It deals with the study of the origin, transport, reactions, effects and fate of chemical species in the environment.

Broadly, environmental studies deal with the sum of all social, economical, biological, physical and chemical interrelations with our surroundings.

Environment

It means surroundings. it consists of four components:

(i) Atmosphere

It is a cover of gases upto a height of about $1600 \mathrm{~km}$ from the surface of the earth. Gases mainly present are $\mathrm{O} _{2}, \mathrm{~N} _{2}, \mathrm{O} _{3}, \mathrm{CO} _{2}$ and $\mathrm{H} _{2} \mathrm{O}$ vapour. It is further divided into four regions:

(a) Troposphere $(0-11 \mathrm{~km})$. It is the domain of all living organisms and is greatly affected by air pollution. Temperature decreases from $15^{\circ} \mathrm{C}$ to $-56^{\circ} \mathrm{C}$.

(b) Stratosphere $(11-50 \mathrm{~km})$. It contains ozone and hence is called ozonosphere. It protects the living organisms from harmful ultraviolet radiation. Its temperature increases from $-56^{\circ} \mathrm{C}$ to $-2^{\circ} \mathrm{C}$.

(c) Mesosphere $(50-85 \mathrm{~km})$. It contains gases in the ionized form ( $\mathrm{NO}^{+}$etc.) and is called ionosphere. Its temperature decreases from $-2^{\circ} \mathrm{C}$ to $-92^{\circ} \mathrm{C}$. (d) Thermosphere $(85-500 \mathrm{~km})$. It is also ionosphere. Its temperature increases from $-92^{\circ} \mathrm{C}$ to $1200^{\circ} \mathrm{C}$.

(ii) Hydrosphere

It is that part which contains water in the form of ocean, rivers, lakes, etc. It covers about $75 %$ of earth’s surface.

(iii) Lithosphere

It consists of solid components like soil, rocks, mountains, etc. The upper part consisting of weathered rocks and organic matter is called soil. The lower $8-40 \mathrm{~km}$ thick part is called crust.

(iv) Biosphere

It consists of animals and plants.

Environmental Pollution

The addition of undesirable material to air, water and soil by natural sources or due to human activity to such a level of concentration that adversely affects - the life on the earth is called environmental pollution.

Pollutant

The undesirable material added to the environment due to human activities or due to natural happenings.

It can be solid, liquid or gaseous substance present in greater concentration than in natural abundance.

Types of pollutants

(i) Primary pollutants

Which after their formation enter into environment directly, e.g., NO formed from $\mathrm{N} _{2}$ and $\mathrm{O} _{2}$.

(ii) Secondary pollutants

Which are formed from primary pollutants, e.g Peroxyactylnitrate (PAN) from oxides of nitrogen and hydrocarbons.

The secondary pollutants may be more toxic than the primary ones.

Classification of pollutants from the ecosystem view point

(i) Degradable

Which are decomposed after some time automatically (e.g. heat) or by microorganisms (biodegradable, e.g. discarded vegetables, domestic sewage etc.).

(ii) Nondegradable

Which are not easily decomposed and remain in the environment in an unchanged form for many decades. e.g. DDT, plastic, heavy metals $(\mathrm{Hg})$, nuclear wastes.

Difference between a pollutant and a contaminant

A pollutant is a substance produced by natural source or human activity or combined effect of both such that its concentration is so high that it has harmful effects on living organisms or non-living components. A contaminant is a substance added

into environment only by human activity and may or may not be harmful to living organisms or nonliving components.

Threshold Limit Value (TLV)

The permissible limit of a pollutant in the atmosphere to which if a worker is exposed for 8 hours a day or 40 hours of a week throughout his life, there is no adverse effect on him is called threshold limit value. TLV of $\mathrm{CO}$ is $40 \mathrm{ppm}$ while that of $\mathrm{CO} _{2}$ is $5000 \mathrm{ppm}$.

Air or Atmospheric Pollution

It is the addition of undesirable materials (solid or gaseous) into the atmosphere either from natural phenomena or human activity which adversely affects the quality of air and hence life on the earth.

