Tetraethyl lead

Excessively rapid burning of gasoline in the engine caused explosions inside the engine which reduced efficiency, wore down the mechanisms, and were loud. Tetraethyl lead was added to gasoline to make "leaded gasoline" to mitigate this problem, but introduced lead accumulation in the cylinder. A volatile bromine compound was added to mitigate that, leading to excessive air pollution.
 Thomas Midgley, Jr. United States 1921 Tetraethyl lead

Excessively rapid burning of gasoline in the engine caused explosions inside the engine which reduced efficiency, wore down the mechanisms, and were loud. Tetraethyl lead was added to gasoline to make "leaded gasoline" to mitigate this problem, but introduced lead accumulation in the cylinder. A volatile bromine compound was added to mitigate that, leading to excessive air pollution.