The ozone layer is a natural layer of gas in the upper atmosphere which protects humans and other living things from the harmful ultraviolet (UV) rays of the sun. Although ozone (O3) is present in small concentrations throughout the atmosphere, most ozone (about 90%) exists in the stratosphere, in a layer between 10 and 50 km above the surface of the earth. This ozone layer performs the essential task of filtering out most of the sun's biologically harmful UV radiation.
Concentrations of ozone in the atmosphere vary naturally according to temperature, weather, latitude and altitude. Furthermore, substances ejected by natural events such as volcanic eruptions can have measurable impacts on ozone levels. However, natural phenomena cannot explain the current levels of ozone depletion.
The scientific evidence shows that certain man-made chemicals are responsible for the creation of the Antarctic ozone hole and the global ozone losses. These chemicals are industrial gases which have been used for many years in a range of products and applications including aerosol sprays, refrigerators, air conditioners, fire extinguishers and crop fumigation.
ODS are broken down by sunlight in the stratosphere, producing halogen (e.g. chlorine or bromine) atoms, which subsequently destroy ozone through a complex catalytic cycle. Ozone destruction is greatest at the South pole where very low stratospheric temperatures in winter create polar stratospheric clouds. Ice crystals formed in these clouds provide a large surface area for chemical reactions, accelerating catalytic cycles. Since the destruction of ozone involves sunlight, the process intensifies during spring time, when the levels of solar radiation at the pole are highest, and polar stratospheric clouds are continually present.
Ozone hole, October 2011
Low concentrations of ozone are
indicated in purple and blue
Ozone destruction is greatest at the South Pole. It occurs mainly in late winter and early spring (August-November). Peak depletion usually occurs in early October when ozone is often completely destroyed in large areas. This severe depletion creates the so-called “ozone hole” that can be seen in images of total Antarctic ozone made using satellite observations. In most years the maximum area of the ozone hole is bigger than the area of the Antarctic continent itself.
Although ozone losses are less radical in the northern hemisphere, significant thinning of the ozone layer is also observed over the Arctic, and even over continental Europe/the EU. The ozone loss over the Arctic is however usually less severe than over the Antarctic and is more variable from year to year due to the climatic and geographical situation in the Arctic. Nevertheless, in March 2011 not only a thinning but an actual ozone hole was observed over the Arctic and parts of Europe for the first time.
Increased UV levels at the earth's surface are damaging to human health. The negative effects include increases in the incidence of certain types of skin cancers, eye cataracts and immune deficiency disorders. Increased penetration of UV results in additional production of ground level ozone, which causes respiratory illnesses.
UV affects terrestrial and aquatic ecosystems, altering growth, food chains and biochemical cycles. In particular, aquatic life occurring just below the surface of the water, which forms the basis of the food chain, is adversely affected by high levels of UV radiation. UV rays also have adverse effects on plant growth, thus reducing agricultural productivity. Furthermore, depletion of stratospheric ozone also alters the temperature distribution in the atmosphere, resulting in a variety of environmental and climatic impacts.
Increased health costs are the most important direct economic impact of increased UV radiation. The medical expenses for millions of additional cases of skin cancers and eye cataracts pose a challenge to health care systems, particularly in less developed countries. Increased UV radiation also reduces the lifetime and tensile properties of certain plastics and fibers.
Indirect economic impacts include a range of additional costs, for instance for combatting climate change or as a result of reduced fish stocks.
Despite existing regulation of ODS, there continues to be severe ozone depletion. This is because once released, ODS stay in the atmosphere for many years and continue to cause damage. However, since smaller and smaller amounts of ODS are being released, the first signs of recovery of the ozone layer are visible. Nevertheless, because of the long lifetime of ODS, and unless additional measures are taken, the ozone layer is unlikely to recover fully before the second half of the century.
Ozone-depleting substances are still present in many older types of equipment and appliances so awareness of how to deal with these is crucial. Here are some practical things individuals can do to help protect the ozone layer:
There is a direct link between increased exposure to UV radiation and a higher risk of contracting certain types of skin cancers. Risk factors include skin type, sunburn during childhood, and exposure to intense sunlight. Recent changes in lifestyle, with more people going on holiday and deliberately increasing their exposure to strong sunlight, are partly responsible for an increase in malignant skin cancers. To minimise the risk of contracting skin cancer, cover exposed skin with clothing or with a suitable sunscreen or sun cream, wear a hat, and wear UV-certified sunglasses to protect the eyes.
While an increased amount of UV radiation is bad for human health, too little exposure can also have negative effects. These are mainly related to the reduced vitamin D production in the skin which is induced by UV radiation. Under-supply of vitamin D is the cause of a number of illnesses such as osteoporosis, osteomalacia (softening of the bones), rickets or cardiovascular problems. Dark-skinned people are particularly vulnerable to a decrease in natural UV radiation. However, most people get adequate exposure to UV radiation in their daily lives. For healthy humans, there is no medical reason to seek additional exposure.