Atmospheric Pollution

Two natural sources of atmospheric pollution are:

1. Disintegration of rocks and soil.
2. Decay of plants and animals, volcanic eruptions.

Two gases which are responsible for the formation of acid rain are:

1. Oxides of sulphur [SO₂]
2. Oxides of nitrogen [NO₂]

1. Harmful ultraviolet rays will reach the earth and cause damage.
2. Humans, animals and plants will be adversely affected by the harmful effects of ultraviolet radiations.

Global warming can be reduced by reducing the emission of greenhouse gases by:

1. Using different fuels which release less greenhouse gases:
   1. Liquefied Petroleum Gas [L.P.G.] — contains mostly propane [C₃H₈]
   2. Liquefied Natural Gas [L.N.G.] — contains mostly methane [CH₄]
   3. Compressed Natural Gas [C.N.G.] — similar to L.P.G. but is not liquefied.
2. Using renewable energy resources like:
   1. Solar energy [from sun's stored energy]
   2. Wind energy [from windmills]
   3. Hydropower energy [from high dams]

CNG is an alternative to petrol and diesel since it causes minimum pollution. It does not contain lead and lowers maintenance cost as compared to vehicles with other forms of fuels.

The warming up of the earth's surface, due to concentration or blanketing effect of the greenhouse gases (Greenhouse effect) results in the rise of atmospheric temperatures. This is not confined to one region but has a global impact and is termed as global warming.

The term 'acid rain' refers to the various ways in which the acids formed in the atmosphere - condense and fall on the earth resulting in acid rain.

Impacts of acid rain :

1. Nutrient leaching — The hydrogen ions which are added to the soil when acid rain falls on the earth interact chemically with existing soil minerals.
   H₂SO₄ ⇌ 2H¹⁺ + SO₄^2-
   Minerals like potassium and calcium interact with the H¹⁺ ions and are displaced from the soil, thus the soil is deprived of nutrients.
2. Affects marine organisms — Toxic metals like mercury, lead, zinc present in the soil, get leached by acid rain thus toxicity enters rivers and streams and destroys aquatic plants and animals.

An advantage of using solar energy:

Solar energy is a renewable source of energy that does not cause pollution and helps in reducing global warming as it does not emit greenhouse gases.

Methods of preventing acid rain are:

1. Using alternate energy sources — alternatives to burning of fossil fuels such as compressed natural gas [C.N.G.] or use of cleaner energy sources such as hydro power or wind energy causes almost no pollution.
2. Usage of technical devices — such as catalytic converters, which can reduce nitrogen oxide emissions from automobiles [usage of electrostatic precipitators in industries].

The breakdown of ozone by CFCs in the stratosphere is brought about in the following way:

1. Chlorofluorocarbons are broken down by ultraviolet radiations in the stratosphere.
2. By products of the breakdown of CFCs results in increase in levels of free radicals of atomic chlorine [Cl].
3. The free radicals initiate and catalyse a chain reaction by reacting with ozone to form chlorine monoxide (ClO) and oxygen (O₂). These reactions are capable of breakdown of over 1,00,000 ozone molecules resulting in ozone depletion.

1. Use of products that contain CFCs to be replaced by alternative products.
2. Substitutes for CFCs have been initiated by scientists and use of HCFC [hydrochlorofluorocarbons] is being considered. Labelling products as CFC free is initiated.
3. International Treaty [Montreal protocol] was also initiated to prevent ozone depletion.

Four gaseous pollutants are:

1. Oxides of sulphur [SO₂],
2. Oxides of nitrogen [NO],
3. Oxides of carbon [CO₂],
4. Hydrogen sulphide [H₂S]

The two forms of depositions of acid rain are:

1. Wet deposits - rain, snow, fog, dew
2. Dry deposits - particles [containing sulphates and nitrates]

1. Natural sources — bacterial decomposition, forest fires, volcanic eruptions
2. Man-made sources — power, industrial and smelting plants and automobile exhausts.

Major green house gases are carbon dioxide, methane, water vapours, oxides of nitrogen and chlorofluorocarbons.

