Air pollution is an unwanted change in the quality of earth's atmosphere
caused by emission of gases due to burning of fossil fuels, outpouring of
ashes and gases from the particulate matter due to soil erosion. Pollen
and organic compounds from vegetation and lightening strokes also pollute
Now, we will study about the different agents that pollute the air. For
convenience, air pollutants can be classified into the following three
The pollutants which come out from natural sources such as forest fires
started by lightening, dispersal of pollen, soil erosion, volcanic
eruptions, volatile organic compounds from leaves and trees, decomposition
of organic matter and natural radioactivity, etc. are natural pollutants.
This type of atmospheric pollution is not a new phenomena. It is perhaps
as old as the earth itself. Nature has its own mechanisms of dealing with
such pollution. In any case, the concentration of pollutants from the
natural sources is often quite low and rarely causes any serious damage.
A primary pollutant can be defined as a harmful chemical that directly
enters the air as a result of a natural event or human activities. For
example, when coal, oil, natural gas or wood is burnt, carbon dioxide and
carbon monoxide are formed, automobiles contributing a large share of
carbon monoxide. All these gases enter the atmosphere. Another important
pollutant is sulphur dioxide (SO2) which is added to atmosphere by burning
of coal and oil containing sulphur as impurity in electric power plants.
Other primary pollutants are oxides of nitrogen, hydrocarbons and
suspended particulate matter.
Secondary pollutants result from harmful chemical reaction between two or
more air components. For example, sulphur dioxide, the primary pollutant
reacts with oxygen in the atmosphere to form the secondary pollutant,
sulphur trioxide (SO3) (2SO2+O2 — 2SO2). The sulphur trioxide can then
react with water vapour in air to form droplets of sulphuric acid (H2SO4)
(SO3+H2O — H2SO4), another secondary pollutants.
SOME MAJOR AIR POLLUTANTS
The major air pollutants are those which are produced in significant
amounts and have health and other environmental hazard. We will describe
here some of the major air pollutants.
Oxides of Sulphur
The oxides of sulphur have deleterious environmental effects. Electrical
power plants which use coal are largely blamed for sulphur dioxide
emissions into the atmosphere.
Sulphur dioxide is itself injurious to plant and animal life. It can also
react with ozone, hydrogen peroxide, .or water vapour in the atmosphere to
form sulphuric acid (H2SO4). Sulphuric acid is one of the strongest acids
known. It corrodes lime stone and metals and destroys clothing. It also
has injurious effects on respiratory tissue. Sulphuric acid is considered
as one of the most toxic and dangerous air pollutants, being a major
component of acid rain. You will read more about acid rain in the later
sections of this Unit.
Since most of the sulphur dioxide comes from burning of 'coal in the power
plants, the control of sulphur dioxide emissions into the atmosphere will
depend upon the production and use of energy as well as on the quality of
the coal used.
Oxides of Nitrogen
Oxides of nitrogen are produced when fuel is burned, at high temperatures.
Nitrogen, which is, ordinarily inert, combines with oxygen in high
temperature flames and tends to stay combined if the exhaust gases are
Oxides of nitrogen are relatively harmless at ordinary concentrations. They
are released into the air mainly from vehicular smoke, electric power
plants, industrial establishments, commercial institutions and residential
units. The automobile emission is the major contributor of nitrogen oxide,
accounting for about 50% of the total. Electric power plants contribute
about 33% and the percentage share of the industrial establishments,
commercial institutions and residential units is 12%, 14% and 1%
respectively. In Indian cities diesel operated vehicles contribute about
90% of the oxides of nitrogen to the air.
Nitric oxide (NO) is the first product of the combination of atmospheric
nitrogen with oxygen at high temperatures. At high concentrations, nitric
oxide causes asphyxiation.
