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.
Photochemical smog is caused by the release of nitrogen oxides, mainly from motor vehicles.
Under the influence of sunlight, these oxides react with certain hydrocarbon compounds to form various substances that are toxic to humans and plants. The smog irritates people's eyes, nose and throat, causing considerable discomfort. Several years ago I found an odd book at the half price bookstore here in Dallas which was the results of extended monitoring and testing of jet aircraft emissions by a Japanese research team. They found that the majority of ozone and air pollution problems were the result of jet emissions. This was when everyone was concerned about freon and the propellant used for underarm deodorant as a major cause of ozone depletion.