Or looking at historical pictures of a city with street lights on at mid-day because of industrial smog ...
https://www.buzzfeed.com/kevintang/stunning-photos-of-pittsb...
It did take Pittsburgh a long time to start fixing its environmental issues, and it took the total collapse of the steel industry to fully clear the air. Even back when I came here (~2011) people had an impression of Pittsburgh as a polluted, industrial hell-hole - I'm so glad that it wasn't the case when I came.
The left image is, amazingly, a daytime shot - the sun is visible in the top-left corner. The smog was so bad on that day ("Black Tuesday", November 1939) that a camera essentially could not capture any detail _in broad daylight_.