Winter has started early in Beijing. Last week we had a dusting of snow (hardly ever snows here) and while it was gone within 24hrs it has stayed unseasonably cold.
Winter = smog because of all the coal and wood burning by China's utilities but also by the poor Chinese. We've been in a few weeks of bad smog, but nothing like poor Shenyang who is currently seeing values around 1400, 50x higher than the WHO suggests and in Beijing we're sitting 10x over the recommended value. I've barely left the house with the babies in 3 weeks.
Here is a picture on our return from vacation in October, that's SMOG not fog and it is only around 200.
Here is an article about the smog in Shenyang: BBC News Article on ShenYang Smog