In space, no one can hear you swallow
<Pollution "permits" are actually a pretty good idea, provided it is legal to buy and sell them on the open market.
Open trade in permits is the very thing that makes it work. A futures market would probably come right on its heels.
Obviously, in space air and water would not be considered a "free" commodity.
Same thing on Mars, which made it easier to for Robinson to entertain the possibilites. And where's Earth? In space, of course.