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Air pollution

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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.

Table of contents

1 Causes

2 Contaminants

3 Further Reading

4 Sources

Causes

The sources of air pollution are divided in two groups: anthropogenic (caused by human activity) and natural.

Natural sources 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.

Anthropogenic sources are mostly related to burning different kinds of fuel. They include:

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.
Aerosols.

Contaminants

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:

Carbon monoxide.
Nitrogen oxides.
Hydrocarbons.
Ozone in the lower part of the atmosphere (in the upper part, it helps to reduce the amount of ultraviolet radiation from the sun that reaches earth).
Sulfur dioxide, which causes acid rain.

The worst single incident of air pollution to occur in the United States occurred in Donora, Pennsylvania in late October, 1948