Chapter 4.
Air Around Us
We can live without food for a couple of days. We can also live without water for a couple
of hours, but we cannot live without air even for a couple of minutes. Air is very important for all living
organisms The earth is surrounded by a thick layer of air which is a mixture of
several transparent gases. This layer of
air is called the atmosphere. In the
absence of air, the earth would remain a frozen, lifeless planet in space like
any other planet. In fact, the
atmosphere that we live in, is the result of gradual and continuous changes
which started about 4600 million years ago and were energized by the sun. Let us study in detail about the air that
envelops the earth. STRUCTURE OF THE
ATMOSPHERE The atmosphere is divided into four different layers. These are: Troposphere, Stratosphere,
Mesosphere and Thermosphere. Let us
study about each of them in detail. ma
Troposphere It is the densest layer of the atmosphere. This is the part we live in and is,
therefore, most familiar to us. It is
this layer of atmosphere where all weather changes continuously take place due
to the presence of water vapors and dust particles. In the troposphere, on an average, the
temperature decreases at a rate of 1 ° C with every 165 m ascend. This is called the Normal lapse rate. This is why, temperature is very low in high
mountains. Layers of Atmosphere
Stratosphere Above the layer of troposphere lies calm and clear air which is
called stratosphere. The tot absence of
water vapors and dust particles in this layer prevents the formation of
clouds. Thus, provides visibility at its
finest. Aircrafts often fly through the
lower layer of the stratosphere becaus it facilitates visibility and this
contributes to easy flying conditions.
The zone, which demarcates in the separation between these two layers
(troposphere and stratosphere), is defined as tropopause 24
The temperature is almost constant in the lower part of the
stratosphere. Do you know? A special form of oxygen, called ozone is the
ultraviolet rays of the Sun can cause skin found in the stratosphere. This ozone layer is cancer and different
kinds of allergies. very important as it
acts as a filter and absorbs harmful ultraviolet sun rays from reaching the
earth's surface. This layer, therefore,
acts as a shield over the earth's surface.
In the absence of the ozone gas in the atmosphere, life would have been
impossible on the surface of the earth.
Mesosphere Above the stratosphere lies another layer known as
mesosphere. It is a cold layer where
temperature generally decreases with increasing altitude. Meteors burn up in this layer. Thermosphere Above the mesosphere is
thermosphere where the air is very thin.
In the lower layer of thermosphere (ionosphere), ion - particles are
present in concentration. These ion -
particles are electrically charged and play an important role in our wireless
communication, Radio waves can be sent to different places through these ion -
particles. They enable wireless
communication over the earth's surface.
Beyond the thermosphere, about 1600 km above the earth's surface, the
earth's atmosphere gradually merges with very thin gases of the outer
space. Do you know? In the upper layer of the atmosphere,
microscopic dust particles scatter incoming solar rays and absorb all colors
except blue, giving blue color to the sky, AIR AND ITS COMPOSITION Nitrogen 78%
DAYEON 20.9% The air which we inhale, is not a single gas , but a mixture of a number of gases. It is found that up to an altitude of 90 km
from the earth's surface, the proportion of three major gases present in the
atmosphere is uniform. These major gases
are nitrogen, oxygen and carbon dioxide.
But above 90 km, the composition begins to change due to increase in the
proportion of lighter gases like helium.
Apart from these gases, the air also argon gases 0.90% Other cases 0.17%
Carbon dioxide 0.03% Composition of Air 25
contains some amount of dust particles and water
vapors. Let us understand the importance
of each of these constituents in the atmosphere. Nitrogen It occupies 78 per cent of the total
volume in the air. It is thus, the most
plentiful gas but has little direct importance to living organisms. When we inhale air, a major amount of
nitrogen is not utilized inside our body system. On the contrary, plants absorb nitrogen
through the soil. This is used by plants
to support their growth and development.
Thus, nitrogen is indirectly useful to us. Oxygen It is the second major gas in volume
which makes up about 21 per cent of the air.
All living organisms whether human beings or animals inhale oxygen from
the surrounding air to stay alive. Thus,
oxygen is known as a life supporting gas.
The atmosphere is continuously replenished of oxygen by the green plants
through the process of photosynthesis and this keeps a healthy balance of
oxygen in the air. Therefore, growing of
trees and bushes is very important to maintain a balance of oxygen supply in
the air. Carbon dioxide Although it
constitutes a very small percentage, i.e.
