Although air pollution can cause irritating symptoms and increased asthma symptoms in some people, it is unlikely to be an important cause of asthma in Australia. 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.
Very small pieces of solid or liquid matter. Particles of dust, sea salt, and material from volcanic eruptions occur naturally in the atmosphere. Sulfate particles are also produced naturally from gases emitted by marine organisms. Industry and motor vehicles add significantly to the concentration of particles in the atmosphere - high concentrations are found in big cities and industrial areas. These particles remain airborne for long periods, lowering visibility.