# Air around Us Notes

## WHAT IS ATMOSPHERE?

The earth’s surface is covered with a thick blanket of air called the atmosphere. It spreads above 500 km of the earth’s surface.
The following influence of the atmosphere on the earth are:-
i. It protects the earth’s surface from the UV rays of the sun.
ii. It maintains the water cycle process and the temperature of the earth.
iii. It contains required gases like oxygen and carbon dioxide that are responsible for the breathing process of living things.
The amount of oxygen is less in the higher altitude regions. Therefore, we carry oxygen cylinders with us to get the proper amount of oxygen to survive.

## Properties of Air

The properties of air are:-
• Air is invisible
We cannot see the air but we can feel its presence while breathing, the movement of leaves of the plants, and moving of a ceiling fan, etc. The movement of the air is called wind.
• Air is matter
Air has both mass and space. Therefore, it is a matter. For example, we can freely move our hands in the air because it has space, and we can calculate its mass also by compressing it.
• Air is colourless, odourless and tasteless
Air has no colour and it's tasteless. For example, we cannot see the air, so it's colourless. While we breathing, we take oxygen in, but we cannot identify its taste. Therefore, it proves air is tasteless. Moreover, pure air has no smell too. We smell food smell coming out of the kitchen due to the mixing of other particles in the air.

## COMPOSITION OF AIR

In the beginning, people believed that air was a single substance. After many years, the study confirmed that the air is a composition of many gases.
On earth, the atmosphere consists of 78% of nitrogen gas, 21% of oxygen gas and the remaining are other gases such as carbon dioxide, argon and neon(Figure 1).

Figure 1: Composition of air

Some of the important gases on earth are:-

### Nitrogen

• It occupies every four or fifth space filled by air.
• During the combustion of fuel, the burning is controlled by nitrogen.
• Plants absorb the molecules of nitrogen in the form of nitrates and nitrites. These molecules are present in the soil that carried by the root along with the water.
• Animals get nitrogen through plants by eating them as food.
• For the production of drugs and dyes, the companies need nitrogen for producing many products.
• Nitrogen is also used for the preservation of foods.

### Oxygen

• Every one-fifth presence of the air in space contains oxygen.
• All living organisms require oxygen to stay alive. It is released by the plants and taken by the animals.
• In aquatic regions, oxygen is dissolved in the water, which helps the aquatic animals and plants to breathe.
• The animals such as earthworms, snakes and rats get oxygen from the pores of the soil.
• Oxygen is also helpful in burning the combustion of fuel.

### Carbon dioxide

• It is one of the essential gas that is required to perform many functions to maintain the balance of the survival.
• The amount of CO2 is very less. It aids in the process of photosynthesis in plants and respiration in animals.
• It is responsible for the greenhouse effect.
• It is used as a refrigerant and is also called dry ice because it can freeze at low temperatures and converts into vapour without melting.
• It is used to manufacture soft drinks and urea.
• It is used to extinguish fire because it does not support combustion.

### ​Water Vapour

• When water gets heated, it boils and starts forming vapours. This process is called evaporation. These vapours are found in gaseous state move to the sky and the formation of clouds takes place. The amount of water vapours present in the clouds is called humidity.
• The presence of water vapours is different in different regions and seasons. For example, coastal areas like Chennai and Mumbai have higher concentration levels of water vapours than the other areas like Rajasthan and Madhya Pradesh.

### Dust and Smoke

• Air contains dust. For example, the corners of the room of the house and you may have observed something that is uncleaned have dust on it. The construction sites have more dust as compared to the well-furnished rooms.
• When we burn anything, the smokes come out and mix with the particles of air. The production of products in the factories and burning woods in the house release smokes that goes out through the chimneys(Figure 2).

Figure 2: Smokes coming out of the factories through chimneys.

## OXYGEN CYCLE

• The maintenance of the amount of oxygen present in the atmosphere is done by plants by the process of photosynthesis.
• The process of respiration in animals required oxygen all day and night. Most probably, photosynthesis takes place in the daytime. During respiration in plants, the amount of oxygen released is sufficient to maintain the level of oxygen in the atmosphere.
• The two main processes that maintain the amount of oxygen in the atmosphere are photosynthesis and respiration.
• The consumption and releasing of the oxygen form a cycle called the oxygen cycle(Figure 3).
• The continuation of cutting trees and plants disturb the level of O2 present in the atmosphere. Meanwhile, the level of CO2 is increasing rapidly.
• Due to the continuation of cutting trees and urbanisation, global warming takes place.

Figure 3: Oxygen Cycle.

## ROLE OF THE ATMOSPHERE

The sunrays first fall on the atmosphere before entering the earth. It reduces the percentage of harmful rays to enter the earth’s surface. The maintenance of temperature during day and night time is done by the atmosphere.
The atmosphere is also responsible for the changes in the weather. The hot air rises up and replaced by cool air.

## Ozone Layer

The main work of the ozone layer is the absorption of UV rays by the sun. It absorbs 93-99% of the UV rays. The ozone gas is present 10 to 50 kilometres high up in the earth’s atmosphere. The UV rays can cause eye problems and skin cancer. The ozone layer is depleting due to the use of chlorofluorocarbons.

## USES OF AIR

• Air is one of the dispersal agents of pollen grains and seeds.
• Air is used to generating electricity by windmills and aerogenerators(Figure 4).
• Air is compressed to inflate tyres of vehicles.
• The important processes of living things such as respiration and photosynthesis required air.
• Flying objects like aeroplanes, helicopters and parachutes also required air to fly.

Figure 4: Windmill

## AIR POLLUTION

The involvement of harmful materials in the air molecules pollute the atmosphere. The substances that pollute the air are called pollutants such as smokes come out from chimneys of the factories
The major causes of air pollution are:-
i. The emissions from factories.
ii. Burning of coal and fuel.
iii. Volcanic eruptions.
iv. Forest fires.
v. Decay processes of vegetation.
Air pollution causes several lungs disorders and eye problems.

• Notes
• Assignments & NCERT Solutions

### Practice Question

Question 1 What is $\frac {1}{2} + \frac {3}{4}$ ?
A)$\frac {5}{4}$
B)$\frac {1}{4}$
C)$1$
D)$\frac {4}{5}$
Question 2 Pinhole camera produces an ?
A)An erect and small image
B)an Inverted and small image
C)An inverted and enlarged image
D)None of the above

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