CFCs are heavier than air, so how can they get all the way up to the stratosphere?
CFC molecules are, in fact, heavier than most air molecules, but in the atmosphere this does not matter. As the wind blows, the molecules are mixed together and are not allowed to “settle out” by gravity. This is a very good thing for us because if the heavier molecules actually dropped to the bottom of the atmosphere we would all die from a lack of oxygen. Gases like carbon dioxide would be at the bottom of the atmosphere where we are and that is simply not what happens in nature.
