When people burned coal in their basements for heat, the effects were apparent. Coal dust covered walls. Soot spewed out of chimneys and coated nearby buildings and rooftops. Haze filled city streets.

The advent of electric transmission lines and natural gas pipelines around the turn of the last century provided separation between most citizens and this pollution. Coal was still burned, of course, but utilities centralized power plants and built them away from where people lived.