Environmental Problems: 7 Current Environmental Problems of India

This article throws light upon the seven current environmental problems of India. The current environmental problems are: 1. Problems of Urbanization 2. Automobile Pollution 3. Climate Changes and Global Warming 4. Green House Effect/Global Warming 5. Acid Rain 6. Ozone Layer Depletion 7. Ozone Hole.

Environmental Problems # 1. Problems of Urbanization:

Urbanization means the concentration of population in the economically developed and industrialized centres and big cities.

It is a problem which has assumed gigantic dimensions in some of the technically and industrially advanced countries of the world. India’s urban population (2006) of 450 million was one of the largest in the world.

The United Nations report projected that the global urban population rose dramatically from 13% (220 million) in 1900, 29% (273 million) in 1950 to 49% (3.3 billion) in 2008. It is likely to rise to 60% (4.9 billion) by 2030.

Major problems of urbanization are listed below:

1. The over-urbanization caused by the migration of persons from the country side to big industrialized cities in search of employment results in the growth of cities in haphazard manner.

2. Migration leads to much congestion and many social, economic and criminal problems. The most noticeable evil associated with over-urbanization is the marked deterioration in the environment of the city and appearance of slums.

3. Being devoid of hygienic and sanitary facilities, the persons living in slums breed all kinds of epidemics. They become the nerve centres of all the vices and crimes and earn their livelihood by dubious means-beggars, thief s, pickpockets, chronic drinkers, gamblers and drug pedlars.

4. In big cities of India, USA and Europe etc. many organised criminal gangs have come into existence.

5. Another serious problem is that of housing for ever-growing population in big cities. Due to paucity of houses to accommodate the people, the once beautiful cities are reduced to slums. This pressure of population has led to the construction of vertically rising sky-scrappers to accommodate the maximum number within the minimum space. But they have themselves given birth to many problems such as fire hazard, insanitary conditions, lack of civic amenities like parks, play grounds, congestion and traffic jams.

6. Urbanization consequent upon industrialization has denied to a large section of the people even elementary civic amenities like pure drinking water, underground drainage, electric supply, hospitals and well built schools or colleges. The absence of these amenities raises the incidence of personal and social pathology that is, crime, prostitution, alcoholism, drug addiction, mental illness etc.

7. Urbanization disturbs the equilibrium between demand and supply in the economic market resulting in larger demand and lesser supply. It is difficult to get pure food, milk and other commodities. Everything is either impure, adulterated or spurious.

8. Urbanization, sociologically has led to the breaking of joint families and the establishment of nucleus families. People in the cities forfeit the ancient ideals of corporate living. They tend to become self-seeking and self-centered without having any social contacts.

9. Lastly, the defence of the country is very much handicapped if the metropolitan cities are subjected to aerial bombardment in the event of a war. Cities which are highly urbanized and densely populated are more vulnerable than those in which the population is diffused and decentralized.

Merits:

Of course, there are certain merits of city life also. Most of the achievements of the modern world like the scientific and technological inventions and discoveries, all are centred in the cities.

How to tackle the problem of urbanization?

1. The most effective way to tackle the problem of urbanization is to make the economy of the villages fully viable. It can be revitalized if the government undertakes a massive rural development programme.

2. Surplus rural man power should be absorbed in the villages themselves. In this way the village economy will become self-sufficient and autonomous. The old cities should be made cleaner and fit places for poor man’s habitation by demolishing slums and jhuggis and also by constructing spacious houses for the poor at subsidized rates.

3. Expansion of buildings should be horizontal and well-spread over.

4. All the basic amenities should be provided and ensured to villagers.

5. The government should not allow any new industries to be set up in the already congested big industrialized cities.

6. Industries, government offices and head-quarters should be diffused and decentralized and shifted to smaller centres.

7. It is within the power of man to create a healthy environment for the human beings. What is needed is a readjustment of social and moral values.

Environmental Problems # 2. Automobile Pollution:

The single most important factor responsible for the deterioration of air quality is the exponential increase in petrol and diesel fueled vehicles.

Principal types of automobiles are:

(i) Two and three wheelers powered by two stroke petrol engines,

(ii) Cars powered by four stroke petrol engines,

(iii) Buses and trucks powered by four stroke diesel engines.

