Air pollution

The major problem that the atmosphere is being subjected to is pollution. Polluted air is harmful
to man and the biosphere on the whole, as well. Air pollution can be defined as 'the change of
composition of air by the addition of harmful substances like the industrial and automobile
gases and particulate matter.'
Sources of Air Pollution
Most of the sources of air pollution are related to man's activities as a result of the modern
lifestyle. Added to this are also natural causes like the volcanoes, anaerobic decomposition of
organic matter, atmospheric reactions, etc.
Burning of Fossil Fuels
Fossil fuels include petroleum and coal. Burning of coal produces a lot of smoke and dust
whereas burning of petrol mainly produces sulphur dioxide. In addition to these, the pollutants
include carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides, hydrocarbons,etc.
Automobiles
Petrol on combustion produces carbon monoxide, hydrocarbons, nitrogen oxides, sulphur
compounds, organic acids and ammonia and carbon particles.
Industries
Fertiliser Plants
They produce oxides, sulphur, nitrogen, hydrocarbons, particulate matter and fluorine.
Thermal Plants
Since they are coal based the pollutants are fly ash, soot and sulphur dioxide.
Textile Industries
They produce cotton dust, nitrogen oxides, chlorine, smoke and sulphur dioxide.
Steel Plants
They produce carbon monoxide, carbon dioxide, sulphur dioxide, phenol, fluorine, cyanide,
particulate matter, etc.
Volcanic eruptions release oxides of nitrogen that pollute the atmosphere.

Major Pollutants
There are six main categories of air pollutants:
 oxides of carbon
 sulphur dioxide
 oxides of nitrogen
 hydrocarbon
 inorganic particulate matter and aerosols
 organic particulate matter
Harmful Effects of the Pollutants in Air
The various categories of air pollutants and their harmful effects are summarised in the given
table:
 Pollutant Source/Cause Effect
Affects the respiratory activity as
haemoglobin has more affinity for
Automobile exhaust,
Co than for oxygen. Thus, CO
photochemical reactions in
combines with HB and thus reduces
Carbon monoxide the atmosphere, biological
the oxygen-carrying capacity of
oxidation by marine
blood. This results in blurred vision,
organisms, etc.
headache, unconsciousness and death
due to asphyxiation (lack of oxygen).
Carbon Burning of fossil
fuels,depletion of forests
(that remove excess carbon Global warming as it is one of the
Carbon dioxide
dioxide and help in greenhouse gases.
maintaining the oxygen-
carbon dioxide ratio).
Respiratory problems, severe
Industries, burning of fossil headache,reduced productivity of
fuels, forest fires, electric plants, yellowing and reduced
generation plants, smelting storage time for paper, yellowing and
Sulphur dioxide
plants, industnal boilers, damage to limestone and marble,
petroleum refineries and damage to leather, increased rate of
volcanic eruptions. corrosion of iron, steel, zinc and
aluminium.
Automobile exhaust and
Hydrocarbons Polynuclear
industries,leaking fuel
Aromatic
tanks, leaching from toxic
Compounds(PAC) and Carcinogenic (may cause leukemia)
waste dumping sites and
Polynuclear Aromatic
coal tar lining of some
Hydrocarbons(PAH)
water supply pipes.
Refngerators, air
Destroy ozone layer which then
Chlorofluoro carbons conditioners, foam shaving
permits harmful UV rays to enter the
(CFCs) cream, spray cans and
atmosphere.
cleaning solvents.
Automobile exhausts,
burning of fossil fuels, Forms photochemical smog, at
forest fires,electric higher concentrations causes leaf
Nitrogen Oxides generation plants, smelting damage or affects the photosynthetic
plants, industnal boilers, activities of plants and causes
petroleum refineries and respiratory problems in mammals.
volcanic eruptions
Photochemical reactions Irritation of eye, throat and
PAN - peroxylacetyl -
of hydrocarbons and respiratory tract, damage to
nitrate
nitrogen oxides. clothes, paint and rubber articles,
 damage to leaves and stomatal
tissue in plants.
Particulate matter Lead Combustion of leaded
Toxic effect in man.
halides (lead pollution) gasoline products
Asbestosis - a cancerous disease of
Asbestos particles Mining activities
the lungs
Stone cutting, pottery, glass
Silicon dioxide manufacturing and cement Silicosis, a cancerous disease.
industries.
Biological matter like the
Flowers Allergy
pollen grains
Fungal spores, bacteria,
Microbes Infectious deseases
virus, etc

Particulate Matter:

Particulate matter or simply PM is a combination of solid particles and liquid droplets that can be
found in the air. PM contains hazardous elements such as arsenic, beryllium, cadmium, chromium,
lead, manganese, and nickel. PM causes significant health problems in humans—specifically,
particles that are smaller than 10 micrometers.

These particles are harmful as they can penetrate past a lung’ barrier defenses and lodge themselves
deep in the lungs. Chronic exposure to these particles increases the risk of developing
cardiovascular and respiratory diseases as well as increasing the risk of developing lung cancer.

Peroxyacyl Nitrate
It is produced in the atmosphere when oxidized volatile organic compounds combine with nitrogen
oxide. It is a component of photochemical smog. PANs create health problems such as reduced
respiratory function and eye irritation, and may also be linked to emphysema, impaired breathing
and other lung problems.

