OZONE LAYER DEPLETION: A DANGER TO OUR ENVIRONMENT
Ozone is the layer of colourless gas that forms a protective covering in the Earth’s upper atmosphere. Ozone is formed when oxygen molecules absorb ultraviolet photons and undergo a chemical reaction known as photo dissociation or photolysis, where a single molecule of oxygen breaks down to two oxygen atoms. The ozone molecules, in turn, absorb ultraviolet rays between 310 to 200 nm wavelengths 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 (O) again combines with the oxygen molecule (O2) to regenerate an ozone molecule (O3). Thus, the total amount of ozone is maintained by this continuous process of destruction and regeneration.
Ozone layer depletion first captured the attention of the whole world in the later half of 1970 and since then, many discussions and researches have been carried out to find out the possible effects and the causes of ozone depletion. Many studies have also been directed to find out a possible solution.
Causes of Ozone Depletion
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. The most important compound, which accounts for almost 80% of the total depletion of ozone in the stratosphere, is chlorofluorocarbons (CFC). These compounds 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 (O2) and forms chlorine monoxide (C10) 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.
What Ozone Layer Does?
The ozone layer protects the Earth from the ultraviolet rays sent down by the sun. If the ozone layer is depleted by human action, the effects on the planet could be catastrophic.
Ozone is present in the stratosphere. The stratosphere reaches 30 miles above the Earth, and at the very top it contains ozone. The suns rays are absorbed by the ozone which is a bluish gas that is formed by three atoms of oxygen. The form of oxygen that humans breathe in consists of two oxygen atoms, 02. When found on the surface of the planet, ozone is considered a dangerous pollutant and is one substance responsible for producing the greenhouse effect.
The highest regions of the stratosphere contain about 90% of all ozone.
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth’s stratosphere (the ozone layer), and a much larger spring time decrease in stratospheric ozone over Earth’s Polar Regions. The latter phenomenon is referred to as the ozone hole. In addition to these well-known stratospheric phenomena, there are also springtime polar tropospheric ozone depletion events.
Danger to Our Environment
Ozone is a natural trace component of the atmosphere. It is created continuously through the action of sunlight and oxygen in the upper atmosphere. For millions of years ozone has been protecting the earth by absorbing ultraviolet or poisonous radiation from the sun. This poisoning of the Earth’s ozone layer is increasingly attracting worldwide concern for the global environment and the health effects of life on the planet Earth. As the ozone layer is getting thinner and thinner, more and more harmful UV (ultraviolet) rays are passing into our atmosphere. These rays cause cancer, cataracts and lowered immunity to diseases. In recent years, scientists have sounded alarms internationally about the depletion of the ozone layer, citing chemical pollution as the major cause.
Causes of Ozone Depletion
There is not just one particular cause for the ozone’s depletion; the accumulation of different pollutants into our ozone layer has all added up and equaled a worldwide problem. Man-made chemicals, fossil fuels, industrial wastes and automobile exhaust all pose a threat to the earth’s ozone. Scientists were concerned when they discovered in the 1970’s the chemicals called chlorofluorocarbons, or CFCs. These CFCs were used as solvents, refrigerants, aerosol propellants and to blow foam plastics. For this reason, the use of CFCs in aerosols has been banned everywhere. Other chemicals, such as bromine halocarbons, as well as nitrous oxides from fertilizers, may also attack the ozone layer. Nitrogen oxides and methane are also compounds which adversely affect the stratosphere’s ozone. It is given off by cow’s dung, marshes, landfills and garbage dumps.
Ways to Protect the Ozone Layer
- Minimize high altitude aircraft flights (oxygen reduction and water vapour deposition)
- Minimize rocket flights (water vapour deposition)
- Encourage growth of plants that produce oxygen, discourage deforestation
- Decrease / control releases of high temperature steam / moisture to the atmosphere
- Eliminate production and release of known ozone depleting chemicals (such as CFCs and HCFCs) where remotely possible. Subsidies production of safer alternatives where possible.
- Establish controls to assure that new compounds to be used in high volume are surveyed for effect on ozone.
Interest in ozone layer depletion
While the effect of the Antarctic ozone hole is decreasing, the global ozone is relatively small, estimated at about 4% per decade, the hole has generated a great deal of interest because:
- The decrease in the ozone layer was predicted in the early 1980s to be roughly 7% over a 60-year period.
- The sudden recognition in 1985 that there was a substantial “hole” was widely reported in the press. The especially rapid ozone depletion in Antarctica had previously been dismissed as a measurement error.
- Many were worried that ozone holes might start to appear over other areas of the globe but to date the only other large-scale depletion is a smaller ozone “dimple” observed during the Arctic spring over the North Pole, Ozone at middle latitudes has declined, but by a much smaller extent (about 4%-5% decrease).
- If the conditions become more severe (cooler stratospheric temperatures, more stratospheric clouds, more active chlorine), global ozone may decrease at a much greater pace. Standard global theory predicts that the stratosphere will cool.
- When the Antarctic ozone hole breaks up, the ozone-depleted air drifts out into nearby areas. Decreases in the ozone level of up to 10% have been reported in New Zealand in the month following the break-up of the Antarctic ozone hole.
Consequences of Ozone Layer Depletion
Since the ozone layer absorbs UVB ultraviolet light from the sun, ozone layer depletion is expected to increase surface UVB levels, which could lead to damage, including increase in skin cancer. This was the reason for the Montreal Protocol. Although decreases in stratospheric ozone are well-tied to CFCs and there are good theoretical reasons to believe that decreases in ozone will lead to increases in surface UVB, there is no direct observational evidence linking ozone depletion to higher incidence of skin cancer and eye damage in human beings. This is partly because UVB, which has also been implicated in some forms of skin cancer, is not absorbed by ozone, and it is nearly impossible to control statistics for lifestyle changes in the populace.
Possible Effects of Ozone Depletion
The effects of ozone depletion are not limited to humans only, as it 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. Phytoplankton, an important component of the marine food chain, can also be affected by ozone depletion. Studies in this regard have shown that ultraviolet rays can influence the survival rates of these microscopic organisms by affecting their orientation and mobility.
The increasing concern for the causes and effects of ozone depletion led to the adoption of the Montreal Protocol, in the year 1987, in order to reduce and control the industrial emission of chlorofluorocarbons. 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.
In conclusion, the protection and conservation of our ozone is vital for the continuation of all biological systems and life forms on Earth. If we decide to let things go on the way they are, extinction will start with the marine ecosystems and then the plants will start to die out, the animals will starve or die of diseases, and eventually the universe will come to an end.