However, it's important to note that TEL is no longer widely used due to its harmful environmental impact.

Here's why:

* Lead pollution: TEL releases lead into the atmosphere, which is a toxic heavy metal that can cause health problems.

* Catalytic converter damage: Lead poisons catalytic converters, which are essential for reducing harmful emissions from cars.

Modern gasoline uses alternative anti-knock agents, such as:

* MTBE (methyl tert-butyl ether)

* Ethanol

* Various aromatic hydrocarbons

These alternatives provide similar anti-knock properties without the harmful effects of lead.