Composition of  air 

Air is a mixture of several gases, water vapour and fine dust particles. A human being respires about 22,000 times everyday and takes in about 16 kg of air. Air contains mainly nitrogen, oxygen and smaller amounts of argon, carbon dioxide, water vapours and traces of  helium, neon, krypton and xenon



 What Is Air Made Up of?

Air is a mixture of different gases and particles; oxygen, water vapour, nitrogen, carbon dioxide, dust and smoke.

  • Air is not one substance but is a mixture.
  • Air is a mixture of some gases, water vapour and dust particles.
  • The gases in the air are mainly nitrogen, oxygen, a small amount of carbon dioxide and some other gases.

Water vapours

Air contains water vapours.

  • When air comes in contact with a cool surface, it gets cooled and fog appears.
  • The presence of water vapour in the air is important for the water cycle in nature.

Dust particles

Air contains dust particles.

  • The presence of dust particles in air varies from place to place and time to time.


  • The component of air that supports burning is called oxygen.
  • Oxygen is necessary for the survival of all living beings. It is required in respiration.
  • Percentage of oxygen in the air is around 20.95%.


  • The major part of the air is nitrogen. It takes up four-fifth of the space (be around 78.11%) that air fills.
  • Nitrogen does not support burning.

Carbon dioxide

  • Carbon dioxide makes up a small component (0.03%) of air around us.
  • It causes a feeling of suffocation.
  • All materials, when they burn, consume oxygen and produce carbon dioxide.
  • It is also produced along with water vapour during respiration.
  • Plants need carbon dioxide for photosynthesis and to live.


  • Our earth is surrounded by air in the form of a thin layer. This thin layer is called the atmosphere.
  • The atmosphere extends up to several kilometres.
  • The air becomes thinner and thinner as we go high up from the surface of the earth.
  • The atmosphere is quite active due to the movement of air, concerning the earth.
  • The processes like cloud formation, thundering, rain etc., occur in the atmosphere.

Constituents of Air

Air is a mixture of a number of gases and some other particles such as:

  1. Water Vapour: Air contains water vapour which helps maintain the water cycle. When air comes in contact with cold surfaces, it is these vapours that turn into or condense into droplets of water. The amount of water vapor in the air from place to place and time to time. At a normal 30°C for instance can contain say up to 4% of water vapour.
  2. Oxygen: It is the oxygen in the air that helps humans and animals carry out the respiration process. Oxygen is also required for fire to keep burning. If we were to keep an inverted tumbler covering a burning candle, the candle will go off in a few seconds because of the lack of oxygen-containing air due to the tumbler. Dry air is said contain about 21% of oxygen.
  3. Nitrogen: Dry air is said to contain about 78% of nitrogen. This component of air helps plants in their growth process.
  4. Carbon dioxide: Carbon dioxide is a very small (only 0.04%) component of air and is a byproduct of respiration by humans and animals. Fire also uses up oxygen to burn and then produces carbon dioxide and a few other gases upon burning. This is why we feel suffocated if there is something burning inside a room. This happens due to an excess of carbon dioxide as the fire continues to burn in the room, choking out oxygen in the air.
  5. Dust and Smoke: Smoke is another component given out when fire burns. It is very harmful and adds fine dust particles and a few other gases to the air. This is why industries use long chimneys in order to release this smoke in the air. But as we know this act is what contributes to air pollution in the environment.

Air also contains very fine dust particles which can be seen when a beam of light enters a dark room. The tiny particles flying around in the beam are actually these dust particles. It is hence advised by our elders to breathe only through our nose and not our mouths so that the fine hair and mucus in the nose is able to filter out these dust particles so that we don’t inhale them and harm ourselves.

The composition of the components of air

As we can see from the Figure above, Oxygen and nitrogen together make up 99% of air while the other components come up to a mere 1% of all air in our environment.

Availability of Oxygen in Water and Soil

It is often asked how animals under the soil and in water are able to breathe. The answer is that both soil and water have air dissolved in them.

  • When we heat or boil water, we often notice that bubbles start to form. These bubbles are in fact, an indication that air molecules are present in the water. When water is heated, the air dissolved in it escapes first followed by water itself getting converted into vapour. This is how animals living underwater are able to respire.

Figure 3 Air bubbles can be seen when water is heated

  • To see the presence of water in the soil, we take a small lump of it in a beaker and add water to it. We see bubbles coming out of it which as we discussed, is proof of the existence of air molecules in the soil. As water is added, it displaces the water molecules in the soil which we see in the form of bubbles. Animals make use of this air to breathe under the soil. Some animals make holes and burrows in the soil to help make pathways for air to enter the soil. When it rains heavily, earthworms and other animals come out of the soil because these pathways get blocked by the water and they need to come outside to find the air to breathe.

Figure 4 Air particles present in soil