Tropospheric and stratospheric pollution are mainly studied as atmospheric pollution.

Major Tropospheric Pollutants

1. Gaseous Air Pollutants : oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants act as gaseous air pollutants.

(a) Oxides of sulphur $\left(\mathbf{S O} _{2}\right.$ and $\left.\mathbf{S O} _{3}\right)$

They enter into atmosphere mainly due to volcanic eruptions. They are also produced due to combustion of sulphur containing coal and fuel oil in thermal power plants and due to roasting of sulphide ores ( $\mathrm{FeS} _{2}, \mathrm{CuFeS} _{2}, \mathrm{ZnS}, \mathrm{PbS}$, etc.). Both $\mathrm{SO} _{2}$ and $\mathrm{SO} _{3}$ are strongly irritating to respiratory tract. $\mathrm{SO} _{2}$ causes throat and eye irritation. It causes breathlessness and affects larynx (voice box). It slows down the formation of chlorophyll in plants causing loss of green colour. It is called chlorosis. They also cause acid rain.

$$ \begin{aligned} & 2 \mathrm{SO} _{2}(\mathrm{~g})+\mathrm{O} _{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{SO} _{3}(\mathrm{~g}) \\ & \mathrm{SO} _{2}(\mathrm{~g})+\mathrm{O} _{3}(\mathrm{~g}) \longrightarrow \mathrm{SO} _{3}(\mathrm{~g})+\mathrm{O} _{2}(\mathrm{~g}) \\ & \mathrm{SO} _{2}(\mathrm{~g})+\mathrm{H} _{2} \mathrm{O} _{2}(\mathrm{I}) \longrightarrow \mathrm{H} _{2} \mathrm{SO} _{4}(\mathrm{aq}) \end{aligned} $$

(b) Oxides of nitrogen ( $\mathrm{NO}, \mathrm{NO} _{2}$, etc)

They are produced due to combustion of fossil fuels (coal, oil, gasoline etc.) both in motor vehicles and power plants where temperature rises so high that $\mathrm{N} _{2}$ and $\mathrm{O} _{2}$ of air combine to form $\mathrm{NO}, \mathrm{NO} _{2}$, etc. $\left(\mathrm{N} _{2}+\mathrm{O} _{2} 1483 \mathrm{~K}, 2 \mathrm{NO} ; 2 \mathrm{NO}+\right.$ $\mathrm{O} _{2} \rightarrow 2 \mathrm{NO} _{2}$ ). At present pollution level neither $\mathrm{NO}$ nor $\mathrm{NO} _{2}$ is harmful. $\mathrm{NO} _{2}$ is more dangerous as it is a toxic gas and affects respiratory system and damages lungs. Concentration > 100 ppm is fatal. Though NO has about 1500 times greater affinity than $\mathrm{CO}$ for haemoglobin but fortunately, it is unable to enter the blood stream from atmosphere. But presence of large amounts may increase $\mathrm{NO} _{2}$ by oxidation and thus become harmful. Further, oxides of nitrogen in air cause acid rain and cause photochemical smog. $\mathrm{NO} _{2}$ is also harmful to various textile fibres and metals.

(c) Hydrocarbons

The main source of hydrocarbon pollutants is the internal combustion engines in which unburnt fuel or partially burnt fuel is emitted in the exhaust gases.

At low concentration, they are not harmful. At concentration $>500 \mathrm{ppm}$, they are carcinogenic and cause cancer. On photochemical reaction with $\mathrm{O} _{2}$ and oxides of nitrogen, they form harmful compounds and produce photochemical smog.

(d) Oxides of Carbon

(i) Carbon monoxide (C0)

One of the most serious air pollutant.

It enters into atmosphere mainly due to incomplete combustion of fossil fuels or hydrocarbon fuels or hydrocarbon fuels of automobiles. It is poisonous because it combines with haemoglobin more easily than oxygen to form carboxyhaemoglobin $(\mathrm{Hb}+\mathrm{CO} \rightarrow \mathrm{HbCO})$ which is much more stable than oxyhaemoglobin. Thus, the function of haemoglobin to transport oxygen to different parts of the body is hindered. Thus, body becomes oxygen-starved. The disease is called anoxia or asphyxiation. If $\mathrm{CO}$ exceeds $100 \mathrm{ppm}$, person suffers headache and dizziness. If $\mathrm{CO}$ exceeds $750 \mathrm{ppm}$, it leads to coma and death. For this reason, a burning coal angithi in a closed room in winter should never be used.

