Air pollution is defined as the excessive
concentration of foreign matter in the air
which adversely affects the well-being of
individual or causes damage to the
property. It also affects plants, animals and
buildings.
SOURCES OF AIR POLLUTION
1. Natural sources of air pollution
2. Man-made sources of air pollution
NATURAL SOURCES OF AIR POLLUTION
1. Products from atmospheric reactions
(chemical reactions like oxidation,
combination, polymerization,
photochemical reactions etc.):
2. Aerosols-Particulates: Aerosols are
finely divided solid or liquid particles of
micro scopic size held suspended and
dispersed in atmosphere. They cause
visibility reduction, soiling of surfaces,
corrosion etc.
The various types of aerosols are
(a) dust, (b) smoke, (c) mists, (d) fog,
(e) haze, (f) fumes.
3. Micro-organisms: Infect plants and
animals.
4. Pollens: Pollens are the small grains
from the anthers of flowers which may
cause allergic reaction.
5. Radioactive minerals:
6. Volcanic ash and gases:
7. Gases and odour from swamps and
marshy lands.
MAN-MADE SOURCES OF AIR POLLUTION
i) Combustion of fuels:
(CO2 ),(SO2 ),(NO2)etc. accumulate in
the atmosphere.
ii) Industries: Emit undesirable gases
(SO2 ,CO2,NO2 ,NH3,CO).
iii) Thermal Power Plants: Mainly they
emit Sulphur dioxide.
iv) Automobiles: Exhaust contains carbon
monoxide (CO), methane, un-burnt
carbon. CO is the main source of air
pollution in congested cities.
v) Agricultural activities: Crop spraying
and field burning.
vi) Nuclear Power Plants: Emit various
radioactive substances.
CLASSIFICATION OF AIR POLLUTANTS
According to the manner in which they are
formed they are classified as:
i) Primary air pollutants, and
ii) Secondary air pollutants.
Primary air pollutants are those which
are emitted directly from the identifiable
sources.
E.g.:
a. Particulate matter such as dust and
aerosols,
b. Pollens
c. Sulphur compounds (
SO2,SO3 ,H2S
d. Nitrogen compounds (N2O,NO ,NH3)
e. Carbon monoxide (CO) and carbon
dioxide (CO2)
f. Photochemical oxidants
g. lead
h. Hydrocarbons
i. Radioactive materials
j. Halogen compounds (Hydrogen
fluoride, hydrochloric acid)
Secondary air pollutants are those which
are formed in the atmosphere as a result of
interaction between two or more primary
air pollutants or by reactions with the
normal atmospheric constituents with orwithout photo activation. These are more
harmful.
E.g.
1. Sulphuric acid
2. Ozone
3. Formaldehyde
4. Peroxy-acetyl-nitrate(PAN)
5. Photochemical smog
Sulphuric acid (H2SO4) is formed by
simple chemical reaction between sulphur
dioxide (SO2) and water (H2O) vapour. It
causes acid rains.
Ozone, formaldehyde, peroxy-acetyl-nitrate
(PAN), etc., are formed by photochemical
reactions caused by sunlight between two
primary pollutants.
No comments: