Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume. It is a major component of motor vehicle emissions (and from stationary internal combustion engines), which can also include: * Crankcase blow-by * Evaporation of unused gasoline