There is a nice site with information about pollution in China called www.pollution-china.com
Here is a short French video made by the French Radio Europe 1 about the air quality in Beijing.
If you are in China and looking for good anti-pollution masks from the British company Respro, then you should also check out that website. I always cycle in Beijing with the mask, especially on heavily polluted days. Here is a pictures of my friends that also use these masks. This picture was taken by another friend some months ago (thanks for the nice picture):