Effects of Air Pollution

Global Warming
Most of the solar radiation entering the earth's atmosphere is reflected back into the space.
However some of the heat is absorbed by the gases like the carbon dioxide. This serves to keep
the earth warm much like the greenhouses. Greenhouses are glasshouses which maintain a
temperature higher than the surroundings for the plants to grow and yield better. The other gases
that contribute to this are water vapour, methane, chlorofluorocarbons (CFCs) and nitrous oxide.
These gases are called the greenhouse gases.
While greenhouse effect is a necessary and natural phenomenon. Every year the temperature are
going up due to pollution and the levels of these greenhouse gases is also going up. This is called
global warming. According to estimates, at the current rate of increase, the average global
temperature will go up by 3oC to 8oC in the next 100 years.
This will have the following effects:
 Climate of different regions
 Distribution of plants and animals
 Disturbance in agriculture and food production
 Melting of snow caps and resultant increase in sea levels. This will submerge parts of
coastal cities of New York, London and other major cities.
Formation of Photochemical Smog
When pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight,
smog is formed. This is a mixture of gases and since it is formed by photochemical reactions, it
is called the photochemical smog. The word 'smog' is derived from the two words-smoke and
fog.
It forms a yellowish brown haze especially during winter and hampers visibility. It also causes
many respiratory disorders and allergies as it contains polluting gases.

Formation of Acid Rain

Sulphur dioxide and nitrogen oxides react with water in the atmosphere producing sulphuric acid
and nitric acid. These acids come down along with the rain. This phenomenon is called acid rain.
The pH of acid rain varies from 3-6. The composition of acid rain is sulphuric acid, nitric acid
and weak carbonic acid.
It has the following adverse affects on the environment:
 Causes respiratory and skin disorders.
 Affects productivity of plants by damaging the leaves.
 Enters the soil and affects the soil pH and other conditions.
 Enters the ground and river waters which causes harm to the aquatic life.
 Causes damage to marble and thus damages buildings and monuments like the Taj Mahal
Control of Air Pollution
Air pollution can be controlled by different methods depending on the source and the pollutant.
The different methods are:
1. One of the major causes of air pollution is the automobiles. The fuels being used should
be lead-free as this will reduce the level of lead in the atmosphere. The carburetor should
be cleaned regularly and good quality fuel should be used.
2. The industrial pollution is best controlled at source. The polluting gases should be passed
through filters so that the harmful matter is removed before the waste gases are released
out. The toxic gases should be detoxified.
3. The domestic and industrial smoke producing units should have long chimneys to take
the polluting gases far above and then disperse over a larger area.
4. The pollution by sulphur dioxide is mainly due to coal-based industries. Alternate non-
sulphur containing fuel must be used.
For effective control and prevention of air pollution it is important to educate people and
create public awareness about the ill-effects of air pollution.
Ozone layer depletion and CFC
It is known that ultraviolet rays of sun is harmful to human beings as well as to plants and
animals. But fortunately, there is a ozone layer in the stratosphere which absorbs UV rays and
behaves as a protective umbrella for the biotic factors on the earth. In absence of this layer, no
life can survive.
Ozone layer serves as protective umbrella to save the living being on the earth from danger
radiations like ultra violet rays, cosmic rays. Ozone layer is a natural gift for living creature
offered by nature. But it is being destroyed by the production of greenhouse gases like CO2, CO,
NO, NO2,SO2,SO3, CH4, C2H6, CFC etc. due to human activities such as industrialization,
deforestation, combustion of coal, diesel, wood and scientific research. These gases diffuse from
earth surface forming hazy layer to the stratosphere region where they react with ozone
and makes hole in the ozone layer. The phenomenon formation of hole in the ozone layer by
destroying it with greenhouse gases like NO2, SO2, SO3, CO2, CO, NO, NO2, CH4, C2H6, CFC is
known as ozone layer depletion.
However NASA scientists in 1958 discovered a hole in the ozone layer in the stratosphere over
Antarctica. It is mainly due to chlorofluoro carbons.

In 1958, NASA scientists observed a hole in the ozone layer over Antarctica and it has been
found that the ozone layer is depleting at an alarming rate. Although all greenhouse gases are
partially responsible for the depletion of ozone layer, but the main culprits are CFCs i.e.
chlorofluorocarbon or Freon’s which extremely stable, noncorrosive and inert compounds. It is
thought that one molecule of CFC has capability to destroy one lakh molecules
of ozone (O3).The probable mechanism of ozone layer depletion is;

Ultra violet rays

CCl2F2(g) CClF2(g) + Cl
Chlorine atom decomposes O3 as
Cl + O3(g) → ClO + O2(g)
U.V
ClO Cl + O
O + O3(g) → 2O2(g)
Hence once the chlorine is produced from decomposition of CFC,
hundred of thousand of ozone molecules are destroyed through above
same chain reactions. It is estimated that one molecule of CFC can
destroy 100,000 molecules of ozone.
Steps to control ozone layer depletion:
Controlling ozone layer depletion can be done in the following ways.

a) Every individual can help reduce ozone layer depletion by taking public
transportation, buying recycled products, conserving electricity, etc.

b) Refrigerators and air conditioners that do not use CFCs as a refrigerant can be used.

c) Preference should be given to those aerosols that do not contain CFCs.

d) When repairing air conditioners or refrigerators, care should be taken by transferring the
refrigerant to a recycling machine rather than exposing it to the atmosphere.

e) Spreading public awareness about the causes, impacts, and controlling measures of ozone
layer depletion.

f) Since this is not a problem limited to a single country, international agreements to restrict
CFC emissions from industries can be developed.