Is darkness in a photo really due to air pollution?

Dear Tom,
I saw a photograph of downtown Chicago taken at State and Lake streets on Feb. 1, 1957, showing darkness that was blamed on severe air pollution. Can you tell me about that day and its weather?
— Jeff Kozinski, Mokena, Ill.
Dear Jeff,
Feb. 1, 1957, was cloudy and gloomy with a high temperature of 33 degrees, low of 28, precipitation 0.01 inch and 0.1 inch of snow. The downtown area was shrouded in dense air pollution consisting of smog (smoke and fog) during the morning hours. A Chicago Tribune photograph taken by Hardy Wieting at 10:15 a.m. at State and Lake streets showed an exceedingly dismal day that was literally as dark as night. The picture is available by searching “February 1, 1957, Chicago” on the web. Dark days such as that are long gone because of current air pollution regulations.
The darkness in a 61-year-old photo taken during the day isn’t just because of cloudy skies. Downtown Chicago’s smog is long gone thanks to regulations.