| | | Ozone Depletion

From WikiVerde

1 What Is Ozone?
2 The Ozone Layer
3 Why Do We Need The Ozone Layer?
4 What Is Ozone Depletion?
5 What Causes Ozone Depletion?
6 The Consequences of Ozone Depletion
7 How Are We Protecting the Ozone Layer?
8 References:

What Is Ozone?

Ozone or O3 is a relatively less stable allotrope of oxygen – a triatomic molecule first discovered by C. F. Schönbein in 1840. Because of the gas’s sharp, distinctive odour when it reacts with other chemicals, Schönbein gave it the name of ozone, from the Greek ‘ozein’ meaning smell.

Ozone arises from the action of UV light on diatomic oxygen molecules. It is a corrosive, colorless gas.

Interestingly, ozone is a gas found in two places – immediately above the surface of the planet, and in the stratosphere, which contains the larger amount. Only 10% of the earth’s ozone lies in the troposphere, the part of the atmosphere closer to the earth. Stratospheric ozone is good for us, while tropospheric ozone has polluting, health-impairing effects. We are concerned here with the former, which covers an area from about 6 miles to 30 miles above the surface of the earth.

The Ozone Layer

The ozone layer forms part of the earth’s atmosphere – this is an area about 15 to 35 km above the planet, which contains a lot of ozone. It was first discovered by Fabry and Buisson and closely studied by Dobson and Chapman. Ozone quantities are measured by the Dobson unit. The ozone that is found high above the earth prevents most of the incidence of UV light.

Why Do We Need The Ozone Layer?

The ozone layer protects us from harmful UV light such as UVA and UVB.

What Is Ozone Depletion?

Ozone depletion refers to the erosion of stratospheric ozone by the effects of human activities such as the use of CFCs or chlorofluorocarbons.

The layer of stratospheric ozone has been decreasing over the last twenty years – at a rate of approximately 10% during winter, and 5% during summer. These seasonal variations in ozone concentration are affected by stratospheric sulphates and chlorine, stratospheric winds, greenhouse gases, and the sunspot cycle, and are measured by the Dobson Spectrometer. Except for areas around the tropics, ozone is being depleted all over the earth.

What Causes Ozone Depletion?

Chlorofluorocarbons were introduced to the world in the 1920s by Thomas Midgely and applications included cooling, cleaning electronics and many industrial processes.

CFCs are largely emitted from Russia, Japan, Europe and North America, used in aerosols, packaging and refrigeration. They last for decades in the atmosphere, but at high altitudes, they are attacked by UV light from the sun, disassociated, and broken down into chlorine and other residues. This chlorine reacts with ozone to form chlorine oxide, thus reducing the amount of ozone in the air. Each chlorine atom catalyzes and breaks down tens of thousands of molecules of ozone during its lifetime. Nitrogen oxides (such as those discharged into the atmosphere by aircraft) and bromine also react with ozone, with the same effect.

Ozone depletion occurs when more ozone molecules are destroyed than are produced. CFC emissions are responsible for about 80% of stratospheric ozone reduction. And because the life of these emissions is so long, with the best efforts, ozone replacement is unlikely to happen before the year 2050.

The earliest hole in the ozone layer was noticed above Antarctica, and its effects will be far-reaching and dangerous to both plant and animal life on earth. The Antarctica ozone hole is now 9 million square kilometers wide.

Ozone depletion due to chlorine increases greatly when polar stratospheric clouds are around. During the cold dark winter months, cloud particles made of nitric acid or ice offer a platform for ozone-destroying chemical reactions, but it is only in spring, when the sun shines brightly, that photochemical reactions cause the polar stratospheric to melt and discharge their lethal contents. This is when the ozone layer destruction happens in these areas, and it heals slowly only when the warmer temperatures at the end of spring bring ozone-heavy air in from warmer latitudes.

The Consequences of Ozone Depletion

With the depletion of the ozone layer, more UVB light will reach the earth. This lack of protection from UVB has been proved to result in increased skin cancer in humans. Basal and squamous cell carcinomas, malignant melanoma and cortical cataracts are all caused by increased UV levels. It can also damage vision (causing cataracts) and the immune system, with children being particularly vulnerable. It is likely that there will be a rise in the incidence of infectious diseases like malaria. Increased tropospheric ozone as another result of high surface UV light are also detrimental to human health. Climatic patterns such as wind directions could change, affecting global weather.

Plants are also affected by UVB radiation – forms and functions can change, resulting in shifts in ecological balance – forests, for example, could be destroyed or severely damaged. Crops like rice retain nitrogen through cyno-bacteria, which are very sensitive to UV light. Marine life is affected adversely by increased UVB radiation with poor survival levels and impairment of development, affecting the rest of the food chain. Many forms of plankton are extra vulnerable to the adverse effects of ultraviolet light.

The bio-geochemical cycles of land and water animals and plants are changed, too, resulting in an increase in the volume of greenhouse gases emitted. Alterations in species balance could have incalculable consequences. Man-made materials can also be damaged by this kind of radiation.

How Are We Protecting the Ozone Layer?

In the attempt to protect the ozone layer, some steps forward have been taken. The practice of using CFCs in aerosols has been stopped by the Montreal Protocol which demanded a gradual reduction in, and then the complete ban of, the practice. This multinational environmental agreement has been accepted by almost 200 nations. The EU’s ozone layer protection policy and the Vienna Convention for the Protection of the Ozone Layer also take substantial strides in this direction.

The use of ozone depleting substances or ODS is being reduced. CFC replacements like HCFCs or hydro-chlorofluorocarbons, whose chlorine content in inhibited by the presence of hydrogen, have been introduced. Measures have also been taken against the use of halon.