What are the symbols of emission standards countries 1 to 6?

The symbols from country one to country six are I, II, III, IV, V and VI respectively. The extended information is as follows: 1. Reasons for setting emission standards: automobiles are mobile pollution sources, and the main pollutants emitted are carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM), which are substances that pollute the environment and need to be controlled. The emission sources of automobile pollutants come from exhaust pipe, crankcase and fuel system. 2. Formulate laws and regulations: With the increasingly serious automobile exhaust pollution, it is imperative to legislate on automobile exhaust emission. As early as the sixties and seventies, countries all over the world established corresponding automobile exhaust emission regulations, which promoted the progress of automobile emission control technology through strict regulations. With the continuous improvement of automobile emission control technology, it is possible to formulate higher standards.