When the Environmental Protection Agency began phasing out leaded gasoline in the 1970s with the passage of the Clean Air Act, aviation got a pass. Because lead was needed to boost octane levels and prevent detonation (also known as "knock") in high-compression piston aircraft engines, leaded avgas was exempted from the law. Lead is a fantastic octane enhancer, but it destroys catalytic converters in automobiles and it's toxic to humans. Today, 100 low-lead aviation gasoline is the only transportation fuel sold in the United States that still contains lead. If the EPA gets its way, soon there will be no leaded transportation fuels sold in this country, and 100LL will be history.
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