What does National IV represent?

[SanLondon]

National IV represents the fourth stage, which refers to the National Fourth Phase Motor Vehicle Pollutant Emission Standards. The main pollutants emitted by vehicles include hydrocarbons, nitrogen oxides, carbon monoxide, and particulate matter. Through the application of technologies such as improved catalytic converter active layers, secondary air injection, and exhaust gas recirculation systems with cooling devices, these standards aim to control and reduce vehicle emissions below specified limits. As the environmental hazards caused by vehicle emissions become increasingly severe, countries and regions worldwide have successively established limits on vehicle exhaust emissions. The European standards set by the European Union serve as a reference standard adopted by most countries and regions. China's National I, II, III, and IV emission standards are based on the emission limits of European I, II, III, and IV standards, respectively.