Originally Posted by
moondog
Yesterday in BJ was really bad. My friend mentioned "400". While I have no idea what that means, I'm guessing "not very good".
A friend of mine recently told me that the intern at the US Embassy who is in charge of reporting this stuff recently reported "crazy bad" (because the numbers were off the scale), but was censured soon thereafter.
The scales vary massively by country. Some countries believe X is bad, others believe (or, perhaps more appropriately, want their citizenry to believe) Y. Without a doubt though, the more open western nations are more honest about giving their air a "crappy" rating than the more closed eastern ones.
Start here (though as with any wiki, take it with a grain of salt):
http://en.wikipedia.org/wiki/Air_quality