Which hypothesis do you find convincing? Any additional ones to add?
1. Social networkers head to Manhattan, and social networkers smoke.
2. In Manhattan it is more important to signal you are cool.
3. Air pollution is higher, so the marginal health cost of smoking is less.
4. New York is colder, and that makes cigarettes more enjoyable.
5. The "artsy" variable is doing most of the work; of course this is related to #1 and #2.
6. NYC life is more stressful, and smoking calms some of these people down.
7. Many of them are poseurs, and these smokers don't have such valuable human capital.
I'd bet first on #2, and also on #7, but I don't have a good theory that will explain the rest of the cross-sectional evidence.
(Source: Marginal Revolution)