unit 1- Structure and composition of atmosphere

1. INTRODUCTION
SYLLABUS
Structure and composition of atmosphere – Definitions, scope
and scales of air pollution –sources and classification of air
pollutants and their effect on human health, vegetation,
animals, property, aesthetic values and visibility – ambient
air quality and emission standards.

2. Structure and composition of
atmosphere
UNIT I

3. ATMOSPHERE
Atmosphere is the air surrounding the earth. It is a
mixture of different gases . It consists of life giving
gases like oxygen for humans and animals and CO2 for
plants. It envelops the earth all around and is held in
place by gravity of earth. Generally atmosphere ends
upto about 1600km from the earth surface

4. STRUCTURE OF ATOSPHERE
The atmosphere is divided into 5 layers
according to the diversity of temperature
and density. They are,
1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere
5. Exosphere

5. Troposphere
•It is the lowermost layer of the atmosphere.
•The height of this layer is about 18 km on the equator and 8 km on the
poles.
•Troposphere contains dust particles and water vapour.
•This is the most important layer of the atmosphere because all kinds of
weather changes take place only in this layer.
•The air never remains static in this layer. Therefore this layer is called
‘changing sphere’ or troposphere.
•The environmental temperature decreases with increasing height of the
atmosphere. It decreases at the rate of 1 degree Celsius for every 165
m of height. This is called Normal Lapse Rate.
•The zone separating troposphere from the stratosphere is known as
tropopause.

6. Stratosphere
•Stratosphere is found just above the troposphere.
•It extends up to a height of 50 km.
•The temperature remains almost the same in the lower part of this layer up to
the height of 20 km. After this, the temperature increases slowly with the
increase in the height. The temperature increases due to the presence of
ozone gas in the upper part of this layer.
•Weather related incidents do not take place in this layer. The air blows
horizontally here. Therefore this layer is considered ideal for flying of aircraft.
•The upper limit of the stratosphere is known as stratopause.
•One important feature of stratosphere is that it contains a layer of ozone gas.
•The relative thickness of the ozone layer is measured in Dobson Units.
•It contains a high concentration of ozone (O3) in relation to other parts of the
atmosphere.
•It is the region of the stratosphere that absorbs most of the sun’s ultra-violet
radiations.

7. Mesosphere
•It is the third layer of the atmosphere spreading over the
stratosphere.
•It extends up to a height of 80 km.
•In this layer, the temperature starts decreasing with increasing
altitude and reaches up to – 100 degree Celsius at the height of 80
km.
•Meteors or falling stars occur in this layer.
•The upper limit of the mesosphere is known as mesopause.

8. Exosphere
•The exosphere is the uppermost layer of the atmosphere.
•Gases are very sparse in this sphere due to the lack of
gravitational force. Therefore, the density of air is very less here.
Thermosphere
•This layer is located between 80 and 400 km above the
mesopause.
•It contains electrically charged particles known as ions, and hence,
it is known as the ionosphere.
•Radio waves transmitted from the earth are reflected back to the
earth by this layer and due to this, radio broadcasting has become
possible.
•The temperature here starts increasing with heights.

9. COMPOSITION OF ATMOSPHERE
• The atmosphere is made up of different gases, water
vapour and dust particles.
• The composition of the atmosphere is not static and it
changes according to the time and place.

10. Gases of the Atmosphere
• The atmosphere is a mixture of
different types of gases.
• Nitrogen and oxygen are the two main
gases in the atmosphere and 99
percentage of the atmosphere is
made up of these two gases.
• Other gases like argon, carbon
dioxide, neon, helium, hydrogen, etc.
form the remaining part of the
atmosphere.
• Similarly, carbon dioxide and water
vapour is found only up to 90 km
from the surface of the earth.

11. CARBON DIOXIDE:
• Carbon dioxide is meteorologically a very important gas.
• It is transparent to the incoming solar radiation (insolation) but
opaque to the outgoing terrestrial radiation.
• It absorbs a part of terrestrial radiation and reflects back some
part of it towards the earth’s surface.
• Carbon dioxide is largely responsible for the greenhouse effect.
• When the volume of other gases remains constant in the
atmosphere, the volume of the carbon dioxide has been rising
in the past few decades mainly because of the burning of
fossil fuels. This rising volume of carbon dioxide is the main
reason for global warming.

12. OZONE GAS:
• Ozone is another important component of the atmosphere found
mainly between 10 and 50 km above the earth’s surface.
• It acts as a filter and absorbs the ultra-violet rays radiating from
the sun and prevents them from reaching the surface of the
earth.
• The amount of ozone gas in the atmosphere is very little and is
limited to the ozone layer found in the stratosphere.

13. Water Vapour
• Gases form of water present in the atmosphere is called water vapour.
• It is the source of all kinds of precipitation.
• The amount of water vapour decreases with altitude. It also decreases from
the equator (or from the low latitudes) towards the poles (or towards the
high latitudes).
• Its maximum amount in the atmosphere could be up to 4% which is found in
the warm and wet regions.
• Water vapour reaches in the atmosphere through evaporation and
transpiration. Evaporation takes place in the oceans, seas, rivers, ponds
and lakes while transpiration takes place from the plants, trees and living
beings.
• Water vapour absorbs part of the incoming solar radiation (insolation) from
the sun and preserves the earth’s radiated heat. It thus acts like a blanket
allowing the earth neither to become too cold nor too hot.

