Ozone is a gas that is naturally present in our atmosphere. Each ozone molecule contains 3 atoms of oxygen and is denoted chemically as ‘O3’. About 10% of ozone is in the troposphere. About 90% of Earth’s ozone resides in the stratosphere.

Located in the stratosphere, ozone is important for blocking out much of the ultra-violet radiation that is emitted by the Sun. Lower, in the troposphere, ozone is a component of smog, and is responsible for breathing difficulties and other ailments.

The ozone layer is a concentration of ozone molecules in the stratosphere, which extends from about 10 km to about 50 km in altitude. It gets warmer at higher altitudes. This warming is caused by ozone absorbing ultraviolet radiation.

It is not really a hole through the ozone layer, but rather a large area of the stratosphere with extremely low amounts of ozone.

One example of ozone depletion is the annual ozone ‘hole’ over Antarctica that has occurred since the early 1980s.

Ozone can be harmful. When inhaled, ozone can damage the lungs. Relatively low amounts of ozone can cause chest pain, coughing, shortness of breath and, throat irritation.

Ozone has a distinctive smell that humans can detect even in small concentrations. The smell has been described as 'Metallic, like a burning wire'.