These vintage photos of Pittsburgh, from before it passed a smoke-control ordinance in 1941, are so hazy that some of them look like they’ve been hit with some kind of artsy-grunge Instagram filter. But this is just what an industrial city looked like in those days — clogged with a low fog of coal-based factory belchings.

You can see way more photos at Retronaut.

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True fact*: These are actually color photos! You just can’t tell because of all the smoke.

* Not a true fact.