Air, Water & Soil: Introduction, Mixture of Gases, Air Pollutants, Oxides of Nitrogen

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  • 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)