By Parag Ranjan Dutta
The airy envelop called atmosphere is vital for various forms of life on the earth’s surface. But this atmosphere is in great danger due to human activities and might lose its present status in the very near future. Some major constituents of the atmosphere like oxygen, carbon dioxide and ozone, though present in insignificant proportions help sustain life on the earth’s surface. Most of the ozone is found at the stratospheric level at an altitude of 15-55 km from the earth’s surface.
Ozone (O3) is a molecule made up of three atoms of oxygen and is naturally formed by chemical reactions in the upper layer of the atmosphere, called the stratosphere in presence of strong ultraviolet radiation and oxygen molecule. Therefore, most of the ozone is not found on the earth’s surface but in the stratospheric layer.
The ozone shield is crucial for various life forms on the earth. The earth’s natural sunscreen, known as the ozone layer or the ozone shield, absorbs and blocks majority of the ultra violet radiation and not only protects humans but also plants and animals. The countries that are likely to be affected most are in the southern hemisphere like Argentina, Chile, South Africa, New Zealand and Australia.
A number of chemicals used are continuously destroying the ozone shield. The pollutants responsible for the destruction are chlorofluorocarbons (CFCs) and nitrogen oxides from fertiliser industries. Most refrigerants used in air conditioners, refrigerators and freezers contain CFCs, which are mainly used as coolants.
Like CFCs, Halons are low toxic and chemically stable compounds and are used in fire extinguishers which contain bromine. It is a greater threat to the ozone layer because it is 10 times more destructive than CFCs.
The pollutants which are responsible for the destruction of ozone are not only CFCs but a host of other chemicals as nitrogen oxide from fertiliser industries and hydrocarbons. Nirtrous oxide emissions as exhaust from aircraft engines at great heights also trigger the depletion of ozone.
In the early 1960s, F Rowland and Mario Molina while studying the atmospheric chemistry expressed their concern about the status of the ozone layer over the sky of Antarctica when they detected a huge vacuum and warned that and it was in great danger. The real danger came much earlier than predicted.
To create a mass awareness, Molina went on a campaign in 1974 to end the use of chlorofluorocarbons. In 1974, Sherwood Rowland and Molina wrote in nature “the chlorofluoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert may remain in the atmosphere for 30-150 years and concentrations can be expected to reach to 10-30 times present levels. The photo dissociation of the chlorofluoromethanes in the stratosphere produces significant amounts of chlorine atoms, which leads to the destruction of atmospheric ozone”.
In 1984, a British Antarctic research team stationed at Halley Bay and Faraday Research Stations in Antarctica discovered that the ozone values were diminishing rapidly when the sun appears every spring and a vacuum had been created over the sky of Antarctica equivalent to the size of the US.
The ozone hole was first discovered by Joe Farman and his associates and the related article was published in Nature in 1985. The work of Sherwood Rowland, Mario Molina and Paul Krutzen was recognised when the Nobel Prize in 1995 was awarded jointly to them for their work in atmospheric chemistry.
The severe destruction of the ozone layer known as the ‘ozone hole’ occurs over the sky of Antarctica because of special atmospheric and chemical conditions that exist over the south pole and nowhere else on the globe. High altitude stratospheric clouds formed at very low temperatures play a major role in the formation of the ozone hole over Antarctica.
CFCs are gaseous compounds that contain carbon, fluorine and chlorine atoms. They are chemically inert, non toxic, non flammable, stable and long lived. Once injected in the atmosphere from various domestic and industrial sources, CFCs drift slowly to the stratospheric level and can be floated up in the atmosphere in its original form for 100 years.
Release of CFCs has serious environmental consequences because some may end up in the higher atmosphere that can destroy the ozone layer reducing the protection it offers. And this is really a serious concern because they will continuously deplete the ozone molecules leaving the various life forms on earth in great danger.
When CFCs are exposed to ultra violet radiation they break up and release one chlorine atom that forms chlorine monoxide, which is highly unstable. This chlorine monoxide is free to attack another ozone molecule and destroy another ozone molecule. Laboratory experiments showed that this feat of destroying ozone by one chlorine atom can be repeated one hundred thousand times. Nitrogen oxide emitted from supersonic jets flying at great heights also depletes the concentration of ozone in the upper layer of the atmosphere.
Effects of strong UV radiation have been shown to be harmful to living organisms. Exposure to higher levels of UV-B radiation affects skin’s top layer which can induce skin cancer. Melanoma, the most dangerous form of skin cancer, may turn into malignant melanoma that kills many in the US every year.
Effect of enhanced UV-B radiation can affect photosynthesis, growth and development of plants and crops. Plants, especially leafy vegetables in the process of absorbing sunlight for photosynthesis, are at great risk. The crops likely to be affected most are soya bean, spinach, pea, turnip, cauliflower and cucumber. The resultant may be less supply of crops.
Ultraviolet radiations can also damage eyes as more than 99 per cent of UV radiation is absorbed by the front of the eyes causing corneal and lens damage. In higher altitude, the UV radiation can cause snow blindness.
Higher concentrations of ultraviolet radiations can impact the production of phytoplankton, the first link in the food chain, and zooplankton that forms the basis of the food chain in the aquatic eco-systems. Phytoplankton and zooplanktons are essential suppliers in the food chain in seas and oceans.
There was an imperative need to act and save Mother Earth from further deterioration. The first global conference on ozone depletion was held in Vienna in 1985 under the auspices of World Meteorological Organisation and the United Nations. The Vienna convention entered into force in 1988 and provided the initial framework and to create regulatory measures which was not a binding agreement.
The convention is a multilateral environmental agreement for the reduction and use of ozone depleting substances. Vienna Convention did not yield any satisfactory result as a number of countries like India did not sign the protocol.
India’s rationale was that per capita consumption of CFCs was only 0.02kg against the world total of 1kg in certain developed countries. The Vienna Convention was followed by the Montreal Protocol, where it was decided to phase out 98 per cent of nearly one hundred ozone depleting substances by 1998. Canada was the first country to sign and ratify this landmark international treaty in 1987.
When 197countries signed the Montreal Protocol, it was the first treaty to achieve universal recognition and the most successful global action on a very serious environmental issue. Another conference on saving the ozone layer was held in London with the initiative of the then Prime Minister of UK Margaret Thatcher where many countries promised to sign the Montreal Protocol.
Despite all these efforts according to a recent report published in Nature, China still continues to use CFCs. Today nearly 40-60 per cent of the total emissions originate from eastern China. According to World Meteorological Organisation’s assessment, the recent status of ozone hole is bright as it is in the path of recovery. So there is a ray of hope at the end of the tunnel for the future generations.
(The author is former head of the Department of
Environmental Science,
St Edmund’s College)