(ii) Carbon dioxide ( $\mathbf{C O} _{2}$

It forms abut $0.03 %$ by volume of the atmosphere.

It is released into atmosphere through many processes like respiration, burning of fossil fuels etc.

$\mathrm{CO} _{2}$ acts as a pollutant when its amount increases from $0.03 %$.

It is the major contributor to global warming.

Greenhouse effect and Global Warming

Natural Greenhouse effect is the natural phenomenon which keeps the earth warm and maintain its temperature.

Gases such as $\mathrm{CO} _{2}, \mathrm{CH} _{4}, \mathrm{O} _{3}, \mathrm{CFCs}$ and water vapour in the atmosphere trap the heat hich earth radiates back to the atmosphere.

If the $%$ of these gases increases from a certain level, then they add to the heating of atmosphere which causes global warming.

$\mathrm{CO} _{2}$ is the major contributor to global warming.

Consequences of greenhouse effect

(i) Due to increase in temperature of earth’s surface, melting of glaciers and polar ice caps will occur. As a result, level of sea water may rise causing floods in the coastal land.

(ii) Due to higher concentration of $\mathrm{CO} _{2}$ in the atmosphere, the plants undergoing photosynthesis will take up the gases at a faster speed. As a result, the plants in warmer climates and adequate rainfall would grow faster.

(iii) Higher global temperature is likely to increase the incidence of infectious diseases like malaria, dengue, yellow fever and sleeping sickness.

Acid Rain

It is the rain water containing $\mathrm{H} _{2} \mathrm{SO} _{4}$ and $\mathrm{HNO} _{3}$ (along with small amounts of $\mathrm{HCl}$ acid) which are formed from the oxides of sulphur and nitrogen present in the air as pollutants and has a pH of 4-5. (Remember that normal rain water has a pH of about 5.6). The acids are produced in the air from oxides of nitrogen and sulphur present as pollutants through the following reactions:

(i) $\mathrm{NO}+\mathrm{O} _{3} \longrightarrow \mathrm{NO} _{2}+\mathrm{O} _{2}, \mathrm{NO} _{2}+\mathrm{O} _{3} \longrightarrow \mathrm{NO} _{3}+\mathrm{O} _{2}, \mathrm{NO} _{2}+\mathrm{NO} _{3} \longrightarrow \mathrm{N} _{2} \mathrm{O} _{5}$, $\mathrm{N} _{2} \mathrm{O} _{5}+\mathrm{H} _{2} \mathrm{O} \longrightarrow 2 \mathrm{HNO} _{3}$

(ii) $2 \mathrm{SO} _{2}+\mathrm{O} _{2} \xrightarrow[\text { or metal ions }]{\text { Noot }} 2 \mathrm{SO} _{3}, \mathrm{SO} _{3}+\mathrm{H} _{2} \mathrm{O} \longrightarrow \mathrm{H} _{2} \mathrm{SO} _{4}$

$\mathrm{HNO} _{3}$ and $\mathrm{H} _{2} \mathrm{SO} _{4}$ formed above combine with $\mathrm{HCl}$ present in air and come down to earth along with rain. It damages buildings made of marble like Taj Mahal at Agra, iron and steel structures. Increase of acid in lakes causes fish to die.

(iii) Acid rain increases the acidity of water in the lakes which is lethal for the fishes. For this reason, some of the lakes have become fishless. Thus, it has greatly affected the fish population.

(iv) Acid rain damages leaves of trees and plants and retards the growth of forests (as it happened in Swedish forests). It also retards the growth of certain crops such as peas, beans, potato, raddish, carrot, spinach, etc.

