I didn’t notice it until I’d been somewhere else for couple of weeks. Centre of town has a background note of exhaust fumes, but the outskirts didn’t.
Don’t miss having a tissue covered in black/grey crud every time I blow my nose now that I live out in the sticks.
It's a kind of a musty, sooty, diesel smell. People living there are probably used to it and don't notice it. But you can smell it as soon as you step off the train. When going home the air feels much richer like there is more oxygen in it.
I noticed a similar thing when I went to Las Vagas, the whole place has a slight smell of jet fuel for some reason.