The lead in exhaust fumes come from the petrol used to drive internal-combustion engines. Crude oil straight from the wells is thick, black and sticky. It has to go through a complicated refining process before it can be used as fuel for the engines of cars, lorries, buses and aircraft. During refining, various substances are added to improve the petrol and for other reasons. For instance, small quantities of dye are put in to standardize the colour. Other substances prevent the formation of gum which would clog up parts of the engine.
Lead, in a liquid form called tetra-ethyl lead, is added to petrol to reduce “engine knock”. This means that it prevents the petrol from igniting in the engine at the wrong moment. When an internal combustion engine is running, the petrol is lit by sparks from the sparking plugs. The petrol burns in what is really a series of small explosions and produces gases which come out through the exhaust pipe as dirty, smelly fumes. And the lead comes with them.
III-health can be caused if quite small quantities of lead in the air are inhaled over a long time. For this reason, the governments of such countries as the United States, Britain, Sweden and Japan are passing laws to reduce the amount of lead in petrol. They are also encouraging car manufacturers to design internal combustion engines which will work efficiently on lead free petrol and have cleaner exhaust fumes. These engines will be more expensive at first, but they will help to make the air cleaner and pleasanter where there is a lot of traffic. Work in progress to invent a satisfactory car engine that runs on alternatives to petrol, such as a battery.