Air Around Us

"Life cannot be imagined without air, as air contains oxygen for respiration and carbon dioxide for photosynthesis."

Air is the invisible mixture of gases that surrounds Earth. Air contain important substance, such as oxygen and nitrogen, that most species need to survive. Sometimes, the word "atmosphere" is used instead of the word "air".

1.0Introduction

Air is the natural mixture of gases that surrounds the earth. One of the reason that the Earth can sustain life is because of its atmosphere, which keeps air readily available for chemical reactions. A number of different gases, including oxygen, make up the Earth's atmosphere in a mixture that keeps plants, animals and people alive. In addition to sustaining life, air plays a role in many other important functions that are best performed when air quality is high.

A weather cock

Matter is anything which has mass and occupies space.

• Air is matter as it has mass, occupied space and exert pressure.

Atmosphere

A layer of air surrounding the earth and retained by the earth's gravity is called atmosphere.

2.0Properties of Air

• Air is a colourless gaseous substance.
• It occupies space.

• Air has weight and exerts pressure in all directions.

Air is called a mixture because

• Air is not a single substance. A barometer is used to measure atmospheric pressure.
• It consists of many gases like nitrogen, oxygen, carbon dioxide and water vapour.
• The constituents of air are not chemically combined.

3.0Presence of Air

We cannot see air, but we can feel when it moves and moving air is called wind. Air is present everywhere around us. Its presence can be feel in many ways - when leaves of the trees rustle and the branches way in the wind or when the clothes hanging on a clothesline swing. This is because of the presence of air.

Presence of air can be felt easily by increase in its speed. For example, if we sit in front of a moving table fan with few pieces of paper, they blow away. It shows the presence of air.

4.0Composition of air

Air is a mixture of many gases. The major component of air is nitrogen gas. Almost fourfifths of air is nitrogen gas. The second major component of air is oxygen gas. About onefifth of air is oxygen gas. In addition to nitrogen and oxygen gases, air also contains small amounts of carbon dioxide gas, water vapour and some other gases (such as argon and helium etc.). The air may also contain some dust particles. The composition of air is not always exactly the same. The composition of air changes slightly from place to place and season to season.

gases and dust particles 1%

5.0Composition of air

For example, the air over industrial cities usually have a higher amount of carbon dioxide in it than the air over open spaces. The air in coastal areas may have more water vapour than inland areas. The air also contains more water vapour in rainy season. Similarly, the amount of dust in the air is more in windy places than other areas.

• Composition of different gases in air is: Nitrogen $\to 78\%$ Oxygen $\to 21\%$ Argon and other noble gases, water vapour and dust particle $\to 0.97\%$. Carbon dioxide $\to 0.03\%$

Water vapour

We have learnt earlier that air contains water vapour. We also saw that, when air comes in contact with a cool surface, it condenses and drops of water appear on the cooled surfaces.

The presence of water vapour in air is important for the water cycle in nature.

Properties of Nitrogen

Properties of Oxygen

• Supporter of combustion
• Essential for respiration
• Slightly soluble in water
• Colourless, tasteless & odourless

Carbon dioxide

In a closed room, if there is some material that is burning, you may have felt suffocation. This is due to excess of carbon dioxide that may be accumulating in the room, as the burning continues. Carbon dioxide makes up a small component of the air around us. Plants and animals consume oxygen for respiration and produce carbon dioxide. Plant and animal matter also consumes oxygen on burning and produces mainly carbon dioxide and a few other gases. It is advisable not to burn dry leaves and discarded remains of the crop, which pollute our surroundings.

Dust and smoke

The burning of fuel also produces smoke. Smoke contains a few gases and fine dust particles and is often harmful. That is why you see tall chimneys in factories. This takes the harmful smoke and gases away from our noses, but brings it closer to the birds flying up in the sky! Dust particles are always present in air.