Sources of Automobile Emissions:

1. Exhaust emissions:

These are NO_X, CO, CO₂, particulates containing un-burnt hydrocarbons and lead compounds.

2. Crank case emissions and combustion process contain mostly hydrocarbons.

3. Evaporative emissions are CO and hydrocarbons. Diesel engines emit NO_X, smoke and particulates.

Other factors contributing to automobile pollution are:

i. Age of the vehicle.

ii. Exhaust pipe of the vehicle.

iii. Fuel composition.

iv. Fuel tank breather, carburetor and spillage losses.

v. Outdated automotive technology.

vi. Congested traffic and poor road conditions.

vii. Height of the emission, meteorology and topography etc.

Effects of Automobile Pollutants:

The assessment of health risks due to toxicity of vehicular emissions is very complex.

However, based on information available, the potential health effects of automobile pollutants are summarised as follows:

Effects of NO_X:

There is normally a cycle of formation and decomposition of oxides of nitrogen in atmosphere which is related to sunlight and traffic density. NO₂ acts as a precursor of peroxy acetyl nitrate (PAN) and ozone which are extremely lethal to living organisms.

NO₂ is a highly toxic gas. NO₂ is easily absorbed by the blood stream causing emphysema, bronchitis, bronchopneumonia and lung cancer. Vehicular exhaust consisting of about 10 ppm of NO₂ retards the photosynthetic rate in plants.

Effects of CO:

If the fuel mixture in vehicles contains too much fuel but little oxygen, then considerable amount of CO is formed. CO is an asphyxiate gas and is extremely fatal to vital organs. It adversely affects human health, plants, buildings and materials.

Effects of SO₂:

Vehicular exhaust consisting of higher level of SO₂ induces desquamation, peeling of surface epithelium in the wind pipe, irritation, cough, dyspnoea, asthma, lung cancer and respiratory diseases etc. in man.

Effects of Hydrocarbons:

In India, automobiles constitute the chief source of hydrocarbons. These are emitted from vehicles either as a result of evaporation or incomplete combustion. Aromatic hydrocarbons like benzene, toluene, benzpyrene, PAHs especially the olefins can react with NO_X, CO, PAN, PBN, PPN, H₂O₂, aldehydes and ketones to produce photochemical smog and ozone. Polycyclic hydrocarbons (PAHs) often adsorbed onto particulate matter are risky portion of vehicular emissions.

A new PAH, called 3-nitro- benzathrone, found in diesel exhaust, is the severe carcinogen till date. The researchers in Japan used the Ames test to measure the number of mutations this compound caused in DNA of standard bacterial stains. 1, 8-Dinitropyrene has been found to be the second most carcinogenic compound which is observed in diesel exhaust.

Control of Automobile Pollution:

Technologies adopted are:

(i) Modifications in internal combustion engines to control CO emission formed during fuel-combustion.

(ii) Developing exhaust system reactors for complete combustion.

(iii) Updating engine design.

(iv) Using new proportion of gasoline and air.

(v) Using gas additives to improve combustion.

(vi) Developing non-polluting power sources.

(vii) Using internal combustion engines of high efficiencies but they require high compression ratios which lead to engine knocking. Engine knocking can be reduced by two ways.

a. Increase the octane number of gasoline by adding methyl tertiary butyl ether (MTBE). Methanol, ethanol or MTBE are oxygen suppliers which can reduce emission of CO during fuel combustion.

b. Engine knocking can be reduced by adding tetraethyl lead (TEL) to gasoline. The free radicals formed in the engine due to high temperature cause preignition or knocking. TEL is a good scavenger of these radicals. It reacts with free radicals before their formation.

Gasoline containing TEL is the major contributor of lead pollution in air.

(viii) Using catalytic converters in two stages. Typical reactions in a dual catalyst exhaust system are shown in fig. 3.

(ix) Current technology involves the use of three way catalyst, which is capable of reducing levels of non-methane hydrocarbons, CO and NO. Catalyst rhodium facilitates the reduction of NO_X to N₂.

In order to oxidise the residual CO, NH₃ and hydrocarbons, air is passed over a second catalyst either Pd or Pt or non-stoichiometric oxides such as Fe₂O₃ or CoO.

However, there are technical problems, i.e., to reduce emission during the warm up period of vehicle operation. Now super additive AK 33X (methyl cyclopentadienyl manganese- tricarbonyl) twice as efficient as TEL can be used but it is highly expensive and photosensitive.

