Environmental studies deal with the sum of all social, economical, biological, physical and chemical interrelations with our surroundings.
Environmental chemistry deals with the study of the origin, transport, reactions, effects and fates of chemical species in the environment.
Some important aspects of environmental chemistry.
ENVIRONMENTAL POLLUTION
Environmental pollution is defined as “the contamination of the physical and biological components of the earth and its atmosphere to such an extent that normal environmental processes are adversely affected.
[Now a days even addition of Energy, such as heat, sound or radioactivity to the environment at a rate faster than it can be dispersed, diluted, decomposed, recycled, or stored in some harmless form is also included in the definition of Environmental pollution.]
POLLUTANTS
Pollutant is a substance, which causes pollution.
Pollutants exists in all the three forms – solids, liquids and gases.
They are always present around us. Only when their concentration increases above a level to which our Mother Nature is not able to clean in time then they are recognised as pollutants.
They may be produced due to human activities or due to natural happenings. We know that an average human being requires nearly 12-15 times more air than the food. So, even small amounts of pollutants in the air become significant compared to similar levels present in the food. Hence let us strive to take fresh air.
जानते हैं यह कहाँ मिलेगी? आप ही के पास। आप ही के छत पर। आपके बाग में। आपके पड़ोस में। केवल सूर्योदय के दो घण्टे पहले उठ कर निकाल जाइए जहां आप इसे पा सकें और सुरक्षित भी रह सकें। उस समय अपने उम्र व शक्ति के अनुसार दौड़िए/ कूदिए/ टहलिए/ तैरिये। यह सब तब तक करिए जब तक की आप हाँफ न जाएँ – जब तक कि गहरी साँस लेना आपकी मजबूरी न बन जाए। जब हम शुद्ध वायु में गहरी गहरी सांसें लेते हैं तब हमारे शरीर के Toxins बाहर निकल जाते हैं। Sedentary Life Style से बना Lactic Acid या तो CO2 & H2O बन कर काफ़ूर हो जाता है और जिन जगहों से वे सांस या पेशाब के रास्ते नहीं निकाल पाता है वहाँ वह glucose तत्पश्चात glyocogen में कन्वर्ट हो कर शरीर के लिए लाभदायक बन जाता है। यह Stored Energy के रूप में मांसपेशियों में जुट जाता है। यही कारण है कि परिश्रम करने से दिमाग खुल जाता है। शरीर भले ही थके – मस्तिष्क तेज हो जाता है। हमारे मनीषियों ने ब्रह्म मूहूर्त की परिकल्पना हमारे इसी कल्याण के लिए की थी।
Types of Pollutants:
Degradable, like discarded vegetables which rapidly break down by natural processes. &
Non Degradable or slowly degradable, which remain in the environment in an unchanged form for many decades. For example, substances such as DDT, plastic materials, heavy metals, many chemicals, nuclear wastes etc.
Pollutants once released into the environment are difficult to remove. They get transported by air or water or are dumped into the soil by human beings themselves.
Types of Pollution:
Air Pollution
Water Pollution
Land Pollution
Noise Pollution
Light Pollution
Plastic Pollution
Nuclear Pollution
In this Unit we will cover only the major three of them, viz.
Air Pollution or Atmospheric Pollution
As mentioned earlier that the pollution of air is the major concern as the same sees no boundaries and effects the entire globe and that too drastically so we will deal it in detail with the following subheads & further divisions as given below:
Tropospheric Pollution
Gaseous Pollutants
Oxides of Sulphur
Oxides of Nitrogen
Hydrocarbons
Oxides of Carbon
Effects of the same
v.1 Global Warming
v.2 Greenhouse Effect
v.3 Acid Rain
Particulate Pollutants – Viable or Non – Viable. Non Viables may be-
Smoke Particulates
Dust
Mists
Fumes
Smog
v.1 Classical Smog
v.2 Photochemical Smog
Stratospheric Pollution
Ozone Hole
In next part we will deal with the following:
Water Pollution – the pollutants may be:
Pathogens
Organic wastes – This topic will introduce us to a term called BOD
Chemicals – This topic will introduce us to a term called Eutrophication
Land Pollution or Soil Pollution
The lesson will end up with
Industrial wastes and its management
Water Recycling
Waste Management
Green Chemistry – Its introduction in day to day life.