Two natural sources of Methane are:

1. Bacterial decay of vegetable matter releases marsh gas which is mainly methane.
2. Natural gas associated with petroleum contains about 75% of methane.

Two man-made sources of Methane are:

1. Natural wet lands and rice paddies
2. Gas drilling, Coal mining, biomass burning

Renewable sources of energy are:

1. Solar energy [from sun's stored energy]
2. Wind energy [from windmills]
3. Hydropower energy [from high dams]

Chemicals responsible for ozone depletion are :

1. Chlorofluorocarbons [CFC i.e., CFCl₃]
2. Methyl chloride [CH₃Cl]
3. Methyl bromide [CH₃Br]
4. Carbontetrachloride [CCl₄]
5. Bromofluorocarbons
6. Methane [CH₄]
7. Nitrous oxide [N₂O]

Atmospheric pollution means conditions of air made unclean due to introduction of foreign elements from (i) Natural sources (ii) Man made sources to the air so as to cause adverse effects on living organisms on earth.

The term 'acid rain' refers to the various ways in which the acids formed in the atmosphere condense and fall on the earth.

Fuels that are derived from organic remains of plants and animals are called fossil fuels.
Principal fossil fuels — coal, petroleum [oil], natural gas.
Sulphur impurities are present in fossil fuels which produce sulphur dioxide when the fossil fuel is burnt. Balanced chemical equation for the same is given below:
S + O₂ ⟶ SO₂

1. When a fossil fuel is burnt in an electric power station sulphur dioxide is formed:
   S + O₂ ⟶ SO₂
2. Sulphur dioxide reacts with water vapour to form sulphurous acid
   H₂O + SO₂ ⟶ H₂SO₃ [aq.]
3. Sulphur dioxide can also be oxidized to sulphur trioxide [SO₃]
   2SO₂ + O₂ ⟶ 2SO₃
   [The reaction is catalyzed by dust particles and water droplets].
4. Sulphur trioxide reacts with water vapour in air forming sulphuric acid
   H₂O + SO₃ ⟶ H₂SO₄ [aq.]

Thus, the acidity of rain is due to reaction of oxides of sulphur with water vapour forming dilute acids.

1. Nitrogen combines with oxygen at high temperatures to give nitric oxide
   N₂ + O₂ ⟶ 2NO
2. Nitric oxide [NO] is oxidized to nitrogen dioxide [NO₂]
   2NO + O₂ ⟶ 2NO₂
3. Nitrogen dioxide [NO₂] reacts with water vapour to form nitrous acid [HNO₂] and nitric acid [HNO₃]
   H₂O + 2NO₂ ⟶ HNO₂ + HNO₃
   [The nitrogen dioxide may also dissolve in atmospheric moisture in the presence of oxygen of the air forming nitric acid in the free state].
   [2H₂O + 4NO₂ + O₂ ⟶ 4HNO₃]

Thus the acidity in the rain is due to reaction of oxides of nitrogen with water vapour forming dilute acids.

The basic function of a catalytic converter in an internal combustion engine is to help reduce pollution.

The reduction catalyst [Pt/Pd] in a converter separates the nitrogen atom from NO and NO₂ molecules freeing oxygen in the form of O₂ molecule.

2NO ⟶ N₂ + O₂
2NO₂ ⟶ N₂ + 2O₂

Thus, the oxides of nitrogen which are pollutants are converted to free nitrogen.

The hydrogen ions which are added to the soil - when acid rain falls on the earth - interact chemically with existing soil minerals.

H₂SO₄ ⇌ 2H¹⁺ + SO₄^2-

Minerals like potassium and calcium interact with the H¹⁺ ions and are displaced from the soil, thus the soil is deprived of nutrients causing nutrient leaching.

Toxic metals like - mercury, lead, zinc present in the soil, get leached by acid rain thus toxicity enters rivers and streams and destroys aquatic plants and animals.

