Trespass is unwelcome encroachment upon another’s property. We recognize it in many forms: trespass to the person (e.g. assault and battery), interference with possession of personal goods (robbery), and trespass onto land. The castle doctrine is the common law concept that persons have no duty to retreat in their home (or “castle”), and may use reasonable force, including deadly force, to defend their property, person, or another person. This is the basis for various stand-your-ground laws. It’s time we recognize pollution as a form of trespass. If a truck dumps toxic waste on your front lawn, it is a trespass violation. If a coal-burning power plant pollutes the air you breathe and pollutants enter your lungs, it is a similar trespass violation. Don’t mess with our clean air.