International Standards for Drinking Water
The Topic Begins
Atmosphere
Earth’s atmosphere is divided into several concentric layers. Each of them has different density of air.
The lowest is Troposphere. It is upto 10 km above sea level.
Above it is Stratosphere. This extends upto 50 km above sea level after troposphere.
Troposphere is a turbulent, dusty zone containing air, much water vapour and clouds. This is the region of strong air movement and cloud formation.
The stratosphere, on the other hand, contains dinitrogen, dioxygen, ozone and little water vapour.
Atmospheric pollution is generally studied as tropospheric and stratospheric pollution.
The presence of ozone in the stratosphere prevents about 99.5 per cent of the sun’s harmful ultraviolet (UV) radiations from reaching the earth’s surface and thereby protecting humans and other animals from its effect.
1.1 Tropospheric Pollution
Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air. The following are the major gaseous and particulate pollutants present in the troposphere.
Gaseous pollutants: These are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.
Particulate pollutants: These are dust, mist, fumes, smoke, smog etc.
1. Gaseous pollutants
Oxides of Sulphur: Oxides of sulphur are produced when sulphur containing fossil fuel is burnt. [Fossil fuel as you know, is a general term used for buried combustible geologic deposits of organic materials, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the earth’s crust over hundreds of millions of years].
Harmful Effects:
The most common oxide of sulphur, sulphur dioxide, is a gas that is poisonous to both animals and plants.
Even a low concentration of sulphur dioxide causes respiratory diseases e.g., asthma, bronchitis, emphysema in human beings. Sulphur dioxide causes irritation to the eyes, resulting in tears and redness.
High concentration of SO2 leads to stiffness of flower buds which eventually fall off from plants.
Uncatalysed oxidation of sulphur dioxide is slow. However, the presence of particulate matter in polluted air catalyses the oxidation of sulphur dioxide to sulphur trioxide.
2SO2 (g) +O2 (g) → 2SO3(g)
The reaction can also be promoted by ozone and hydrogen peroxide.
SO2 (g) +O3 (g) → SO3(g) + O2 (g)
SO2(g) + H2O2(l) → H2SO4(aq)
Oxides of Nitrogen:
Dinitrogen (N2) and dioxygen (O2) are the main constituents of air. These gases do not react with each other at a normal temperature. At high altitudes when lightning strikes, they combine to form oxides of nitrogen.
[Q. What happens? A. Heat & energy produced during lightning is so high that the stable triple bonded N2 gets dissociated and become highly reactive]
NO2 is oxidised to nitrate ion, NO3 − which is washed into soil, where it serves as a fertilizer. [This process is called Nitrogen Fixation. Nitrogen Fixation occurs Biological also and is called diazotrophy. It is an important microbially mediated process that converts dinitrogen (N2) gas to ammonia (NH3) using the nitrogenase protein complex (Nif).[2][3]
Nitrogen fixation is essential to life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen-containing organic compounds, such as amino acids and proteins, nucleoside triphosphates and nucleic acids. As part of the nitrogen cycle, it is essential for agriculture and the manufacture of fertilizer. It is also, indirectly, relevant to the manufacture of all nitrogen chemical compounds, which includes some explosives, pharmaceuticals, and dyes.
In an automobile engine, (at high temperature) when fossil fuel is burnt, dinitrogen and dioxygen combine to yield significant quantities of nitric oxide (NO) and nitrogen dioxide ( NO2 ) as given below:
N2 (g) + O2 (g) ⎯ 1483K → 2NO(g)
NO reacts instantly with oxygen to give NO2
2NO (g) + O2 (g) → 2NO2 (g)
The process of Nitrogen Fixation occurs even in the stratosphere (the upper layer of atmosphere). In fact the Rate of production of NO2 is faster when nitric oxide reacts with ozone, which is present there in abundance.