Acid rain affects:

1. Plants in numerous ways — affects transpiration, decolourises leaf pigments, retards growth of crops and reduces rate of photosynthesis.
2. Humans — Acid rain gets absorbed by plants, animals and directly or indirectly toxicity enters food chain affecting humans.
3. Material Damage — Corrodes metallic surfaces, disintegrates paper and leather, weakens building material such as statues, sculptures, marbles, limestone [CaCO₃] etc.
   CaCO₃ + H₂SO₄ ⟶ CaSO₄ + H₂O + CO₂

Ways to control acid rain:

1. Using alternate energy sources - alternatives to burning of fossil fuels such as compressed natural gas [C.N.G.] or use of cleaner energy sources such as hydro power or wind energy causes almost no pollution.
2. Usage of technical devices - such as catalytic converters, which can reduce nitrogen oxide emissions from automobiles [usage of electrostatic precipitators in industries].

Green house gases are those gases that contribute effectively in retaining heat in the atmosphere.

Green house effect is the warming up of the earth's surface, due to concentration or blanketing effect of the green house gases.

The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as global warming.

The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as global warming.

In absence of green house gases the surface temperature on earth is maintained since -

1. The solar radiations emitted as heat radiations, passes through the clear atmosphere.
2. It reaches the earth's surface where it is absorbed and retained.
3. Some of the absorbed heat radiation is reflected back into the atmosphere. [radiation from the earth takes place in two ways - reflected solar radiation and emitted thermal infrared radiations]

Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth.

Balanced equations for formation of carbon dioxide during combustion of fossil fuels are given below:

1. Burning of Coal
   C + O₂ ⟶ CO₂ + Δ
2. Burning of Natural gas
   CH₄ + 2O₂ ⟶ CO₂ + 2H₂O + Δ

Oxides of nitrogen (namely nitrous oxide), are released into the atmosphere from various natural and man-made sources. The natural sources are:

1. Anaerobic respiration — Activities of micro organisms in soil release nitrogen, nitric oxide and nitrous oxide.
2. The lightning discharge in the atmosphere creates high temperatures causing Nitrogen (N₂) and Oxygen (O₂) to combine forming Oxides of Nitrogen.

The man-made sources are:

1. Use of nitrogenous fertilizers for agricultural activities release oxides of nitrogen.
2. Automobile exhausts.
3. Burning of biomass.

Impact of green house gases on:

1. Geographic conditions — Global warming increases melting of ice-caps which results in rising of sea levels causing coastal flooding and erosion.
2. Climatic conditions — Tropical regions experience more rainfall. Northern latitudes experience shorter and wetter winters.
3. Agricultural conditions — Affects due to climatic changes:
   1. the life cycle of trees and survival and reproduction of plants.
   2. the soil fertility and amount of soil water retained in the soil.

The following fuels can be used which are better than fossil fuels as they release less green house gases:

1. Liquefied Petroleum Gas [L.P.G.] - contains mostly propane [C₃H₈]
2. Liquefied Natural Gas [L.N.G.] - contains mostly methane [CH₄]
3. Compressed Natural Gas [C.N.G.] - similar to L.P.G. but is not liquefied.

Ozone layer is the layer in the earth's atmosphere which contains relatively high concentration of ozone. It absorbs 97-99% of the sun's high frequency U.V. light which is damaging to life on earth. Thus, Ozone layer protects life on earth from harmful solar rays.

Distribution of the Ozone Layer in the Stratosphere:

1. Ozone layer is mainly located approximately 20-30 kms above the earth's surface.
2. The thickness of the ozone layer varies geographically and seasonally.
3. It is thinner near the equator and larger towards the poles.
4. It is generally thicker during spring in the northern hemisphere.
5. Most of the ozone is created over the tropics, but the stratospheric wind circulation transports it polewards to northern and southern hemispheres.

Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O₂] into two oxygen atoms. This reaction is photodissociation or photolysis.

Highly reactive oxygen atom [O] can then react with oxygen molecule [O₂] to form ozone [O₃]

O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]

O₂ + [O] ⟶ O₃ [ozone]

Ozone is formed in the stratosphere — Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O₂] into two atoms. This reaction is photodissociation or photolysis.