14. Dust Particles
• Dust particles are generally found in the lower layers of the
atmosphere.
• These particles are found in the form of sand, smoke-soot,
oceanic salt, ash, pollen, etc.
• Higher concentration of dust particles is found in subtropical and
temperate regions due to dry winds in comparison to equatorial
and polar regions.
• These dust particles help in the condensation of water vapour.
During the condensation, water vapour gets condensed in the
form of droplets around these dust particles and thus clouds are
formed.

16. Air Pollution

17. Definition
Air pollution is the introduction of chemical particulate
matters or biological matters that cause harm or
discomfort to the human or other living organisms or cause
damage to the natural environment into the atmosphere. It
is the contamination of air by harmful gases, dust and
smoke. Them composition of gases present in the
atmosphere which gets collapsed .

18. Scope of air pollution
The scope of air pollution explained by the three associations were:
1) Engineering Built Council of USA
2) American Medical Association
3) Indian standard
The types of exposure classified on the three basis were:
1) Personal exposure
2) Occupational exposure
3) Community exposure

19. Causes Of Air Pollution
Population
Industrial development
Radio-active materials
Natural causes
Volcano Eruptions
Increase in transport facilities
Household and Farming Chemicals
Deforestation
Fossil-Fuel Emissions (while mining)

20. Scales of air pollution
Air pollution problem may occur in three scales
1.Micro scale: Few meters (e.g. House)
2.Meso scale: Few Hectares (e.g. City/ State)
3.Macro scale: Regional or continental scale (e.g. Country)

21. SOURCES OF AIR POLLUTION
Many types of pollutants are released into the air from various sources. The
major sources are,
1. Natural sources
a) (NO2 ) from electrical storms
b) HF and HCL from volcanoes
c) Air borne particles from soil
2. Manmade sources
a) Burning of fossil fuels
b) Deforestation of forest
c) Industrial activities

22. 1) Natural sources
a) (NO2 ) from electrical storms:
The rapid heating and cooling of the gases within a lightning bolt
produces nitric oxide (NO), which combines with oxygen to
create nitrogen dioxide (NO2) which is much harmful.
b) HF and HCL from volcanoes
When magma ascends close to the surface, volcanoes can emit the
halogens fluorine, chlorine and bromine in the form of hydrogen halides (HF,
HCl and HBr). These species are all strong acids and have high solubility;
therefore they rapidly dissolve in water droplets within volcanic plumes or the
atmosphere where they can potentially cause acid rain.
c) Air borne particles from soil:
Airborne dust is particle, or Particulate Matter (PM) made up of tiny solid
particles or liquid droplets that float in the air we breathe and cause
serious health problems. Fine particles are also the main cause of reduced
visibility (haze)

23. 2. Manmade sources:
a) Burning of fossil fuels:
Burning of fossil fuels pollute the atmosphere by emitting Sulphur
dioxide, nitrogen, carbon dioxide, and particulate matter such as dust
smoke etc.
b) Deforestation of forest:
Deforestation has an effect on global air quality as less water vapour
is released into the air which means an imbalance occurs and we start to
see the effects of global warming and temperature raise.
b) Industrial activities:
Industries such as chemical industries, paper and pulp mill, cotton
mills, petroleum refineries produce most air pollution.
Burning of Sulphur in thermal power plant produces Sulphur dioxide
in air which combines with oxygen and water to form sulphuric acid in the
atmosphere which forms the base for acid rain.

24. CLASSIFICATION OF AIR POLLUTANTS
The air pollution can be classified in three ways. They are,
1) According to origin
2) According to state of matter
3) According to source

25. According to origin:
Air pollution are classified into two types based on the origin.
1) Primary Pollutants
The pollutants that are emitted directly from identifiable
sources produced from natural events. (e.g. dust storms and
volcanic eruptions)
2) Secondary Pollutants:
The pollutants that that are formed in the atmosphere by
chemical interactions between primary pollutants and
atmospheric constituents. (e.g. Ozone, Sulphuric acid- by the
reaction of Sulphur dioxide and water; Nitric acid – by the
reaction of NO2 and water.)

26. According to state of matter:
Air pollution are classified into two types based on the state of matter.
1. Gaseous air pollutants:
These pollutants are in gaseous state in normal pressure and
temperature. (e.g. NO2 , SO2 ,CO2 )
2. Particulate air pollutants:
These are suspended droplets, solid particles, or the mixture
of both gases and solids.
According to the sources:
Air pollution are classified into two types based on source.
1. Natural sources
a) (NO2 ) from electrical storms
b) HF and HCL from volcanoes
c) Air borne particles from soil
2. Manmade sources
a) Burning of fossil fuels
b) Deforestation of forest
c) Industrial activities

27. EFFECT ON HUMAN HEALTH :
The air we breath has not only life supporting property but also
life damaging property when polluted. Emission from different transport
modes, the burning of fossil fuels, industrial production, forest fires are
the main cause of air pollution. Such sources f emission liberate gasses
and substances that are toxic to human beings.
AIR POLLUTION ON HUMAN HEALTH:
Our physical psychological wellbeing is affected differently by the
kind of air pollution we are exposed to. There are many organs and body
functions that can be harmed. Th e consequences includes
• Respiratory disease
• Cardiovascular damage
• Fatigue, head ache & anxiety
• Irritation of eyes nose and throat
• Damage to reproductive organs
• Harm to liver spleen and blood
• Nervous system damage

30. Effects of gases on human health:
• Carbon monoxide effect
• Ozone effect
• Nox Effect
• Lead Effect
• Mercury Effect