Environmental Problems # 3. Climate Changes and Global Warming:

Climate Changes:

Climate means the average pattern in which weather varies in time. The climate of a region depends on the presence or absence of water, the reflection of solar radiation or albedo, the ability to transfer water to the atmosphere (evaporation), the capacity to store heat, topography and texture of the region. Metropolitan areas emit the bulk of air pollutants that influence temperature, visibility and precipitation as well as other climatic elements.

Human beings exert a dramatic influence on local climates. The air-borne pollutants not only cause a more intense heat island but also alter the vertical temperature structure in a way that hinders their own dispersion. The excess CO₂, CH₄ and chlorofluoro carbons remain trapped in the earth’s atmosphere causing green-house effect and global warming.

Conversely, an increase in particulate matter in the atmosphere, such as smoke and ash reflect back the incoming solar radiation before it reaches the earth’s surface. This could result in a drop in the temperature of earth, eventually leading to glacial period or ice-age for our planet.

Weather:

Weather and climate are not the same thing. Weather refers to the conditions of temperature, cloudiness, windiness, humidity and precipitation that prevail at a given moment. The weather is variable.

Environmental Problems # 4. Green House Effect/Global Warming:

The term Green-house effect, first coined by J. Fourier in 1827, is also called global warming, atmospheric effect or CO₂ problem. Green house means a building made of glass, with heat and humidity regulated by plants. Atmosphere, like glass absorbs some of the long wave radiations emitted by earth and radiates the energy back to the earth.

A green house is that body which allows the short wavelength incoming solar radiation to come in, but does not allow the long wavelength outgoing terrestrial infrared radiation to escape.

In a similar way, the earth’s atmosphere bottles up the energy of the sun and acts like a green house where CO₂ acts as glass windows. Carbon dioxide and water vapour in the atmosphere transmit short wavelength solar radiation but reflect the longer wavelength heat radiation. So they trap and re-enforce the solar heat stimulating a heating effect. The net result is that earth’s surface gets heated and the phenomenon is known as green-house effect (Fig. 4).

It may be defined as follows:

a. Green-house effect is progressive warming up of the earth’s surface due to blanketing effect of man-made CO₂ in the atmosphere.

b. Green-house effect means the excessive presence of those gases blocked in the IR radiation from the earth’s surface to the atmosphere leading to an increase in temperature, which in turn would make life difficult on earth.

Green House Gases:

The major green-house gases are CO₂, CH₄, N₂O, CFCs. Ozone and SO₂ also enhance global warming. CH₄ and CFCs contribute about 19% and 17% to green-house effect. By 2010-2100 we would have 380 to 495 ppm of CO₂ in the air which is certainly a highly dangerous concentration. Recently scientists in US and Europe have observed that the gas trifluoromethyl sulphur pentafluoride SF₅CF₃ is present at the height of 8 to 32 kms above the earth surface and is 18000 to 22000 times more powerful in trapping atmospheric CO₂.

Relative Contribution of Green House Gases:

The relative contributions of radioactively active gas to temperature is:

Recent report (2012) indicates that the global green-house gases emission is 47 billion tonne per year which is required to decrease to 20 billion tonnes per year by 2050.

Global Warming Potential (GWP):

The potential of a green-house gas to cause global warming is expressed by GWP originally defined by United Nations Intergovernmental Panel on climate change, which is a function of both the infrared sorption characteristics and the life time of the gas.

CFC is 38 million times stronger, N₂O 3800 times and CH₄ 21 times stronger than CO₂ in terms of GWP

Current Status Report:

Currently, a landmark Conference in Denmark- Copenhagen Climate Summit was held from December 7 to December 18, 2009 with delegates from 192 countries to tackle climate change and global warming catastrophic effects. The CO₂ emissions (million tonnes) by different countries in 2006 were: China 6103, US 5975, Europe 3914, India 1510, Japan 1274, Brazil 352 and Indonesia 333.

The stated aim to reduce carbon emission upto 2020 is : China 40-45%, US 30%, Europe 30%, India 20-25%, Japan 20%, Brazil 38%, Indonesia 26%.

Effects of Climatic Changes and Global Warming:

The climate system consists of the atmosphere, the hydrosphere, the cryosphere, the lithosphere and the biosphere. Disturbance in any one system will affect the others and result in adverse events.

