Ozone is a form of oxygen. It is a colourless gas that has a very pungent odour. It exists naturally at low concentrations in the stratosphere, where it absorbs ultraviolet radiation. In the troposphere it exists naturally at extremely low concentrations. But these concentrations increase when sunlight acts on various gases coming mainly from vehicle exhausts, and ozone then becomes a pollutant in the troposphere.
Ozone is a highly corrosive gas and is poisonous to most organisms.
The lead comes from the exhausts of cars running on leaded petrol and is poisonous. Babies and young children can be badly affected by lead because it can stop their nervous systems developing properly and it can damage their brains. Once lead has found its way into your body it is difficult to get it out. Particles in the air can cause breathing difficulties, increased asthma symptoms and worsen respiratory diseases. Some particles contain cancer-causing materials.