What are the symbols for National Emission Standards I, II, III, IV, V, and VI?

[DiGia]

National Emission Standards I, II, III, IV, V, and VI are represented by Roman numerals: I-1, II-2, III-3, IV-4, V–5, VI-6, VII. China's standards: Compared with advanced foreign countries, China's automobile exhaust emission regulations started relatively late and were at a lower level. Based on China's actual conditions, a phased implementation plan was adopted starting in the early 1980s, prioritizing easier tasks first. The implementation has mainly been divided into three stages up to now. Definition of automobile emissions: Automobile emissions refer to harmful gases such as CO (carbon monoxide), HC+NOx (hydrocarbons and nitrogen oxides), and PM (particulate matter, soot) discharged from exhaust. These are all harmful gases produced during the engine's combustion process.