Well folks the weather in Bejing has turned downright awful. I was there last week and it was some of the worst conditions ever. It's often bad in winter as more coal is used for heating, more cars are on the roads, etc. But these past few weeks both Beijing and Shanghai have been downright awful!
Take a look at this article...
http://news.yahoo.com/air-pollution-beijing-goes-off-index-053809937.html#
