What does iv represent in terms of national emission standards?

[JosephineDella]

iv represents the National IV emission standard. iv is a Roman numeral symbol representing 4. The National IV emission standard is the fourth stage of China's motor vehicle pollutant emission standards. Vehicles meeting the National IV standard need to reduce pollutants by an additional 30% to 50% compared to National III standards to comply. Automobile emissions refer to the collective term for exhaust emissions, evaporative emissions, and crankcase emissions from vehicles - collectively referred to as harmful substances discharged by automobiles. Exhaust emissions include CO, HC, NOx, SOx, Pb compounds, and carbon smoke particles from engine exhaust pipes. Evaporative emissions refer to harmful oil vapors from fuel tanks, fuel supply systems, lubrication systems, as well as solvent vapors from automotive paints.