As reported in the Chicago Daily news, sister publication of the Chicago Sun-Times:
If Chicagoans of 1970 needed another reason to rally for Earth Day, a perfect “Exhibit A” showed itself on the inaugural celebration of the holiday.
The April 23, 1970 edition of the Chicago Daily News reported “heavy haze and air pollutants” spreading across parts of the city that day.
The air above two schools — Taft High School in Norwood Park East and Austin High School in South Austin — contained “a highly dangerous sulphur dioxide reading,” the report said. The reading above Taft was .32 parts per cubic feet of air, which was .21 ppm above the “danger point for the elderly and infants.”
Above Austin, the haze factor was “more than four times normal,” the report continued.
According to the U.S. National Library of Medicine, exposure to sulphur dioxide can cause burning sensations in the nose, throat and lungs and long-term harm to the respiratory system.
Luckily, a swift wind blew through the air and dispersed the poisonous gas. Still, for environmentalists, their case had been made.
