The Ozone Layer

The word Ozone originates from the Greek word "ozein" meaning 'to smell'. Ozone is a toxic, gaseous, bluish molecule which has a strong odour and contains three Oxygen atoms with the formula O3. The ozone is situated in the in the part of the atmosphere called the Stratosphere about 12-35 km above the Earth's surface [1]. Ozone is formed when an oxygen molecule (O2) in the stratosphere is broken into two oxygen atoms (O + O) due to it absorbing UV rays emitted by the Sun; this oxygen atom (O) then reacts with another oxygen molecule (O2) to produce an ozone molecule (O3).

[1]

Ozone either protects or harms organisms on Earth depending on the height at which it is found. In the high Stratosphere "good" ozone acts like a shield protecting Earth's flora and fauna against the Sun's ultraviolet (UV) radiation. An excess of UV radiation increases the risk of contracting forms of skin cancers or ocular diseases. It may also weaken the natural immunity of human beings and animals. Although near the surface, in the air we breathe, ozone is a pollutant, which in large amounts causes damage to huamans, animals and plants. It makes up about 10% ozone, and is produced, not by the exhaust pipe of cars, the smoke stacks of power plants, or from any other pollution source but instead it is produced in polluted air by a combination of pollutants that chemically react when sunlight shines through the air.

If the ozone didn't absorb the harmful rays of the ultraviolet radiation, the earth would be uninhabitable; the ozone prevents UV penetration to the earth's surface. UV rays are short-wave, energetic electromagnetic radiation released by the sun. Much of the solar ultraviolet radiation is absorbed in the stratosphere, where the production and destruction of ozone is involved [2], thus this cycle has kept the ozone stable.

[2]

Ultraviolet Radiation come in three different forms; Ultraviolet A (UV-A), Ultraviolet B (UV-B) and Ultraviolet C (UV-C) with wavelengths between 290-320 nanometers. The ozone layer completely blocks out UV-C, partially UV-A though it is not harmful to the DNA of humans, and roughly around 80-90% UV-B. UV-B can be tremendously harmful to any form of life because this radiation can enter cells and destroy the DNA. Damage to DNA which carries the characteristic information of a species from generation to generation would consequently mutate the individual genes in distressing and even fatal ways. UV rays can cause non living things such as paints, plastics and various other materials to decay rapidly.

The effects UV rays have on all living and non living things on earth are endless.

UV rays would cause all types of skin cancer: Melanoma, Basal Cell and

Squamous cell which are all extremely damaging to humans. UV rays can also

cause an increase in eye cataracts causing clouding of the cornea. The ozone layer is important to our health as it acts as a sunscreen, blocking out most of the UV rays which cause harm to plants and humans by causing various diseases (stated above). Not only could the UV rays cause harm to humans but it could also produce a reduction of the efficiency in Photosynthesis in plants and also of ecological systems such as agriculture, hence our crops, food, soil and more would be not as productive as it now is, causing issues in the doof chain.

Even though the ozone layer is an invisible shield, scientists have found numbers of ways to calculate how much ozone is in the atmosphere. An instrument called the Spectrometer, which was discovered by Mr. Gordon Dobson, measures the total ozone from the ground by measuring the concentration of solar UV radiation at four wavelengths in which two of those wavelengths are absorbed by the ozone and two of which are not [3]. The unit that this is measured by is called the Dobson Unit, 1 Dobson Unit (DU) is identified to be 0.01 mm thick at standard pressure and time. Ozone is what is known as a trace gas, meaning there is very little of it in the atmosphere; out of every million molecules of gas in the atmosphere, less than ten are ozone. Therefore ozone in the atmosphere is about 300 Dobson's, which means if you brought all of the ozone in the atmosphere down to earth's surface, it would be about three millimeters thick. Another effective way the ozone could be measured is to use helium filled balloons that carry measuring instruments into the atmosphere and transmit information back to Earth.

[3]

In the ozone layer a hole develops every spring, from September to early December, due to sunlight activating chemical reactions with chlorine being released from the CFCs rapidly destroys ozone molecules. The hole as big as the USA is up to 70% over Antarctica, in the South Pole and a smaller hole develops each year up to 30% over the Arctic, at the North Pole. The ozone hole over Antarctica gradually became larger between August 12th and November 11th 2003 as shown in this animation http://www.epa.gov/docs/ozone/science/hole/holeanim.html; it can be seen that during the first few months the hole wasn't that large, matching the colours to the Dobson Units chart, it seemed to be about 210-240 DU in the blue zone. As the months progressed it could be seen that the ozone was only 100-120 DU in the grey dark reddish zone [4]. There are signs that the ozone layer is getting thinner all over the planet. Scientists have discovered that the ozone hole over Antarctica started in 1979 and that the ozone layer generally started to get thin in the early 1980's. The loss of the ozone layer occurs when more ozone is being destroyed then nature is creating. One group of gases in particular, damages the ozone layer; these gases are called CFCs, Chloro-Fluoro Hydrocarbons.

[4]

The cause of the ozone hole is commonly due to be CFC compounds which break down due to Ultraviolet light and become free radicals high in the Earth's atmosphere. Free radicals (free chlorine atom) are uncharged atoms or molecules with unpaired electrons or an open shell design. These then activate when the sunlight forms a chemical reaction with them, therefore destroying as many ozone molecules as possible.

CFC's are used in some spray cans to force the contents out of the can. They are also used in refrigerators, air conditioning systems and some fire extinguishers and in the plastic industry.