A project Report on ozone depletion. This project report will help you to learn about: 1. Meaning of Ozone Depletion 2. Occurrence of Ozone Depletion 3. Formation 4. Process 5. Mechanisms 6. Ozone Depletion in Mesosphere 7. Effects 8. Causes of Ozone Depletion of Biodiversity 9. Consequences.
Contents:
- Project Report on the Meaning of Ozone Depletion
- Project Report on the Occurrence of Ozone Depletion
- Project Report on the Formation of Ozone Depletion
- Project Report on the Process of Ozone Depletion
- Project Report on the Mechanisms of Ozone Depletion
- Project Report on the Ozone Depletion in Mesosphere
- Project Report on the Effects of Ozone-Depletion
- Project Report on the Causes of Ozone Depletion of Biodiversity
- Project Report on the Consequences of Ozone Depletion
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Project Report # 1. Meaning of Ozone Depletion:
Ozone gas is perceptibly blue in colour and has a characteristic pungent smell. It occurs throughout the atmosphere, but only in small quantities. Indeed, if all the ozone contained in the first.60 km or so of the atmosphere could be brought down and assembled at the Earth’s surface, it would form a layer only some 3 mm thick.
Under average conditions, at ground level, each cm of ah contains around 1019 molecules of all the gases present of which ozone concentration is about 0.1 ppm. However, nearly 90% of the atmospheric – ozone lies in the stratosphere, which is located in between 15-50 km above the earth surface.
Ozone is a form of oxygen, but whereas molecules of ordinary oxygen each contain two atoms, the ozone molecule has three.
In industrial societies ozone is now being generated at ground level by the action of sunlight on gaseous pollutants, but the Earth’s natural ozone factory is the stratosphere. Here the raw materials are ordinary oxygen seeping up from the troposphere, and sunlight, but the process involved depends on how both oxygen and ozone respond to that radiation.
Ordinary oxygen absorbs UV with wavelengths below about 2.4 x 10-7m; this provides the energy needed to split up or photo dissociate the molecule into a pair of highly reactive oxygen atoms. Once released, an oxygen atom can combine with an intact oxygen molecule, forming ozone.
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This process not only produces ozone; it also thereby filters out most of the incoming solar UV rays with wavelengths less than 2.0 x 10-7m and some of that in the 2.0 x 10-7 to 2.4 x 10-7m region as well.
But up in the stratosphere, the odds are stacked against ozone. The crucial point is that ozone is constantly being created and destroyed in the stratosphere. There are a number of pollutant trace gases like NO, NO2, CI, CIO etc. known, which could easily react with O3 and thus produce O2 (Table 17.1). This is commonly known as “Ozone depletion“.
Project Report # 2. Occurrence of Ozone Depletion:
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Ozone depletion occurs when the natural balance between the production and destruction of strato-spheric ozone is tipped in favour of destruction. Although .natural phenomena can cause temporary ozone loss, chlorine and bromine released from man-made synthetic compounds are now accepted as the main cause of this depletion.
It was first suggested, by Drs. M. Molina and S. Rowland in 1974, that a man-made group of compounds known as the chlorofluorocarbons (CFCs) were likely to be the main source of ozone depletion. However, this idea was not taken seriously until the discovery of the ozone hole over Antarctica in 1985.
Chlorofluorocarbons are not “washed” back to Earth by rain or destroyed in reactions with other chemicals. They simply do not break down in the lower atmosphere and they can remain in the atmosphere from 20 to 121 years or more. As a consequence of their relative stability, CFCs are instead transported into the stratosphere where they are eventually broken down by ultraviolet radiation, releasing free chlorine.
The chlorine becomes actively involved in the process of destruction of ozone. The net result is that two molecules of ozone are replaced by three of molecular oxygen, leaving the chlorine free to repeat the process:
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CI + O3 → CIO + O2
CIO + O → CI + O2
Ozone is converted to oxygen, leaving the chlorine atom free to repeat the process up to 100,000 times, resulting in a reduced level of ozone. Bromine compounds, or halons, can also destroy strato-spheric ozone. Compounds containing chlorine and bromine from man-made synthetic compounds are known as industrial halocarbons (Fig. 15.5).
Global ozone levels have declined an average of about 3% between 1979 and 1991. This rate of decline is about three times faster than that recorded in the 1970s. In addition to Antarctica, ozone depletion now affects almost all of North America, Europe, Russia, Australia, New Zealand, and a sizeable part of South America.
