Inspired by @DaXia's "OT: Statistics about China?!?" topic, I decided to share three web sites that I use in my travel around the Chinese-speaking world. Keep in mind that these are all government web sites, but they should at least be helpful for comparing areas within a given country. I've definitely used such data to inform my decisions about where to live.

China:
http://english.sepa.gov.cn/

Taiwan:
http://taqm.epa.gov.tw/taqm/en/

Malaysia:
http://www.doe.gov.my/portal/

I've used similar lists on Chinese air pollution as well as general pollution to locate travel destinations.

The difference is that I used it not to find clean spots but to find China's dirtiest cities. These tend to be particularly charming.

@Foo Choo Choon, that's hilarious.

Me... using these methods I found Taitung, Taiwan, but to each their own!

@Chris nice! That prompts me to go out for a jog in green Taipei! Which by the way I find less polluted than Paris (especially along the rivers and in the mountains). If you know Paris's pretty lousy air, that's not saying a lot, but it does go against stereotypes.