organization estimates.

A growing body of evidence shows dirty air not only triggers asthma and other respiratory conditions, over time it may damage heart and blood vessels, and even cause birth defects.

"Whenever we have days with bad pollution, we get significantly more patients with symptoms like high blood pressure, feeling of suffocation, and chest pains," Ding said in an interview at the hospital, where she's worked since 1996.

On days of extreme pollution, heart and stroke cases at the 1,450-bed center can increase as much as 40 percent to 280 patients, she said.

Limits on car sales

The rapid growth of car ownership in Beijing has hobbled efforts to improve air quality. In 2010, there were 4.8 million vehicles on Beijing roads -- triple the number in 2000, according to government data.

Last January, the municipality of Beijing imposed a monthly limit of 20,000 new car registrations, a policy that reduced car sales by 70 percent.

The central China city of Guiyang enacted a similar measure in July, and two southern cities, Guangzhou and Shenzhen, may follow suit.

Early this year, Credit Suisse warned that car sales in China might plunge as much as 17 percent if other Chinese cities adopted similar curbs on car ownership.

Car ownership in China has offset the benefits of the past decade's efforts to limit industrial emissions, said Xu Dongqun, deputy director of the Institute for Environmental Health and Related Product Safety at the Chinese Center for Disease Control and Prevention.

"The level of fine particulate matter is still increasing because it comes not just from industrial emission and coal-burning, but also from the large amount of cars on the roads," Xu said.

Xu outlined Beijing's air pollution woes during a Dec. 5 interview in a second-floor meeting room in central Beijing, where murky haze outside rendered the housing blocks across the street barely visible.

The Chinese CDC would like to see coordinated warning data broadcast on the nightly news, Xu said. Publicizing the data may have implications for businesses if it means more people are worried about air quality and are reluctant to live in the city.

Emissions data on small particulates, or PM2.5, is scheduled to be made publicly available throughout China's cities, including Beijing, by 2016.

The timeframe is too slow, concluded a Dec. 8 editorial in the state-owned China Daily newspaper, which called on the government to be "brave enough" to measure the tiny contaminants.