Most of the really zealous anti-smoking types are reformed holier than thou given-uppers. If somebody visits my flat I say, please feel free to smoke and promptly produce an ash tray. The polution on the streets is likely to do you more harm than cigarette smoke.

Street pollution is hazardous indeed. Constantly jogging ahead of the guy in front of you doing second hand smoke backdrafts can be an exhausting experience in China. On the other hand, I have had people in my family pass away early from smoking, and i don't smoke myself. I do not consider myself to be holier than anybody else, but asking guests to not smoke in my living quarters is asking for a respect of boundaries and space of which I am sure most expats are happy to oblige to. Can always go on to the porch to light one up if it really bothers you.