1. Extreme Weather Events:

a. Natural factors such as solar radiation changes and volcanic activity have contributed to hot years, viz., 1990, 1994, 1998, 2002, 2009. But green-house gases are blamed as the dominant force in recent climate change.

b. In 1994, the northern hemisphere experienced the coldest winter in 50 years in Europe and USA. Most of Europe was affected by heavy snow fall, blizzards and floods. In Asia, the worst blizzards in 25 years smashed Japan and Korea while Thailand reeled under the coldest winter in 50 years due to penetration of cold Arctic winds far to the south.

Such intensely cold winter was followed by one of the worst summers. For London it was the driest summer in 300 years and for Germany it was the hottest summer ever. Japan had record-breaking day temperatures and drought was so severe that it had to close down 2000 factories.

c. There was a super-clone in 1999 in Orissa where winds blew with more than 221 kmph velocity. A warmer world in some regions and drier in other will cause dislocations that are beyond control of any modern society.

d. The highest air temperature increases is expected to occur in the northern hemisphere at high latitudes as a result of a substantial reduction in the amount of sea ice and snow cover on the land because of the warming. Normal sea ice acts as a thermal blanket between the water and the air. The lack of sea ice allows the heat stored in the ocean to warm air above it and increase the winter air temperature.

2. Rise in Sea Level:

a. Warming up of earth will make the ice at poles to be increasingly converted to water resulting in rise in world sea level.

b. Higher sea level will mean coastal loading, increased storm, erosion and disappearance of many small islands. According to IPCC, the mean sea level has risen by 12 cm during the past century, but has been rising more rapidly during the past 10 years.

c. Low lying area of Kolkata and Dhaka will be flooded. Major coastal cities such as New York, London, Leningrad, Amsterdam, Washington DC, Stockholm, Venice, Hamburg, Bangkok, Singapore and Jakarta may be flooded. Since India lies at low latitudes, change in seasons will be insignificant.

3. Effects on Human Health:

a. Increased rainfall in tropical and subtropical regions producing more stagnant water will be breeding areas of mosquito and thus causes malaria in man. An increase of flowing water, will provide a reproductive habitat for the black fly and the dread River Blindness disease known as onchocerciasis, may increase in tropical countries. The black fly is a purveyor of this parasite.

b. Rivers, streams and lakes will be affected in many ways by increasing levels of CO2. More flooding of tropical water sheds may lead to an increase of Schistosomias which is a chronic parasitic disease potentially fatal to human and other mammals. It is spread by snails that act as hosts for the larvae of the parasite. It leads to weight loss and liver disorders ensue.

4. Effects on Animals:

a. With a general warming of the earth, there will be a shift of animal populations toward higher latitudes. Abundant species may accommodate to the shifting climate and dominate whereas endangered species may become extinct being less able to accept additional stress or competition.

5. Effects on Agriculture:

a. Plants will respond favourably to increased CO₂ concentrations by increasing rates of photosynthesis. If CO₂ concentration doubles, photosynthetic rates in most cases will increase from 20 to 50%.

b. Cotton yields will increase with increase in temperature and CO₂. Wheat yield will decrease with increasing temperature but increasing levels of CO₂ may mitigate this and stabilise yields.

6. Increase in Global Temperature:

a. The increase in global mean temperature in the range 1 to 6°C would be the highest known in the past 10000 years.

7. Changes in Earth’s Albedo:

a. Changes in earth’s albedo may also be implicated in climate changes. Although large-scale cultivation, damming of rivers to form lakes and cutting down of forests all result in minor change in the earth’s albedo.

Measures to Check Global Warming:

To slow down the enhanced global warming, following measures may be adopted:

a. Reduce consumption of fossil fuel and the use of CFCs.

b. Use renewable energy sources.

c. Trap and use methane as a fuel.

d. Adopt sustainable agriculture and plant more trees.

Environmental Problems # 5. Acid Rain:

The term acid rain was first used by Robert Angus Smith in 1872. Literally it means the presence of excessive acids in rain water. Acid rain is, infact, cocktail of mainly H₂SO₄ (60-70%), HNO₃ (30-40%) and HCl where the ratio of these acids may vary depending upon the sulphur, nitrogen and chlorine emission.

