How can CFCs (Chlorofluorocarbons) get to the Stratosphere if they are heavier than air?

Gnomon

It is a common myth that heavy gases sink and light gases rise. It is true to a certain extent: you can pour carbon dioxide out of a jar and put out a candle with it. But over time, gases mix together. Eventually there will be the same amount of heavy gases in the upper atmosphere as there is at ground level. It is just as well that this is true. Since our atmosphere is more or less 80% Nitrogen and 20% Oxygen, all the Oxygen would sink to the bottom and the Nitrogen would go to the top, leaving us in a band of pure oxygen. As well as us all rushing around like maniacs on speed, anything combustible will quickly catch fire and we'd be burnt up. Instead, diffusion causes each gas to spread out until it is evenly spread throughout the atmosphere. Dec 04 02, 8:31 AM