NO (g) + O3 (g) → NO2 (g) + O2 (g)
Harmful Effects:
The irritant red haze in the traffic and congested places is due to oxides of nitrogen. Higher concentrations of Nitrogen dioxide (NO2) damage the leaves of plants and retard the rate of photosynthesis.
Nitrogen dioxide is a lung irritant that can lead to an acute respiratory disease in children.
It is toxic to living tissues also.
Nitrogen dioxide is also harmful to various textile fibres and metals.
Hydrocarbons:
Hydrocarbons are composed of hydrogen and carbon only and are formed by incomplete combustion of fuel used in automobiles.
Harmful Effects:
Hydrocarbons are carcinogenic, i.e., they cause cancer.
They harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs.
Oxides of Carbon
There are two oxides of Carbon. Carbon monoxide, (CO) and dioxide, (CO2)
Carbon monoxide: It is one of the most serious air pollutants. It is a colourless and odourless gas.
It is produced as a result of incomplete combustion of carbon. Carbon monoxide is mainly released into the air by automobile exhaust.
Other sources, which produce CO, involve incomplete combustion of coal, firewood, petrol, etc.
The number of vehicles has been increasing over the years all over the world. Many vehicles are poorly maintained and several have inadequate pollution control equipments resulting in the release of greater amount of carbon monoxide and other polluting gases.
Harmful Effects:
It is highly poisonous to living beings because of its ability to block the delivery of oxygen to the organs and tissues. It binds to haemoglobin to form carboxyhaemoglobin, which is about 300 times more stable than the oxygen-haemoglobin complex. In blood, when the concentration of carboxyhaemoglobin reaches about 3–4 per cent, the oxygen carrying capacity of blood is greatly reduced. This oxygen deficiency, results into headache, weak eyesight, nervousness and cardiovascular disorder. This is the reason why people are advised not to smoke.
In pregnant women who have the habit of smoking the increased CO level in blood may induce premature birth, spontaneous abortions and deformed babies.
Carbon dioxide:
Carbon dioxide (CO2) is released into the atmosphere by respiration, burning of fossil fuels for energy, and by decomposition of limestone during the manufacture of cement. It is also emitted during volcanic eruptions. Carbon dioxide gas is confined to troposphere only (only the lower level of atmosphere).
Normally it forms about 0.03 per cent by volume of the atmosphere. With the increased use of fossil fuels, a large amount of carbon dioxide gets released into the atmosphere.
Excess of CO2 in the air is removed by green plants and this maintains an appropriate level of CO2 in the atmosphere. Green plants require CO2 for photosynthesis and they, in turn, emit oxygen, thus maintaining the delicate balance. Deforestation and burning of fossil fuel increases the CO2 level and disturb the balance in the atmosphere. The increased amount of CO2 in the air is mainly responsible for global warming.
Global Warming and Greenhouse Effect
[What is a Green House? A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plants requiring regulated climatic conditions are grown. A miniature greenhouse is known as a cold frame. The interior of a greenhouse exposed to sunlight becomes significantly warmer than the external temperature, protecting its contents in cold weather.]
So, at cold places flowers, vegetables and fruits are grown in glass covered areas called greenhouse.
How does a Green House work?
In a greenhouse, solar radiations pass through the transparent glass and heat up the soil and the plants. The warm soil and plants emit infrared radiations. Since glass is opaque to infrared radiations (thermal region), it partly reflects and partly absorbs these radiations. This mechanism keeps the energy of the sun trapped in the greenhouse.
Do you know that we humans also live in a greenhouse?
Of course, we are not surrounded by glass but a blanket of air called the atmosphere, which has kept the temperature on earth constant for centuries. But it is now undergoing change, though slowly. Just as the glass in a greenhouse holds the sun’s warmth inside, atmosphere traps the sun’s heat near the earth’s surface and keeps it warm. This is called natural greenhouse effect because it maintains the temperature and makes the earth perfect for life.
About 75 % of the solar energy reaching the earth is absorbed by the earth’s surface, which increases its temperature.