Rain tends to be naturally acidic with a pH of 5.6 due to the reaction of CO₂ with water to produce carbonic acid. This small amount of acidity is, however, sufficient to dissolve minerals in earth crust and make them available to plant and animal life.

Other atmospheric substances from volcanic eruptions, forest fires and other natural phenomena also contribute to natural sources of acidity in rain. But it is the contributions of SO_X, NO_X etc. from anthropogenic activities that disturb this acid balance and convert natural acidic rain into precipitation and far reaching environmental consequences.

On April 10, 1984, when a rain storm hit Pitlochry in Scotland, it beat the world record not for heavy volume but for acidity. The rain was more acidic than vinegar. However, several questions arise. Which acids are present? What are their precursors? How are they formed? Does oxidation occur in the gas phase, in aerosol, fog, cloud, rain droplets or on the surface of solids?

Composition of Rain:

Analysis of acid rain sample showed the following species: H⁺, NH⁺_–, Ca²⁺, Na⁺, Mg²⁺, K⁺, NO^–₃, SO^2-₄, CI^–. Various sulphur species released into the atmosphere and rain include SO₂, H₂S, COS, CH₃SH and CS₂.

Formation of Acid Rain:

1. Oxidation of NO₂ to HNO₃ forming Acid Rain:

Much of the NO_X entering the atmosphere is converted into nitric acid. In day time, nitric oxide is oxidised by O₂, O₃ and ROO.

NO₂ so formed, contributes to O₃ and OH radical formation and is partially responsible for the initiation of a photochemical smog sequence. In this process nitric oxide is regenerated and is again available for O₃ and smog formation.

The removal of NO₂ from the atmosphere is by conversion to nitric acid.

After sunset, the mechanism becomes different. The nitrate radical, NO₃ is formed both during day and night time. But it accumulates only at night. In day time it is destroyed by photolysis.

A small amount of NO₂ may also be converted into PAN.

2. Oxidation of SO₂ in Troposphere forming Acid Rain:

SO₂ is oxidised to SO₃ by air which reacts with moisture to give H₂SO₄. Sulphates or H₂SO₄ occur as aerosols.

Adverse Effects of Acid Rain:

Acid rain represents one of the major consequences of air pollution because of large SO_X and NO_X emissions from industrial areas into the atmosphere. The longer the SO_X and NO_X remain in air, the greater the chances of their oxidation to H₂SO₄ and HNO₃ by various photochemical and catalytic chemical reactions.

Acid rains may cause extensive damage to materials and terrestrial ecosystems such as water, fish, vegetation, soil, buildings and aquatic biota. Sulphuric acid is the major contributor to acid precipitation, HNO₃ ranks second and HCI third.

Effects of Acid Rain on Human Health:

Acid rain has been found to be very harmful to the living organisms as it can destroy life. Acidification can play havoc with human nervous system, respiratory system and digestive system by making the person an easy prey to neurological diseases.

1. Acid contaminates potable water and enters man’s body. The heavy metals released by acid rain may cause potential threat to human health.

2. Acidification of drinking water reservoirs and consequent increase in heavy metal concentrations may cause injurious effects.

3. The extent of damage due to acid rain depends upon factors such as climate, topography, geology, biota and human activity.

Effects of Acid Rain on Aquatic Biota:

Acid rain declines productivity of fish, plankton and amphibians, .causes skeletal deformities and increased fish mortality. There are 15,000 fishless lakes in Sweden and 100 such lakes in the Adirondack region of USA because of increased acidity of lakes. About 237 lakes in Adirondack have a pH below 5.

1. Many bacteria and blue green algae are killed due to acidification, disrupting the whole ecological balance. Acidic water can also leach aluminium from the soil. This run-off carry dissolved aluminium to lakes, rivers and streams. It causes death of fish by clogging its gills and deprives it of oxygen.

2. Acidification of a lake or stream results in disruption of the food web. Nutrient cycles are disrupted and as a result soil bacteria and fungi die.

3. Fresh water lakes are fairly alkaline with Ca²⁺, Mg²⁺ and HCO^–₃ as the dominant ions. Phytoplankton and zooplankton are affected by acidity of water.

4. In winter, acid rain accumulates as acid snow. When it melts it gives a jolt of acid water to lakes. This acid jolt is most damaging to young fish, algae and insects.

