Nate Berg on a study by Qian Hui Tan on the societal effects of segregated smoking:

The influence of smell, Tan argues, is perhaps one of the strongest determinants of how people interact with or avoid one another in the public sphere – whether it’s cigarette smoke, days without a shower or the undeniable stench of vagrancy. How exactly cigarette smells shape the use of public space is likely different from place to place. But this research argues that smell and personal habits can be a major force in shaping city life.