Short-term losses of ozone can be much greater than the long- term average. In Canada, ozone depletion is usually greatest in the late winter and early spring. In 1993, for example, average ozone values over Canada were 14% below normal from January to April.
Project Report # 3. Formation of Ozone Depletion:
Ozone is formed by photochemical reaction, followed by three body reaction.
O2 + hV (242 nm) → O + O
O + O2 + M(N2 or O2) →Oz + M
The third body M absorbs the excess energy liberated by the above reaction and there by stabilise the O3 (Ozone) molecule. A close look at the evolution at the life on earth reveals that initially the atmosphere was devoid of oxygen but photosynthetic activities of blue green algae and other anaerobic unicellular organisms helped in building up oxygen level in the atmosphere. It is believed that first multi-colour organism appeared when the stratosphere ozone layer in a thin layer of ozone gas, generated.
However ozone layer may be depleted by reactions involving a variety of compounds which reach the stratosphere of particular concern are the water vapour and nitrogen oxides released by high altitude aircraft.
Nitrous oxide produced by the action of bacteria in soils (amount of which have become significant with the large scale use of nitrite fertilizers) and chloro-fluoro hydrocarbon which are widely used as aero spray propellants and refrigerants.
It is postulated that the combined effect of aircraft halogen nitrate fertilizers and effluent would considerable depletion of the ozone layer and could result in an increase in ultraviolet radiation reaching the earth tending to crop damage and marked rise in cases of skin cancer. The recent reports of the zone hole in the atmosphere over the Antarctica is a cause for great concern.
There has been much hue and cry about the destruction of stratospheric ozone and issue has now assumed global dimensions. The problem of ozone depletion and its adverse consequences have threatened the existence of life on the planet. The roll of ozone is very crucial and significant because it acts as a protective shield in the biosphere Eco-system against their exposure to deadly and dangerous ultraviolet radiation.
The world watch institute, USA released the first authentic and well documented picture on the threat of ozone loss authored by Cynthia Pollock Shea in 1988. Now NASA- OTP (Ozone Trend is a global affairs and not a phenomenon confined only to the atmosphere lying over Antarctica.)
Project Report # 4. Process of Ozone Depletion:
Ozone depletion in the stratosphere leads to an increase of UV-B on ground with its harmful effects on health, ecosystems, aquatic system, materials etc. It was estimated that about 3-5.5% O3 depleted in northern hemisphere during 1969-1988.
In general, there are three principal ways of O3 destruction:
(a) Hydrogen system (OH system)
(b) Nitrogen system (N2O system)
(c) Chlorine system (CFCl3 or CF2Cl2 system).
The OH system destroys only 10% of O3. This reaction is seen above 40 km over the earth’s crust.
The details are:
Project Report # 5. Mechanisms of Ozone Depletion:
It includes:
(1) The natural process,
(2) The anthropogenic process.
(1) The Natural process:
The atmospheric oxygen absorbs ultraviolet radiation at shorter wavelength than 240 nm and photo-dissociate into two oxygen atoms. These unites with other O2 molecules to form ozone. During the process surplus energy of nascent O3 is often transferred to the nearby molecules as kinetic energy which slightly releases the surrounding atmospheric temperature.
Ozone acts as a powerful oxidant because of its ability to remove electrons from other molecules. It occurs as a natural component of air. It is also formed in ambient air by photochemical reaction of primary pollutant. Its higher concentration is found in large urban area of the world, which are characterized by automobile dependent transportation and petroleum dependent energy production etc.
CFCs and halons remain inactive in the troposphere and it takes about 20 – 40 years for these chemicals to travel to reach the stratosphere, but after that their intermediate product (chlorine atom) remains active for more than 100 years.
The travelling time for CFCs and halons to reach to stratosphere may range from 20 to 40 years, that is CFCs and halons reach to stratosphere, the chlorine and bromine atoms present in these chemicals are released as a result of interaction with UV radiation’s in the stratosphere.
CFCs, UV CL halons, UV Br:
The chlorine monoxide molecule is eventually split up by interaction with another ozone molecule to give oxygen molecule and a freed chlorine atom.
CL + O3→ CLO + O2 CLO → O3 2O2 + CL
This CL atom again repeats the cycle of destruction of ozone in the stratosphere. One chlorine atom released by the action of UV radiation on CFCs break two molecules of ozone into three oxygen molecules and the again the same chlorine atoms acts on a new ozone molecule to begin cycle of destruction.
