Like petrol and diesel, LPG (Liquefied Petroleum Gas), which is sometimes also called autogas in the car industry, comprises hydrocarbon compounds. The main components of LPG are propane and butane. Large quantities of petroleum gases are released when extracting oil and natural gas, and refining crude oil. Compressing these petroleum gases convert them to a liquid state, and creates LPG.
LPG is a cleaner fuel compared to petrol and diesel. So using LPG as a vehicle fuel helps to improve the air quality.