Air is a mixture of different gases. It contains oxygen, Nitrogen, Argon, Carbon dioxide and traces of some inert gases. It also contains water vapour.

O2, N2 and CO2 are directly or indirectly useful to all living organisms. Air above the earth exerts a force on earth’s surface which is called atmospheric pressure. Atmospheric pressure decreases with altitude.

Oxygen - O2 

  • Necessary for respiration of almost all living organisms.
  • Supports combustion. Finds use in cutting and welding torches in the form of hydrogen or acetylene torches.
  • Mixture of oxygen and nitrous oxide is used as anesthesia in surgical operations.
  • Rusting of metals occurs in presence of oxygen and water.

Nitrogen - N2

  • Main constituent of amino acids, proteins and enzymes.
  • Subdues the activities of oxygen such as metabolism, combustion and corrosion.

Carbon dioxide - CO2

  • During photosynthesis green plants absorb CO2 and H2O and convert them into sugars.
  • Used for food preservation.
  • Solid CO2 is called dry ice which is used as refrigerant.
  • It is used in soft drinks and in fire extinguishers.
  • It also acts as a green house gas.

Water vapour

  • It causes heating or cooling of atmosphere and day to day change in weather.
  • Water evaporates from water bodies due to heat of sun, forms clouds and then falls as rain.

Air Pollution: Air pollution is caused by harmful chemicals, biological wastes and particulate matter introduced in the atmosphere through human activities. Air pollution has harmful effects on all living organisms. Primary pollutants include CO, CO2, Volatile organic compounds, CFCs, Particulate matter. Secondary pollutants include photochemical smog, ground level ozone.