Methods to reduce the formation of acid rain

Acid rain is due to emission of sulphur dioxide and nitrogen dioxide in the atmosphere. Therefore, to reduce the formation of acid rain, the emission of these gases has to be controlled. The following steps may be taken:

(i) By using less vehicles driven by fossil fuels.

(ii) By using less sulphur content fossil fuels for power plants and industries, e.g., by using natural gas which is a better fuel than coal or using coal with less sulphur content.

(iii) By using catalytic converters in cars so that $\mathrm{NO}$, present in the exhaust gases is converted into $\mathrm{N} _{2}$ at $573 \mathrm{~K}$. (The main component of the converter is a ceramic honeycomb coated with precious metals like Pt and Rh).

(iv) By adding powdered limestone to neutralize the acidity of the soil.

2. Particulate Pollutants

These are small solid particles and liquid droplets suspended in the air. They are present in the air in the form of soot (produced due to incomplete combustion of fossil fuels), fly ash (coming with the furnaces), inorganic particles (metallic, metal oxides, lead halides, asbestos dust, sulphuric acid and nitric acid) and organic particles (paraffins, olefins, polycyclic aromatic hydrocarbons, i.e., PAH, etc.). The particulates may also be classified as viable and nonviable. Viable particulates are small size living organisms such as bacteria, fungi, moulds, algae, etc. Non-viable particulates are formed by disintegration of large size materials or condensation of small size particles or droplets. These include mist, smoke, fumes and dust. These particulates pass through the nose (bigger than 5 microns) easily and enter the lungs (having the size of about 1.0 microns), where they act as sites for adsorption of carcinogenic compounds causing lung cancer and bronchital asthma.

This disease is common in industrial workers and is called pneumoconiosis, (asbestosis due to asbestos, silicosis due to silica, etc.). They scatter light and hence affect visibility on foggy nights. They counteract the greenhouse effect as they reflect back heat of sunlight.

Smog and its kinds, The word ‘smog’ is a combination of ‘smoke’ and ‘fog’ because earlier, it was found to be formed by condensation of fog on carbon particle.

(i) London smog/Sulphurous smog/Classical smog

This type of smog was first observed in London in 1952. It is formed due to presence of $\mathrm{SO} _{2}$ and humidity in the air which combine to form $\mathrm{H} _{2} \mathrm{SO} _{4}$ fog which deposits on particulates. It involves smoke and fog. It is formed in the months of winter particularly in the morning hours when the temperature is low. It causes bronchitis irritation i.e., problem in the lungs. As it contains $\mathrm{C}$ and $\mathrm{SO} _{2}$, it is reducing in nature and therefore, called as reducing smog.

$$ \begin{aligned} & 2 \mathrm{SO} _{2}+\mathrm{O} _{2} \longrightarrow 2 \mathrm{SO} _{3} \\ & \mathrm{SO} _{3}+\mathrm{H} _{2} \mathrm{O} \longrightarrow \mathrm{H} _{2} \mathrm{SO} _{4} \end{aligned} $$

(ii) Photochemical smog/Los Angeles smog

It was first observed in Los Angeles in 1950. It is formed due to photochemical reactions taking place when air contain $\mathrm{NO} _{2}$ and hydrocarbons.

Formation of photochemical smog

$\mathrm{NO} _{2} \xrightarrow{\text { hv }} \mathrm{NO}+\mathrm{O}$

$\mathrm{O}+\mathrm{O} _{2} \rightleftarrows \mathrm{O} _{3}$

$\mathrm{O} _{3}+\mathrm{NO} \longrightarrow \mathrm{NO} _{2}+\mathrm{O} _{2}$

$\mathrm{RCO}+\mathrm{O} _{2} \longrightarrow \mathrm{RCO} _{3}$

$\mathrm{RCO} _{3}+$ Hydrocarbons $\longrightarrow \mathrm{RCHO}, \mathrm{R} _{2} \mathrm{C}=0$

$\mathrm{RCO} _{3}+\mathrm{NO} \longrightarrow \mathrm{RCO} _{2}+\mathrm{NO} _{2}$

Harmful effects of photochemical smog

(i) All these compounds (particularly ozone and PAN) produce irritation in the eyes and also in the respiratory system.

