Emissions
Compressed air cars are emission-free at the exhaust. Since a compressed air car's source of energy is usually electricity, its total environmental impact depends on how clean the source of this electricity is. Different regions can have very different sources of power, ranging from high-emission power sources such as coal to zero-emission power sources such as wind. A given region can also update its electrical power sources over time, thereby improving or worsening total emissions.
However a study showed that even with very optimistic assumptions, air storage of energy is less efficient than chemical (battery) storage.
Read more about this topic: Compressed Air Car