5. Snails, clams, oysters etc. having their shells of calcium carbonate are among the first animals to perish in acidic lakes.

6. Black flies, mosquitoes, deer flies, dragon fly and other worms grow abundantly and flourish in acidic lakes.

Effects of Acid Rain on Terrestrial Ecosystem:

Acid precipitation causes damage to crops, forests and soil. Potential impact of acid deposition on plant include : Damage to leaf cuticle, interference with normal stomata opening and closing, germination, flowering, photosynthesis, interference with nitrogen fixation by inhibiting microbial or fungal activities, possible synergistic interactions with other environmental stress factors.

1. Demineralisation of soil occurs. Cations like Ca²⁺, Mg²⁺, Na⁺, K⁺ are leached away and replaced by other cations such as Al³⁺ ions.

2. The capacity of nitrifying bacteria to fix nitrogen diminish rapidly below pH 6.

3. Acidification of soil adversely affects soil fauna and leads to reduced forest productivity.

4. Acid rain has retarded the growth of vegetables such as pea, beans, raddish, spinach, broccoli and carrots etc.

5. Acid deposition weakens the trees like pine, spruce, birch which can be attacked by pathogens and droughts. Soils in these regions have little buffering capacity and are subjected to leaching of minerals.

Injury to Vegetation:

Sulphur dioxide injures the vegetation by initial disruption of cellular integrity which usually appears in the spongy parenchymal cells affecting palisade layer.

1. Continuous chronic exposure to low levels of acidic water causes diffuse chlorosis in the leaves of plants.

2. Acidic water containing SO₂ affects the functional cells near the stomata. Apparently the cells have capacity to detoxify SO₂ or SO^2-₃ by conversion to SO^2-₄ . If the concentration of SO₂ is in large excess, the sulphite ions build up, the water relation of the cell are disrupted and plasmolysis occurs.

Effects of Acid Rain on Buildings:

Acid rain causes extensive damage to buildings and structural materials of marble, limestone, slate and mortar etc. The attack of acid on marble is termed as stone leprosy.

CaCO₃ +H₂SO₄ → CaSO₄ +H₂O + CO₂

1. Acid rain corrodes houses, monuments, statues, bridges, fences and railings that cost the world 1450 million dollar a year. British Parliament building also suffered enough damage due to acid rain. Much of the falling snow in Britain is highly acidic. If it does not melt it may turn into a pollution time bomb.

2. Valuable ancient sculptures, carved from marble, limestone, sand stone etc. deteriorate by acid components because of pitting and mechanical weakening.

3. Architectural monuments like Taj Mahal in Agra, India may be destroyed due to slow corrosion by acid deposition and air pollutants released from Mathura refinery. At St. Paul Cathedral, the stone work is being corroded at the rate of an inch per 100 years. Throughout Europe and Greece many famous buildings, monuments and art treasures have deteriorated at an alarming rate because of erosional effects of acid deposition.

4. Ornamental stone work on a church in Bristol was corroded by acid rain.

5. H₂S tarnishes silver and blackens leaded house paints. Traces of radio-elements in rain severely damage the buildings.

6. Acid precipitation causes damage to steel, oil-based paints and automobile coatings. It disintegrates textiles and papers etc.

The situation in India is likely to worsen further in the near future with increased dependence on thermal power plants. Today, the need of the hour is to take some critical decision to control the emission of gases which can form acid rain.

Control of Acid Rain:

The phenomenon of acid rain is a highly interactive problem and remedial measures to control it are very expensive. The only practical approach to counter the problem of acid rain is to reduce SO_X and NO_X emission from thermal power stations.

The following general options may be considered for this purpose:

1. Desulphurisation and denitrification of fuels of stack gases and increased use of fuels naturally low in sulphur content or to use new technologies that reduce the SO_X and NO_X emissions.

2. Reduction of SO_X emissions can be accomplished by removing the sulphur content before the fuel is burnt with the help of techniques such as coal cleaning, coal gasification and desulphurisation of liquid fuels.

3. Reducing the sulphur content during combustion, as in fluidized bed combustion.

4. Removal of sulphur emission after combustion, as in stack or flue gas desulphurisation systems or scrubbers.

5. Removal of NO_X emission from stationary combustion sources can be achieved by modification of furnace and burner design and operating conditions. NO_X emissions from mobile combustion sources may be achieved by lowering the combustion temperatures in the engine and catalytic removal of NO_X from exhaust gases using devices like a 3-way system that reduces carbon monoxide, hydrocarbons and NO_X simultaneously.

