Air is difficult to own, it's a gas and hard to fence off. As the quality of air gets worse there will be an attempts to own better areas and reserve them for the use of certain people. The privileged will want less poisoned air. Already, in several cities of the world, oxygen is dispensed in the city centers. We need equally to question a social order which poisons the air in the name of the people.
Water is also pretty difficult to own, though almost all water on land is now owned.
In the oceans, it belongs to all, is the source of most rain and the home of the systems which produce most of the planet's oxygen and much of its food. A necessity for human life, defining water rights has been a social concern since the first agricultural societies formed, and possibly even before that. Roman-Dutch law is still concerned with access to and rights over water. Rivers flow across national boundaries, and water tables do not respect human borders. Like air, water blurs the boundaries of the world, carrying poisons from here to there, connecting continents and systems, providing a path for the great whales and the minute plankton.