Beijing did a lot to improve the air quality leading up to the Beijing Olympics, with mixed results. The days before the opening ceremony were pretty bad, but a burst of rain cleared the air and pollution became less of a talking point.

Almost straight after the closing ceremony the hazy skies returned. A few days later there was heavy rain and the last two days Beijing has had glorious weather - clear skies. warm weather and not too much humidity.

I turned to Wikipedia to find out more on cloud seeding and they have a good entry on the topic, with quite a few references to