Highly reactive oxygen atom [O] can then react with oxygen molecule [O₂] to form ozone [O₃]

O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]

O₂ + [O] ⟶ O₃ [ozone]

Ozone is also broken down in the stratosphere — In unpolluted air containing minimal chemical compounds, unstable ozone molecule, in presence of solar radiations may split into molecular oxygen [O₂] and an atom of atomic oxygen [O].

The atomic oxygen then combines with another ozone molecule to form two molecules of molecular oxygen.

O₃ $\xrightarrow[\text{light}]{\text{U.V.}}$ O₂ + [O]

O₃ + [O] ⟶ 2O₂

Thus a continuing process called 'ozone oxygen cycle' is maintained between the amount of ozone [O₃] being produced and being destroyed. As a result, the total concentration of ozone remains almost the same.

The balance is disturbed by release of chemicals — such as chlorofluorocarbons containing atomic chlorine and bromine and other free radicals which breaks the ozone molecule causing ozone depletion.

Damage to Humans and Animals:

1. Sunburn and skin cancer
2. Eye cataract and eye damage
3. Early aging of skin
4. Weakening of immune system
5. Disruption in function of DNA
6. Severe damage to cells of animals.

Damage to plants:

1. Retards plant growth.
2. Inhibits pollen germination
3. Reduces chlorophyll content
4. Affects the quality of vegetables
5. Disrupts ecosystem
6. Increases harmful mutations

Chlorofluorocarbons (CFCs) is the main chemical responsible for more than 80% ozone depletion.

Man-made applications making use of Chlorofluorocarbons (CFCs) are:

1. Aerosol sprays
2. Coolants in refrigeration and A.C.s
3. Drycleaning fluids
4. Cleansing agents for cleaning electronic components

Ozone is broken down by chlorofluorocarbons in the following way:

1. Chlorofluorocarbons are broken down by ultraviolet radiations in the stratosphere.
2. By products of the breakdown results in increase in levels of free radicals like atomic chlorine [Cl].
3. The free radicals reacts with ozone to form ClO[g]. This causes ozone depletion. The Cl free radicals initiate and catalyze a chain reaction capable of breakdown of over 1,00,000 ozone molecules resulting in ozone depletion.

Ozone layer can be protected by:

1. Use of products that contain CFCs to be replaced by alternative products.
2. Substitutes for CFCs have been initiated by scientists and use of HCFC [hydrochlorofluorocarbons] is being considered. Labelling products as CFC free is initiated.
3. International Treaty [Montreal protocol] was also initiated to prevent ozone depletion.

(a) The main substances present in water which are beneficial to life are:

1. Dissolved oxygen in water which is essential for aquatic life.
2. Essential minerals like calcium, potassium, zinc and copper.

(b) The main substances present in water which are harmful to life are:

1. Toxic heavy metals like mercury and lead.
2. Agricultural wastes like pesticides.
3. Industrial chemical wastes like benzene.
4. Bacteria and viruses like E. coli.

Minamata disease is a severe neurological disorder caused by mercury poisoning.
The adverse effects of Minamata disease are:

1. Severe sensory disturbances.
2. Lack of coordination.
3. Hearing and speech impairment.

Organic matter on bacterial decomposition

Reason — When organic matter decomposes by bacterial action, it releases hydrogen sulphide, a foul-smelling gas. This gas gets oxidised in air to form sulphur dioxide which further reacts with water vapour to produce sulphuric acid, causing acid rain.
Smelting plants release sulphur dioxide directly, but not a foul-smelling gas. Internal combustion engines release nitrogen oxides. Sulphuric acid plants release sulphur dioxide, not typically a foul-smelling gas.

Less than pH of natural rain water

Reason — Natural rainwater has a pH of about 5 to 6 due to presence of carbon dioxide which dissolves in rain water to form weak carbonic acid. Acid rain contains strong acids such as sulphuric acid and nitric acid, so its pH ranges between 5.6 to 3.5.

Bacterial decay of vegetable matter

Reason — During bacterial decomposition of dead plants and organic matter, carbon compounds break down and release carbon dioxide naturally into the atmosphere.
Power plants, exhaust from automobiles, Burning of fossil fuels are man-made sources.

