Air, Water & Soil: Introduction, Mixture of Gases, Air Pollutants, Oxides of Nitrogen (For CBSE, ICSE, IAS, NET, NRA 2022)

Doorsteptutor material for competitive exams is prepared by world's top subject experts: get questions, notes, tests, video lectures and more- for all subjects of your exam.


  • Air we breathe, Water we drink and the land we live on are the three most important living resources for the existing humankind.
  • Human activities cause a variety of substances to get released into the atmosphere.
  • A few Pollutants are discharged into the environment and get mixed with air, water, or soil.
  • Primary pollutants are the chemicals discharged into the air having a direct impact on the environment. For e. g. Nitrogen oxides (NOx) , Sulphur oxides (SOx) , etc.
  • Secondary pollutants are produced when the primary pollutants react with other elements in the air. For e. g. Ozone


  • It is a mixture of gases that is composed of 78 % Nitrogen, 21 % Oxygen with a very small percentage of water vapour and other gases.
  • Some of the air borne disease are the flu, the common cold, Chickenpox, Measles, Mumps, Whooping cough, etc.

Classes of Air Pollutants

  • Oxygen of carbon
  • Oxides of Sulphur
  • Oxides of nitrogen
  • Volatile organic compounds
  • Photochemical oxidants
  • Suspended particulate matter
  • Radioactive substances
  • Hazardous air pollutants

Oxides of Carbon

Carbon Monoxide (CO)

  • It is a colorless and odorless gas.
  • It is a primary pollutant produced the incomplete combustion of fossil fuels. For e. g. it is present in Cigarette smoke.
  • When this meets hemoglobin, oxygen supply to the cells get obstructed.
  • Dizziness, nausea, drowsiness, etc. can be caused. Also, at higher concentrations death may occur.
  • Using catalytic converters and oxygenated fuels, CO pollution from automobiles can be reduced.

Carbon Dioxide

  • This gas is produced due to the complete combustion of fossil fuels.
  • This gas heats up the atmosphere by absorbing infrared radiations and hence is also known as a greenhouse gas.
  • Global warming may be caused due to the excess amounts of carbon dioxide released into the atmosphere.
  • One of the ways to reduce carbon dioxide emissions is to limit the amount of fossil fuels being burned.

Oxides of Sulphur

  • This includes Sulphur dioxide (SO2) and Sulphur trioxide (SO3) .
  • These oxides are produced by the combustion of coal and oil.
  • On meeting atmospheric water, they get precipitated in the form of acid rain or acid fog.
  • Inhalation of oxides of Sulphur can lead to respiratory system issues.
  • Acid rain affects the aquatic life by acidifying lakes, streams, etc.
  • Oxides of Sulphur can be removed by electrostatically precipitating the Sulphur, by filtration, etc.

Oxides of Nitrogen

  • This includes nitric oxide (NO) , nitrogen dioxide (NO2) , and nitrous oxide (N2O) .
  • Nitric oxide being a colorless gas is formed during the combustion of fossil fuels.
  • Nitrogen dioxide (a reddish-brown gas) is formed when nitric oxide reacts with atmospheric oxygen.
  • On meeting atmospheric water nitric acid is formed which gets precipitated as acid rain.
  • Nitrous oxide is a greenhouse gas.
  • Using catalytic converters automobile emissions of these pollutants can be reduced.

Suspended Particulate Matter

  • It consists of tiny particles of dust, soot, asbestos, and salts.
  • It may also contain microscopic droplets of liquids such as sulphuric acid and pesticides.
  • These pollutants are produced by the combustion of fossil fuel (e. g. diesel engines) and road and building construction activity.
  • Respiratory irritation, reduction of lung capacity, lung cancer, etc. can be caused due to exposure to the suspended particulate matter.

Photochemical Oxidants

  • These are produced during the formation of photochemical smog.
  • These are the secondary pollutants.
  • For e. g. Ozone being a highly reactive, irritating gas can cause breathing problems, throat irritation, etc.
  • Other harmful effects include damaging of plants, reduced visibility and degraded rubber, paint, and clothes, etc.
  • By reducing the amount of nitrogen dioxide in the atmosphere, photochemical oxidants can be controlled.

Hazardous Air Pollutants

Benzene (C6H6)

  • It is a common organic solvent with numerous industrial uses.
  • Cancer, birth defects, etc. can be caused.

Carbon Tetrachloride (CCl4)

  • It was formerly used as a solvent in the dry-cleaning business.
  • Cancer, central nervous system problems, etc. can be caused.

Volatile Organic Compounds (VOCs)

  • Methane (CH4) (Hydrocarbon)
  • Propane (C3H8) (Hydrocarbon)
  • Octane (C8H18) (Hydrocarbon)
  • Dichlorodifluoromethane (CCl2F2) (Chlorofluorocarbons)

Developed by: