MADISON, Wis. -- On the opening day of the Beijing Olympics, there was serious concern for athletes' health.

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According to the World Bank Web site, China contains 16 of the world's 20 most polluted cities. And, pollution levels in Beijing are five times over the benchmark set by the World Health Organization.

During opening day ceremonies Beijing's pollution index reached above 90.

By comparison, New York City's pollution index reached between 20 and 30 on the same day. The World Health Organization's standard for healthy air is anything below 50.

The Chinese government has spent $18 billion to try to clear Beijing's air, including limiting vehicle traffic and shutting down some factories.

"The air quality is going to have a dramatic impact on everybody breathing air," said Environmental Health Services Supervisor for Public Health John Hausbeck.

Hausbeck said that because athletes have a larger lung capacity and take in more air, they may notice the effects sooner.

"It's going to reduce lung function," said Hausbeck. "It's going to cause you to have more symptoms such as coughing or irritation in the throat and respiratory system."

Madison hasn't had any clean air action days this summer, but when an alert is issued Madison runner Tom Kaufman pays attention.

"If the air quality is bad it makes air exchange harder and it makes it more difficult to maintain whatever pace, level you might be running at," said Kaufman. "The faster you go, the more air you have to move in and out -- the greater the difficulty."

Kaufman said he doesn’t stay indoors, but he does scale back his strict running regime.

Olympic athletes don't have that luxury right now; it's make it or break it time.

"Clearly air pollution levels, when you're trying to run a marathon or do these other strenuous activities outside, is really going to have a dramatic impact on the person's ability to perform," said Hausbeck. "When tenths of a second make the difference surely it will have some impact."

"Long distance running, probably the 1500M or 800M and up, the longer the distance the greater the effect, soccer, cycling would notice it," said Kaufman. "I don't think it would have as much impact on the swimmers because the swimmers will be inside and the air will be air conditioned or filtered or something like that."

Still, Kaufman understands why many athletes have chosen to train elsewhere and will come to Beijing only before their event.

"The men's marathon is the last day, I believe," said Kaufman. "So I would imagine that the men's marathon runners from various countries probably are not going to show up and spend two weeks in this air if they don't have to."

In a news release dated Aug. 6, the International Olympic Committee said the air quality measurement and analysis they are undertaking for these Olympics is unprecedented.

With regard to athletes' health, the IOC said, "The IOC will make all competition decisions, working with the relevant sports federations and BOCOG to take all the measures necessary to make sure that athletes’ health is protected."