Ten facts about the shield in the atmosphere that protects us
Ozone gas is a form of oxygen (O3). Ninety percent of the ozone in the Earth’s atmosphere lies in a layer in the upper part of the stratosphere. The other 10 percent is in the troposphere (10-16 km above the Earth). The ozone in the stratosphere is called «good» ozone as it plays a beneficial role, whereas the ozone in the troposphere is known as «bad» ozone as it is an element in city smog and causes irritations, breathing difficulties and headaches in people and harms plants and animals. Why is the ozone in the stratosphere beneficial? Because it absorbs a large part of the harmful solar ultraviolet rays (UVB). It also helps to neutralize pollutants such as carbon monoxide and nitrogen oxide as well as greenhouse gases such as methane. What problems does ultraviolet radiation cause? Overexposure to solar ultraviolet radiation can cause skin cancer, eye cataracts and damage to the immune system. A reduction of 1 percent in the ozone layer increases skin cancer and cataracts by 2 percent. Has the protective ozone layer been depleted? Unfortunately, yes. Since 1980 when ozone depletion was first observed, it is estimated that concentrations of «good» ozone have decreased by 4 percent. The depletion is much greater above the poles and less over the equator. The ozone hole is above the Antarctic. What exactly is the ozone hole? The ozone hole is where the ozone layer has become considerably depleted over the Antarctic. It was first observed in 1980. It is a seasonal phenomenon that occurs between the end of winter and the beginning of spring in the South Pole (August-November). The size of the hole is huge and can cover the whole continent. There is also ozone depletion over the North Pole, but the depletion is less. What damages the ozone layer? A number of chemical compounds containing chlorine and bromine which are produced in manufacturing are the main culprits. Compounds such as chlorofluorocarbons (CFCs) used in refrigerators, air-conditioning systems and sprays are released into the lower layers of the atmosphere and rise to the stratosphere with the movement of air masses. Here chemical reactions and sunlight create chlorine (ClO) and bromine (BrO) oxides, which destroy the ozone. Unfortunately, they are extremely active as one chlorine or bromine atom can destroy hundreds of ozone atoms before being neutralized by another substance. These destructive compounds can last for up to 200 years. Why has the ozone hole formed over the Antarctic? Extensive damage to the ozone layer requires particularly low temperatures as in the Antarctic. Frozen clouds are formed there, known as polar stratospheric clouds, where bromine and chlorine act. The very strong winds in the South Pole also isolate the air masses, thus facilitating the destruction of ozone. Have measures been taken to tackle the problem? Since 1987, when the Montreal Protocol was signed, there have been regulations and limitations on the production of ozone-depleting gases. Today 190 states have signed the protocol which has been updated (London 1990, Copenhagen 1992, Beijing 1999). The protocol stipulates that CFCs be replaced by hydrochlorofluorocarbons (HCFCs), which are 88 to 98 percent less harmful to ozone as they remain in the troposphere. But HCFCs must also be reduced gradually and be withdrawn by the middle of the century. Have attempts to protect the ozone layer borne results? Yes, over the last few years the concentration of ozone-depleting gases has been reduced. If all states fulfilled their obligations it is estimated that by the end of the 21st century ozone levels will have reached pre-ozone hole levels. What will replace these substances? The so-called «clean» fluoride compounds (HFC) that do not destroy the ozone. The problem is that these compounds contribute to the greenhouse effect and are among the list of gases that need to be eliminated, according to the Kyoto Protocol. Further scientific research is thus required.
