credit: Smoke Control Lantern Slide Collection, ca. 1940-1950, AIS.1978.22, Archives Service Center, University of Pittsburgh.
These days when we think of eye-watering, lung-blackening smog, we mostly picture Chinese cities. Things get so bad there that during the Beijing Summer Olympics in 2008, a significant fraction of the country's power generation, industrial production, and transport sector had to be shut down just to allow athletes to breathe half-decent air and perform well.
But China's not special, it's just that they are industrializing later than others. The situation was similar in many areas of the United States not so long ago, as these photos from Pittsburgh in the 1940s show very clearly. They were taken right before "smoke control" laws took effect.
Don't miss the slides at the end that show how whole buildings had to be steam-washed to remove the grime, and the "after" shots that show how much better the air quality was in Pittsburgh after the law took effect.