Fuel with lower environmental standards has appeared at gas stations: K4, K3, and even K2.
The standard determines the amount of sulfur, benzene, and aromatic hydrocarbons that can be present in gasoline or diesel, but you cannot determine the standard by looking at the fuel.
Excess sulfur increases the load on the catalytic converter and reduces the lifespan of engine oil, while benzene and aromatics affect engine power and cause engine wear.