6.0Uses of Air

• Air supports life. We all need air to survive. Air contains oxygen and carbon dioxide which is very useful for plants and animals. Plants use carbon dioxide present in the air to make their own food by a process called photosynthesis.
• Air is used for burning fuels. (like wood, coal and kerosene, etc.)
• Compressed air is used to fill tyres.
• Air helps in the dispersal of seeds.
• Blowing air (called wind) is used to turn the blades of wind-mills.

• A wind-mill being used to run a pump to draw water from the ground. Let us see how this wind-mill works to draw water from the ground. The blowing air (or wind) rotates the wind-mill blades continuously. When the blades rotate, the crank attached to the blades also rotates. When the crank rotates, then its U-bend lifts the pump rod up and down continuously. The rod works the pump which lifts the water from ground.
• Air helps in the movement of yachts (sailing boats), parachutes, gliders and aeroplanes.
• Air helps the birds, bats and insects in flying.
• Air plays an important role in the water cycle in nature.
• Earthworm takes in air through their skin surface. The skin is kept moist with the help of a substance called mucous. Oxygen present in the air gets directly absorbed through the moist skin and carbon dioxide is given out.

• Antoine Lavoisier, was the person who recognised oxygen as the gas responsible for combustion.

7.0Oxygen Cycle

The continual interchange of oxygen between the atmosphere and the water, the plants and animals and mineral matter is called the oxygen cycle.

In photosynthesis plants make their own food and oxygen is produced along with it. Plants also consume oxygen for respiration, but they produce more of it than they consume. That is way we say plants produce oxygen. It is obvious that animals cannot live without plants. The balance of oxygen and carbon dioxide in the atmosphere is maintained through respiration in plants and animals and by the photosynthesis in plants. This shows the interdependence of plants and animals. Oxygen cycle is critical to both our health and the health of our environment. We need it for respiration. The oxygen that we breath oxidises the sugar in the food to generate energy. During this process carbon dioxide is released in the atmosphere.

• Humans need oxygen to breathe.
• Oxygen is needed for decomposition of organic waste.

• Water can dissolve oxygen and it is this dissolved oxygen that supports aquatic life.

8.0Air pollution

When the air contains harmful or undesirable substances, generated by the activities of man or nature, such that their concentration interferes with human health or is injurious to plants or animals. It is said to be polluted air and the undesirable substances are called pollutants.

Effects of air pollutants

Controlling methods for air pollution

(i) By checking the emission of smoke from motor vehicles. (ii) By checking or controlling the emission of smoke from factories. (iii) By using the devices which can filter the agents causing the pollution. (iv) Reforestation methods. (v) Controlling the usage of fertilisers, spreading of dust particles and educating the people about the pollution of air and its prevention methods.

9.0Memory Map

• How do we know the presence of air? Presence of air can be felt easily by increase in its speed. For example, if we sit in front of a moving table fan, we feel its presence. If we place a few pieces of paper in front of it, they are blown away.

• How will you show that oxygen is present in air? Invert a glass on a burning candle flame. After few seconds, the flame of the covered candle goes off. This happens because the oxygen inside the glass is used up in burning.
• How will you prove that air supports burning? Two lighted candles are taken. One candle is covered and fixed in a tumbler containing water. This candle is covered by an inverted glass. After sometime, the covered candle gets extinguished as soon as all the oxygen present in tumbler is used up.

10.0Basic Terminology

• Atmosphere - A layer of air surrounding the earth.
• Weather cock - It is a instrument which shows the direction of wind.
• Mixture - A substance which have two or more component.
• Transparent - Material through which we can see clearly.
• Odourless - Things which do not have any smell is called odourless.
• Gas - State of matter which do not have fix shape, size and volume.
• Element - Those substance which is made up of single type of atom is called element. Eg: Gold, Silver, Hydrogen, etc.
• Compound - Those substance which is made up of two or more different of atom combine chemically is called compound. Eg: water, salt, etc.
• Wind - Moving air is called wind.
• Windmill - Windmill is device for tapping the energy of the wind by means of sails mounted on a rotating shaft.