Pennsylvania’s Killer Smog tells the story of a freak weather event that caused the worst air pollution disaster in US history, gripping the small, industrial town of Donora in its clutches for five long days in 1948. By the time the smog lifted twenty of the town were dead. Four years later a similar event occurred in London, England that killed thousands. The double tragedy radically altered the way we interact with our environment. The documentary brings the tragic events to life and unpicks the science behind them through interviews with experts and survivors, gripping archive footage, lively science demonstrations and dramatic reconstruction.