When most people think about the Olympic Games, they envision blazing torches, gold medals, and triumphant athletes. But a handful of scientists saw the 2008 Beijing Olympics as a once-in-a-lifetime opportunity to find out what happens when a major industrial city suddenly cuts back on air pollution. The first analysis of this "experiment" concludes that China's efforts produced only a slight improvement in Beijing's air quality.
Beijing sits in a soupy haze of pollution from nearby factories, coal-fired power plants, and traffic that increases dramatically by the day, making the city one of the most air polluted in the world. China spent billions of dollars trying to control emissions that could hinder athlete's performances on game day. From 20 July to 20 September 2008, the Chinese government temporarily closed factories and regulated the number of cars on the road in Beijing and in nearby areas, all with the hopes of curbing aerosols--fine particles suspended in the atmosphere. China tried a similar traffic strategy in 2006 during a 3-day political summit and achieved 40% to 60% reductions in aerosol concentrations, according to one study. But this study covered only a short period and concentrated on aerosols at ground level, not throughout the larger atmosphere . For the 2008 Olympics, Chinese officials called for reductions of 60% to 70% in automobile emissions and up to 30% in industrial emissions.
To find out how successful they were, atmospheric scientist Jan Cermak of the Swiss Federal Institute of Technology Zurich and a colleague used satellite data to measure the overall amount of particulates hanging over Beijing from 1 August through 19 September for each year from 2002 through 2008. This technique allowed them to analyze aerosol concentrations in the atmosphere from top to bottom but didn't allow them to decipher exactly where they were in that space. But just monitoring aerosols isn't enough, because weather also affects air pollution's severity--a rainy day can flush pollutants from the air, whereas a windy day can bring in pollutants from far-off industrial areas or carry them out of the city. So the researchers also collected data on wind speed and direction, rainfall, and relative humidity. They then applied these relationships to predict what air pollution would have been in 2008 without any emission controls.
It turns out that the Chinese only achieved a modest reduction in aerosols. The researchers report in a paper in press in Geophysical Research Letters that pollution-control efforts reduced the overall amount of aerosols in the atmosphere by about 10% to 15%. That small change highlights the importance of factors such as wind direction in determining local pollution, says Cermak. In spite of the reduction in local emissions, winds from the south and southeast sullied Beijing's air by bringing in pollution from distant industrial areas, he says.
Tad Anderson, an atmospheric scientist at the University of Washington, Seattle, says that this paper shows that China's attempt to curb pollution was "based on a flawed understanding of the nature of atmospheric aerosols." He points out that aerosols can stay in the air for days and easily travel thousands of kilometers. "You take out the local sources in Beijing and you've still got the regional [sources], which are the dominant cause of pollution."
Still, it's too early to dismiss China's pollution control efforts, says atmospheric scientist Qi Zhang of the State University of New York at Albany. She cautions that the satellite data can't tease out the effects of the emissions controls at ground level, where people breathe.