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Dust is a general name for minute solid particles with diameters less than 500 micrometers (otherwise, see sand or granulates) and, more generally, for finely divided matter. On Earth dust occurs in the atmosphere from various sources: soil dust lifted up by wind, volcanic eruptions, and pollution are some examples. Airborne dust is considered an aerosol and can have a strong local radiative forcing on the atmosphere and significant effects on climate. In addition, if composed of a flammable substance (such as flour or coal dust), under some circumstances it can be an explosion hazard.
Dust is responsible for the lung disease known as Pneumoconiosis, including black lung disease that occurs among coal miners. These dangers have resulted in a number of laws regulating environmental standards for working conditions.
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House dust
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The particles which create house dust are generated by the inhabitants, as skin cells slough off. Some atmospheric dust from the outdoors is also present. Observing dust particles in direct sunlight may reveal unpalatable hook shapes, as other organisms are present in house dust and live in it. On average, approximately 6 mg/m2/day of house dust is formed in private households, depending primarily on the amount of time spent at home.
Insects and other small fauna found in houses have their own subtle interactions with dust that may have adverse impact on the health of its regular occupants. Thus, in many climates it is wise to keep a modicum of airflow going through a house, by keeping doors and windows open or at least slightly ajar. Once outside, dust particles are borne away by the breeze or disintegrated by sunlight. In colder climates, it is essential to manage dust and airflow, since the climate encourages occupants to seal even the smallest air gaps, and thus close the building envelope to all outside air infiltration.
House dust mites are on all surfaces and even suspended in air. Dust mites feed on minute particles of organic matter, the main constituent of house dust. They excrete enzymes to digest dust particles; these enzymes and their feces, in turn, become part of house dust and can provoke allergic reactions in humans. Dust mites flourish in the fibers of bedding, furniture and carpets.
The particles that make up house dust can easily become airborne, so care must be exercised when removing dust, as the removal activity may stir dust up. House dust can be removed by two methods: wiping, swiping or sweeping with a hand, a dust cloth or sponge, a duster or a broom; or by suction from a vacuum cleaner or air filter. In the latter cases, a variety of technologies have been developed for the avowed purpose of removing, and perhaps sanitizing, accumulated house dust. Vacuum cleaners equipped with HEPA filters purport to trap even microscopic particles. An air filter is often used to screen outside air drawn into a building, and air exchangers recirculate indoor air while filtering it through HEPA filters. Air purifiers employ ionization to purportedly "eliminate" dust particles. Some of these dust removal methods create their own comparably bad sources of pollution. (See ozone and noise pollution.)
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Dust in outer space
Cosmic dust is widely present in space, where gas and dust clouds are primary precursors for planetary systems. The zodiacal light, seen in the sky on a dark night, is produced by sunlight reflected from particles of dust in orbit around the Sun. The tails of comets are produced by emissions of dust and ionized gas from the body of the comet. Dust also covers solid planetary bodies, and vast dust storms can occur on Mars that can cover almost the entire planet. Interstellar dust is found between the stars, and high concentrations can produce diffuse nebula and reflection nebula.
Dust samples returned from outer space could provide information about conditions in the early solar system. Several spacecraft have been launched in an attempt to gather samples of dust and other materials. Among these was Stardust, which flew past the comet Wild 2 in 2004 and returned a capsule of the remains of the comet to the U.S. in January 2006. The Japanese Hayabusa spacecraft is currently on a mission to collect samples of dust from the surface of an asteroid.
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Dust in fiction
In Philip Pullman's bestselling series His Dark Materials, dust (or "Dust", as it is spelled in the books) plays an important part by creating a connection between different worlds.
In the TV comedy Little Britain, Fat Fighters group leader Marjorie Dawes distinctively instructs the dieters to eat dust as it is "low in fat".
In Clark Ashton Smith's short horror story "The Treader In The Dust" *, a scholar unwittingly calls forth a demon which personifies dustiness.
In Hal Clement's short science fiction story "Dust Rag", two astronauts struggle with dust that stuck to their helmets, blinding them.
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Dust in religion
In the Bible:
In Genesis 3:19, God—following The Fall, Adam and Eve's transgression—states to the couple (representing humanity):
By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return. Emphasis added
This latter clause is used in the Ash Wednesday service in some churches for the administering of ashes.
I will make your offspring like the dust of the earth, so that if anyone could count the dust, then your offspring could be counted.
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See also
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Reference
Holmes, Hannah; (2001)The Secret Life of Dust. Wiley. ISBN 0-471-37743-0
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Sources
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