Bromofluorocarbon

Reason — Bromofluorocarbons contain bromine and fluorine. In the stratosphere, bromine-containing free radicals destroy ozone molecules, causing ozone depletion. Bromofluorocarbons also act as greenhouse gases and trap heat in the atmosphere, thus contributing to global warming.
Carbon tetrachloride mainly causes ozone depletion. Methane and carbon dioxide mainly cause global warming.

O₂ ⟶ 2[O]

Reason — O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]

Highly energetic ultraviolet radiations from the sun breaks down the oxygen molecule into two oxygen atoms. This chemical reaction is called photodissociation or photolysis.

Both A and R are true but R is not the correct explanation of A.

Reason — A is true as the greenhouse effect traps heat in the atmosphere, leading to global warming and climate change worldwide.
R is true as plants absorb carbon dioxide during photosynthesis, helping reduce greenhouse gases.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

Natural rain water produced in an unpolluted atmosphere is slightly acidic as CO₂ present in traces in unpolluted air dissolves in rain water forming weak carbonic acid [H₂CO₃].

H₂O + CO₂ ⟶ H₂CO₃ [carbonic acid]

Organic matter releases hydrogen sulphide [H₂S] on bacterial decomposition. Hydrogen sulphide is oxidised in air to sulphur dioxide.

2H₂S + 3O₂ ⟶ 2H₂O + 2SO₂

In internal combustion engines, combustion of fossil fuel occurs with an oxidiser (air). The air drawn from the atmosphere contains about 80% nitrogen. The nitrogen combines with oxygen at high temperature producing oxides of nitrogen.

N₂ + O₂ ⟶ 2NO [at high temp.]

Thus, exhaust gases of all internal combustion engines release oxides of nitrogen.

The impact of global warming on the countries economy are:

1. Higher temperatures, droughts and floods reduce crop production, causing losses to farmers and increase in food prices.
2. Cyclones, floods, heat waves and storms damage roads, buildings, industries and public property, leading to huge economic losses.
3. Reduction in forest resources, fisheries and wildlife affects industries dependent on them and decreases tourism income.

Differences between global warming and climate change are:

Global warming and ozone depletion are directly or indirectly interconnected because:

1. In the stratosphere, CFCs break down ozone molecules and cause ozone depletion. At the same time, CFCs trap heat in the atmosphere and act as greenhouse gases, contributing to global warming.
2. The ozone layer absorbs harmful ultraviolet (UV) radiation from the Sun. When ozone is depleted, more UV rays enter the atmosphere. This changes atmospheric heating patterns and can disturb climate systems, wind circulation and rainfall patterns.

Ozone holes occur mainly over the Antarctic region because very low temperatures in the Antarctic stratosphere help in the formation of polar stratospheric clouds. On the surface of these clouds, inactive chlorine compounds formed from CFCs are converted into active chlorine radicals.
During spring, sunlight returns and activates these chlorine radicals. They rapidly break down ozone molecules, so ozone depletion becomes maximum during spring.

The causes of acid rain and ozone depletion can be compared as follows:

1. Acid rain is caused mainly by sulphur dioxide and nitrogen oxides whereas ozone depletion is caused mainly by chlorofluorocarbons.
2. Acid rain mainly affects the lower atmosphere and Earth’s surface whereas ozone depletion affects the stratospheric ozone layer.

The effects of acid rain and greenhouse gases are related in the following ways:

1. Both disturb ecological balance — Acid rain damages forests, crops, lakes and soil. Global warming changes climate, rainfall and temperature, affecting plants and animals.
2. Both affect water bodies and living organisms — Acid rain increases acidity of rivers and lakes, harming aquatic life. Global warming raises water temperature and causes melting of ice and sea-level rise.
3. Acid rain and greenhouse gases are both caused by atmospheric pollution and both adversely affect plants, animals, water bodies, soil and the overall ecological balance.

The advantages and disadvantages of the greenhouse effect are:

Water vapour contributes to the greenhouse effect by absorbing and trapping heat radiated from the Earth’s surface. This trapped heat warms the atmosphere and prevents it from escaping into space easily. As global temperature rises, more water evaporates, increasing the amount of water vapour in the atmosphere, which further increases warming. Thus, water vapour acts as a greenhouse gas and strengthens the greenhouse effect.

