I forgot this - I have two friends who lived in Beijing for years but moved to LA when they had kids, in large part because the air pollution was so bad they said they could feel it in their throats when they woke up each morning if it was going to be a bad day. Nobody likes to feel like their they breathe is killing them each day.

There was a comment (I think on Top Gear, so take it with a grain) that if you drive a new Porsche through Beijing, the air coming out the tailpipe is cleaner then the air going in the front.