Credit: PA

In the summer of 2008, all eyes were on Beijing. Host to the Olympic and Paralympic Games, China was keen to put on a spectacular show. However, images of athletes arriving in the city wearing face masks and stadiums shrouded in smog cast a shadow over events.

Rapid industrialization has resulted in severe pollution problems in China. Industrial waste spills into rivers, heavy metals weigh down the soils and acid rain falls from the skies. One of the greatest environmental and human health concerns is the level of atmospheric pollutants, a particular problem in China's cities, where concentrations of ozone and particulate matter often exceed World Health Organization guidelines. Thus when Beijing was chosen as host for the 2008 Olympic Games, concerns — particularly about the health of the athletes — ran high.

In an attempt to rectify the problem and ease some of these concerns, factories were shut down, construction works were stopped and half of the city's 3.3 million cars were banned from the roads. In total, the Chinese government spent US$17.58 billion on pollution reduction measures. But did they have any effect?

Jan Cermak and Reto Knutti, of the Institute of Atmospheric and Climate Science, Zurich, argue that they did (Geophys. Res. Lett. doi: 10.1029/2009GL038572; 2009). They compared satellite observations of aerosol levels over Beijing during the games, with model predictions of the aerosol burden assuming no emission controls, based on meteorological conditions. Observed aerosol levels were ∼15% lower than model projections. Although the reduction is low compared with natural variability, it is noticeable, and suggests that pollution controls were a partial success.

However, despite massive emission controls hundreds of kilometres outside the capital, aerosol reductions were confined to Beijing and its immediate surroundings. Outside this area, control measures had little effect.

The magnitude and scale of the reduction is disappointing, although expected given that regional transport is a major determinant of atmospheric aerosol levels. But it is encouraging to note just how quickly the benefits of pollution control measures are realized (many of the controls were implemented just months before the games began).

With plans to make the 2012 Olympic Games carbon neutral, London is next in sight. Whether the city can pull off plans to make these games the greenest in history remains to be seen. But, like in Beijing, the event could prove a test bed for the effectiveness of the chosen environmental improvement schemes.