In the early 70s, we traveled to Birmingham, Alabama frequently to see family. These were the days before so much industrial regulation, and the industry in Birmingham was going at breakneck speed. We used to joke that you could smell Birmingham 20 miles before you got there, if the wind was right.
I remember going into town and seeing smoke of all colors spewing from smokestacks in the distance. The smoke came in red, black, gray, white and even pink, and the stacks were short, tall, thin and fat. Seeing Birmingham in that era meant you saw a lot of active smokestacks.