dust

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dust Dust can be loosely defined as a suspension of solid particles in air, or a deposit of such particles which have been transported and deposited by the wind. Dust particles which are transported in suspension in the Earth's atmosphere are mostly smaller than 100 micrometres (μm) and a high proportion is less than 20 μm. This is because grains larger than 20 μm have relatively high settling velocities and tend to fall back quickly to the ground surface except under conditions of very strong turbulent winds.

Atmospheric dust originates from several different sources, including volcanic eruptions, industrial emissions, and outer space (cosmic dust), but wind deflation of particles from surface sediments and soils is quantitatively most important. At the present day the most significant sources of dust are arid and semi-arid regions, particularly those affected by periodic droughts and human activities such as cultivation, overgrazing, and construction. The Sahara desert and the deserts of northern China provide the two most important individual source regions for dusts. They produce dust plumes which extend thousands of kilometres over the equatorial Atlantic and North Pacific, respectively. During cold stages of the Quaternary, very large amounts of dust were also generated by wind erosion of extensive fluvioglacial outwash deposits, notably in North America, Europe, and Siberia.

Many different types of wind system are involved in dust transport, including small-scale dust devils (whirlwinds), mountain and valley winds, trade winds, thunderstorm downdrafts, monsoonal winds, and winds associated with mid-latitude depressions. Localized dust blowing may be caused by any set of conditions that produces steep thermal or pressure gradients. However, long-range transport of dust usually requires the dust to be lifted to relatively high levels in the troposphere, where it becomes incorporated in fast-moving upper-level wind systems.

Dust transport is of considerable geological, geochemical, and biological importance. As much as two-thirds of the sea-floor sediments in parts of the North Pacific consist of deposited dust derived from the Asian deserts, while in north-central China terrestrial accumulations of dust, known as loess, exceed 300m in thickness. These deposits form some of the most fertile soils in the world and support a population of more than 600 million people. The iron present in windblown dust provides an important control on the levels of biological activity in remote oceanic areas, and as such might exert a significant indirect influence on the global carbon budget, concentrations of atmospheric carbon dioxide (CO₂) and climate. Deflated soil dust and volcanic dust can also influence climate directly through their effect on the proportion of light reflected by the atmosphere (its albedo) and the Earth's radiation budget, particularly if the dust reaches the stratosphere, where residence times can be of the order of several years.

In areas of frequent dust-storm activity, blowing dust poses a significant hazard to human health and results in significant economic costs. High atmospheric dust loadings are associated with high incidences of respiratory diseases and a range of bacterial and viral infections. Reduced visibility caused by blowing dust is a significant cause of vehicle and aviation accidents, while the list of adverse economic effects includes contamination of drinking water supplies; damage to crops, engines, and electronic equipment; and interference to radio transmissions and telecommunications. In the more developed parts of the world where dust storms are a hazard, such as the south-western United States and south-eastern Australia, dust-storm warning systems have been set up in an attempt to minimize their negative impacts. Dust transport and deposition may, however, also have positive effects, including the neutralization of acid rain, the addition of mineral nutrients to soils, and the formation of stabilizing surface crusts in areas of active sand dunes.

K. Pye

Bibliography

Pye, K. (1987) Aeolian dust and dust deposits. Academic Press, London.

dust / dəst/ • n. 1. fine, dry powder consisting of tiny particles of earth or waste matter lying on the ground or on surfaces or carried in the air: the car sent up clouds of dust they rolled and fought in the dust. ∎  any material in the form of tiny particles: coal dust. ∎  [in sing.] a fine powder: he ground it into a fine dust. ∎  [in sing.] a cloud of dust. ∎ poetic/lit. a dead person's remains: scatter my dust and ashes. ∎ poetic/lit. the mortal human body: the soul, that dwells within your dust. 2. [in sing.] an act of dusting: a quick dust, to get rid of the cobwebs. • v. [tr.] 1. remove the dust from the surface of (something) by wiping or brushing it: I broke the vase I had been dusting pick yourself up and dust yourself off | [intr.] she washed and dusted and tidied. ∎  (dust something off) bring something out for use again after a long period of neglect: a number of aircraft will be dusted off and returned to flight. ∎  Baseball (dust someone off) deliver a pitch very near a batter so they must fall to the dirt to avoid being hit by it. 2. (usu. be dusted) cover lightly with a powdered substance: roll out on a surface dusted with flour. ∎  sprinkle (a powdered substance) onto something: orange powder was dusted over the upper body. 3. inf. beat up or kill someone: the officers dusted him up a little bit. PHRASES: dust and ashes used to convey a feeling of great disappointment or disillusion about something: the party would be dust and ashes if he couldn't come. the dust settles things quiet down: she hoped that the dust would settle quickly and the episode be forgotten. eat someone's dust inf. fall far behind someone in a competitive situation. gather (or collect) dust remain unused: some professors let their computers gather dust. leave someone/something in the dust surpass someone or something easily: today's modems leave their predecessors in the dust.DERIVATIVES: dust·less adj.

dust Small particles of solid matter found in space: in the Solar System (interplanetary dust and cometary dust), around stars (circumstellar dust), and between the stars (interstellar dust). The individual particles are usually called dust grains, and are of size 10 nm and upwards. Dust comprises about 1 % by mass of interstellar matter. It extinguishes and reddens starlight, and can also be detected by its absorption and emission of infrared radiation and by its polarizing effect on starlight. The exact composition of interstellar dust is uncertain: silicates, graphite, and carbides are among the components identified through infrared absorption measurements. Dust may account for the diffuse interstellar bands in the optical spectra of stars. Dust is produced in the cool outer envelopes of red-giant stars, in novae, and in supernovae. Dust is also present in the Solar System as interplanetary dust and cometary dust. Some dust is driven out of the Solar System by the radiation pressure of the Sun's light, while new dust is generated by asteroid collisions and the break-up of comets. See also Grains, Interplanetary; Grains, Interstellar.

dust sb. OE. dūst = MDu. donst, dūst (LG. dust, Du. duist meal-dust, bran), ON. dust. The primary notion seems to be ‘that which rises in a cloud’; cf. OHG. tun(i)st wind, breeze, G. dunst vapour.
Hence dust vb. †rise as dust XIII; †reduce to dust XV; soil with dust; free from dust XVI (whence duster XVI). dusty OE. dūstiġ.

dust dust and ashes used to convey a feeling of great disappointment of disillusion about something; originally with allusion to the legend of the Dead Sea fruit.
shake the dust off one's feet depart indignantly or disdainfully; originally with allusion to Matthew 10:14.

See also ashes to ashes, dust to dust, a peck of dust in March.

dust Dust is used as a simile for annihilation (2 Kgs. 13: 7). In the NT dust on the head was a sign of repentance (Rev. 18: 19) but when shaken off the feet it was either a warning of judgement to come (perhaps Matt. 10: 14) or a gesture of anger or of renunciation of all further responsibility (Acts 13: 51).

dust Solid particles, the size of clay and silt particles (see PARTICLE SIZE), that can be raised and carried by the wind.

dust •adjust, august, bust, combust, crust, dust, encrust, entrust, gust, just, lust, mistrust, must, robust, rust, thrust, trust, undiscussed •stardust • sawdust • angel dust •bloodlust • wanderlust • upthrust