What Is Air Pollution?


Air pollution can be defined as the presence of toxic chemicals or compounds (including those of biological origin) in the air, at levels that pose a health risk. In an even broader sense, air pollution means the presence of chemicals or compounds in the air which are usually not present and which lower the quality of the air or cause detrimental changes to the quality of life (such as the damaging of the ozone layer or causing global warming).


Air pollution is probably one of the most serious environmental problems confronting our civilization today. Most often, it is caused by human activities such as mining, construction, transportation, industrial work, agriculture, smelting, etc. However, natural processes such as volcanic eruptions and wildfires may also pollute the air, but their occurrence is rare and they usually have a local effect, unlike human activities that are ubiquitous causes of air pollution and contribute to the global pollution of the air every single day.

Types of Air Pollutants

A large number of contaminants may pollute the air in a large variety of forms. Almost any toxic chemical could make its way into the atmosphere to pollute the air that we breathe. Aerosol particles (clouds of liquid and solid particles in a gas) that are found in the air may also contain pollutants.

The chemical compounds that lower the air quality are usually referred to as air pollutants. These compounds may be found in the air in two major forms:

  • in a gaseous form (as gases),
  • in a solid form (as particulate matter suspended in the air).


The most common air pollutants are:

  • Sulfur oxides (SOx) - toxic gases produced by the volcanic activity, industrial processes, and burning of fossil fuels.
  • Nitrogen oxides (NOx) - toxic gases.
  • Carbon monoxide (CO) - extremely toxic, produced by incomplete combustion and vehicle exhaust.
  • Carbon dioxide (CO2) - not toxic, but may dislocate oxygen and produce death through asphyxiation. Additionally, it is a greenhouse gas, emitted by combustion processes, microbial activity, plant respiration, and also naturally volatilizing from oceans and seas.
  • VOCs (Volatile Organic Compounds) - toxic and carcinogenic, generated through many human activities such as industrial processes and waste disposal.
  • Particulate matter (PM) of volcanoes and wildfires, also produced by fossil fuels, mining, foundries, etc.
  • Hg in gaseous form - results from industrial processes, mining, foundry activities, and other processes.
  • Ammonia (NH3) - usually emitted from agricultural processes.
  • Radioactive pollutants - produced through radioactive decay and nuclear explosions, war explosions, etc.

Examples of Air Pollutants

In most cases, air pollutants cannot be seen or smelled. However, that does not mean that they do not exist in high enough amounts to be a health hazard! Additionally, a number of gases are linked to the so-called "greenhouse effect", which means that those gases retain more heat and thus contribute to the overall global warming. The most common example of a greenhouse gas is carbon dioxide, which is emitted from many industrial processes. Another example is methane, which is also an explosive gas. 

Examples of the main air pollution causes and air pollution sources can also be found in the chart below:

Air Pollution CauseAir Pollution Source
Volcanic activities Magma and toxic gases resulted from eruptions
Winds and air currents Dust or dirt from bare areas of land
Methane formed through anaerobic (in the absence of oxygen) degradation of plants and animals
Wildfires Burning of wood and other materials from the soil
Microbial decaying processes Organic matter of the living organisms and the chemical or biological materials in the environment
Radioactive decay processes Earth’s crust, and materials which emit radon gas when decaying
Increasing temperatures Volatile materials in nature (e.g., dissolved carbon dioxide from oceans and seas)
Mining & Smelting
Mine tailing disposal
Natural mineralogical deposits
Foundry activities Raw metallic materials; natural mineralogical deposits
Industrial processes Raw materials used in the manufacture of products; fossil site fuels like petroleum 
Transportation Fossil fuels (e.g. gasoline, diesel and other petroleum products) used by combustion engines
Construction & Demolition Construction materials, including pipes and paints
Coal Power Plants & Heating of the Buildings Fossil fuels (e.g. petroleum products, coal)
Waste incineration Burnt chemical waste
Landfill disposal practices Various types of waste
Agriculture Pesticides/insecticides/herbicides sprayed
Controlled burning Wood and other burnt materials
Military activities Toxic gases; fuel for airplanes, helicopters, ships, rockets, etc.
Smoking Toxic gases and the particulate matter resulted from burning tobacco
Storage and use of household products Organic solvents (VOCs), lead (Pb) from paints
Dry cleaning Chlorinated solvents (PCE) or petroleum solvents used by dry cleaners

The Effects of Air Pollution on Human Health

Air pollution has serious effects on the human health. Depending on the level of exposure and the type of pollutant inhaled, these effects can vary, ranging from simple symptoms like coughing and the irritation of the respiratory tract to acute conditions like asthma and chronic lung diseases.

Skin problems and irritations can develop due to prolonged exposure to several air pollutants, and a variety of cancer forms may develop after inhaling air contaminants. Do not neglect potential diseases caused by air pollution.

Air pollutants that have serious negative effects on the human health can be classified as toxic and non-toxic.

Toxic Pollutants


asbestos, PCE, TCE, vinyl chloride (VC), benzene, PAHs (such as benzo[a]pyrene), ethylene dibromide (EDB), ethylene dichloride (EDC), PCBc, As, Cd, Ni, Cr, some Hg compounds, arsenic oxide, some nitrates, pesticides/insecticides/herbicides, radon;


lead, carbon monoxide, ammonia, acetone

Non-Toxic Pollutants

These pollutants can still asphyxiate by oxygen depletion, therefore they are still not safe in certain quantities and/or contexts.


carbon dioxide



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