The rest of the heat radiates back to the atmosphere.
Some of the heat is trapped by gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapour in the atmosphere. Had they not been there the same would have left out to space and would not have had any effect. But with increase in the pollutants more and more heat is getting trapped.
Thus, they add to the increased heating of the atmosphere. This causes global warming.
Global warming
Global warming is the long-term warming of the planet’s overall temperature. Though this warming trend has been going on for a long time, its pace has significantly increased in the last hundred years due to the burning of fossil fuels. As the human population has increased, so has the volume of fossil fuels burned. Fossil fuels include coal, oil, and natural gas, and burning them causes what is known as the “greenhouse effect” in Earth’s atmosphere.
Harmful Effects:
If these trends continue, the average global temperature will increase to a level which may lead to melting of polar ice caps, expansion of warmer seas and flooding of low lying areas all over the earth.
Increase in the global temperature increases the incidence of infectious diseases like dengue, malaria, yellow fever, sleeping sickness etc.
[It is causing the climate to change. Climate change refers to changes in weather patterns and growing seasons around the world].
What can we do to reduce the rate of global warming?
If burning of fossil fuels, cutting down forests and trees add to greenhouse gases in the atmosphere, we must find ways to use these just efficiently and judiciously. One of the simple things which we can do to reduce global warming is to minimise the use of automobiles. Depending upon the situation, one can use bicycle, public transport system, or go for carpool. We should plant more trees to increase the green cover. Avoid burning of dry leaves, wood etc. It is illegal to smoke in public places and work places, because it is harmful not only for the one who is smoking but also for others, and therefore, we should avoid it. Many people do not understand the greenhouse effect and the global warming. We can help them by sharing the information that we have.
[What are the Green House Gases: A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth’s atmosphere are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Chlorofluorocarbons (CFCs) are man-made industrial chemicals which too are acting similarly. Without greenhouse gases, the average temperature of Earth’s surface would be about −18 °C (0 °F) rather than the present average of 15 °C (59 °F). The atmospheres of Venus, Mars and Titan also contain greenhouse gases.] Lets see the details of some of the GHG one by one.
Carbon dioxide molecules trap heat. They are transparent to sunlight hence allow it to come to the earth. But they are not transparent to the heat radiation emitted by earth. Hence they trap it. If the amount of carbon dioxide crosses the delicate proportion of 0.03 per cent, the natural greenhouse balance may get disturbed. Carbon dioxide is the major contributor to global warming.
Methane is produced naturally when vegetation is burnt, digested or rotted in the absence of oxygen. Large amounts of methane are released in paddy fields, coal mines, from rotting garbage dumps and by fossil fuels.
Chlorofluorocarbons (CFCs) are man-made industrial chemicals used in air conditioning etc. CFCs are also damaging the ozone layer
Nitrous oxide occurs naturally in the environment. In recent years, their quantities have increased significantly due to the use of chemical fertilizers and the burning of fossil fuels.
Acid rain
We are aware that normally rain water has a pH of 5.6 due to the presence of H+ ions formed by the reaction of rain water with carbon dioxide present in the atmosphere.
H2O (l) + CO2 (g) <-> H2CO3 (aq)
H2CO3 (aq) <-> H + (aq) + HCO3 – (aq)
When the pH of the rain water drops below 5.6, it is called acid rain. Acid rain refers to the ways in which acid from the atmosphere is deposited on the earth’s surface. Oxides of nitrogen and sulphur which are acidic in nature can be blown by wind along with solid particles in the atmosphere and finally settle down either on the ground as dry deposition or in water, fog and snow as wet deposition.
Acid rain is a byproduct of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere. As mentioned earlier, burning of fossil fuels (which contain sulphur and nitrogenous matter) such as coal and oil in power stations and furnaces or petrol and diesel in motor engines produce sulphur dioxide and nitrogen oxides. SO2 and NO2 after oxidation and reaction with water are major contributors to acid rain, because polluted air usually contains particulate matter that catalyse the oxidation.
