Folks didn't always worry about air quality.
Take one winter London day in 1952, as an example. Londoners fought off the cold and damp by burning cheap coal, as they often did. To their dismay, a fog trapped the coal smoke in London, creating a dense smog full of levels of sulphur dioxide, nitrogen oxides, and soot that the world had never seen before.
The stench of rotten eggs engulfed the city, and the blackness prevented commuters from driving. The smog stayed for four miserable days -- blackening faces, halting school attendance, coating building facades, and creeping indoors. As it gradually dissipated, a sigh of relief could be heard all over town.