The Physics
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Diameter of a Speck of Dust

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"Dust." Microsoft Encarta. CD-ROM Microsoft Corporation, 2003. "The size of dust particles varies from about half a micrometer (0.00002 in) to several times this size." 0.5 μm
Ristenbatt Vacuum Cleaner Service. HEPA and ULPA Filtration Specifications. "It will retain all particles as small as 0.3μm (micrometers-formerly microns) in size with an efficiency rating of 99.97%." 0.3 μm
Giovannacci, David. ADEME Research Program Planning, Contribution to the study of the exchanges to the interface liquid bubble, resulting from an ejector venturi, for the treatment of dust, June 2002. "The dominating mechanism in the trapping is then with the inertial effects with the range of diameter of dust [2;4] μm for which the trapping is optimum." 2-4 μm
HORIBA, Dust Detective Work. "A 0.5-1 micrometer dust particle on a 5 millimeter square IC is analogous to a ladybug somewhere in the large Tokyo Dome stadium." 0.5-1 μm
The Electric Cosmos, A Model of the Space Around Our Solar System. "So when we model our Sun and the nearest star to us, we have two specks of dust, each 1/100inch in diameter, four and a half miles apart from one another." 254 μm
Lide, David R. "Characteristics of Particles and Particle Dispersoids." Handbook of Chemistry and Physics,75th Edition. Florida: CRC Press, 1994.
Particle Name Size μm
Dust 1-10,000
Coal Dust 1-100
Cement Dust 3-100
Insecticides Dusts 0.4-10
Atmospheric Dust 0.001-20
0.001-10,000 μm

Households spend many hours removing dust from furniture and the air. The size of one of these particles, which is the cause of problems such as asthma, can be found in the range of several nanometers (10−9 m) to just under a millimeters (10−3 m). More commonly, however, dust are those particles between 1 and 100 micrometers (10−6 m).

Three thirds of the sources determined the diameter of a speck of dust to be a small number and/or a range, but one source referred to the diameter as specifically 254 micrometers. That is odd and may not be completely accurate. The Handbook of Chemistry and Physics provided the most different answer. The range of the size of dust was very large and specific to the type of dust.

The dust that fills the air is composed of many things, such as fibers, hairs, pollen, bacteria, and molds. Large cities also have smoke and tarry soot in their atmospheric dust. They also have a greater concentrations of dust than in smaller cities or mountainous areas. Dust is a major contributor to atmospheric pollution but it can also serve as a nuclei for the condensation of water vapor into droplets. Without them, fog, mist and clouds would not exist.

There are also several hazards that can come from dust.When found in high concentration in some types of mills and mines, they are an explosion hazard. Also, when silica is found in dust, it can ruin machinery because of how rigid it is and can cause problems if it is inhaled.

Marina Bolotovsky -- 2003