Clean air is an important part of Colorado…fresh, clean mountain air. But by the 1970s Denver had a lot of pollution hanging over the city. Pollution so bad it could be seen from all over just hanging over the downtown area. The dirty cloud was dubbed “the Brown Cloud.” Denver’s location at the foot of the Rocky Mountains make it prone to temperature inversions in which warm air traps cooler air near the ground, preventing pollutants from rising into the atmosphere. Denver has done a lot to clean up it’s bad air and brown cloud in the winter time, but it can still be seen on cold days. I had two special guests help me do a simple experiment to explain temperature inversions and Denver’s brown cloud.