Particles atmospheric dust

The name dust , is used in a variety of ways, and with different meanings. These range from the material that accumulates on the earth s surface, such as on streets and in living and working environments, to the particulate material suspended in the atmosphere. In this paper I wish to consider these two materials in terms of their chemical composition, sources and relationship between them. The names used for the two materials will be surface dust and atmospheric dust . The word aerosol may also be used for atmospheric dust but it more properly applies to the finer particles of atmospheric dust and includes liquid aerosol (i). Botfi surface and atmospheric dusts are increasingly seen to be a hazard to human beings as they are a source of intake of toxic materials such as heavy metals. For this reason study is important of the composition and sources of the dusts. 

The contribution of atmospheric dust to surface dust depends on the dust falling to the earth. This occurs either as dry dust fall or wet washout with rain, snow or hail (1-6,8-10). Dry dust fall occurs by s imentation, impaction, interception or diffusion. Sedimentation, the fall under gravity, may be estimated using Stoke s law which relates the density and diameter of particles to their falling velocity. A particle of density 1.0 g cm"3 and diameter around 0.1 pm would fall with a velocity of around 9 x 10" cm s" ... 

Fig. 1. The size distribution of particles in an urban atmospheric dust showing the three size modes. Based on Whitby, 1977 4).

The ash of peat forming plant species contains a predominant amount of silicon. This element is particularly abundant in the Sphagnum, where its content achieves 36% by ash weight. Iron and aluminum are the next abundant. The first is accumulated during the peat formation process. The accumulation of calcium and potash is more pronounced than sodium, and the sulfur content is also remarkable. A large amount of mechanically admixed mineral particles (40-80% by ash weight) is found in mosses. This is due to the deposition of fine dispersed mineral material from snowmelting waters and atmosphere dust deposition (Table 1). 

The micrometeorites that melt during passage through Earth s atmosphere tend to solidify as spheres. These are termed cosmic spherules. The mineralogy of these spherules is given in Table 13.2. Their high iron and nickel content make them much denser (3 to 6g/cm ) than continental rock ( 2.7g/cm ). Like aeolian particles, cosmic dust deposited on the sea surface eventually settles to the seafloor via pelagic sedimentation. 

The pumps of the DRYVAC family are the classic dry compressing claw vacuum pumps that are preferably used in the semiconductor industry, whereby the pumps need to meet a variety of special requirements. In semiconductor processes, as in many other vacuum applications, the formation of particles and dusts during the process and/or in the course of compressing the pumped substances to atmospheric pressure within the pump, is unavoidable. In the case of vacuum pumps operating on the claw principle it is possible to convey particles through the pump by means of so called pneumatic conveying". This prevents the deposition of particles and... 

In the early 1940s, Leiter et al. (1942) demonstrated that a similar phenomenon occurred with organic extracts of ambient air particles—that is, injection of tars extracted from atmospheric dusts collected at locations throughout New York City produced subcutaneous sarcomas in mice. Shortly thereafter, Leiter and Shear (1943) reported that marginal doses of 3,4-benzpyrene (known today as benzol a jpyrene, BaP, I), the powerful carcinogen earlier isolated from coal tar and synthesized by Cook et al. (1933), also produced subcutaneous tumors in mice. 

Lindberg, J. D., and J. B. Gillespie, 1977. Relationship between particle size and imaginary refractive index in atmospheric dust, Appl. Opt., 16, 2628-2630. 

Tests of the WWEP were conducted with 4 in, 8 in and 16 in diameter units at flow rates ranging from 100 to 4000 ft /min. Particle collection efficiency of these units was measured with atmospheric dust, AC fine test dust (mass mean diameter (MMD) 12 pm), artificial cotton dust (MMD = 4.0 pm) and cotton dust drawn from the processing area of a card (MMD = 3.0 pm). 

Iron, an important plant micronutrient, is adsorbed rapidly onto particles and becomes unavailable for uptake by phytoplankton. The major source of iron to the ocean is in the form of atmospheric dust. Relatively little is known about the temporal variability of total iron in surface waters,... 

At rest, an adult human inhales 6 to 8 L of air each minute (1 L = O.OOl m3) and, during an 8-hour workday, can inhale from 5 to 20 m3 depending on the level of physical activity. The optimum size range for aerosol particles to get into the lungs and remain there is 0.5 to 5.0 [im. As instrumentation used to collect atmospheric dust have become more precise, particulate matter (PM) in the size range of 2.5 to 10 xm have come under increasing scrutiny, because many potential toxicants are adsorbed to their surfaces. These particles are inhaled and will remain in the lungs and allow the compounds to pass into the bloodstream. 

Many processes are operative in the environment that contribute to the regional elimination of a contaminant by altering its distribution. Contaminants with sufficiently high vapor pressure can evaporate from contaminated terrestrial or aquatic compartments and be transferred through the atmosphere to new locations. Such processes of global distillation are considered largely responsible for the worldwide distribution of relatively volatile organochlorine pesticides such as lindane and hexachlorobenzene. Entrainment by wind and upper atmospheric currents of contaminant particles or dust onto which the contaminants are sorbed also contribute to contaminant redistribution. Sorption of contaminant to suspended solids in an aquatic environment with commensurate sedimentation can result with the removal of contaminants from the water... 

Temperature is also increased by people heating engineers tend to assume that each person in a building is equivalent to just under half a kilowatt of heating. The more interesting effect of visitor flows is the chemical source to the atmosphere that they represent For some pollutants (particularly reduced sulfur and some VOCs as well as particles and dust), people or their clothes can represent significant in-situ sources and transportation routes (Brimblecombe, Shooter and Kaur, 1992 Nazaroff et al., 1993 Brimblecombe and Yoon, 2000 Yoon and Brimblecombe, 2001 Lloyd et al., 2002 Ankersmit, Tennent and Watts,... 

In this figure it will be seen that the average size of atmospheric dust particles is below 1 fi. This is much lower than that obtained for industrial dust shown in the same figure. A cumulative plot of the curves for the two dusts indicates that more than 50 percent of in-... 

Petrographic identification of atmospheric dust particles. U. S. Bur. Mines Rept. Investigations 3368. 

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