Essays

In another major atmospheric challenge that has been traced to human technology/ the work of environmental scientists again has uncovered a serious problem for which there was no prior warning. Our knowledge of the workings of the atmosphere has been appallingly poor, and one consequence of that lack of understanding is the strong possibility that ultra-violet radiation will increase in intensity all over earth.

Radiation from the sun includes Ultra-Violet (UV) radiation, alongwith the visible light. On penetrating the atmosphere and being absorbed by biological tissues, UV radiation damages protein and DNA molecules at the surface of all living things, This is what occurs when you get a sunburn. If the full amount of UV radiation falling on the Stratosphere reached the Earth's surface, it is doubtful that any life would survive. We are spared from the more damaging effects of the UV rays because most of the UV radiation (over 99%) is absorbed by Ozone in the upper Stratosphere. For this reason, Stratospheric Ozone is commonly referred to as the Ozone Shield or the Ozone Layer

In the autumn of 1985, some British atmospheric scientists working in Antarctica reported a gaping 'hole' (actually, a thinning of one area) in the stratospheric ozone layer of the South Pole. There is an area equal to the size of the United States, where Ozone levels were 50% lower than normal. Scientists had assumed that the loss of Ozone, if it occurred, would be slow, gradual and uniform over the whole planet. The 'hole' came as a surprise, and if it had occurred anywhere but over the South Pole, the UV damage would have been extensive.

News of the ozone 'hole' stimulated an enormous research effort. A unique set of conditions were found to be responsible for the ozone 'hole'. In summer, gases such as Nitrogen Oxide and Methane react with Chlorine Monoxide and Chlorine to trap the chlorine, forming so-called chlorine reservoirs, preventing much ozone depletion.

High above the Earth is the stratosphere where a small number of ozone molecules shield all life from harmful ultra-violet radidtion. Ozone, an unstable form of oxygen containing 3 oxygen atoms (03), falls apart into an oxygen atom (0) and an oxygen molecule (02) when it absorbs ultra-violet radiation. However, a fresh supply of ozone forms continually in the stratosphere, producing a delicate chemical balance in which a layer of less than 4.5 trillion kilograms of ozone, about 3 or 4 ozone molecules for every million molecule of air, blankets the planet. That balance is threatened by chemicals called chlorofluoro carbons or CFCs, such as the Fluoro Carbon'11. They decompose and release chlorine atoms, which cause ozone to break down. The difference is that each chlorine atom destroys as many as 100,000 ozone molecules faster than nature can replenish them, As a result, the ozone layer is thinning, forming a hole that lets damaging ultra-violet radiations reach the Earth.

The depletion of ozone layer, allows more UV radiation to reach the Earth. It has been estimated that a 5% loss of ozone results in a 10% increase in UV radiation. Some of the important effects of ozone depletion are that in humans, the increased UV radiation increases the incidence of cataract, skin cancer and decline in the functioning of the Immune system. Secondly, the elevated level of UV radiation damages nucleic acids in living organisms. Thirdly, UV radiation inhibits photosynthesis in plants and photoplanktons which in turn affects the whole food chain.

Ozone losses have not been confined to Earth's Polar Regions, although they are most spectacular there- A worldwide network of Ozone-measuring Stations send data to the World Ozone Data Centre in Toronto, Canada. Reports from the centre reveal a rate of loss of 2-4% per decade since 1979 over mid-latitudes in the Northern Hemisphere, Ozone loss was expected to start showing in the year 2001, when, the chlorine and bromine concentrations in the stratosphere started to decline as a consequence of the international agreements that have been forged. However, according to a report published in 2010, the ozone holes, high in the stratosphere over each of the Polar Regions, have stopped growing due to the phase out of nearly 100 ozone-depleting substances once used in products like refrigerators and spray cans, as per the study by United Nations scientists. Over the past decade, global ozone and ozone in the Arctic and Antarctic regions is no longer decreasing but is not yet increasing, the study finds.

The ozone story is a remarkable episode in the human history. From the first warnings in 1974 that something might be amiss in the stratosphere because of a particularly inert and useful industrial chemical, through the developments of Montreal Protocol and the final steps of CFCs phase out that are still being undertaken, the world has shown that it can respond collectively to a clearly perceived global threat The scientific community has played a crucial role in this episode, first alerting the world and then plunging into intense research programmes to ascertain the validity of the threat and its remedial actions.