What is unleaded gasoline?

Unleaded gasoline is now being promoted at automobile gas stations. It turns out that the gasoline typically used in cars contains lead. Why is there lead in gasoline? That's to improve the detonation resistance of the gasoline. In addition to increasing the iso-octane number in gasoline, you can also add a kind of "lead water", tetraethyl lead, to the gasoline to improve the resistance to detonation. Tetraethyl lead is a colorless oily liquid containing lead. Although it can be added to gasoline to improve the explosive resistance of gasoline, but it will bring other hazards. Currently used gasoline contains about 0.5 grams of lead per liter. Although the content of lead is small, it is toxic. Direct contact with it will produce obvious symptoms of poisoning. What is more dangerous is that it produces serious air pollution when burned. Therefore, countries are promoting unleaded gasoline. Generally speaking, unleaded gasoline is not completely lead-free and contains less than 0.13 grams of lead per liter of gasoline.