It refers to contamination in earth’s atmosphere mainly through gaseous emissions from industry, thermal power stations, automobiles, domestic combustion etc. Air pollution is a significant cause for a number of pollution-related diseases like respiratory infections, heart disease, and stroke and lung cancer. A pollutant can be solid particles, liquid droplets or gases and these may be of natural origin or man-made.


  1. Natural origin- The natural origin activities, however affects limited areas where it occurs.
  • Volcanic activities emit sulfur, chlorine and ash particles.
  • Smoke and carbon monoxide from wildfires
  • Decomposition of dead materials, vegetation, animals
  • Radon gas from radioactive decay within the Earth’s crust
  • Dust from natural sources where large areas of land with little or no vegetation
  1. Anthropogenic (Manmade) sources- these are mainly related to the burning of fuel.
  • Smoke stacks of fossil fuel power stations,manufacturing facilities (factories) and waste incinerators, as well as furnaces and other types of fuel-burning heating devices. Traditional biomass burning (wood, crop waste and dung) is the major source of air pollution, especially in poor and developing countries.
  • Petroleum refineries are the chief source of gaseous pollutants like SO2, NO and NO2.
  • Mobile sources include motor vehicles, marine vessels, and aircraft. In the major metropolitan cities, automobile exhausts accounts for 70% of all CO, 50% of all hydrocarbon, 30-40% of all oxides and 30% of all suspended particulate matters.
  • Burning for forest and farming management and other farming practices. Fertilized farmland may be a major source of nitrogen oxides
  • Fumes from paint, hair spray, varnish, aerosol sprays and other solvents
  • Waste disposal areas generate methane which is highly inflammable
  • Military resources, such as nuclear weapons, toxic gases, rocketry etc.