(ii) They also damage many materials such as metals, stones, building materials, etc.

(iii) Ozone is particularly destructive to rubber (in which cracks are developed).

(iv) It is also harmful to fabrics, crops and ornamental plants.

(v) $\mathrm{NO} _{2}$ present gives a brown colour to the photochemical smog which reduces visibility

Stratospheric Pollution

Formation and Breakdown of Ozone layer

Ozone layer exists at an altitude of $25-30 \mathrm{~km}$ (in the stratosphere). It absorbs the harmful UV radiation coming from the sun and hence protects life on the earth. So, it is important to maintain the ozone shield.

Formation of $\mathrm{O} _{3}$

$\mathrm{O} _{2}(\mathrm{~g}) \xrightarrow{\mathrm{UV}} \mathrm{O}(\mathrm{g})+\mathrm{O}(\mathrm{g})$

$\mathrm{O}(\mathrm{g})+\mathrm{O} _{2}(\mathrm{~g}) \stackrel{\mathrm{UV}}{\rightleftarrows} \mathrm{O} _{3}(\mathrm{~g})$

$\mathrm{O} _{3}$ is thermodynamically unstable

Depletion of Ozone layer (Creation of ozone hole) is taking place due to reaction with NO (produced from natural sources or human activity or in the exhaust gases of engines of supersonic planes) or by reaction with chlorofluorocarbons (CFCs), called freons (produced from aerosol sprays used in propellants or from refrigerators where they are used as coolants).

$$ \begin{aligned} & \mathrm{NO}+\mathrm{O} _{3} \longrightarrow \mathrm{NO} _{2}+\mathrm{O} _{2} \\ & \mathrm{NO} _{2}+\dot{\mathrm{O}} \longrightarrow \mathrm{NO}+\mathrm{O} _{2} \\ & \mathrm{CF} _{2} \mathrm{Cl} _{2}(\mathrm{~g}) \longrightarrow \mathrm{uv} \longrightarrow \dot{\mathrm{Cl}}(\mathrm{g})+\dot{\mathrm{C}} \mathrm{F} _{2} \mathrm{Cl}(\mathrm{g}) \\ & \dot{\mathrm{Cl}}(\mathrm{g})+\mathrm{O} _{3}(\mathrm{~g}) \longrightarrow \dot{\mathrm{C}} \mathrm{O}(\mathrm{g})+\mathrm{O} _{2}(\mathrm{~g}) \\ & \dot{\mathrm{ClO}}(\mathrm{g})+\mathrm{O}(\mathrm{g}) \longrightarrow \dot{\mathrm{Cl}}(\mathrm{g})+\mathrm{O} _{2}(\mathrm{~g}) \end{aligned} $$

Ozone Hole

Depletion of ozone layer, known as ozone hole.

A special type of clouds known as polar stratospheric clouds which forms over Antarctica in winter season are responsible for $\mathrm{O} _{3}$ depletion.

A series of chemical reactions takes place on the surface of clouds which leads to the formation of $\dot{\mathrm{Cl}}(\mathrm{g})$ (Chlorine radical).

Effects/Consequences of depletion of ozone layer

(i) It has been found that with increase in the exposure to ultraviolet radiation, the chance for occurrence of skin cancer increases.

(ii) Exposure of eye to ultraviolet radiation damages the cornea and lens of the eye and may cause cataract or even blindness.

(iii) Exposure of plants to ultraviolet radiation adversely affects the plant proteins and results in the reduction of chlorophyll and harmful mutation.

(iv) Ozone depletion has a very strong effect on climate. Ozone layer absorbs the ultraviolet radiation and heats up the stratosphere, setting up a temperature gradient from $-56^{\circ} \mathrm{C}$ to $-2^{\circ} \mathrm{C}$ as the altitude increases from 11 to $50 \mathrm{~km}$. Depletion of ozone layer will upset the heat balance of the earth.

