Contents
The Biology Topics of biotechnology involve using living organisms to develop new products or solve problems.
Ozone Depletion and Climate Change – Important Global Initiatives to Combat Climate Change
Ozone Layer of the Atmosphere
The ozone layer is a layer in the Earth’s stratosphere that absorbs most of the Sun’s UV radiation. It contains relatively high concentrations of ozone (O3), although it is still very small with regard to ordinary oxygen, and is less than ten parts per million, the average ozone concentration in the Earth’s atmosphere being only about 0.6 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometers (12 to 19 mi) above the Earth, though the thickness varies seasonally and geographically.
Among the different layers of the atmosphere, the stratosphere consists of a thick layer of Ozone (03), which is called the ozoneosphere. It is at a height of 23-25 km above the equator. The thickness of the ozone in a column of air if it were all squeezed into a single layer is measured in the Dobson unit (D.U). The thickness of ozone is 300 Dobson Units (Equivalent to a layer of 3 mm or 0.12 inches) i.e., 0.3 ppm. If condensed, the total thickness of ozone is 0.29 cm above the equator but 0.40 cm above the poles. The main characteristic of ozone is, it gets formed in the stratosphere and gets photodissociated constantly. This mechanism is the basis for 03 to protect the earth from UV radiations, by dissipating their energy.
\(\mathrm{O}_3 \rightleftharpoons \mathrm{O}_2+[\mathrm{O}]\)
The protection of the earth from UV rays is proportional to the thickness of the ozone layer. So, the depletion of ozone layer is posing a problem on O3 activity.
Ozone is produced naturally in the stratosphere by a two-step reaction process. In the first step, solar ultraviolet radiation (sunlight) breaks apart an oxygen molecule to form two separate oxygen atoms. In the second step, each oxygen atom collides with another oxygen molecule and forms an ozone molecule in a binding reaction. In the overall process, three oxygen molecules plus sunlight react to form two ozone molecules. Ozone in the stratosphere absorbs a large part of the Sun’s biologically harmful ultraviolet radiation. Stratospheric ozone is considered “good” ozone because of this beneficial role. In contrast, ozone formed at the Earth’s surface in excess of natural amounts is considered “bad” ozone since it is harmful to humans, plants, and animals. Sun emits three types of UV radiation. UV-C (100-280 nm), UV-B (280-315 nm) and UV-A (315-415 nm). UV-C is particularly harmful to all life forms. UV-C radiation is entirely absorbed by the ozone layer along with most UV-B radiation.
Ozone near the Earth’s surface in excess of its natural amount is formed by reactions involving air pollutants emitted from human activities, such as nitrogen oxides (NOx), carbon monoxide (CO), and various hydrocarbons. This bad ozone reduces crop yields and forest growth, reduces lung capacity; and causes chest pains, throat irritation, and coughing. Total ozone column values are often reported in Dobson units denoted as “DV”. Typical values vary between 200 and 500 DU over the globe.
Nature of Ozone Depletion
The details of polar ozone hole formation differ from that of mid-latitude thinning, but the most important process in both is the catalytic destruction of ozone by atomic halogens. The main source of these halogen atoms in the stratosphere is the photodissociation of man-made halocarbon refrigerants, solvents, propellants, and foam-blowing agents (CFCs, HCFCs, freons, halons). These compounds are transported into the stratosphere after being emitted at the surface. Both types of ozone depletion have been observed to increase as emissions of halocarbons increase.
CFCs and other contributory substances are referred to as ozone-depleting substances (ODS). Since the ozone layer prevents most harmful UVB wavelengths (280-315 nm) of ultraviolet light (UV light) from passing through the Earth’s atmosphere, the decrease in ozone has generated worldwide concern. Chlorofluorocarbons are chiefly released by developed and to some extent by developing countries as well gradually enter the stratosphere and the winds push them towards the poles. During winter months, the temperature is extremely low about -85°C in Antarctica and there is no sunlight. This condition favours the formation of ice clouds. The frozen crystals that make up polar stratospheric clouds provide a catalytic surface for the reaction of chlorine atoms and the degradation of ozone.
