Air pollution

We explain what air pollution is, and explore its causes and effects. In addition, we discuss its characteristics, possible solutions, and more.

Air pollutants may be chemical, physical, or biological.

What is air pollution?

Air pollution occurs when there are substances or types of energy in the air that cause temporary or permanent damage to humans, other living beings, and the environment.

Air pollutants can be solid, liquid or gaseous substances, and they may be chemical, physical, or biological. The majority of air pollutants are produced by industries and by the burning of fossil fuels, mainly vehicles using internal combustion engines and power generation plants.

The main air pollutants are carbon monoxide (CO), sulfur dioxide (SO2), chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), nitrogen oxides, sulfur hexafluoride (HF6), methane (CH4), particulate matter, and smog (mixture of air and pollutants at high pressures causing air and pollutants stagnation). 

Air pollutants can deposit on people, animals, crops, rivers, lakes, seas, and human-made structures. For example, when it rains in areas with gaseous pollutants in the air, rainwater sweeps these pollutants downward, contaminating the water in rivers, lakes, seas, soils, and living organisms inhabiting those areas.

Sources of air pollution

Volcanic eruptions release particles into the air that cause difficulty in breathing.

The sources of air pollution are the activities, operations, or processes, whether natural or artificial, which produce pollutants that are released into the air. The sources of air pollution can be:

  • Natural sources. They are the result of natural phenomena. They are usually not considered pollutant emitters per se unless they affect living organisms and the environment. For example: volcanic eruptions and animal overpopulation generating large quantities of animal feces.
  • Artificial sources. They are the result of industrial, domestic, and recreational human activities. For example: oil refineries and vehicles with internal combustion engines.
  • Local sources. They are sources polluting a small area. For example: a small factory or a carpentry workshop.
  • Global sources. They are sources that pollute a vast area or directly impact the balance of the whole planet. For example: industries producing gases that contribute to the greenhouse effect and global warming.
  • Mobile sources. They are sources that do not remain in one place. For example: transportation vehicles using combustion engines such as cars, trains, and airplanes.

Effects of air pollution on the environment

Over the years, air pollution has been causing changes in weather patterns that have affected the various ecosystems of the planet. These changes have occurred mainly due to the greenhouse effect and ozone layer depletion.

What is the greenhouse effect? It is the process by which thermal radiation produced by the Earth's surface is absorbed by greenhouse gases and then returned to the Earth's surface. This process naturally warms the Earth's surface.

Gases which are the result of burning fossil fuels significantly contribute to the increase of the greenhouse effect. This leads to a greater amount of thermal radiation being returned to the Earth's surface, thereby increasing global warming. Some of these gases include nitrous oxides, chlorofluorocarbons, tropospheric ozone, and methane.

The ozone layer is a layer composed of ozone (O3). It absorbs part of the ultraviolet rays, preventing them from reaching the Earth's surface and causing harm to living beings and their environment. The main compounds that damage the ozone layer are chlorofluorocarbons.

Effects of air pollution on humans

The World Health Organization (WHO) estimates that approximately 7 million people die each year from causes associated with air pollution.

The most vulnerable groups to air pollutants include the elderly, people with underlying medical conditions, and children. Breathing polluted air can cause severe lung damage, cardiovascular disease, and even death. It can also lead to bronchitis, pneumonia, and asthma.

Additionally, air pollutants can enter living organisms through the consumption of contaminated food.

Types of air pollutants

Primary pollutants

Primary pollutants are those that are emitted directly from an emission source. They affect living organisms and their environment directly. For example: sulfur dioxide (SO2) affects vegetation and lungs.

Secondary pollutants

Secondary pollutants are those that are formed from chemical reactions between primary pollutants or non-polluting species and atmospheric chemical phenomena. For example, sulfuric acid (H2SO4) forms due to the oxidation of sulfur dioxide (SO2).

Most air pollutants are gaseous or exist in the form of aerosols:

  • Gaseous pollutants. These are pollutants in gaseous state coming mainly from the burning of fossil fuels. Examples include carbon dioxide, carbon monoxide, nitrogen dioxide, ozone, and smog.
  • Aerosols. These are heterogeneous mixtures of solid or liquid particles in a gas. When pollutants come in the air, they cause severe damage to living organisms and the environment. Examples include aerosols from paints, insecticides, and CFC aerosols.

Major air pollutants

  • Chlorofluorocarbons (CFCs). A group of gases used mainly in the refrigeration industry and in thermal insulation. They have a very long atmospheric lifetime (50 - 200 years) and are the main cause of ozone layer depletion.
  • Carbon monoxide (CO). A very toxic gas that may cause death if inhaled in high doses. It is produced by the combustion of gasoline, kerosene, coal, oil, tobacco, and wood.
  • Carbon dioxide (CO2). A colorless gas naturally present in Earth's atmosphere. It is produced in the aerobic respiration of organisms. Artificially, it is generated from the burning of fossil fuels, increasing its levels in the atmosphere and causing an increase in the greenhouse effect.
  • Sulfur dioxide (SO2). A highly irritating gas and one of the primary causes of acid rain, as it transforms into sulfuric acid (H2SO4) in the atmosphere.
  • Methane (CH4). A colorless gas insoluble in water. It is produced naturally as a result of the anaerobic decomposition of plants. It is a component of natural gas, with concentration varying depending on the extraction site. Methane is a greenhouse gas.
  • Tropospheric ozone (O3). A colorless gas produced by a chemical reaction between nitrogen oxides and volatile organic compounds derived from the burning of fossil fuels. It is part of smog and may cause damage to living beings.
  • Nitrogen oxides (NxOy). A group of chemical compounds typically formed as a result of high-temperature combustion. They are produced by the combustion of diesel vehicle engines, and in the combustion of coal, oil, and natural gas. These gases have harmful effects on the health of living beings.

How to reduce air pollution

Contaminación del aire - energía solar
Using solar energy on a daily basis helps minimize air pollution.

There are actions that can be taken at the individual level to reduce air pollution:

  • Choose public transportation or bicycles.
  • Whenever possible, install non-polluting household energy sources (solar or wind energy).
  • Avoid excessive use of gas and other fossil fuels for heating and cooking.

In addition, governments and organizations can:

  • Establish a network of clean energy sources, such as hydropower, wind, and solar energy, through state investment or by encouraging private investment.
  • Increase green areas, as plants consume carbon dioxide and turn it into oxygen.
  • Promote scientific research and technological development of alternative fuels to fossil fuels.

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How to cite

ONDARSE ÁLVAREZ, Dianelys. "Air pollution".
Encyclopedia of Humanities. 23 February, 2024,

About the author

Author: Dianelys Ondarse Álvarez

Bachelor of Science in Radiochemistry / PhD in Science and Technology

Translated by: Marilina Gary

Degree in English Language Teaching (Juan XXIII Institute of Higher Education, Bahía Blanca, Argentina).

Updated on: 23 February, 2024
Posted on: 21 February, 2024

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