Acid rain is a regional problem because the pollutants causing it, mainly oxides of sulphur and nitrogen, form acids in the atmosphere and fall with rain, snow, fog or dew over a limited region. Hence, its effects are mainly seen on the soil, water bodies, plants, buildings and organisms of that region.

Global warming is a global problem because greenhouse gases like carbon dioxide, methane, water vapour and oxides of nitrogen spread throughout the atmosphere and retain heat due to their blanketing effect. This raises atmospheric temperature worldwide and causes global effects such as melting of ice-caps, rise in sea level and climatic changes.

1. B: Sulphur dioxide

2. C: Methane

3. A: Oxygen

4. B: Methyl chloride

5. C: Hydro power

1. Sulphur trioxide to sulphuric acid
   H₂O + SO₃ ⟶ H₂SO₄

2. Nitrogen to nitrogen dioxide in internal combustion engine
   N₂ + O₂ ⟶ 2NO [At High Temperatures]
   2NO + O₂ ⟶ 2NO₂

3. Methane to carbon dioxide
   CH₄ + 2O₂ ⟶ CO₂ + 2H₂O + Δ

4. A molecule of ozone to two molecules of oxygen gas
   O₃ $\xrightarrow[\text{light}]{\text{U.V.}}$ O₂ + [O]
   O₃ + [O] ⟶ 2O₂

5. Oxygen to ozone gas by photolysis
   O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]
   O₂ + [O] ⟶ O₃ [ozone]

Natural rain water produced in unpolluted air is slightly acidic as CO₂ present in traces in unpolluted air dissolves in rain water forming weak carbonic acid [H₂CO₃].

H₂O + CO₂ ⟶ H₂CO₃ [carbonic acid]

The reduction catalyst [Pt/Pd] of the catalytic converter separates the nitrogen atom from NO and NO₂ molecules freeing oxygen in the form of O₂ molecule.
2NO ⟶ N₂ + O₂
2NO₂ ⟶ N₂ + 2O₂

Thus, the oxides of nitrogen which are pollutants are converted to free nitrogen by the catalytic converter thereby reducing pollution.

In absence of green house gases the surface temperature on earth is maintained since -

1. The solar radiation emitted as heat radiation, passes through the clear atmosphere.
2. It reaches the earth's surface where it is absorbed and retained.
3. Some of the absorbed heat radiation is reflected back into the atmosphere. [radiation from the earth takes place in two ways - reflected solar radiation and emitted thermal infrared radiation]

Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth and the surface temperature of earth is maintained.

Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O₂] into two oxygen atoms. This chemical reaction is called photodissociation or photolysis.

The highly reactive oxygen atom [O] can then react with oxygen molecule [O₂] to form ozone [O₃]

O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]

O₂ + [O] ⟶ O₃ [ozone]

Destruction of ozone layer is harmful for humans because U.V. radiations from the sun cause the following damage to humans:

1. Sunburn and skin cancer
2. Eye cataract and eye damage
3. Early aging of skin
4. Weakening of immune system
5. Disruption in function of DNA
6. Severe damage to cells of animals.

U.V. radiations also damage plants in the following ways:

1. Retards plant growth.
2. Inhibits pollen germination
3. Reduces chlorophyll content
4. Affects the quality of vegetables
5. Disrupts ecosystem
6. Increases harmful mutations

1. NO
2. Snow
3. Chlorofluorocarbons [CFCs]
4. CH₄ [methane]
5. Oxygen atom.

1. Decreases
2. Increases
3. Decreases
4. Decreases
5. Decreases

1. The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as 'global warming'.
2. Process which releases – CO₂ is respiration and
   the process which absorbs – CO₂ is photosynthesis.
3. C.N.G. causes minimum pollution. It does not contain lead and lowers maintenance cost as compared to vehicles with other forms of fuels.
4. Biofertilizers reduce the green house gas N₂O as nitrogenous fertilizers release N₂O when used in agricultural activities.
5. The sea level rises due to global warming as increase in temperature melts ice on mountains, ice-caps.