2SO2 (g) + O2 (g) + 2H2O (l) → 2H2SO4 (aq)
4NO2 (g) + O2 (g)+ 2H2O (l) → 4HNO3 (aq)
Ammonium salts are also formed and can be seen as an atmospheric haze (aerosol of fine particles).
[An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas.]
Aerosol particles of oxides or ammonium salts in rain drops result in wet deposition. SO2 is also absorbed directly on both solid and liquid ground surfaces and is thus deposited as dry-deposition.
[Wet deposition is rain, sleet, snow, or fog that has become more acidic than normal. Dry deposition is another form of acid deposition, and this is when gases and dust particles become acidic. Both wet and dry deposition can be carried by the wind].
Harmful Effects:
Acid rain is harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth.
It causes respiratory ailments in human beings and animals.
When acid rain falls and flows as ground water to reach rivers, lakes etc. it affects plants and animal life in aquatic ecosystem.
It corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and copper into the drinking water.
Acid rain damages buildings and other structures made of stone or metal. The Taj Mahal in India has been affected by acid rain.
how we can help to reduce the formation of acid rain.?
This can be done by reducing the emission of sulphur dioxide and nitrogen dioxide in the atmosphere. We should use less vehicles driven by fossil fuels; use less sulphur content fossil fuels for power plants and industries. We should use natural gas which is a better fuel than coal or use coal with less sulphur content. Catalytic converters must be used in cars to reduce the effect of exhaust fumes on the atmosphere. The main component of the converter is a ceramic honeycomb coated with precious metals — Pd, Pt and Rh. The exhaust gases containing unburnt fuel, CO and NOx, when pass through the converter at 573 K, are converted into CO2 and N2.
We can also reduce the acidity of the soil by adding powdered limestone to neutralise the acidity of the soil.
Many people do not know of acid rain and its harmful effects. We can make them aware by passing on this information and save the Nature.
Taj Mahal and Acid Rain The air around the city of Agra, where the Taj Mahal is located, contains fairly high levels of sulphur and nitrogen oxides. It is mainly due to a large number of industries and power plants around the area. Use of poor quality of coal, kerosene and firewood as fuel for domestic purposes add up to this problem.
The resulting acid rain reacts with marble, CaCO3 of Taj Mahal
(CaCO3 +H2SO4 → CaSO4 + H2O+ CO2)
causing damage to this wonderful monument that has attracted people from around the world. As a result, the monument is being slowly disfigured and the marble is getting discoloured and lustreless. The Government of India announced an action plan in early 1995 to prevent the disfiguring of this historical monument. Mathura refinery has already taken suitable measures to check the emission of toxic gases.
This plan aims at clearing the air in the ‘Taj Trapezium’– an area that includes the towns of Agra, Firozabad, Mathura and Bharatpur. Under this plan more than 2000 polluting industries lying inside the trapezium would switch over to the use of natural gas or liquefied petroleum gas instead of coal or oil. A new natural gas pipeline would bring more than half a million cubic metres of natural gas a day to this area. People living in the city will also be encouraged to use liquefied petroleum gas in place of coal, kerosene or firewood. Vehicles plying on highways in the vicinity of Taj would be encouraged to use low sulphur content diesel.
Particulate Pollutants
Particulates pollutants are the minute solid particles or liquid droplets in air. These are present in vehicle emissions, smoke particles from fires, dust particles and ash from industries. Particulates in the atmosphere may be viable or non-viable. साधारण अर्थ में viable का अर्थ होता है व्यवहार्य या practicable एवं non viable का अक्षम या अलाभकारी। परंतु यहाँ इनका अर्थ क्रमशः जीवित एवं निर्जीव है।
The viable particulates e.g., bacteria, fungi, moulds, algae etc., are minute living organisms that are dispersed in the atmosphere.
Human beings are allergic to some of the fungi found in air.
They can also cause plant diseases.
Non-viable particulates may be classified according to their nature and size as follows:
Smoke particulates consist of solid or mixture of solid and liquid particles formed during combustion of organic matter. Examples are cigarette smoke, smoke from burning of fossil fuel, garbage and dry leaves, oil smoke etc.