These chlorine or bromine atoms remain active for more than 100 years and are capable of breaking thousands of ozone molecules before the released chlorine gets converted into dilute HCl and come down in the form of acid rain.
The process of decomposition is also enhanced in the presence of greenhouse gases such as CO2, CH4, NOx etc. It is due to continuous breakdown of ozone molecules, that ozone layer is getting depleted and at certain lacerations holes have been created in the ozone layer.
(2) The Antropogenic Process:
Nitrogen Oxide Hypothesis:
Scientists are rather worried about the anthropogenic activities which play a significant role in the matter of NOx lead to the stratosphere affecting ozone concentrations. The supersonic air crafts (SST) fly at ozonosphere cruising altitudes because of low air resistance which is essential to maintain speed of the supersonic. Their exhaust gases directly provide water vapours and NOx into stratosphere.
It was in 1971 the P.J. Curtzen and his collaborators of National Centre for Atmospheric Research at Boulder, USA pointed out that the supersonic transport (SST) fleet could add significant quantities of oxides of N2 leading to about 40% reduction in ozone concentration.
Nuclear explosions produce large quantities of NOx which directly enter into stratosphere. Studies indicate that nuclear tests conducted by USA and USSR reduced O3 concentration by about 40%.
Following reactions between O3 and NOx are known to exist:
Species of molecules such as NO3, OH and NO2 are highly reactive but may have relatively long life-times in regions where the total concentration of molecules is low. The net result is that NOx increases the rate of O3 destruction with no change in the concentration of NO.
Project Report # 6. Ozone Depletion in Mesosphere:
Mesosphere lies above stratosphere between the altitude ranging from 30 km to of 100 km. In general temperature rises with altitudes in the regions. The ionosphere which overlaps the mesosphere extends from about 30 km to thousands of kms.
At a height of 100 km, sun’s ultraviolet radiation causes photoionization, producing species of ions such as N2, O2 and O, which undergo ion – molecular reactions in the following manner:
Atomic oxygen can also be generated photolytically,
The molecular nitrogen is not easily dissociated by sun’s ultraviolet radiation. Some of the species produced during these reactions are known to be in an electronically excited state and their decay to the ground state is responsible for the “auroras” observed in the northern hemisphere.
Decay of oxygen atom follows the course:
Wave length of this transition falls in the visible range at about 5577 A (green) and 6300 A to 6364 A (red).
Appearance of blue and violet colours is due to the following transition:
Project Report # 7. Effects of Ozone-Depletion:
I. Effects on human body:
Ozone at low concentration is also known to cause accumulation of inflammatory cells at the site of lung injury causing severe damage to the lung. The capacity of lung phagocytes which normally fight bacterial infections is also affected resulting in increasing incidence of respiratory infections.
Emphysema, a destructive lung disease, and chronic obstructive lung disease such as chronic bronchitis and development of asthama might be the ultimate results of chronic ambient ozone exposure. Exposure to ozone has been shown to be associated with lung cancer, DNA breakage, inhibition and alteration of its replication and formation of DNA adduct, which has been implicated in premature aging and finally cell death.
Effect of ozone on human health:
Ozone exposure has also been implicated in dizziness and visual impairment – a sign of central nervous system damage, enlargement of spleen and thymus and impairment of the immune system.
‘Photochemical smog’ is the major cause of ozone-exposure causing urban air pollution posing a threat to human health.
Ozone, in highly populated areas occurs with concentration ranging from 0 – 0.4 ppm. OT 0.7 ppm in air, while in upper atmosphere its concentration is more than 1.0 ppm. So the crew and passengers of flying commercial aircrafts often suffer adverse reaction from ozone present in unfiltered air cabin.
Any increased concentration of ozone brings about changes in the nucleic acids, DNA and RNA. So increased UV absorption will have drastic results.
Ozone has been reported to be a strong irritant and is supposed to reach the lungs and respiratory tract much faster than the oxides of sulphur. Even its low concentration causes pulmonary edema.
II. Effects on Biotic Community:
1. Many micro-phytoplankton’s would die because of their exposure to UV solar radiation.
2. The marked reduction in the productivity of phytoplankton’s would in turn adversely affect zoo planktons. The marine animals, fishes etc. will starve in the absence of sufficient supply of food.
3. The loss of fish population would directly affect the inhabitants of coastal areas.
4. Studies carried out on microorganisms indicate that both irreversible and photo reversible types of injury are caused.
