No matter how hard they try, officials of the 2008 Beijing Olympics cannot think of everything. Normally, athletes are concerned about their competition, but it seems they now have something else to worry about. Something the eager officials cannot not fix - no matter how efficient they are. Pollution.

"We know how to train for heat and humidity, but not a lot of research has been done on running in the polluted atmosphere we think we'll find in Beijing," Kyle O'Brien, an American marathoner who ran at the track and field world championship in Osaka, said Tuesday.

Therein, lies the problem.

Air pollution levels in China's capital are nearly five times higher than the World Health Organization's recommended safety level. A mix of major pollutants such as ozone, nitrogen dioxide and particulate matter are common. Sulfate and carbon also float regularly in the air.

It's not that officials haven't noticed.

China is spending billions to close dirty factories and build new subways, and in an experiment for the Olympics, the city earlier this month pulled 1 million private vehicles a day off the streets. The congestion eased, but a gray haze remained.

Sounding an alarm recently, International Olympic Committee president Jacques Rogge warned that choking smog might force some endurance events to be postponed.

During this week's world championships in Japan, the stifling heat regularly has hit the mid-90s with humidity in the 60 to 70 percent range.

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