Dust is composed of fine solid particles (over 1μm in diameter), produced during crushing, grinding and attribution of solid materials. Sand from sand blasting, saw dust from wood works, pulverized coal, cement and fly ash from factories, dust storms etc., are some typical examples of this type of particulate emission.
[1 mm = 1000 μm (micormeter). Micron is also the same thing. It is non – SI name of micrometer] [हमारे बालों की मोटाई अक्सर 50 से 90 μm होती है।]
Mists are produced by particles of spray liquids and by condensation of vapours in air. Examples are sulphuric acid mist and herbicides and insecticides that miss their targets and travel through air and form mists.
Fumes are generally obtained by the condensation of vapours during sublimation कपूर को धुआ होते देखे हैं न, या कीड़े भगाने के लिए Moth balls या naphthalene की गोलियाँ देखे हैं न – वे कैसे गायब हो जाते हैं।], distillation, boiling and several other chemical reactions. Generally, organic solvents, metals and metallic oxides form fume particles.
Harmful Effects:
The effect of particulate pollutants are largely dependent on the particle size. Airborne particles such as dust, fumes, mist etc., are dangerous for human health. Particulate pollutants bigger than 5 microns are likely to lodge in the nasal passage, whereas particles of about 10 micron enter into lungs easily. [हल्के वाले नाक के mucous में चिपक कर रह जाते हैं जबकि बड़े वाले अंदर सीधे फेफड़े तक चले जाते हैं।]
Lead used to be a major air pollutant emitted by vehicles. Leaded petrol used to be the primary source of air-borne lead emission in Indian cities. This problem has now been overcome by using unleaded petrol in most of the cities in India. [Branded high-performance fuels like SPEED and POWER are different thing. They are only normal petrol with some additives].
Lead interferes with the development and maturation of red blood cells.
Smog धुंध या कोहरा
The word smog is derived from smoke and fog. This is the most common example of air pollution that occurs in many cities throughout the world.
There are two types of smog:
(a) Classical smog occurs in cool humid climate. It is a mixture of smoke, fog and sulphur dioxide. Chemically it is a reducing mixture and so it is also called as reducing smog.
(b) Photochemical smog occurs in warm, dry and sunny climate.
It is visible as a brown haze, and is most prominent during the morning and afternoon, especially in densely populated, warm cities.
The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. Photochemical smog has high concentration of oxidising agents and is, therefore, called as oxidising smog.
Formation of photochemical smog
When fossil fuels are burnt, a variety of pollutants are emitted into the earth’s troposphere. Two of the pollutants that are emitted are hydrocarbons (unburnt fuels) and nitric oxide (NO). When these pollutants build up to sufficiently high levels, a chain reaction occurs from their interaction with sunlight in which NO is converted into nitrogen dioxide (NO2). This NO2 in turn absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom. Free Oxygen atoms are very reactive and combine with the O2 in air to produce ozone.
The ozone formed now reacts rapidly with the NO(g) emitted even if found in traces (requirements of high levels mentioned above is no more required after production of ozone) to regenerate NO2. So this cycle starts and is self sustained.
NO2 is a brown gas and at sufficiently high levels can contribute to haze.
Ozone is a toxic gas.
Both NO2 and O3 are strong oxidising agents and can react with the unburnt hydrocarbons in the polluted air to produce chemicals such as formaldehyde, acrolein and peroxyacetyl nitrate (PAN).
Harmful Effects of Photochemical Smogs:
It causes serious health problems.
Both ozone and PAN act as powerful eye irritants.
Ozone and nitric oxide irritate the nose and throat.
High concentration of ozone and nitric oxide causes headache, chest pain, dryness of the throat, cough and difficulty in breathing.
It leads to cracking of rubber and extensive damage to plant life.
It causes corrosion of metals, stones, building materials, rubber and painted surfaces. Fig.
How can photochemical smog be controlled?