5. Ozone is reported to be highly toxic to fish in the concentrations ranging from 0.1 to 1.0 ppm. Anaerobic break down of organic phosphorus compounds results in the formation of phosphate and its 7.6 ppm concentration is highly lethal to fishes.
6. The increased UV radiation will increase the mortality rate of larvae of zoo planktons. Enhanced radiation also impairs fish productivity.
III. Effects on Plants:
1. Exposure to air containing toxic result in the lesions to plants, usually confined to the upper surfaces of leaves. These lesions are characterized by the uniformly distributed white or brown flecks and stipples in irregularly distributed blotches.
2. Ozone flecking is observed with the plants of grape, citrus and tobacco. At 0.02 ppm, it damages tomato, pea, pine and other plants. In pine seedlings it causes tip burn.
3. Plant proteins are also susceptible to UV injury, because they absorb strongly around 280 nm. 20-50% chlorophyll reduction and harmful mutation have also been observed.
4. In USA and California fruits and vegetable yields have reduced due to ozone pollution.
5. Ozone along with, other pollutants like SO2 and NO2 is affecting crop losses of over 50% in European Countries. In Denmark, O3 affects spinach, potato, clover and alfalfa etc.
6. In limited pockets O3 level can be potentially harmful.
7. O3 level can reduce yields of bean, potato and poplar.
8. In plants O3 enter through stomata. It causes visible damage to leaves there by reducing their photosynthetic-rate.
IV. Effects of Ozone-Depletion on Climate:
Scientists believe that ozone-reduction in stratosphere may drastically change the weather elements like temperature, wind pattern, acid rains and precipitations etc. By absorbing UV radiations the ozone-layer heats the atmosphere. The added heating up of the surrounding stratosphere causes a temperature inversion between 15 and 50 km. Altitude from-58°C to 2°C.
This defines the stratosphere as having a temperature gradient, while tropospheric temperature increases steadily. Today industrial operations are increasing the amount of trapped radiation leading to rapid rise in global temperature by letting ozone-eaters such as CFCs, NOx and SO2 etc.
Every molecule of either of two common CFCs – CCL3F and CC12F2 has the some global warming effect as 10,000 carbons dioxide molecules. Ozone depletion changes spectral composition of solar electromagnetic radiation. The increased solar UV radiation caused greenhouse effect changing the global energy and radiation balance.
V. Ozone Depletion Create Ecological Effect on Ecological Balance:
The depletion of ozone, if not controlled, would enormously affect the ecosystem productivity, ecological stability and overall environmental equilibrium. It would also trigger several changes in the biospheric ecosystems.
The resultant climatic alterations would cause certain physiological changes in man and animals. Change in energy balance and radiation would affect the survival of living organisms. The changes in thermal conditions of biosphere would affect type, density and stability of vegetation which in turn would affect several cycles occurring in nature.
Project Report # 8. Causes of Ozone Depletion of Biodiversity:
Human activities has altered nearly every landscape on.
1. Habitat Loss:
Due the destruction of the land, natural habitat of animal have been reduced. Thus, due to the habitate loss our important biodiversity is getting reduced.
2. Over Exploitation:
The second reason is over exploitation, commercial harvesting has been a threat to many species. Over exploitation has been the cause of extition of some large terrestrial habitate.
3. Pollution:
Pollution is the third reason for the growing loss of species. Pollution have affected several birds and other organisms. Both air and water pollution stress ecosystem.
4. Introduction of exotic species:
The fourth reason for the loss of species in introduction of other species as they threatened natural flora and fauna by predation competition or by alternating the natural habitate.
Project Report # 9. Consequences of Ozone Depletion:
The ultraviolet light in the 220-320 nm range (i.e., uv-C and uv-B) is filtered from sunlight mainly by ozone molecules, O3, that spread through the middle and lower stratosphere.
However, uv-A (320-400 nm) penetrates through O3 layer mostly, when then screened through troposphere. Thus O3 depletion in stratosphere leads to the loss of filtering ability of uv light, which are mostly harmful to biological systems in a variety of ways.
The most obvious cause for concern about ozone loss stems from its role as filter of the Sun’s ultraviolet radiation. The band labeled uv-C (2.0-2.9 x 10-7 nm) is virtually eliminated by the atmosphere.
This is just as well, because uv-C is lethal to microorganisms (whence its use in germicidal lamps) and can destroy both nucleic acids and proteins:
In the range from 2.4 – 2.9 x 10-7 nm. Protection from uv-C is due entirely to absorption by ozone.