Water pollution

It is the contamination of water by foreign substances which make it harmful for health of animals or plants or aquatic life and make it unfit for domestic, industrial and agricultural use. Depending upon the source, we may have following type of water pollutions:

(i) Ground water pollution

It is water present below the surface of the earth and is pure because it collects after passing through the soil. However, due to industrial effluents and fertilizers and pesticides, it gets contaminated.

(ii) Lake water pollution

It occurs due to flow of inorganic nutrients from agricultural land and toxic materials from urban areas or dumping of industrial effluents into them.

(iii) River water pollution

It occurs due to discharge of industrial wastes and domestic sewage into them.

(iv) Sea water pollution

It occurs due to wreckage of oil tankers or oil leakage from pipe lines or refineries located nearby or deliberate marine pollution by crude oil. The spreading of oil, into sea is called oil-spill and layer on the surface is called oil slick. It causes heavy damage to fishery and sea birds and aquatic animals.

Sources of water pollution

(i) Sewage and domestic wastes

(ii) Industrial effluents

(iii) Agricultural nutrients

(iv) Thermal power plants (causing increase of temperature)

(v) Radioactive discharges

(vi) Polychlorinated biphenyls (PCBs) used in transformers and capacitors.

Point Source

Easily identified source or place of pollution e.g, municipal and industrial discharge pipes.

Non point source

Non point sources of pollution are those where a source of pollution cannot be easily identified. e.g., agricultural run off, acid rain.

Causes of Water Pollution

(i) Pathogens

Most serious water pollutant. Pathogens include bacteria and other organisms that enter water from domestic sewage and animal excreta.

(ii) Organic wastes

One of the major water pollutant. These include leaves, grass, trash etc. These wastes are biodegradable.

Biochemical Oxygen Demand (BOD) of water

Aquatic life needs dissolved oxygen However, human sewage and organic wastes of industry create a problem. Similarly, leaves, grass trash etc., also enter into water due to run off. They result in excessive phytoplankton growth. The microorganisms which decompose this organic waste need oxygen which depends upon amount of waste present. The total amount of oxygen consumed by microorganisms (bacteria) in decomposing the waste (organic matter) present in a certain volume of a sample of water is called Biochemical Oxygen Demand (BOD) of water. This decomposition requires a long time (20-30 days). Hence, we determine $\mathrm{BOD} _{5}$, i.e., oxygen consumed in 5 days. This is done by first saturating the water with oxygen and incubating it for 5 days at $20^{\circ} \mathrm{C}$. Oxygen remaining after 5 days is determined and oxygen consumed is found by subtraction. Pure water has $\mathrm{BOD} _{5}<5 \mathrm{ppm}$ and polluted water $>17 \mathrm{ppm}$.

(iii) Chemical Pollutants

This class of pollutants includes a variety of inorganic chemicals (heavy metals such as $\mathrm{Cd}, \mathrm{Hg}$, Ni), organic chemicals, acids, salts, petroleum products and industrial chemicals (e.g., polychlorinated biphenyls (PCBS)).

Any pollutant which is not an organic waste or pathogens comes under chemical pollutant.

Chemical Oxygen Demand (COD)

This is a quicker method. It consists in treating the given sample of water with a known amount of an oxidizing agent, generally $\mathrm{K} _{2} \mathrm{Cr} _{2} \mathrm{O} _{7}+$ dil $\mathrm{H} _{2} \mathrm{SO} _{4}$. All pollutants get oxidized. The amount of $\mathrm{K} _{2} \mathrm{Cr} _{2} \mathrm{O} _{7}$ left is found by titration against Mohr salt and result is calculated.

Eutrophication

The process in which nutrient enriched water bodies support a dense plant population, which kills animal life by depriving it of oxygen and results in subsequent loss of biodiversity is known as Eutrophication.

International standards of drinking water

(i) Fluoride $<1 \mathrm{ppm}\left(1 \mathrm{mg} \mathrm{dm}^{-3}\right)$ - protects teeth against decay by converting hydroxyapatite (teeth enamel) into harder fluorapatite.

(ii) Lead $<50 \mathrm{ppm} _{\text {or }} \mathrm{ug}^{-3}-$ Higher concentration causes damage to kidney and brain.