Many techniques are used to control or reduce the formation of photochemical smog. If we control the primary precursors of photochemical smog, such as NO2 and hydrocarbons, the secondary precursors such as ozone and PAN will automatically be reduced.
Usually, catalytic converters are used in the automobiles, which prevent the release of nitrogen oxide and hydrocarbons to the atmosphere. [आपको प्रदूषण के छमाही जांच के विषय में तो पता ही होगा]
Certain plants e.g., Pinus, Juniparus, Quercus, Pyrus and Vitis can metabolise nitrogen oxide and therefore, their plantation could help in this matter.
1.2 Stratospheric Pollution
[अब Air Pollution का दूसरा भाग प्रारम्भ होता है – 10 किलोमीटर के ऊपर के भाग की कहानी]
Formation and Breakdown of Ozone
The upper stratosphere consists of considerable amount of ozone (O3), which protects us from the harmful ultraviolet (UV) radiations (λ 255 nm) coming from the sun. [λ is symbol of wave length and is called lambda]
These radiations cause skin cancer (melanoma) in humans. Therefore, it is important to maintain the ozone shield.
Ozone in the stratosphere is a product of UV radiations acting on dioxygen (O2) molecules. The UV radiations split apart molecular oxygen into free oxygen (O) atoms. These oxygen atoms combine with the molecular oxygen to form ozone.
O2 (g) –> O(g) + O(g)
O(g) + O2 (g) –> O3 (g)
Ozone is thermodynamically unstable and decomposes to molecular oxygen. Thus, a dynamic equilibrium exists between the production and decomposition of ozone molecules.
In recent years, there have been reports of the depletion of this protective ozone layer because of the presence of certain chemicals in the stratosphere.
The main reason of ozone layer depletion is believed to be the release of chlorofluorocarbon compounds (CFCs), also known as freons. These compounds are nonreactive, non flammable, non toxic organic molecules and therefore used in refrigerators, air conditioners, in the production of plastic foam and by the electronic industry for cleaning computer parts etc. Once CFCs are released in the atmosphere, they mix with the normal atmospheric gases and eventually reach the stratosphere. In stratosphere, they get broken down by powerful UV radiations, releasing chlorine free radical.
CF2Cl2 (g) — uv → Cl• (g) + C • F2Cl (g) (i)
The chlorine radical then reacts with stratospheric ozone to form chlorine monoxide radicals and molecular oxygen.
Cl• (g) + O3 (g) → ClO• (g) + O2 (g) (ii)
Reaction of chlorine monoxide radical with atomic oxygen produces more chlorine radicals.
ClO• (g) + O (g) → Cl• (g) + O2 (g) (iii)
So this works like a chain reaction where continuously generating Chlorine radicals keep on breaking Ozone, depleting the ozone layer. Continuous emission of CFCs keeps on adding to the problem.
THE OZONE HOLE
The ozone hole is not technically a “hole” where no ozone is present, but is actually a region of exceptionally depleted ozone in the stratosphere over the Antarctic (The South Pole of earth).
Harmful Effects of Depletion of Ozone layer:
With the depletion more UV radiation filters into troposhpere leading to ageing of skin, cataract, sunburn, skin cancer, killing of many phytoplanktons, damage to fish productivity etc.
Plant cells get mutated.
It also increases evaporation of surface water through the stomata of the leaves and hence decreases the moisture content of the soil.
Increased level of UV radiations damage paints and fibres, causing them to fade faster.
OZONE LAYER RECOVERY
The 1987 Montreal Protocol on Substances That Deplete the Ozone Layer began the phaseout of CFCs in 1993. Various such efforts have started yielding results.
Scientists in 2014 observed a small increase in stratospheric ozone—the first, they thought, in more than 20 years—which they attributed to worldwide compliance with international treaties regarding the phaseout of ozone-depleting chemicals and to upper stratospheric cooling because of increased carbon dioxide. Upon more thorough study, however, scientists in 2016 announced that stratospheric ozone concentrations had actually been increasing in the upper stratosphere since 2000 while the size of the Antarctic ozone hole had been decreasing.