However, more important as far as ozone loss is concerned is the band between 2.9 x 10-7 nm and 3.2 x 10-7 nm known as ‘biologically active uv‘ or uv-B. Here the attenuation of the solar input is evident, due to ozone, but the effect is less complete; a fraction of uv-B penetrates all the way to the ground.
Because of this, the proportions of uv-B reaching the surface should be highly sensitive to changes in the ozone column—an increase of around 2% for each 1% loss of ozone being generally accepted.
Most of these effects are damaging—but few are sufficiently well understood at present for the impact of enhanced uv-B to be quantified:
(a) Human Health:
The link between uv-B and the incidence of skin cancer is particularly emotive:
Here, there are two main strands of evidence. First, skin cancer is predominantly a disease of white-skinned people and the dark pigment—melanin—is known to be an effective filter of uv-B. The second strand comes from epidemiology—a study of the factors that influence the occurrence of the disease in human populations.
Melanoma—the particular form of skin cancer as reported in many areas—is actually much rarer than other types, but it is the most serious with a substantial high mortality rate. Incidence of the more common non-melanoma skin cancers is loosely correlated with long term uv-B exposure—occurring predominantly on light-exposed areas of the skin, in the elderly and in those who spend considerable time outdoors.
These cancers are distressing, but can usually be treated successfully.
By contrast, the epidemiology of melanoma is more complex:
It affects relatively young people and, unlike other skin cancers, it has been increasing over the last few decades in all white-skinned populations-studied.
This and the observed correlation with indoor working and social class, have led to the suggestions that melanoma is associated with intermittent, but intense exposure to uv-B the sort of exposure associated with sunshine holidays and other recreational activities.
Correlations between the attendant increase in uv-B and the estimated ozone loss may affect rates of skin cancer. Possibly the best current estimate comes from the EPA.
This suggests that every 1% decrease of O3 column will result in a 3% rise in the incidence of non-melanoma skin cancers, which translates into some 12-15,000 extra cases a year in the US, together with a possible 1% increase in mortality from melanoma (Fig. 17.6).
Exposure to enhanced levels of uv-B can also have other directly harmful effects on the human body, the two most serious being a tendency to suppress the body’s immune responses and to cause damage to the eyes, especially in the development of cataracts.
Although even more difficult to quantify it was noticed that these effects would touch all populations, with some consequences—possible increases in the incidence on severity of infectious diseases, for example—being particularly severe for people in tropical and subtropical areas.
(b) Terrestrial Plants:
Plants are mostly adapted to present levels of visible radiation, but rather little is known about their response to enhanced levels of uv-B.
Today, most studies have focused on agricultural crops typical of mid-latitudes of the 300 or so species and cultivars screened for tolerance to uv-B, some two-thirds have been found to be sensitive—although the degree of sensitivity varies widely, even among cultivars within a given crop species.
Typically, sensitive plants show reduced growth and smaller leaves; unable to photosynthesize as efficiently as other plants, they yield smaller amounts of seeds or fruit. In some cases, these plants also show changes in their chemical composition—which can affect food quality.
The limited data available so far suggests that increased uv-B levels may also affect forest productivity.
Potentially more important, it is possible that subtle changes in plant growth induced by uv-B could upset the delicate balance in natural ecosystems—thereby changing the distribution and abundance of plants. Quantifying this effect remains 3 key area of uncertainty, as indeed do the more direct impacts on food production and forestry.
(c) Aquatic Ecosystems:
Life in the oceans is also vulnerable to uv-radiation. Although not as important as visible light or temperature of nutrient levels, there is evidence that ambient solar uv-B radiation is nevertheless an important limiting factor in marine ecosystems.
The potential impact of any increase in uv-B will depend critically on the depth to which it penetrates— more than 20 m in clear waters, but only up to 5 m or so in turbid water. Moreover, certainly enhanced uv-B has been shown to damage a range of small aquatic organisms—zooplanktons, larval crabs and shrimp and juvenile fish—as well as slowing photosynthesis in phytoplankton.
(d) Climate:
A further area of concern derives from ozone’s other major role in the atmosphere. As ozone cycles through its round of creation and destruction, there is an overall absorption of solar radiation, which is ultimately dumped as heat into the stratosphere. This warms the stratosphere and produces the temperature inversion at the tropopause: indeed, there would be no stratosphere without the ozone layer.
Thus any depletion of stratospheric ozone is predicted to cool this region and, hence, change the temperature structure of the atmosphere to some extent. A schematic representation of climate change associated with O3 depletion is presented in Fig. 17.7.