Pollutants emitted into the atmosphere by human activity

  • Carbon dioxide (CO2) – it is one of the major greenhouse gases and considered the worst pollutant. Its major sources are burning of fossil fuel (coal, oil etc.) either for domestic use or for industrial use. CO2 currently forms about 410 parts per million (ppm) of earth’s atmosphere, compared to about 280 ppm in pre-industrial times, and billions of metric tons of CO2 are emitted annually by burning of fossil fuels. CO2 increase in earth’s atmosphere has been accelerating that result into disastrous effect like greenhouse effect. However CO2 is a natural component of the atmosphere, essential for plant life and given off by the human respiratory system.
  • Carbon monoxide (CO) – It is a product of combustion of fuel such as natural gas, coal or wood. Automobiles are the main source of CO, while open fire, forest fire, burning coal mines, factories, power plants, stoves etc. are other sources. It creates a smog type formation in the air that is linked with many lung diseases and disruptions to the natural environment and animals. In atmosphere its concentration is 0.5 ppm, whereas, the level of CO in urban area is 5-50 ppm. CO is very harmful to those who are exposed to congested highways to a level of about 100 ppm. CO combines with hemoglobin of blood reducing its O2 carrying capacity. The inhaled CO combines with hemoglobin and forms carboxyhemoglobin about 210 times faster than O2 does. And this formation leads to decrease the overall O2 carrying capacity of blood to different cells resulting into oxygen deficiency known as hypoxia.
  • Sulfur oxides (SOx) – Mainly SO2 which is produced by volcanoes and in various industrial processes. Coal and petroleum often contain sulfur compounds, and their combustion generates sulfur dioxide. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rainis formed. SO2 causes irritation to eyes and respiratory tract. Plants are more sensitive to SO2 than animals. It causes necrosis of leaf. The indicator plant of SO2 pollution is Nerium indicum in Delhi. Industrialization has increased the problem of acid rain. About 60-70% of the total SO2 emitted globally comes from the burning of fossil fuels for power generation.
  • Nitrogen oxides (NOx)- about 95% of the nitrogen oxides is emitted as NO and only 5% as NO2. Nitrogen oxides, particularly nitrogen dioxide, are expelled from high temperature combustion, and are also produced during thunderstorms by electric discharge. NO after combining with O2 or O3 forms more poisonous nitrogen oxide (NO2) and this NO2 after reacting with water vapor in air forms HNO3. In the urban areas and metropolitan cities maximum nitrogen oxides come from automobiles. NO2 is widely prevalent air pollutant and is the main constituent of photo-chemical smog (smog = smoke+ fog) in such cities. The oxides of sulfur and nitrogen in the atmosphere changed into sulfuric acid (H2SO4) and nitric acid (HNO3) and then dissolved in water and falls to the ground known as Acid Rain.
  • Chlorofluorocarbons(CFCs) – This is harmful to the ozone layer and products, which emit this gas, are currently banned from use. Such gases are released from air conditioners, refrigerators, aerosol sprays, etc. On release into the air, CFCs rise to the stratosphere and come in contact with other gases and damage the ozone layer. This allows harmful ultraviolet rays to reach the earth’s surface. This can lead to skin cancer, eye disease and can even cause damage to plants.
  • Hydrocarbons– the main pollutants are benzene, benzpyrine and methane, which all come from mainly motor vehicles. Benzene is a liquid pollutant emitted from gasoline, while benzpyrine is present in smoke, tobacco charcoal boiled stakes and gasoline exhaust. Both are cancer inducing pollutants. Methane is an extremely efficient greenhouse gas which contributes to enhance global warming. Methane is produced from decaying garbage, aquatic vegetation etc. it is released from burning of natural gas and factories.
  • Particulate matters- These are tiny particles of solid or liquid suspended in a gas. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. The main sources of PM are (1) fuel combustion and industrial operation such as mining, smelting, polishing, textiles, pesticides etc. and industrial fugitive processes. (2) Non-industrial fugitive process and (3) transportation sources.  Aerosol refers to combined particles and gas. It consists of sulfate, soot, organic carbon and mineral dust.
  • Metals- Toxic metals, such as lead and mercury, especially their compounds released from industries and human activities in the air. The mercury toxicity causes fatigue, anxiety, loss of appetite, headache and damage the nervous system, liver, eyes etc. lead compounds damage red blood corpuscles (RBCs) resulting in anemia and infections of liver and kidney.
  • Ground level Ozone (O3) – Ozone layer protects us from UV-rays of the sun by absorbing the UV-radiations and heats up the stratosphere causing the temperature inversion. It is formed from NOx and volatile organic compounds. At abnormally high concentrations brought about by human activities largely the combustion of fossil fuel; it is a pollutant and a constituent of smog.

Health effects of Air pollution

The health effects caused by air pollution include difficulty in breathing, coughing, asthma and worsening of existing respiratory and cardiac conditions. The human health effects of poor air quality are far reaching, but principally affect the body’s respiratory system and the cardiovascular system. Individual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, and the individual’s health status and genetics. Children aged less than five years that live in developing countries are the most vulnerable population in terms of total deaths attributable to indoor and outdoor air pollution. Besides, on the other hand, air pollution also costs the world economy through health cost.

Image courtesy- Wikipedia


Prevention & control of air pollution

For the prevention, control and eventually reduce the air pollution, here are some steps/ways that must be taken-

  • Use of alternative & clean Energy production- The most basic solution for air pollution is to move away from fossil fuels, replacing them with alternative energies like solar, wind and geothermal. To check the pollutants emitted from the industry and for the removal of particulate matter, equipment like cyclone collectors and electronic precipitators are used.
  • Conservation of energy– the production of clean energy along with to reduce our consumption of energy by adopting responsible habits and using more efficient devices are crucial.
  • Eco-friendly Automobiles/transportation- to check the emission of pollutants from automobiles, measures like shifting to electrical and hydrogen vehicles are important. Engineers can also control the emission by changing the process, modification in the equipment or through conversion of raw materials. Growing plants such as Daucus carota, phaseolus vulgaris and Pinus, which absorb CO and NOx from the air, are effective.
  • Appropriate act and rules- it is very important to make standards enforcing through the appropriate acts and rules.

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