Dust is a general name for minute solid particles with diameters less than 500 micrometers. Dust occurs in the atmosphere from various sources such as soil dust lifted up by wind, volcanic eruptions, and pollution. Dust in homes, offices, and other human environments consists of human skin cells, plant pollen, human and animal hairs, textile fibers, paper fibers, minerals from outdoor soil, and many other materials which may be found in the local environment.
Composition and types
The precise composition of domestic dust can vary widely:
The quantity and composition of house dust varies greatly with seasonal and environmental factors such as the surroundings, exchange of outside air, age of the house, building materials and their condition, and the quantity of furniture and carpets, as well as their state of preservation. It varies further with ventilation and heating systems, cleaning habits, activities of the occupants or users of a room, etc. House dust consists of inorganic and organic matter, yet the relative proportions of these components may vary considerably. "House dust" from kindergartens often consists almost completely of inorganic materials such as sand, loam, and clay from sand pits. On the other hand, house dust from residences of animal owners with worn out carpets may consist nearly completely of organic material. The proportion of organic matter in 318 house dust samples was found to vary between <5% and >95% (Butte and Walker, 1994). Fergusson et al. (1986) reported the organic content of house dust from 11 homes in Christchurch, New Zealand, to be within the range from 25.7% to 56.5%. Floor dust from seven Danish offices had a mean organic fraction of 33% (Mølhave et al., 2000).
According to the German Environmental Survey, approximately 6 mg/m²/day of house dust is formed in private households, depending primarily on the amount of time spent at home. Nearly 1000 dust particles per square centimeter settle on domestic surfaces every hour. Some dust consists of human skin; it is estimated that the entire outer layer of skin is shed every day or two at a rate of 7 million skin flakes per minute, which corresponds to a mass emission rate of about 20 mg/minute. "Dust bunnies" are little clumps of fluff that form when sufficient dust accumulates.
Domestic dust and humans
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
. Dust may worsen hay fever
. 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. 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 eliminate any possibility of fresh air entering.
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 fibres of bedding, furniture, and carpets.
On the other hand the hygiene hypothesis suggests that the modern obsession with cleanliness may be counterproductive; that it may in fact encourage the development of health conditions including hay fever and asthma.
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 enough of the minute particles are dispersed within the air in a given area (such as flour or coal dust), under certain circumstances this can be an explosion
Coal dust is responsible for the lung disease known as Pneumoconiosis, including black lung disease, which occurs among coal miners. This danger has resulted in a number of laws (only some being passed) regulating environmental standards for working conditions.
Dust kicked up by vehicles travelling on roads
may make up 33% of air pollution
. Road dust consists of deposition of vehicle exhausts and industrial exhausts, tire and brake wears, dust from paved roads or potholes
, and dust from construction sites. Road dust represents a significant source contributing to the generation and release of particulate matter
into the atmoshpere . Control of road dust is a significant challenge in urban areas, and also in other spheres with high levels of vehicular traffic upon unsealed roads such as mines and garbage dumps. Road dust may be suppressed by mechanical methods like sweeping vehicles, with vegetable oils, or with water sprayers.
Dust control is the Suppression
of solid particles with diameters
less than 500 micrometers. This is because dust in the air is a serious health threat to children, older people, and those with respiratory illnesses
Control of domestic dust
House dust can be controlled by many methods and devices, including:
The particles that make up house dust can easily become airborne, so care must be exercised when removing dust, as the activity intended to sanitize or remove dust may make it airborne. The device being used traps the dust; however, some may become airborne and come to settle in the cleaner's lungs, thus making the activity somewhat hazardous. Another way to repel dust is with some kind of electrical charge .
Control of atmospheric dust
The U. S. Environmental Protection Agency
(EPA) mandates facilities that generate dust must work to minimize it in their operations. The most frequent dust control violations occurred at new residential housing developments in urban
areas. Federal law
in the United States
requires permits for earth moving at construction sites
, include plans to control dust emissions
. Control measures include such simple practices as watering down construction and demolition
sites, as well as preventing dust from being tracked out onto adjacent roads. US federal laws require dust controls on sources such as vacant lots, unpaved parking lots, and unpaved roads. Dust in such places may be suppressed by mechanical methods include paving or gravel, or by stabilizing the surface with water, vegetable oils or other dust suppressants, or with water misters for dust which is already airborne .
Dust in other contexts
Dust in outer space
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 nebulae
and reflection nebulae
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 Comet Wild 2 in 2004 and returned a capsule of the comet's remains to Earth in January 2006. The Japanese Hayabusa spacecraft is currently on a mission to collect samples of dust from the surface of an asteroid.
Dust in fiction
Dust in religion
- In ancient Sumerian mythology the afterlife consists of the dreary "House of Dust and Darkness".
- In Genesis 3:19, God — following The Fall, Adam and Eve's transgression — states to the couple: 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, and is adapted in funeral services to the common prayer "Dust to Dust".
- In Genesis 13:16, God states to Abram (later Abraham): 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.
- Note however that in both of these Biblical passages, the Hebrew word is עפר (`âfâr), which can also mean earth or dirt.
- In John 8:1-11, Jesus writes on the ground, or as it is often interpreted, dust.
- Holmes, Hannah; (2001)The Secret Life of Dust. Wiley. ISBN 0-471-37743-0
- Steedman, Carolyn; (2002) Dust. Manchester University Press. ISBN-13: 978-0719060151