Atmospheric Cycles

The term atmospheric cycles refers to the movement and circulation of gases and particles in the atmosphere, how they are utilized, and how long they remain there. Much is known about oxygen, and it is probably the gas that has the simplest cycle. Plants on the land and in the seas produce oxygen during photosynthesis, releasing it directly into the atmosphere or the water. Some of the oxygen is removed by animals during breathing and is incorporated into cellular materials or released in the form of carbon dioxide. Oxygen is also absorbed into fresh and marine water at the air-water interface, where it is utilized by organisms or involved in chemical reactions with materials within the water column or on the bed of the water body. Oxygen is also removed from the atmosphere during the weathering of rocks on the surface as it combines with the rock, forming minerals.

Fires of all kinds, whether cook fires, burning forests, or the result of warfare, remove oxygen from the atmosphere. About 23 percent of the atmosphere is oxygen, and the residence time has been estimated at about 7 million years.

Nitrogen, the most abundant gaseous component, making up 76 percent of the atmosphere, circulates slowly and has an estimated residence time of 44 million years and a complex cycle because it also combines in complex ways with other gases of the atmosphere. While it takes a great deal of energy to break apart a molecule of nitrogen gas, many species of bacteria take nitrogen from the atmosphere and transform it into an important component of soil. Some bacteria also release nitrogen back into the atmosphere as they break down organic material.

Particles in the atmosphere come from natural and anthropogenic sources. Natural sources include volcanic eruption, dust kicked up during windstorms, and salt from the evaporation of ocean spray. The residence time for these particles is measured in days and weeks, but in the case of volcanic eruptions, in which the particles are blasted high into the atmosphere, particles can remain for years before settling down on the land or sea.

Anthropogenic sources of particles come from a variety of activities, such as the burning of fossil fuels, industrial processes, forest fires, smoking cigarettes, and the wearing away of automobile brake linings. The residence time of these particles, as well as of those from natural sources, varies according to such factors as wind speed, precipitation timing, and height in the atmosphere. Although the concern regarding airborne particles whether anthropogenic or natural is usually related to health, successive volcanic eruptions over a long period of time can produce a shield to solar radiation, reducing the temperature of the earth's surface and thus altering the climate. Concern about gases, however, revolves around their role in global warming, discussed elsewhere in this work.

—Sidney Horenstein

See also: Atmosphere; Climatology; Global Climate Change; Hole in the Ozone Layer; Nitrogen Cycle; Oxygen, History and Presence in the Atmosphere


Berner, Elizabeth K., and Robert A. Berner. 1996. Global Environment: Water, Air, and Geochemical Cycles. Upper Saddle River, NJ: Prentice Hall; Laing, David. 1991. The Earth System: An Introduction to Earth Science. Dubuque, IA: Wm. C. Brown; Lutgens, Frederick K., and Edward J. Tarbuck. 2001. The Atmosphere: An Introduction to Meteorology, 8th ed. Upper Saddle River, NJ: Prentice Hall; Post, W. M. 1991. "The Global Carbon Cycle," American Scientist 78: 310-326.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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