I grew up in Chicago in the 1960s, near Gary, Indiana’s steel mills. Air pollution was constant in my life - it was orange, thick, and scary. In summer, the smog hung over the city, thanks to frequent thermal inversions trapping the pollution. It smelled metallic and sulfuric, and like rust. It filled your nose, and burned your eyes. In the early 60s, we had a snowstorm which buried the Midwest and shut down the steel mills. We saw and felt the difference. Instead of black soot coating the snow, it stayed white. That was unheard of in Chicago. Not only could we breathe better, the decreased...