Pittsburgh was a city of coal-heated homes and coke-powered blast furnaces set in river valleys, and in the '60s and earlier was dark at noon: http://www.buzzfe

Pittsburgh was a city of coal-heated homes and coke-powered blast furnaces set in river valleys, and in the '60s and earlier was dark at noon: http://www.buzzfeed.com/kevintang/stunning-photos-of-pittsburghs-air-pollution-in-the-1940s#.xyoMpJwwd http://www.buzzfeed.com/kevintang/stunning-photos-of-pittsbu... Many of the older brick-and-stone buildings are still covered in black stains.