The Ozone Hole

Ozone is a reactive gas mostly found in the so-called ozone layer in the lower stratosphere. The highest ozone concentrations are usually seen at altitudes between 20 and 40 km (at the poles between 15 and 20 km). But it is a very thin layer of about 1-10 ppm (parts per million) ozone. In both the formation and the destruction of ozone, UV radiation is absorbed. Under the influence of UV radiation, oxygen molecules are split into oxygen atoms. The adsorption of UV radiation by the ozone layer is crucial, for without it, life on land would be impossible. 

However, over-exposure to UV radiation will have a variety of damaging effects: Genetic mutation and subsequent effects on health, damage to living tissues, Cataract formation in eyes, skin cancers, suppression of the immune system, Damage to photosynthetic organisms, especially phytoplankton, damage to consumers of photosynthetic organisms, especially zooplankton. 

UV radiation can cause mutations — changes in a species' DNA. This risk is especially high in Australia and New Zealand where the number of cases of skin cancer in humans has increased dramatically. People arc advised to wear clothes on the beach and to use sun blocks to protect their skin. In New Zealand the daily weather report in summer includes isolines to show burn times. 
It also causes cataracts in the lenses of eyes when the protein of the lens denatures and turns cloudy instead of dear, causing blindness if untreated. 

Since the 1950s, scientists have been measuring the amount of ozone in the stratosphere above Antarctica. They discovered what later would be called the ozone hole: the amount of ozone decreased significantly during the spring (September and October) and increased again in November. Apart from this annual ozone cycle, the scientists discovered that the ozone hole was growing. During the last 30 years, the minimum thickness of the ozone layer has reduced drastically and recovery has been taking longer. These results were later confirmed by NASA satellite data. Reductions in the amount of stratospheric ozone have been observed in other areas including the arctic region.

Ozone is depleted because of human-made substances called Ozone-depleting substances (ODS), like chlorofluorocarbons and methyl bromide in pesticides. While replacing CFCs in spray cans and as blowing agents for plastic foam is relatively easy, it is much more difficult to find a suitable refrigerant. The refrigerants used before the introduction of CFCs are not an option because of their dangerous properties. The most suitable CPC replacements are the so-called hydrochlorofluorocarbons (IICFCs). These substances are nearly as good as refrigerants as CFCs and are also non-toxic and inflammable. However, HCFCs also destroy ozone and they contribute to the greenhouse effect. Only their shorter lifetime in the atmosphere makes them less harmful to the ozone layer than CFCs. 

The Montreal Protocol was an international agreement at the UNEP deciding to regulate the use of CFCs, and it succeeded to a great degree as their usage has decreased since the late 80s, partly because it was the first universally ratified international agreement. More international cooperation to battle threats like the thinning of the ozone layer is the need of the hour.