Ozone is composed of three oxygen atoms.

What is Ozone?

Ozone is created in the atmosphere when the sun's rays split oxygen molecules into single atoms. These atoms combine with nearby oxygen to form a three-oxygen molecule, called ozone. Even as it's being made, ozone is also destroyed by sunlight and reactions involving natural compounds that contain chlorine, nitrogen, and hydrogen. Most of the earth's ozone is contained in the stratosphere, a layer of the atmosphere 10–40 km above the surface of the earth. The amount of ozone in the stratosphere is fairly constant when viewed globally. However, it changes throughout the year and from one place to another. Most of the world's ozone is created over the Tropics, and is then pushed by stratospheric winds over the rest of the planet.

In the Arctic, ozone typically collects in the stratosphere during the winter darkness.

The earth's atmosphere consists of three main layers that differ in thickness and chemistry. The thickness of the innermost layer, the troposphere, decreases from the equator to the poles. The greatest amounts of ozone occur in the stratosphere.

The ozone layer is typically thicker over the poles than over the equator for three reasons. First, there is a lack of sunlight during an arctic winter to break it down. Second, seasonal weather systems and wind patterns in the upper atmosphere push more ozone toward the poles in winter. Third, the vertical structure of the atmosphere affects thickness. Near the equator, the troposphere makes up about 18 kilometres of the atmosphere. At the poles, it thins to only 8-kilometres thick. The boundary between the layers, called the tropopause, slopes downward from the equator to the poles like the bottom of a swimming pool. Over the Arctic, at the deepest part of the "pool", the thicker stratosphere can hold more ozone than over the Tropics or middle latitudes. The atmosphere over the Arctic also holds more ozone than in the Antarctic, because stratospheric winds in the Southern Hemisphere are less effective at transporting ozone.

Ozone molecules in the upper atmosphere are spread so thinly that if they were compressed to pure ozone here on the earth's surface, they would make a band only 3-millimetres thick!