What is ozone and why has a hole?

Ozone is an unstable gas composed of three atoms of oxygen (O 3). It is formed when an oxygen molecule (O 2) is divided and each oxygen atom (O) binds to another molecule of O 2 to form two molecules of ozone (O 3). Ozone is found naturally in our atmosphere, but in much smaller amount than the oxygen we breathe (O2). The oxygen we breathe is a stable molecule, so the natural formation of ozone depends on ultraviolet light and electrical discharges that break the molecule of oxygen (O 2), freeing the individual oxygen atoms that can assemble and form the ozone. For every three ozone molecules in the atmosphere are about ten thousand oxygen molecules (O 2). However, ozone plays an important role in the atmosphere.

The vast majority of ozone (90%) is in the stratosphere, the part of the atmosphere which lies between 10 and 50 kilometers (6 to 30 miles) away from the surface of the earth.

The main function of the ozone layer is to absorb solar radiation and filter the light to protect us from UV-B rays. Without the ozone layer, we and the other animals on the planet we would be exposed to dangerous levels of UV-B (the most harmful rays of the sun) rays. For humans, this could lead to a higher incidence of cancer, especially skin cancer.

Another important function of the ozone layer is the regulation of the temperature of the atmosphere. When absorbs ultraviolet radiation, ozone is heated and the temperature of the stratosphere, thus influencing climate patterns around the globe. The ozone layer naturally fluctuates according to the season but is also greatly affected by human activities.

The ozone found in the troposphere (near the surface of the earth) is not part of the ozone layer. Although in chemical terms is exactly the same molecule, their instability makes react with other molecules and because this is toxic and causes environmental problems.

Chemicals produced by humans adversely affect the ozone layer, causing depletion of the ozone layer. While there may be thin areas in various parts of the world, the ozone hole largest found in the stratosphere above Antarctica in 1985. It reached its maximum size in September 2000 and broke the record again in 2006. On both occasions the ozone depletion zone measured about 28.3 million square kilometers (11 million square miles), equal to three times the size of the United States. It is important to note that an ozone hole is not really a hole where there is no ozone, it is an area that has a lower level of ozone at 220 Dobson units (the unit used to measure the concentration of ozone).

Thanks to policies implemented at international level – mainly the control of substances that damage the ozone layer, according to the Montreal Protocol in 1987 – the ozone depletion was reduced by 9% between 2000 and 2014.

The ozone layer is impaired by substances produced by humans and used for refrigeration, climate control, fire extinguishers, blowing agents and aerosol propellants. Substances that damage the ozone layer include

Most of these substances have already been banned or limited because of the damage they cause. However, chlorine and bromine remain in the atmosphere for a long time, so the ozone depletion will continue in existence for a few more decades.