The Games themselves could provide a great opportunity to study health effects, Kanner said. "If it's messy, I hope someone does measurements, to follow the athletes and see what happens. I suspect markers of inflammation will appear. Any harm, though, may not show up for 20 years. It's not a simple thing."

Kanner said bad air may initially trigger bronchospasms. That they'll stop over time may not be good. Bronchospasm may keep ozone from going deep into the lung. "It causes an oxidative reaction, probably the reason we age and fall apart over the years. It's like smoking. In a healthy young athlete, you might see some change in pulmonary function before and after. It could affect performance."

Air quality can change quickly, as Utah's Olympic Games show. The day before the Feb. 8, 2002, opening ceremonies, the inversion had cast a milky haze over the Salt Lake Valley.

Measurements were high for PM2.5, ultrafine particulates from the soot from chimneys and industrial stacks and vehicle exhaust. A PM2.5 reading above 35 is "unhealthy," but the number soared to 89 that day, according to Division of Air Quality records.

"It was a big concern as we were going into the opening ceremonies," said Bryce Bird, Utah DAQ planning branch manager.

During months of planning, strategies were devised to encourage less idling time for buses taking fans and media between Olympic venues. Businesses were asked to reduce emissions wherever possible. People were encouraged to commute during off hours. None of it seemed to have a noticeable impact — until Mother Nature intervened.

"We had a front come through and clear everything out," Bird said.

When the Games began in Utah, the Salt Lake Valley's PM2.5 reading was a mere 7.5. Its peak during the two weeks would be 57 on Feb. 11. But even that day in 2002 when the PM2.5 was 89 would be just an average day in Beijing, where average pollution is about 10 times higher than it is in Utah, said DAQ toxicologist Steve Packham. He quoted a 2007 scientific journal that recorded a record-high PM2.5 reading for Beijing at 216. The highest-ever in Utah was recorded in Logan a few years ago at 135.

The risk for athletes in Beijing, he said, is that lung health will suffer permanent damage, such as developing a sensitivity to allergens, exacerbating symptoms of asthma or inflaming lung tissue — the common denominator for causing some respiratory diseases.

But the decision to compete or not belongs to the athletes, he said.

"What I can tell you as a Ph.D. toxicologist, any time you increase the dose of anything by 100 times or 10 times, you're usually talking about a significant change in the response you get. ... It's a significant issue, I would think, for them."

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E-mail: lois@desnews.com, sspeckman@desnews.com