Oded Balilty / AP A man flies a kite at Tiananmen Square on a heavily polluted day in Beijing, Dec. 27, 2007

While Steven Spielberg's withdrawal from his role as an artistic adviser was a public relations blow to the Beijing Olympics, the announcement this week that Haile Gebrselassie would not run in the marathon at this summer's Games hints at a more serious challenge facing the organizers. Unlike Spielberg's, the decision of the Ethiopian world record holder in the marathon has nothing to do with politics: Gebrselassie is asthmatic, and he is concerned that Beijing's polluted air could damage his health over the 42-kilometer race. (He still plans to run the far shorter 10,000-meter event.) And the Ethiopian's concern has underscored the stakes in a showdown between city officials and an 26-year-old American environmental consultant who has raised serious questions about Beijing's official air pollution statistics.

Steven Q. Andrews has written two op-eds for the Asian version of the Wall Street Journal, in which he accuses Beijing's Environmental Protection Bureau of tweaking its method of calculating the city's air pollution index. That index is critical, because it is used to tabulate "blue sky days," which are the chief measure of Beijing's ability to control air pollution. When the blue-sky program was launched in 1998, there were just 100 days; last year the city recorded 246. But Andrews alleges that by changing the makeup of Beijing's air-pollution index, and dropping monitoring sites in areas with poor air quality, the city has been able to show improvements that don't match the reality of its smoggy skies.

Andrews first encountered bureaucratic evasion on environmental issues while doing research in 2003-04 on coal fires in China that became part of his senior thesis at Princeton. Such fires, which can occur naturally or are ignited by mining operations, are found worldwide and can burn for years, causing heavy environmental damage. In China's western Xinjiang province, Andrews visited a site where authorities had claimed a long-burning fire had been put out. "I decided go to see how it was extinguished, and flames were visible and the entire thing was still burning," he says. "They said it was put out, and who is to say otherwise?"

On returning to China after a stint doing humanitarian work in Africa, his experience at the Xinjiang coal fire prompted him to research Beijing's air-pollution reports. In 2006 and 2007 Andrews worked at the Natural Resources Defense Council's office in Beijing while on a fellowship with the Princeton In Asia program. But Andrews stresses that he did the research that has put him at loggerheads with the authorities independently of the NRDC, which has posted a statement on its website dissociating itself from Andrews' air pollution study.

Using only the data that had been officially released by the State Environmental Protection Bureau and the Beijing Environmental Protection Bureau, Andrews has raised questions about just how Beijing managed to meet its blue-sky targets. In 2000, the city stopped including measurements of nitrogen oxides in its tabulations of the air pollution index, and instead measured nitrogen dioxide. While switching the pollutant measured isn't necessarily a problem, Andrews claims, nitrogen dioxide was a smaller contributor to the overall air pollution index score.

Similarly, two monitoring stations located in high transportation areas that had consistently contributed to high API scores were dropped out of the tabulations in 2006. Had those stations not been dropped from the equation, Beijing would have had 38 fewer blue sky days in 2006 and 55 fewer last year, which would have made for total lower than that in 2002, Andrews says. He also noted that in 2006 and 2007, there was a concentration of days with API levels at or below the 100-point cut off, but few just above. That imbalance began after the city began setting targets for individual monitoring stations, he says.

The response from the government has come from Du Shaozhong, the deputy head of the Beijing Environmental Protection Bureau. He was named one of China's top "green personalities" in 2006 for his work in reducing pollution, including program to urge Beijing car owners to give up driving one day a month. When asked at a press conference last month about Andrews' allegations that the city that the city stopped including the results from certain air monitoring stations to increase blue-sky days, Du responded, "This phenomenon does not exist." He said that the placement of Beijing's air pollution monitors met national regulations, and that concentrations of pollutants had further improved in January and February.

Beijing has spent nearly $17 billion to improve its environment ahead of the Olympics. The government plans to limit car traffic during the event, and is continuing a program of closing and moving the most polluted factories away from the city. This week plans were announced to suspend all construction projects between July 21 and September 20. And observers believe the authorities will take even more extreme measures, such as extending the car reduction plan to weeks before the Aug. 8 Olympic start date if it appears that pollution targets won't be met.

Andrews is more concerned about what will happen after this summer's games. "There are legitimate concerns about air quality during the Games," he says. "But there's a bigger question: is there a sustainable legacy?"