Further, nitric oxide combines easily with the atmospheric oxygen to form
nitrogen dioxide (NO2). Nitrogen dioxide may create a variety of human
ailments, from mere gum inflammation to internal bleeding, pneumonia, lung
Hydrocarbons are compounds made up of carbon and hydrogen. Some
hydrocarbons have direct effect on human beings and are carcinogenic in
nature. They are produced during the production of coke and smoldering of
refuse piles near coal mines or during improper burning of coal.
Carbon monoxide (CO) is one of the major pollutants from automobiles
comprising 80% of all automobile exhausts. Small amounts are also emitted
from volcanoes and
forest fires Carbon monoxide is a product of incomplete combustion of
fuels. Carbon monoxide reduces the oxygen carrying capacity of the blood.
It can be fatal at concentrations exceeding 1000 ppm. Therefore, it is not
advisable to work in closed rooms with open coal fire.
Carbon dioxide (CO2) is one of the basic end-products of the burning of
fossil fuels, paper, leaves, tobacco and other carbon containing
materials. Carbon dioxide is considered relatively innocuous because it
has no direct effect on health. But it has several important side effects.
It contributes towards acid rain and greenhouse effect.
Lead is a chemical pollutant which enters the atmosphere from automobile
exhaust. A compound of lead, tetraethyl lead (TEL) is used as an anti-
knock agent in petrol or gasoline for smooth and easy running of vehicles.
If the octane rating of petrol is low, the fuel and air mixture can ignite
prematurely and disturb the smooth running of the engine and cause
knocking. Therefore, the octane rating of gasoline is raised by the
addition of TEL in concentrations between 0.3 and 0.6 grams per litre.
Developed countries have by and large discontinued the use of TEL as an
antiknock agent and have increasingly gone over to the use of other
methods for raising the octane number of gasoline. It is a matter of
concern that we, in India, still use leaded gasoline.
The lead mixed air, if inhaled, may produce injurious effects on the
kidneys, blood and liver. It can get mixed up with water and food and can
create cumulative poisoning. The effects are far-reaching in case of
growing children. The increase in level of lead in children may cause
lowering of intelligence. Hence, it forms an important parameter of air
<h4><strong>Suspended Particulate Matter
Any small solid particles and liquid droplets suspended in the air are
known as particulate matter. The size and weight, in particular, determine
their suspension from a few seconds to months in the atmosphere. Most of
such particulate matter is emitted by establishments which use coal as
fuel. These air pollutants are also known as aerosols.
The aerosols remain constantly under the influence of gravitational force
of earth. The aerosols in the atmosphere are of two kinds: one is the
natural, such as fog, bacteria, plant spores, pollen, etc. These usually
do not cause any atmospheric pollution. The second type of aerosols, such
as cement powder, flue dust from coal dust combustion, quartz and asbestos
powder, oil smokes, tobacco smokes and radioactive aerosols are air
pollutants due mainly to man's activities and cause constant damage and
threat to the atmosphere.
The term refers to the smoking of tobacco, but many other substances can
also be smoked, for example, opium, dhatura and other herbs. Cigarette
smoking is responsible for many diseases due to the presence of
carcinogenic tars in cigarette smoke. The effectiveness of carcinogenic
tars is lesser ir case of cigar and pipe smoking due to lower temperature
at which tobacco is smoked. It is because of the harmful effects that the
Government of India has made statutory provisions for cigarette
manufacturers in the country to print on every packet of cigarettes a
warning saying that "smoking is injurious to health"
Besides, it has also been established that non-smokers whose work
conditions lie in smoke-filled rooms are also vulnerable to health
In spite of warnings, cigarette smoking continues, and more and more
problems are predicted in future years to come. The most common health
problem is the occurrence of cancer of the lungs and larynx. The other
health problem associated with smoking is coronary (heart) disease. The
well known 'smokers' cough' is of local nature which may bring irritation
and bronchitis. Finally, the death rate in middle aged people, who smoke
more than 20 cigarettes a day, is more than twice that of non-smokers,
taking all diseases into account.
The smoking habit, however, can be controlled only by 'will power' and in
some cases by substituting disagreeable lozenge for the cigarette.
