15.4 Air Pollution
Air is one of the most
important constituents of man’s environment. Every individual person breathes
approximately 22,000 times per day, inhaling about15-22kg of air daily. Air
Pollution is the most challenging from the public health point of view. Air pollution may be defined
discharge of undesirable foreign substances into the atmospheric air there by
adversely affecting the quality of air and
causing damage to human, plant and animal lives.
The air pollutants are
classified as primary and secondary. Primary
air pollutants are the one that are
emitted from specific sources directly (e.g. Carbon dioxide, Nitrogen dioxide) whereas secondary
air pollutants are the one formed in the atmosphere as a result of interaction between the primary
air pollutants. (e.g. Ozone, photo chemical smog and peroxy acetyl nitrate)
The world’s worst chemical
disaster happened in the Indian city of Bhopal in the early morning hours
of December 3 1984.An explosion at a
union carbide pesticide plant released a cloud of toxic gas (methyl isocyanate)
into the air. Since the gas was twice as heavy as air, it did not drift away but formed a ‘blanket’ over the surrounding area. It attacked people’s
lungs and affected their breathing. Thousands of people died and the lives of many were
ruined. The lungs, brain, eyes, muscles as well as gastro-intestinal,
neurological and immune system of those who survived were severely affected.
is the region of air present above the earth’s surface. It extends up to a
height of about 500km from the earth’s surface. The major regions of atmosphere
and the main constituents are listed
in Table 15.1
Height from earth’s surface(km)
O2, N2, CO2,
Table 15. 1 Major regions of the atmosphere
The lowest region of atmosphere
in which the human beings along with other organisms live is called troposphere.
It extends up to the height of 11km from sea level. Above the troposphere
between 11km and 50km above sea level lies stratosphere. Atmospheric pollution mainly involves
the study of tropospheric and
15.5 Tropospheric Pollution
Tropospheric pollution occurs
due to the presence of undesirable solid or gaseous particles in the air. The
following are the major air pollutants present in the troposphere:
Gaseous Air Pollutants:
These are oxides of nitrogen sulphur, and carbon, hydrogen
sulphide, hydrocarbons, ozone and other oxidants.
These are dust, mist, fumes, smoke, smog metal
Gaseous Air Pollutants:
Oxides of Nitrogen
Nitrogen combines with oxygen
to form a family of oxides like
nitrous oxide (N2O) nitric oxide (NO), nitrogen dioxide (NO2),
dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4)
and dinitrogen pentoxide (N2O5). Nitrogen oxide, nitric
oxide and nitrogen dioxide are important pollutants. They are collectively represented as NOx. These gases are produced from the
combustion of fuels like coal, diesel, petrol etc. They also originate from industries ,forest fires and denitrifying bacteria.
At primary level, high level of
nitrogen dioxide exposure causes cough and breathing problems. Long term
exposure leads to respiratory
problems . At a secondary level they enter into
chemical reaction with other constituents of the atmosphere producing acid rain, photo chemical smog etc . This may be discussed in 15.5.3, 15.5.4 of this chapter.
Oxides of Sulphur
The term sulphur oxide includes
sulphur dioxide and sulphur trioxide. The most common is sulphur dioxide. It is a poisonous gas to
both animals and plants.
It is produced by burning coal, petroleum refining, power plants and some
industrial processes, such as production of paper and smelting of metal.