“ For decades , pollution was created by very powerful industries , and the state investigations were very friendly to industry ,” says Leif Fredrickson , a historian at the University of Virginia and a member of the Environmental Data and Governance Initiative . “ So [ the people of Donora ] were rightly concerned about that and wanted the federal government to get involved . But as it turns out , the Public Health Service was pretty concerned about their relationship with state researchers , and this is before the federal government has much say over what happens in terms of pollution control in state and local areas .”
The federal agency sent 25 investigators to Donora and Webster , where they took health surveys from residents , inspected crops and livestock , measured different sources of air pollution , and monitored wind speed and meteorological conditions . They found that more than 5,000 of the 14,000 locals had experienced symptoms ranging from moderate to severe , and that the American Steel & Wire Plant and the Donora Zinc Works emitted a combination of poisonous gases , heavy metals and fine particulate matter .
“ If you looked at the X-rays of their lungs , they looked like the survivors of poison gas warfare ,” Davis says .
A preliminary report was released in October 1949 , with inconclusive results . Rather than singling out the mills and the effluent they produced , the researchers pointed to a combination of factors : the mills ’ pollution , yes , but also a temperature inversion that trapped the smog in the valley for days ( a weather event in which a layer of cold air is trapped in a bubble by a layer of warm air above it ), plus other sources of pollution , like riverboat traffic and the use of coal heaters in homes .