The Moon is the only celestial body on which human beings have orbited and landed. The first man-made object to escape Earth’s gravity and pass near the Moon was the Soviet Union’s Luna 1, the first man- made object to impact the lunar surface was Luna 2, and the first photographs of the normally occluded far side of the Moon were made molecule and forms a molecule of ozone.

The ozone molecules, in turn, absorb ultraviolet rays between wavelength 310 to 200 nm and thereby prevent these harmful radiations from entering the Earth’s atmosphere. In the process, ozone molecules split up into a molecule of oxygen and an oxygen atom. The oxygen atom again combines with the oxygen molecule to regenerate an ozone molecule. Thus, the total amount of ozone is maintained by this continuous process of destruction and regeneration.

The cause of ozone depletion is the increase in the level of free radicals such as hydroxyl radicals, nitric oxide radicals and atomic chlorine and bromine. CFCs or chlorofluorocarbons account for almost 80 per cent of the total depletion of ozone in the stratosphere. CFCs are very stable in the lower atmosphere of the Earth, but in the stratosphere, they break down to release a free chlorine atom due to ultraviolet radiation.

A free chlorine atom reacts with an ozone molecule and forms chlorine monoxide (CIO) and a molecule of oxygen. Now chlorine monoxide reacts with an ozone molecule to form a chlorine atom and two molecules of oxygen. The free chlorine molecule again reacts with ozone to form chlorine monoxide. The process continues and the result is the reduction or depletion of ozone in the stratosphere.

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The ozone layer above the Antarctic has been particularly impacted by pollution since the mid-1980s. This region’s low temperatures speed up the conversion of CFCs to chlorine. In the southern spring and summer, when the sun shines for long periods of the day, chlorine reacts with ultraviolet rays, destroying ozone on a massive scale, up to 65 per cent. This is referred to as the ‘ozone hole’.

The ozone layer is important as it prevents the ultraviolet rays of the Sun from passing through the atmosphere of Earth. Ultraviolet rays of the Sun are associated with a number of health related and environmental issues including an increased risk of developing several types of skin cancers like malignant melanoma, basal and squalors cell carcinoma. Even the incidents of cortical cataracts can also increase significantly with the increased exposure to ultraviolet rays.

Depletion of ozone layer in the stratosphere can lead to an increase in the ozone present in the lower atmosphere. Ozone present in the lower atmosphere is mainly regarded as a pollutant and a green house gas that can contribute to global warming and climate change. However, the lifespan of atmospheric ozone is quiet less as compared to stratospheric ozone. At the same time, increase in the surface level of ozone can enhance the ability of sunlight to synthesize vitamin D, which can be regarded as an important beneficial effect of ozone layer depletion.

Increasing amounts of ultraviolet (UV) radiation impact plankton and other tiny organisms at the base of the marine food web—the original food source for all other living organisms in the oceans. Ultraviolet rays can affect the orientation and mobility of phytoplankton and influence their survival rates. Phytoplankton and zooplankton are highly sensitive to ultraviolet radiation, as they lack the protective UV-B-absorbing layers that higher forms of plants and animals have.

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More UV-B radiation reduces the amount of food phytoplankton create through photosynthesis. Zooplankton, which feed off the phytoplankton, is also affected. UV-B also damages small fish, shrimp and crab larvae. It has been estimated that on shallow coastal shelves, a 16 per cent reduction of the ozone layer would kill more than 50 per cent of anchovy larvae, and cause a five per cent drop in plankton numbers and a similar drop in fish yield.

The depletion of the ozone layer reduces the effectiveness of the carbon dioxide sink in the oceans, thus increasing the rate of greenhouse warming. Since Phytoplankton in the oceans assimilates large amounts of atmospheric carbon dioxide, increased ultraviolet radiation will reduce phytoplankton activity significantly. This means that large amounts of carbon dioxide will remain in the atmosphere.

Ozone layer depletion can affect animals and plants as well. It can affect important food crops like rice by adversely affecting cyanobacteria, which helps them absorb and utilize nitrogen properly. Rice production ray be drastically reduced by the effects of UV-B on the nitrogen assimilating activities of micro-organisms. With a diminishing ozone layer, the supply of natural nitrogen to ecosystems, such as tropical rice paddies, will be significantly reduced.

Most plants and trees grow more slowly and become smaller and more stunted as adult plants when exposed to large amounts of UV-B. Increased UV-B also inhibits pollen germination. Thus, a high increase in ultraviolet radiation may disrupt many ecosystems on land.

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UV-B stimulates the formation of reactive radical’s molecules that react rapidly with other chemicals, forming new substances. The hydroxyl radicals, for example, stimulate the creation of tropospheric ozone and other harmful pollutants. Smog formation creates other oxidized organic chemicals, such as formaldehydes. These molecules can also produce reactive hydrogen radicals when they absorb UV-B. In u-ban areas, a 10 per cent reduction of the ozone layer may result in a 10-25 per cent increase in tropospheric ozone.

More UV-B radiation also causes global increases in atmospheric hydrogen peroxide, the principal chemical that oxidizes sulphur dioxide to form sulphuric acid in cloud water, making it an important part of acid rain formation. Moreover, ultraviolet radiation causes many materials to degrade more rapidly. Even small increases of ultraviolet radiation reduce lifetimes of plastic materials used outdoors. Similarly, PVC sidings, window and door frames, pipes, gutters, etc. used in buildings degrade faster.

The increasing concern for the causes and effects of ozone depletion led to the adoption of the 1987 Montreal Protocol in order to reduce and control the industrial emission of chlorofluorocarbons. The Protocol was later amended to ban CFC production after 1995. As part of Title VI of the Clean Air Act, all Ozone Depleting Substances (ODS) were monitored and conditions were set forth for their use. Initially, the amendments were to phase out ODS production by the year 2000, but it was later decided to accelerate the phase out to 1995.

International agreements have succeeded to a great extent in reducing the emission of these compounds, however, more cooperation and understanding among all the countries of the world is required to mitigate the problem.