Air pollution is a broad term applied to all chemical and biological agents that modify the natural characteristics of the atmosphere.
Some definitions also consider physical perturbations such as noise pollution, heat, radiation or light pollution as air pollution. Some definitions include the term harmful as a requisite to consider a change to the atmosphere as pollution.
The sources of air pollution are divided in two groups: anthropogenic (caused by human activity) and natural.
Natural sources include:
Anthropogenic sources are mostly related to burning different kinds of fuel. They include:
- Volcanic activity
- Dust from natural sources, usually large areas of land with little or no vegetation
- Gases, such as methane, emitted by the digestion of animals, usually cattle.
- Smoke from wildfires.
- Dust and chemicals from farming, especially of erodible land, see Dust Bowl
- Industrial activity in general.
- Vehicles with internal-combustion engines.
- Stoves and incinerators, specially coal ones.
- Paint fumes, or other toxical vapors.
Contaminants of air can be divided in particles and gases.
Particles are classified by their sizes. A usual division is in PM10 and PM2.5. PM10 are particles whose size is less than 10 microns (0.01 mm); they are dangerous to humans because they can be breathed and reach the lungs. PM2.5 are particles whose size is less than 2.5 microns (0.0025 mm), and they are even more dangerous because they can pass the alveoli and reach the blood.
Important pollutant gases include:
The worst single incident of air pollution to occur in the United States occurred in Donora, Pennsylvania
in late October, 1948
- Davis, Devra, When Smoke Ran Like Water: Tales of Environmental Deception and the Battle Against Pollution, Basic Books, 2002, hardcover, 316 pages, ISBN 0-465-01521-2