What exactly is Ozone?

Oxygen exists in several forms. It can exist as a single oxygen atom, which is very rare. Usually, it exists as a diatomic molecule composed of two oxygen atoms linked by a chemical bond. Diatomic oxygen is the form of oxygen that we breathe every day.

Ozone is yet another type of oxygen. Ozone is a triatomic molecule composed of three oxygen atoms linked by chemical bonds. Like its molecular cousin, diatomic oxygen, ozone is an important component of the earth's atmosphere.

The atmosphere can be divided into two main regions. The troposphere is a layer of gases that extends about 10 km above the earth's surface. The stratosphere is located above this layer, extending an additional 40 km away from the earth. Diatomic oxygen is located throughout both the troposphere and stratosphere, whereas ozone is present mainly in the middle of the stratosphere.

Ozone is produced in the stratosphere by chemical reactions involving diatomic oxygen and sunlight. Light, in fact, can cause many chemical reactions because light carries energy. For example, the visible sunlight that reaches the earth's surface provides energy for plants to make food via the photosynthesis reactions. Similarly, ultraviolet light from the sun provides energy for the production of ozone.

Ultraviolet light has a higher energy than the visible light that we see every day. Due to its higher energy, ultraviolet light can break chemical bonds in a process known as photolysis. This is precisely how ozone is produced. Ultraviolet light emitted from the sun strikes diatomic oxygen molecules in the stratosphere, providing enough energy to split the oxygen molecules into single oxygen atoms. These oxygen atoms then crash into other diatomic oxygen molecules and combine with them to form ozone.

Ozone itself can be split by ultraviolet light back into diatomic oxygen and a single oxygen atom. This leads to a cycle where ozone is produced and destroyed, and ultraviolet light is constantly absorbed. This is an important process because it prevents ultraviolet light from reaching the earth, where it would cause harmful photolysis reactions in living organisms.