(iii) Sulphates $<500 \mathrm{ppm}-$ Higher concentration has laxative effect.

(iv) Nitrates $<50 \mathrm{ppm}$-Excess causes methemoglobinemia (stomach cancer).

(v) $\mathrm{pH}$ 5.5-9.5.

(vi) Other Metals: Some metals are present in drinking water in a limited concentration. If the concentration exceeds from a certain value then these metals become harmful.

Soil pollution

Soil is the uppermost part of earth’s crust. It consists of

(i) Mineral matter (gravel, sand etc. formed from rocks).

(ii) Organic matter (formed from fallen trees, leaves, etc. and remains of dead animals and decomposed by microorganisms and converted into humus).

(iii) Biological material (like algae, bacteria, etc.).

(iv) Soil water (which acts as a solvent for organic and inorganic materials).

(v) Soil air (present in the pores of the soil).

The main pollutants of soil are

(i) Industrial wastes

(ii) Urban wastes

(iii) Radioactive wastes and

(iv) Agricultural materials viz; fertilizers containing excess of nitrates and phosphates and pesticides.

Pesticides consist of

(a) Insecticides (used to kill the insects which destroy the crop, e.g., DDT, BHC or now used are Aldrin and Dieldrin).

(b) Herbicides (used to control weeds, e.g., $\mathrm{NaClO} _{3}, \mathrm{Na} _{3} \mathrm{AsO} _{3}$ or now used are triazines).

(c) Fungicides (used to stop growth of fungi, e.g., organo-mercury compounds).

Control/Management of environmental pollution

Two main sources of environmental pollution are

(i) household waste and

(ii) industrial waste.

Household waste

can be managed by using separate garbage-bins for biodegradable and non-biodegradable (re-cyclable) wastes like polythene bags which choke the sewers.

Industrial waste

can be managed by (i) recycling waste like glass, plastic (ii) Burning and incineration, e.g., plant leaves (iii) sewage treatment before disposing it off (iv) Digesting, e.g., degradation of toxic organic waste by microorganisms, (v) Dumping of sewage sludge into land.

Strategies to control Environmental Pollution

(i) Waste Management

It is the reduction of the waste and proper disposal of waste. Recycling of materials and energy is also a part of waste management.

(ii) Adoption of Environmental friendly methods in day-to-day life, which results in the reduction of environmental pollution.

Green Chemistry

It is a cost effective approach which involves reduction in material, energy consumption and waste generation.

It deals with producing chemicals of our daily needs using such reactions and chemical processes which neither use toxic chemicals nor emit such chemicals into the atmosphere. The techniques generally used in green chemistry are

(i) Use of sunlight and microwaves (photochemistry)

(ii) Use of sound waves (sonochemistry)

(iii) Use of enzymes.

A few examples of use of green chemistry in everyday life are

(i) Dry cleaning of clothes and laundary (using liquefied $\mathrm{CO} _{2}$ along with a suitable detergent instead of tetrachloroethene used earlier).

(ii) Bleaching of paper (using $\mathrm{H} _{2} \mathrm{O} _{2}$ in place of $\mathrm{Cl} _{2}$ ).

(iii) In synthesis of chemicals using environmental friendly chemicals and conditions.

Objective Questions

1. The gas emitted by supersonic jet planes that slowly depletes the ozone layer is

(a) $\mathrm{CO}$

(b) NO

(c) $\mathrm{SO} _{2}$

(d) $\mathrm{O} _{2}$

2. The $\mathrm{pH}$ of normal rain water is

(a) 6.5

(b) $ 7.5$

(c) 5.6

(d) 3.5

3. The process of ’eutrophication’ is due to

(a) increase in concentration of insecticide in water .

(b) increase in concentration of fluoride ion in water.

(c) the reduction in concentration of the dissolved oxygen in water due to phosphate pollution in water.

(d) attack of younger leaves of a plant by peroxyacetyl nitrate.

