Primary Air Pollutants

  • Primary Air pollutants
Carbon Dioxide


Natural Sources:

Exhalation through organisms.

  • Forest fires and volcanoes, hot springs and geysers
  • It is freed from carbonate rocks by dissolution in water and acids.
  • Carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers and also in seawater.

Anthropogenic sources:

Burning of fossil fuels (coal, oil and natural gas) for industrial, domestic and transport purposes releases significant, though relatively smaller, amounts.

On Environment

It is one of the main “greenhouse gases” contributing to global warming.

It dissolves in water to form carbonic acid and creates CO2 which is a major cause of ocean acidification.

On Health

  • At normal environmental concentrations, carbon dioxide has no impacts on human health.
  • At extremely high (artificial) concentrations in an enclosed space the      reduction in oxygen levels could lead to suffocation.
  • CO2 is an asphyxiant gas. Asphyxia which a condition arising when the body is deprived of oxygen, causing unconsciousness or death.
Carbon MonoxideNatural Sources:

  • Worldwide, the largest source of carbon monoxide is natural in origin, due to photochemical reactions in the troposphere.
  • It is released into the atmosphere by volcanoes as they erupt, from the smoke of forest fires, from thenatural gases in coal mines, and even from lightning.
  • Other natural sources of carbon monoxide are marsh gases, which are also called methane and produced by plants decomposing under water, marine algae, kelp and seed germination growth.
  • Man-made sources include vehicular pollution, crackers, burning of waste etc.
Health effects of CO

1.Inhalation of carbon monoxide at high concentrations can be fatal, because it prevents the transport of oxygen (in blood) around the body.

2.It combines with hemoglobin to produce carboxyhemoglobin, which usurps the space in hemoglobin that normally carries oxygen.

3.Long-term exposure to lower concentrations (such as through smoking) could harm unborn babies or cause neurological damage


Environmental Effects:

When carbon monoxide is emitted into the atmosphere it affects the amount of greenhouse gases, which are linked to climate change and global warming. Also, land and sea temperature increases changing to ecosystems, increasing storm activity, and causing other extreme weather events.

  • Vehicles and industries which are major source of ground-level ozone emissions.
  • Carbon monoxide, Nitrogen dioxide play a major role in converting O2 to O3.
  • Vegetation can also emit organic chemicals that help form ozone.
Impact On human health:

  • Ozone can irritate the lining of the nose, airways, and lungs.
  • Makes our eyes itchy, and watery. It lowers our resistance to cold and pneumonia.
  • People with asthma might have more attacks and athletes might find it harder to perform as well as usual.

On Environment:

Ozone as a gas is a major pollutant when it is present at surface level otherwise it protects humanity from harmful UV rays.

Sulphur Oxides (SOx)
  • Released naturally by volcanic activity and also from forest fires.
  • Also, from various industrial processes: production of paper and smelting of metals, oil refineries, roasting of sulfide ores such as pyrite, sphalerite, and cinnabar (mercury sulfide)
  • Burning coal in thermal power plants and diesel fuels.
  • Reactions involving Hydrogen Sulphide (H2S) and oxygen.
Environmental Impacts:

  • It contributes to acid rain : Oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thusacid rain
  • It can damage sensitive buildings or monuments, damages vegetation and wildlife and pollutes water bodies
  • Sulphur dioxide can damage plants and reduce crop yields.
  • Conversely, its antifungal properties can be beneficial for some plants.

Health impacts:

  • Sulphur dioxide can irritate the eyes and respiratory system (air passages and lungs).
  • It also weakens the functioning of certain nerves.

Note: Sulphur dioxide pollution contributed to the “great London smog in 1952 which is thought to have contributed to around four thousand premature deaths of people with lung disease or bronchitis.

Nitrogen Oxides (NOx)Natural Sources:

  • Produced during thunderstorms by electric discharge.
  • Natural fires
  • Also, from microbial processes in soils and water bodies.

Anthropogenic Sources:

  • From biomass burning (burning of forest and agricultural lands following harvest)
  • From the burning of fossil fuels (including vehicle emissions),
  • Agricultural fertilization and the use of nitrogen fixing plants also contribute to atmospheric NOx, by promoting nitrogen fixation by microorganisms


Impact on Environment:

  • High levels of nitrogen dioxide and nitrogen monoxide damages plant life.
  • Nitrogen dioxide contributes to the formation of acid rain which damages vegetation, buildings and water bodies.
  • Nitrogen dioxide is also involved in the formation of ground level ozone which damages vegetation and other materials.
  • When NOx and volatile organic compounds (VOCs) react in the presence of sunlight, they form photochemical smog.
  • Nitrogen dioxide can react with other air pollutants to form peroxyacetyl nitrates (PANs) which then carry reactive and potentially damaging nitrogen-containing species for long distances.
  • NOx emissions cause global cooling through the formation of -OH radicals that destroy methane molecules, countering the effect of greenhouse gases.


Impact on human health:

Inhalation of higher than average environmental levels of nitrogen dioxide / nitrogen monoxide (found around congested urban roads for example) can cause respiratory problems, particularly in sensitive individuals such as asthmatics.

Volatile Organic Compounds (VOC)


What are they?

They are categorized as either methane (CH4) or non-methane (NMVOCs). Other hydrocarbon VOCs are significant greenhouse gases because of their role in creating ozone and prolonging the life of methane in the atmosphere.


Impact on human health:

Irritation of the eye, nose and throat, headaches, nausea and loss of coordination.


Long term impact – suspected to damage the liver and other parts of the body.


The aromatic NMVOCs benzene, toluene and xylene which are suspected carcinogens and may lead to leukemia with prolonged exposure.


Particulate Matters


Natural Sources:

Some particles occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray.


Anthropogenic sources:

●      Burning of fossil fuels in vehicles, power plants

●      Different Industrial processes

Impact on Human health:

  • Anthropogenic aerosols—are made by human activities—currently account for approximately 10% of our atmosphere.
  •  Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.
  •  Particulates are related to respiratory infections and can be particularly harmful to those already suffering from conditions like asthma.
  •  Persistent free radicals connected to airborne fine particles are linked to cardiopulmonary disease.
Chlorofluorocarbons (CFCs)Sources: They are released from

  •  Air conditioner
  • Refrigerators,
  • Aerosol sprays, etc.


  • Environmental & Health impact: On release into the air, CFCs rise to the stratosphere.
  • When CFC comes in contact with other gases and damages 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.



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