It's hard enough running a marathon when the air is cool, crisp, and pristine. Add coal smoke, ozone, and particulate matter to the mix, and you'll have runners wheezing their way to the finish line—if they even make it that far. Unfortunately, that's exactly the type of air that will clog the lungs of more than 10,000 athletes next year at the Olympics in Beijing.

On days when there is no rain or wind, ozone and fine dust are often two to three times the maximum levels suggested by the World Health Organization, making the Chinese capital one of the world's dirtiest cities. Endurance athletes such as marathoners and cyclists will have the toughest time—they inhale up to 150 liters of air per minute, more than 10 times what an office worker does. Spectators who are elderly, very young, or chronically ill may also encounter problems, including asthma, sore throats, and allergic reactions, all of which occur even among healthy visitors.

"I wouldn't expect a world record in the marathon in Beijing," says a physician who advises the British Olympic Committee.

The Beijing Olympics won't be the first time athletes will have to contend with poor air quality. More than 20 percent of U.S. athletes had breathing problems due to smog in Athens in 2004, says a manager of the U.S. Olympic team. British runner Steve Ovett said Los Angeles's air pollution made him collapse in the 1984 Olympics.

Beijing is committed to making its Olympics the "Green Games," and is investing more than $3 billion to clean the air, but it's unclear if it can succeed. Areas outside the city are responsible for a substantial amount of the pollution, and over 1,000 new cars hit the streets each day.

In the end, athletes may be left gasping for glory.

[Photo: PETER PARKS/AFP/Getty Images]