Environmental Problems # 6. Ozone Layer Depletion:

Creation of Ozone Layer:

Ozone is a photochemical product of oxygen which is formed by solar radiation of short wavelength. While 0₂ plays an important role in troposphere, O₃ plays a key role in stratosphere. This upper layer of the atmosphere enveloped by ozone (15 to 30 kms) is known as ozonosphere, ozone layer, protective stratospheric layer or ozone umbrella.

Ozone concentration differs by about 10 ppm in stratosphere compared to 0.05 ppm in troposphere. The existence of ozone belt around the earth is mainly responsible for filtering out some of the lethal ultraviolet radiation from reaching the earth, thereby acting as a protective shield for sustaining life of man, animals and plants.

In the absence of ozone layer, all the ultraviolet rays of the sun will reach the earth’s surface. Consequently the temperature of the lower atmosphere will rise to such an extent that the biological furnace of the biosphere will turn into a blast furnace.

Thus ozone layer strongly absorbs the short wave ionising UV rays and protects the life on earth from severe radiation damage. Ozone is more plentiful near the poles than at equator and more abundant in winter than in summer. The maximum concentration of ozone around an altitude of 25 km in the stratosphere is 5×10¹² molcm^-3.

Mechanism of Ozone Formation:

In the lower mesosphere, the atmospheric oxygen absorbs UV radiation at < 240 nm and photodissociates into two oxygen atoms. These O-atoms combine with O₂ of upper
stratosphere forming O₃. Ozone is also capable of absorbing short wavelength UV radiations releasing oxygen atoms.

Thus ozone is constantly created by solar radiation on earth’s atmosphere and eliminated by reaction with atomic oxygen, reactive hydroxyl radicals and nitric oxide (later is produced in the stratosphere).

Mechanisms of Ozone Depletion:

Ozone layer is destroyed by man-made processes in varying degrees by free radicals such as HO _X, NO _X and C10_X.

1. Ozone depletion by hydroxyl radicals:

Hydroxyl radicals are formed by following photochemical reactions.

These hydroxyl radicals decompose ozone.

2. Ozone depletion by NO_X:

NO₂ undergoes photochemical dissociation to NO in the mid and upper stratosphere.

NO so formed may be oxidised by O₃ leading to cyclic chain reaction and net ozone destruction.

In the stratosphere, nitrous oxide, N₂O also undergoes photochemical decomposition to NO, which in turn depletes ozone layer.

The chain may be broken only when N0₂ is completely converted into HNO3 by hydration. The supersonic air craft’s discharge large quantities of NO_X in their exhaust gases into the stratosphere which reduces ozone level by about 40%.

3. Ozone depletion by chlorine radical, CIO_X:

Ozone in the stratosphere is also destroyed by man-made chlorofluoro carbons (CFCs) and halons. These are used in air conditioners and refrigerators. They slowly pass from troposphere to stratosphere and once there, they stay for 100 years. In presence of intense ultraviolet radiation, CFCs are subjected to photochemical dissociation into CI which readily consumes O₃.

The free radical, Cl is regenerated which sustains chain reaction. It is estimated that one Cl atom can destroy one lakh ozone molecules.

Bromine from halons, can replace Cl in the cycle and destroy ozone level.

Environmental Problems # 7. Ozone Hole (A Hole in the Sky):

In Antarctica, ozone hole was first detected within Antarctic polar vortex in October 1980 by Chubachi Shigeru of Meteorological Research Institute, Japan. NASA and satellite measurements have indicated the ozone loss by 30%. CFC was the prime suspect for causing ozone depletion. Polar whirl winds also play a central role in ozone destruction.

According to some scientists, tiny ice particles in winter act as catalyst to enhance conversion of Cl to CIO, i.e., in ozone destroying form. Reactions which take place on the surface of ice particles within the stratospheric clouds release Cl₂ and Br₂ from CFCs and halons in the active form that accumulate through winter. When the sun rises in the spring, the clouds break up to release active Cl₂ and Br₂ which rapidly destroy ozone. The hole thus appears during Antarctica spring.

