Composition of Air

Air is a mixture of gases and is one of the main abiotic components of the environment. Air is an extremely important natural resource, as living organisms breathe in air.

Air is found everywhere. Air in motion is called wind. It is also present in water and soil.

Composition of Air

Ancient philosophers considered air as a most vital element. Mayow in 1674 proved that air is not an element but is a mixture of two substances, one of which is active and the other is non-active. Lavoisier in 1789 named the active element as oxygen and said that it is 1/5th of the total volume of air. The non-active element in air is nitrogen and it is about 4/5th of the total volume of air. The ratio of oxygen and nitrogen in the air is about 1:4 by volume.

Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour and a few other gases. Some dust particles may also be present in it. 

  • Nitrogen (N2): 78.03%
  • Oxygen (O2) 20.09%
  • Argon (Ar): 0.94%
  • Carbon dioxide (CO2): 0.033%
  • Inert gases (Ne, He, Kr, Xe): 0.0020%

Concentration of water in air varies drastically from location to location.

Oxygen, nitrogen and carbon dioxide are directly or indirectly useful for human beings, other animals and plants. Without oxygen and nitrogen it is impossible for living beings to survive. Water vapour also plays a very important role in our life.

Oxygen

We live on the surface of the earth, and we are surrounded by air, which contains oxygen. Oxygen is one of the major components of air and life is not possible without oxygen.

A. General uses

  • Oxygen is necessary for respiration in almost all living beings.

  • It is the supporter of combustion and therefore materials burn easily in the presence of oxygen.

  • Liquid O2 called as LOX (Liquid oxidant) is used as oxidant in rockets to burn the fuel.

  • Oxygen from air gets dissolved in water which keeps the water and aquatic life fresh.

  • Oxygen cylinders are carried by climbers, during high altitude climbing, by aviators during high altitude flying and firemen during fire fighting.

  • Rusting of iron takes place in the presence of oxygen and water.

B. Medical uses

  • Oxygen is given to the patients suffering from asthma or gas poisoning and for artificial respiration in hospitals.

  • A mixture of oxygen and nitrous oxide is used as anesthesia in surgical operations.

C. Industrial use

  • In steel industry: Impurities present in iron are removed by burning in presence of oxygen.

  • For cutting and welding purposes: Oxygen is mixed with hydrogen (hydrogen torch) or acetylene (oxyacetylene torch). These mixtures are burnt to produce very high temperatures and are used for cutting metals and for welding.

  • Oxygen is also used for the manufacture of sulphuric acid from sulphur and nitric acid from ammonia (NH3).

D. Harmful Effects of Oxygen

Corrosion means deterioration of metals by an electrochemical process. The most common example of corrosion is the rusting of iron. Oxygen gas and water must be present for iron to rust. Similarly, articles made of other metals like aluminum and copper also corrode slowly in the presence of oxygen.

Oxygen combines with almost all elements to form oxides.

Nitrogen

Nitrogen is the main constituent of proteins. A number of amino acids containing nitrogen join together to form a protein. Proteins build the body. Enzymes which act as catalyst in biochemical reactions occurring in the body are mostly proteins.

Main uses of nitrogen are:

  • Nitrogen subdues the activity of oxygen. If concentration of oxygen in air is increased, processes like metabolism, combustion and corrosion are speed up and this shall have a harmful effect. Hence, due to the presence of nitrogen, oxidation of food and combustion of fuel occur at a moderate rate.

  • The compounds of nitrogen are of vital importance to plants as they help them to manufacture proteins. Animals and humans obtain proteins from plants.

Carbon dioxide

The percentage of carbon dioxide in air varies from place to place.

Main uses or carbon dioxide are:

  • During photosynthesis, plants absorb carbon dioxide and water vapour from atmosphere and convert into carbohydrates (sugars) in the presence of chlorophyll and sunlight.

  • Carbon dioxide dissolves in water to form carbonic acid H2CO3 which reacts with rocks that contain calcium carbonate (CaCO3) or magnesium carbonate (MgCO3 to form Ca(HCO3)2 and Mg(HCO3)2 salts. These salts give the taste of natural water and also supply Ca2+ and Mg2+ ions to the plants which are necessary for their growth.

  • It is also used in food preservation. When stored in an atmosphere of CO2, the grains are prevented from being destroyed by insects.

  • Solid CO2 which is known as dry ice, is used as refrigerant.

  • Dissolved in water, CO2 is used in the preparation of soft drinks. The effervescence that comes out when we open a soft drink bottle is carbon dioxide.

  • CO2 is used in fire extinguishers.

Harmful Effects of CO2

CO2 is a greenhouse gas. It traps infrared radiation which raises the atmospheric temperature and results in global warming.

Water Vapour

Air contains water vapour. Its amount in the air is not the same everywhere. It is the maximum in low latitudes and over oceans and is low in the atmosphere over polar regions. It is also more in summers than in winters.

Though water vapour comprises a very small part of the atmosphere, it plays an important role in heating and cooling of the atmosphere and in the day to day change in weather. In fact clouds, rain, snow, fog, frost and dew that we experience, all result from water vapour present in the atmosphere.

But how does water vapour come into the atmosphere? It comes into the atmosphere through a process called evaporation. Evaporation is a process in which water from any source change into vapour state due to heat. Water evaporates from water bodies due to heat of the sun forms clouds and then falls
as rain upon condensation.

Cloud Formation

Condensation of water vapour in the atmosphere leads to the formation of clouds. Clouds are formed when moist air rises upwards. When dew point is reached, condensation of water vapour occurs resulting in the formation of very tiny droplets of water. They cling to the dust particles in the air. These millions of very minute water droplets or tiny ice crystals almost hang in the air rather than fall.

They are blown as clouds by the wind. Clouds are of different types according to their shapes and height.

Dew Point: The temperature at which the water vapour begins to change into water drops.

Rain

When clouds rise up, they are cooled when blown into cooler regions of the atmosphere. The small droplets of water in them become still cooler and they, come closer to each other. A number of small droplets combine to form a big drop of water. These drops are so big that they can no longer float in the air and they fall down on the earth as rain.

As they fall, they pickup more and more small drops of water on their way down. The falling of these big drops of water from the clouds is known as rain and the process is called precipitation. The instrument used to measure rainfall is called rain gauge. Rainfall is measured in centimeters.

Relative Humidity

The presence of water vapour in the atmosphere is known as humidity. Humidity of the air is related to its temperature. For example, during summer, there are days when both the temperature and humidity are high.

Relative humidity is the ratio of the mass of water vapour actually present in a certain volume of air at room temperature to the mass of water vapour required to saturate the same volume of air at that temperature. While mentioning the relative humidity, it is necessary to mention the temperature. The instrument used to measure relative humidity is called hygrometer.