How do you make a model on land pollution for a school science exibition?

My personal favorite (probably saw it on Bill Nye the Science Guy) is a fish tank with a solid lid (representing the closed system of the earth), cardboard cutout of city skyline and a road (preferably not flammable), matchbox cars with small pieces of incense stick where the tailpipe is; light the incense, put the cars on the road, put the lid on the fish tank and watch as the smoke fills the tank.

u can give the outline of the model to make it more convinien..