Causes of Ozone Depletion
Depletion in the concentration of ozone over Antarctica has resulted in an Ozone hole. The ozone layer during 1956-1970 was about 280-325 D.U., but in 1994, it reduced to 94 D.U. The Ozone hole was discovered by Farman et al, in 1985. It was produced due to the reaction of sunlight over pollutants like nitrogen oxides, chlorofluorocarbons, sulfur dioxide, halons, carbon tetrachloride, etc. which release chlorine and thus destroy ozone.
A single atom of chlorine can react with more than 1,00,000 molecules of O3 acting in a chain, converting them into oxygen, thus forming an ozone hole. Thus, the ozone hole formed over Antarctica was very large, estimated to be 28.3 million sq. km in 2000. Another ozone hole was also observed over the North Pole in 1990. Thinking of the Ozone layer will lead to increased entry of harmful UV-B radiations. It occurs at a rate i.e., 1% loss of ozone will allow 2% more radiation to enter and 5% depletion of ozone will allow 10% UV-B to reach the earth. Such an increase in UV-B amount will cause skin cancer in 2,50,000 more persons, and make 5,00,000 more people blind.
Effects of Ozone Depletion
1. Biological Effects:
The main public concern regarding the ozone hole has been the effects of increased surface UV radiation on human health. So far, ozone depletion in most locations has been typically a few percent and, as noted above, no direct evidence of health damage is available in most latitudes. The high levels of depletion seen in the ozone hole are ever to be common across the globe, and the effects could be substantially more dramatic. As the ozone hole over Antarctica has in some instances grown so large as to reach southern parts of Australia, New Zealand, Chile, Argentina, and South Africa, environmentalists have been concerned that the increase in surface UV could be significant.
Ozone depletion would change all of the effects of UV on human health, both positive and negative. UVB (the higher energy UV radiation absorbed by ozone) has a curve length of 280-315 nm and is generally accepted to be a contributory factor to skin cancer, blindness or increased a cataract, higher number of mutations, immune system malfunctions and produces Vitamin D. In addition, increased surface UV leads to increased tropospheric ozone, which is a health risk to humans.
2. Effects on Crops:
An increase in UV radiation would be expected to affect crops. A number of economically important species of plants, such as rice, depend on cyanobacteria residing on their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV radiation and would be affected by its increase. Despite mechanisms to reduce or repair the effects of increased ultraviolet radiation, plants have a limited ability to adapt to increased levels of UVB, therefore plant growth can be directly affected by UVB radiation.
Global Initiatives to Subdue Global Changes
United Nations Environment Programme (UNEP) has undertaken various protocols to solve the problems of ozone depletion and global warming.
1. Montreal Protocol 06th September 1987):
The agreement was made by 27 industrialized countries to limit the production of CFCs to half the level in 1986.
2. Helsinki Declaration (May, 1989):
Montreal Protocol was amended by another 82 nations at Helsinki, to cut the emission of CFCs to half by 2000. In June 1990, the same was amended by 93 nations again. To date, 175 nations have agreed to this amendment.
3. Intergovernmental Panel on Climate Change (IPCC, 1988):
It played a crucial role in preparing a worldwide view on the extent of climate change around the globe.
4. Earth Summit (United Nations Conference on Environment and Development, 1992):
Recommendations of the Convention on Climate Change (CCC) for reducing greenhouse gases were made at the summit, held at Rio-de-Janeiro, Brazil. 154 nations signed and pledged to reduce the levels of emission of Greenhouse gases below the 1990 level.
5. Kyoto Protocol (December, 1997):
It too, obtained commitments to reduce emission of greenhouse gases at 5% level below 1990, by 2008-2012. It was held in Kyoto, Japan.
6. Beijing Protocol (1999):
It mentioned the steps taken by developed and developing countries to reduce the emission of ozone-depleting substances.