The Element of AIR

I've had a difficult time deciding what will demonstrate the power of AIR (because air is invisible). I've considered a small scale tornado, or some vapor emitting from a point. I needed something that fit into a 3ft x 3ft scale approximately.
Then I thought about a cloud. I felt that clouds demonstrate air flow and also could fit into the scene nicely.
So then I needed to consider how this cloud would act. It could be light and fluffy, like a cloud in the sky, or it could be more interactive like dry-ice.
I felt that dry-ice has more potential to show the movement of air; however, I don't want the element of AIR taking on the feel of water, so I have to be careful.
I like the weight and movement of Dry ice, but perhaps it would be effective if I have the substance die off, or dissolve into "thin air". This would separate the substance from feeling like water.

some references that I'm keeping in mind for this substance are: Dry Ice, cigarette smoke (for how the smoke dilutes and dies off), and the color of real and natural clouds. Also, the film How To Train Your Dragon is useful when studying animated smoke. The scene that comes to mind is when the main character (Hiccup) is battling the two headed dragon and one of the two heads spews a green gas. The green gas has a similar weight and consistency as to what I'm looking for.