4. Excess nitrate in drinking water can cause

(a) methemoglobinemia

(b) kidney damage

(c) liver damage

(d) laxative effect

5. The maximum prescribed concentration of cadmium in drinking water in ppm is

(a) 0.05

(b) 3

(c) 2

(d) 0.005

6. Which of the following is true about photochemical smog?

(a) It is reducing in nature

(b) It is formed in winter

(c) It is a mixture of smoke and fog

(d) It causes irritation in eyes

7. The smog is essentially caused by the presence of

(a) $\quad \mathrm{O} _{2}$ and $\mathrm{O} _{3}$

(b) $\quad \mathrm{O} _{2}$ and $\mathrm{N} _{2}$

(c) $\quad $ Oxides of sulphur and nitrogen

(d) $\quad \mathrm{O} _{3}$ and $\mathrm{N} _{2}$

8. London smog is found in

(a) Summer during day time

(b) Summer during morning time

(c) Winter during morning time

(d) Summer during day time

9. Photochemical smog is formed in

(a) Summer during morning time

(b) Summer during day time

(c) Winter during morning time

(d) Winter during day time

10. Depletion of ozone layer causes

(a) blood cancer

(b) lung cancer

(c) Skin cancer

(d) breast cancer

11. Pick up the correct statement

(a) CO which is a major pollutant resulting from the combustion of fuels in automobiles plays a major role in photochemical smog.

(b) Classical smog has an oxidizing character while the photochemical smog is reducing in character.

(c) Photochemical smog occurs in day time whereas the classical smog occurs in the morning hours.

(d) During formation of smog the level of ozone in the atmosphere goes down.

12. In Antarctica, ozone depletion is due to the formation of the following compound

(a) Acrolein

(b) peroxy acetyl nitrate

(c) $\mathrm{SO} _{2}$ and $\mathrm{SO} _{3}$

(d) chlorine nitrate

13. Which of the following is nota greenhouse gas?

(a) Methane

(b) Ozone

(c) Carbon dioxide

(d) Nitrogen

14. Identify the wrong statement in the following:

(a) Ozone layer does not permitinfrared radiation from the sun to reach the earth.

(b) Acid rain is mostly because of oxides of nitrogen and sulphur.

(c) Chlorofluorocarbons are responsible for ozone layer depletion.

(d) Green house effect is responsible for global warming.

15. Which of the following is the coldest region?

(a) Troposphere

(b) Mesosphere

(c) Stratosphere

(d) Thermosphere

16. Which of the following is a secondary pollutant?

(a) $\mathrm{CO} _{2}$

(b) $\mathrm{N} _{2} \mathrm{O}$

(c) $\mathrm{SO} _{2}$

(d) PAN

17. All are primary pollutants except

(a) $\mathrm{SO} _{2}$

(b) $\mathrm{H} _{2} \mathrm{SO} _{4}$

(c) $\mathrm{NO} _{2}$

(d) Particulate matter

18. The gas leaked from a storage tank of the Union Carbide plant in Bhopal gas tragedy was

(a) Phosgene

(b) Methylisocyanate

(c) Methylamine

(d) Ammonia

19. Which one of the following statement is not correct?

(a) DDT and BHC are not good insecticides because they are highly soluble in water.

(b) DDT and BHC are not good insecticides because they are absorbed by the soil and contaminate food crops.

(c) Aldrin is not a good insecticide because it is not biodegradable.

(d) All the above are incorrect.

20. Green chemistry means such reactions which

(a) produce colour during reactions

(b) reduce the use and production of hazardous chemicals

(c) are related to the depletion of ozone layer

(d) study the reactions in plants

21. Which one of the following statement is not true?

(a) Oxides of sulphur, nitrogen and carbon are the most widespread air pollutant

(b) $ \mathrm{pH}$ of drinking water should be between 5.5-9.5

(c) Concentration of $\mathrm{DO}$ below $6 \mathrm{ppm}$ is good for the growth of fish

(d) Clean water would have a BOD value of less than $5 \mathrm{ppm}$

22. The aromatic compounds present as particulates are

(a) Benzene

(b) Toluene

(c) Nitrobenzene

(d) Polycyclic hydrocarbons

23. Ozone layer is present in

(a) troposphere

(b) stratosphere

(c) mesosphere

(d) exosphere