Environmental Pollution
Environmental Pollution
Environmental
pollution is an undesirable change in physical, chemical or biological
characteristics of our surroundings (air, water or land). It can affect human,
animal and plant life as well as materials. Pollution may be natural or man-made.
It can be classified according to the components of the environment being
damaged. These are:-
(i)Air
Pollution
(ii)Water
Pollution
(iii)
Soil (land) Pollution
Pollutant
When the
concentration of a substance already present in nature or of a new substance
increases to undesirable proportions causing danger to human beings, other
animals or vegetation and other materials, the substance is treated as a
pollutant. The pollutants spoil the environment and are harmful to living
organisms and other materials. The common pollutants are :
(i)Gases
like carbon monoxide, sulphur dioxide, oxides of nitrogen, etc.
(ii)Compounds
of metals like lead, mercury, zinc, cadmium, arsenic, etc
(iii) Pollen
grains, dust.
(iv) Pesticides and detergents
(v) Sewage
and
(Vi) Radioactive substances.
Threshold Limit Value (TLV)
This indicates the permissible limit of a pollutant
toxic in atmosphere to which a healthy worker is exposed during 8 hours a day or
40 hours a week for life time without any
adverse effects. For example, TLV of CO is 50 ppm and that of CO2 is 5000 ppm. But TLV for a poisonous gas phosgene is only 0.1
ppm.
Atmosphere
The gaseous
envelope surrounding the earth is known as atmosphere. The two major components
of dry and clean air in the atmosphere (by volume) are nitrogen (78.09%) and
oxygen (20.95%). Argon (0.934%) and carbon dioxide (0.034%) are the minor
components of the atmosphere. Air can hold water vapour from 0.1 to 5% by
volume and also contains traces of elements such as noble gases (neon, helium,
krypton, xenon), hydrogen, methane, Sulphur dioxide, ammonia, ozone etc. The
atmosphere surrounding us may be divided into four regions :
(i)Troposphere
(8 to 12 km above earth’s surface)
(ii)
Stratosphere (11 to 50 km above earth’s surface)
(iii)
Mesosphere (50 to 90 km above earth’s surface)
(iv)
Thermosphere (90 to 500 km above earth’s surface)
About 80% of
the total mass of air and almost all of the water vapours of the atmosphere is
found in the inner layer known as troposphere.
The chemical
and photochemical reactions play a significant role in governing the chemical
species present in the atmosphere.
Air Pollutants
There are two types of air pollutants:-
1.Primary
air pollutants
2.
Secondary air pollutants
1.
Primary air pollutants :- A primary air pollutant is a harmful chemical substance that directly
enters the air as a result of natural events or human activities. For example,
(i)Carbon
oxides (CO and CO2)
(ii) Nitrogen oxides
(NO)
(iii) Sulphur oxides
(iv) Hydrocarbons
(v) Suspended
Particulate matter.
2. Secondary air
pollutants:- A secondary air pollutant is a harmful chemical that forms in the
air due to a chemical reaction between two or more air components or a primary
pollutant and one or more air components. For example, Sulphur dioxide is a
primary pollutant in air. It reacts with oxygen gas in the atmosphere to form
the secondary pollutant sulphur trioxide (So3). Even the sulphur trioxide formed may react with the water
vapour in air to form sulphuric acid.
Sulphuric
acid is, therefore, also a secondary pollutant.
Usually Co2 is not considered as
pollutants.
Other air
pollutants are metals like Be, Ba, Cd, Fe, Mn, Pb, Hg, Ni, Zn (from mining and
metallurgy), non-metals such as As, P, Se (from combustion of industrial fuels,
fertilizers), radioactive substances (from nuclear power plants).
Tropospheric Pollution
The
tropospheric pollution occurs because of the presence of undesirable solid or
gaseoud particles in the air. The pollutants may be brodly classified into two
major types :
1. Gaseous air
pollutants:- these include oxides of Sulphur, nitrogen and carbon, hydrogen
sulphide, hydrocarbons, ozone and other oxidants.
2. Particulate
pollutants:- These are dust, dumes, mist, spray, smoke etc.
Particulates in Air Pollution
1. Particulates
:- The small sized solid particles and liquid droplets which range in size from
are collectively called as Particulates. These
particles are usually individually not visible to the naked eye. However, small
particles often collectively form a haze that restricts the visibility. The
common particulates are smoke, mists, fumes, dust etc.

The particulates in the
atmosphere may be viable or non-viable. The viable
particulates are the small living organisms which are dispersed in the
atmosphere. These include bacteria, moulds, fungi, algae, etc. Some of these
viable particulates cause allergic reactions on human beings. Fungi can also
cause plant diseases.
Non-Viable
particulates
are formed either by the breakdown of large materials or by the condensation of
minute particles and droplets.
The effect
of particulates pollutants depend upon the size of the particles. The coarser
particles of size more than 5 microns are likely to lodge in the nasal passages
whereas the smaller ones are more likely to penetrate into the lungs. The rate
of penetration is inversely proportional to the size of the particles. Some of
these particles are carcinogens. Continuous inhaling of these small particles
for long periods of time irritates the lungs and causes scarring or fibrosis of
the lung lining. This type of disease is very common in industrial settings and
is known as ‘pneumoconiosis’.
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