The thin periphery of the ozone layer around the puncture has reached New Zealand and Southern Australia. There, the UV radiation is so intense that the estimated burn time (usually 15 minutes) is broadcasted after the news bulletin. In the Arctic atmosphere, sulphate aerosol acts as a catalyst for the removal of NO_X from the polar stratosphere. Hence one of the ozone corroding species (NO_X) is eliminated which is associated with holding cycles that tie up CIO radicals.

Current Status Report:

Currently, a study by NASA scientists revealed that the amount of ozone over thickly populated northern hemisphere decreased by 3% between 1969 and 1986. In June, 1992 Japanese scientists announced that ozone hole was 13 times wider in 1991 than it had been in 1981. In 2000, the hole in the ozone layer was three times larger than earlier. An ozone hole layer larger than 11 million square km has been detected.

In 2001, the Antarctic ozone hole reached a maximum size of 26.6 million square km-larger than the entire area of North America including US, Canada and Mexico. In September 2002, the ozone hole was much smaller that is, 15.6 million sq. km. and it has split into two parts. The hole’s total column ozone was measured below 220 dobson units.

To protect the ozone umbrella, the developed countries at London Conference agreed to 100% ban of CFCs by 2003 instead of 50% as per Montreal protocol.

Effects of Ozone Layer Depletion:

It has been universally accepted that the ozone layer in the stratosphere protects us from the harmful UV radiations coming from sun. The change in stratospheric structure could influence the world climate whereas increased UV radiations at the surface would affect biological systems. Ozone accounts for only three parts in ten millions of earth’s atmosphere, but plays crucial roles in the radiation balance of the planet.

Effects on Human Health:

1. People living in the equatorial latitudes are exposed to more UV-B radiation than those living in temperate on polar regions.

2. UV-radiations trigger immunological effects. The irradiated skin develops red patches.

3. The three forms of skin cancer-basal cell carcinoma, squamous cell carcinoma and malignant melanoma are caused by prolonged cumulative exposure to UV-B rays.

4. UV radiations cause blood vessels near the skin surface to carry more blood causing sun burns and skin aging.

5. UV radiations are also absorbed by cornea and lens in the eye leading to photo keratitis and cataracts. Since the radiation is not sensed by the visual receptors of the eye, the damage is caused without the individual knowing about it.

6. The capacity of lung phagocytes which normally fight bacterial infections is also affected resulting in increasing incidence of respiratory infections.

7. Emphysema, a destructive lung disease, bronchitis and development of asthma might be the ultimate results of ambient ozone exposure.

8. 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.

9. 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.

10. Photochemical smog is the major cause of ozone exposure causing urban air pollution posing a threat to human health.

11. Any increased concentration of ozone brings about changes in the nucleic acids, DNA and RNA. So increased UV absorption will have drastic results.

12. 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.

Effects on Biotic Community:

1. The marked reduction in the productivity of phytoplanktons adversely affect zooplanktons. The marine animals, fishes etc. will starve in the absence of sufficient supply of food.

2. Ozone is reported to be highly toxic to fish in the concentrations ranging from 0.1 to 1.0 ppm.

Effects on Plants:

1. Plants are sensitive to UV rays below 300 nm.

2. Exposure to air containing ozone results in the lesions to plants, usually confined to the upper surfaces of leaves. These lesions are characterised by the uniformly distributed white or brown flecks and stipples in irregularly distributed blotches.

3. 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.

4. Plant proteins are also susceptible to UV injury, because they absorb strongly around 280 nm. About 20-50% chlorophyll reduction and harmful mutation have also been observed.

5. Ozone along with, other pollutants like SO₂ and NO_X is affecting crop losses of over 50% in European countries. In Denmark, O3 affects spinach, potato, clover and alfalfa etc.

Climatic Effects of Ozone Depletion:

Ozone reduction in troposphere may drastically change the weather elements like temperature, wind pattern, acid rains and precipitations etc. By absorbing UV radiation the ozone layer warms the atmosphere. The absorbed heat of surrounding stratosphere causes a temperature inversion between 15 to 50 km.

This defines the stratosphere as having a temperature gradient while tropospheric temperature increases steadily. The trapped radiation causes rapid rise in global temperature by letting ozone eaters such as NO_X, SO_X and CFCs etc.