London was called "The Smoke" because, as you approached it, it looked smoky.
No city on the eastern seaboard has ever been called the Smoke. LA has, because of the inversion layer.
Even in the victorian era (Luc Sante correct me if I'm wrong) nothing on the eastern seaboard was ever called the Smoke because of:
very different methods of generating power and entirely different weather
NYC is not a misty, foggy, smoky place. That doesn't describe anywhere in the BAMA. If Metropolis is part of BAMA (ye auld atlas put it in Delaware) it was never smoky like London. Moreover, you would have approached it either from above (because the eastern seaboard is nothing but Appalachian drainage), or from the sea, so again, you would never have the experience of being enveloped by city smoke.
And this is why calling Metropolis the Smoke makes no sense to me and would make even less sense to a Kansan. It would be The City.