Air pollution

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.

Air Pollutants are classified as either Primary or Secondary. A primary air pollutant is one that?s added directly to the air from a given source. An example of a primary air pollutant would be carbon dioxide because it is added to the air from the burning of fossil fuels.

A secondary air pollutant is formed in the atmosphere through chemical reactions. An example of a secondary air pollutant would be the formation of ozone in photochemical smog.

Deaths

3 million people die of air pollution every year worldwide. 2.8 million of the 3 million die from indoor air pollution. 90% of the 3 million are deaths in developing nations. 70,000 die each year in the U.S. (Some estimates are as low as 50,000 or as high as 100,000).

Causes

The sources of air pollution are divided in two groups: anthropogenic (generated 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 micrometres; 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 micrometres, 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 of America occurred in Donora, Pennsylvania in late October, 1948

See also

• pollution
• emissions trading
• Greenhouse effect
• Kyoto Protocol

Further Reading

• 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

Sources

• - Website of the environmental agency of Chile
• - On a site by the Australian Academy of science