0.03 per cent of the air, it is an important gas in carrying the life
cycle of plants over the earth. The
carbon dioxide gas absorbs heat of the sun and warms up the lower atmosphere of
the earth's surface. Human beings and
animals release carbon dioxide during the process of respiration. The green plants draw this carbon dioxide
from the atmosphere and use it during the process of photosynthesis. In this way, a balance is Do You Know? maintained in the atmosphere. If the amount of global warming can be
prevented by minimizing of carbon dioxide is more in the air, it can the use of
CO, CFCs, methane, etc. adversely affect
the living beings. Since, the carbon
dioxide has a property to absorb heat, it increases temperature of the
atmosphere, which, in turn, increases the temperature over the earth's
surface. This is the cause of global
warming, which is threatening the life support system of this planet. Apart from these three major gases, the atmosphere
also has some other gases like argon, helium, methane, etc. , in small volumes. The water vapors and dust particles are the
other important components present in the atmosphere. They have their own relevance. The atmosphere also holds solid particles of
dust, salt, pollen, etc. These dust
particles act as mydroscopic nucleus around which water vapors get condensed to
form clouds. 2 26
OVO 100 1010 May sto POLLUTANTS IN THE AIR Besides the
natural combination of gases, water vapors and dust particles, the atmosphere
continuously receives man - made substances of both solid and gaseous nature
largely due to multiple human activity.
For example, plying automobiles in cities releases gaseous pollutants
like carbon mono oxide, sulphur dioxide and lead particles, causing air
pollution which, in turn, is a cause of several diseases. The smoke particles when combined with fog
form smog, causing serious air pollution health problems like irritation in
eyes, skin disease, respiratory disease, etc.
Occasionally, volcanic eruptions in some countries also add solid and
gaseous substances in large quantity to the atmosphere. Sometimes, forest fires add Do You Know? pollutants and cause further damage to the
atmosphere. We should have an awareness
of pollution is also caused by burning of husk by these pollutants so that they
are reduced in the farmers.
atmosphere. ATMOSPHERIC
TEMPERATURE AND PRESURE Most of the life forms on the earth exist in the lower
part of the poster spinde atmosphere.
Although we may never feel the pressure or weight of air over us but it
constantly presses us. This pressure or
weight of air is measured by means of an instrument called barometer. The unit of air pressure is known as
millibar. The normal air pressure at sea
level is 1,013 millibar. As we go higher
on the mountains or travel in air, we notice our ears pop; This is due the drop in air temperature and
atmospheric pressure. This variation in
atmospheric temperature and atmospheric pressure divides the atmosphere in
different layers. CHANGE% Lever system
Android call Barometer 27
Wind In an area where temperature rises high, the air gets
heated and rises upward. This causes
fall in air pressure and the area, thus, becomes low pressure area. The space vacated by hot air is replaced by
cold, denser air of the surrounding high pressure area. This flow or movement of air is called
wind. Thus, wind always flows from high
pressure area to low pressure area. The
phenomenon of monsoon is a good example of such seasonal winds. This change is caused due to unequal heating
of land and water. Our country receives
monsoon rains which support our agricultural economy. Thus, our country is very much dependent on
the monsoonal rainfall. Windwane Do You
Know? Atmospheric temperature and
pressure are opposite to each other on the earth's surface. Highes the temperature, lower is the air
pressure. Driven Trumpas.com Mechanism
of Rainfall As the hot air rises, it reaches high in the atmosphere where it
cools down due to the presen of low temperature there. Thus, the water present in the form of water
vapors condenses in tiny droplets of water or crystals of ice. In due course of time, these tiny particles
join together and form clouds. Due to
further cooling, these tiny condensed droplets join and form larger
droplets. In the course of time, these
droplets become so heavy that the air cannot hold them. Hence, they fall down as rainfall or snowfall,
depending upon the atmospheric temperature of the region mechanism of rainfall
(28
Do you know? The
rainfall is very important to all of us as it brings water to the earth which
is essential for the survival of all kinds of life on it. When the rainfall is scarce or very low, it
causes drought. On the other hand,
excessive rainfall causes floods. The
rainfall can be measured with the help of an instrument called rain gauge. The unit of measuring rainfall is centimetre
or millimetre. Rain gauge MONITORING
WEATHER CONDITIONS It is important to know that weather refers to the state of
atmosphere that includes its temperature, pressure and humidity for a specific
place and for a short period of time.
Weather may change in different places of the same city or locality. On the other hand, climate refers to the
state of atmospheric condition that includes temperature, rainfall, pressure
over a long period of time and covers a larger area, e.g. the climate of India is monsoonal. It is important for us to know the daily
temperature and pressure conditions of the place where we live. Further, when we travel to any distant place,
we should know these variables to prepare ourselves for a particular weather
condition. For our benefit, the weather
reports are given daily in the newspapers, radio and television. It includes all information regarding
atmospheric conditions e like forecast of temperature, humidity, rainfall, wind
velocity, sunrise and sunset. These are
useful to o all of us in different ways and we should make it our habit to read
the weather report on daily basis. Keywords
global warming: a gradual increase in the overall temperature of the earth's
atmosphere. humidity: amount of water
vapours in the atmosphere. monsoons:
seasonal reversal of the wind direction according to the change in season. photosynthesis: plants absorb carbon dioxide
in the presence of sunlight and turn that energy into food. 29
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