Beijing's notoriously dirty air was cleaner during last summer's Olympic games, but pollution levels were still much worse than at recent Olympics, despite a massive Chinese cleanup campaign, a new report said.
Athletes in Beijing faced pollution levels that were up to 3.5 times higher than those in recent Olympic cities like Athens, Atlanta and Sydney, said the study published Friday in the journal Environmental Science and Technology. The pollution often exceeded what the World Health Organization considers safe.
The joint American-Chinese study, the first major one published on air pollution during the Olympics, also found that the weather, and not the Chinese government's strict controls imposed in the run-up to the games, played the largest role in clearing the air.
The government's plans to control air pollution for the event gave international researchers a unique opportunity to observe a large-scale experiment. Scientists from Oregon State University and Peking University looked at Beijing's worst air pollutant, tiny dust particles known as particulate matter, over an eight-week period before, during and after the games.
China poured some $20 billion into "greening" the city after it won the bid in 2001, including doubling the number of subway lines, retrofitting factories with cleaner technology and building urban parks.
Government officials also imposed drastic cleanup measures just before the games in mid-July, including pulling half the city's 3.3 million vehicles off the roads, halting most construction and shutting down dozens of factories.
The study, funded by the National Science Foundation in the U.S. and the National Science Foundation in China, found that the level of particulate pollution in Beijing was twice as bad as in Athens, Greece; three times as bad as in Atlanta, Georgia; and 3.5 times as bad as in Sydney, Australia.
Researchers found that particulate air pollution did drop by about one-third during the two-week Olympic period. But coarser particulate matter, PM 10, exceeded levels the WHO considers safe about 81 percent of the time, while the smaller particulate pollution PM 2.5, which can cause more serious health consequences, exceeded WHO guidelines 100 percent of the time.
"It was a giant experiment and a noble effort. But in the end, the extra added measures didn't help reduce PM concentration as much as had been expected," said Staci Simonich, an associate professor of chemistry and toxicology at Oregon State University who worked on the study. There has been no evidence so far of any health problems linked to the short-term exposure of athletes or spectators during the Olympics, researchers noted.
Further investigation suggested that weather conditions, such as rainfall and strong winds from the north and northwest, played a much larger factor in clearing the air than the pollution curbs.
Meteorological conditions accounted for 40 percent of the variation in concentrations of coarser particulate matter, while pollution control measures accounted for only 16 percent, the study said.
The findings also showed that the weather ushered some air pollution into Beijing from industrial regions south of the capital that had less severe pollution curbs, including Hebei, Shandong, and Shanxi. Those results indicated the difficulties in trying to control pollution at a local level when air masses tend to move regionally.
The findings don't invalidate the government's efforts, said Zhu Tong, professor at Peking University's College of Environmental Sciences and Engineering, and a co-researcher on the project.
"We learned a lot about how air pollution forms in a mega-city like Beijing, and how much pollution comes from which sources," Zhu said.
Scientists also noted that their pollution measurements were about 30 percent higher than official figures by the Beijing Environmental Protection Bureau, though they said that reflected a difference in methodology.
Pollution expert Fang Ming, now retired from Hong Kong University of Science and Technology, said the findings don't break new ground in terms of understanding how air pollution works.
"Having said that, it is useful to know the effectiveness of the huge 'green Olympic' effort to clean up the air in Beijing," he said in an e-mailed response.
Overall, the Olympic pollution control efforts were worthwhile because "it demonstrated to the Chinese government that they need to pay more attention to the environment and it is good for the country. It also says that this is doable and the people have to be a part of the effort," he said.