You must be aware that radioactive substances disintegrate with emission of
radiation. Three kinds of radiation namely alpha, beta and gamma have been
identified. These radiations interact with living tissues and damage them.
The sources of radiation can be natural, which include both—cosmic and
terrestrial, and artificial or man-made. Cosmic rays are the primary source
of radiation which enter the atmosphere from outer space. The primary
radiation on entering the atmosphere produces secondary radiation through
interactions with atoms in the atmosphere.
Terrestrial radioactivity originates from radioactive materials of the
earth. A large proportion of this radiation is from radioactive materials,
such as uranium, thorium, actinium, potassium and carbon. However,
strontium-90 which is a major long-term hazard gets incorporated into
vegetation, dairy products and even building materials like bricks,
concrete, etc. These materials are believed to have been present in the
earth since its inception.
In recent decades radioactive materials have been increasingly used for
generation of power, research and medicinal purposes. The radiation from
industrial and research units is believed to be absolutely negligible, as
these are so shielded by fool-proof measures that the radiation level
outside the reactor's core seems to be very much lower than the danger
dose. Furthermore, these reactors are so designed that they cannot explode
like atomic bombs. The real danger comes from the use of radioactive
material for destructive purposes. The world has not yet forgotten the
destruction caused by two fission bombs which were dropped in Hiroshima
and Nagasaki towards the end of Second World War.
The harmful effects of radiation, are cancer, gene mutation, damage to the
central nervous system, blood forming tissues, eyes, skin, and a host of
other organs and systems. Although, at present, the total radiation from
all of the man-made sources is considerably low, it may, however, increase
in future years with expanded use of radioactive materials. Therefore, the
adverse biological effects of the exposure must be evaluated carefully.
The particulate matter and noxious gases floating in the atmosphere can trap solar heat in a
process known as the greenhouse effect. Ideally, the sun’s rays should penetrate the
atmosphere and the Earth’s surface should reflect excess radiation back out of the
atmosphere. However, air pollution bounces some of that excess heat back down to Earth and
contributes to climate change. The Environmental Protection Agency reports on its website
that if the current trend of rising temperatures continues, it could lead to the melting of the
polar icebergs, rising sea levels and flooding in coastal areas.
Air pollution’s destruction of the ozone layer exacerbates the problem of the greenhouse
effect and leads to its own complications. The ozone layer serves as a filter limiting the sun’s
ultraviolet, or UV, radiation entering the atmosphere. Chlorofluorocarbons, or CFCs, carbon
dioxide and other ozone depleters react with the sun’s radiation and break down to their
component atoms, which then rob the ozone of oxygen atoms. Currently, the ozone layer’s
concentration decreases by about 2 percent each year, allowing for more and more UV
radiation to reach the Earth’s surface. The increase in radiation can cause skin cancer,
damage to the human immune system and eye damage. It also kills small aquatic organisms
like plankton, affecting marine food chains and releasing additional carbon dioxide into the
atmosphere when the life forms decompose.
Many people are affected by air pollution, whether or not they know it. FuelEconomy.gov
reports that in 2007, about 150 million Americans lived in areas where monitored air
pollution reached unhealthy levels. Although industry does cause air pollution, the vehicles
crowding the highways produce many, if not most, of the chemicals that cause smog and
pollution-related health problems.
In this industrial age, air pollution cannot be eliminated completely, but steps can be taken to
reduce it. The government has developed, and continues to develop, guidelines for air quality
and ordinances to restrict emissions in an effort to control air pollution, reports Dr. Cheryl E.
Merritt of the Yale-New Haven Teachers Institute. On an individual level, you can reduce
your contribution to the pollution problem by carpooling or using public transportation.
Additionally, buying energy-efficient light bulbs and appliances or otherwise reducing your
electricity use will reduce the pollutants released in the production of electricity, which
creates the majority of America’s industrial air pollution, according to the Oberlin College
Resource Conservation Team.