Propane is a flammable derivative of the oil- or natural gas-refining process. It can be transported in certified tanks of many sizes, a feature that makes it a popular fuel for powering outdoor stoves. Propane stoves are convenient, but can also pose safety risks such as fire and carbon monoxide poisoning.

Cars contribute only a modest amount of pollution on their own, but there are, according to Yale University, a fleet of 246 million vehicles in the United States alone, making them a potent polluting force in bulk.