Before there was smog in Denver, there was a constant dust cloud, going back as far as there are observers who recorded their observations. If you go out on the praire far enough to be unable to see the smog over Denver and the lights from anything except stars are night, you will find air which is as pristine as it ever was, according to human senses.
The smog now extends from almost Pueblo to almost Cheyenne. It is merely an indication that more people value a comfortable lifestyle over a less-polluted outdoor environment, something which should be clearly understood by someone studied in Austrian economics.
Most of the population is driven by perverse incentives rather than thoughful contemplation.