Air pollution used to be bad. How bad?

Seeing a photograph of streetlights on during the day in Pittsburgh prompted me to investigate how bad air pollution really was back then. Voila: a 1979 journal article by Cliff Davidson notes that typical Total Suspended Particulates (a now-deprecated measure) in Chicago in 1913 were 0.3-2.0 mg/m3, with a maximum of 9.3. Cleveland in 1915 […]