http://www.huffingtonpost.com/2012/06/0 ... ref=topbar
Many people have heard of the pea soup-thick London fogs of the late 19th and early 20th centuries, the coal smoke-choked mists that plagued the U.K. capital's citizens with respiratory illnesses, culminating in the deaths of thousands during the Great Smog of 1952. But it wasn't long ago that similar conditions existed in the United States.
Pittsburgh might be known as the "steel city" for its legendary production of that iron alloy (which carries its own environmental hazards), but it's been called other names -- such as "Hell with the lid taken off" or "the capital of Hell" -- for its air pollution.
The Smoke Control Lantern Slide Collection, housed in the archives of the University of Pittsburgh, documented urban pollution in the steel city at its worst.