Aerosol dust, chemical composition

Particles in the atmosphere come from different sources, e.g., combustion, windblown dust, and gas-to-particle conversion processes (see Chapter 6). Figure 2-2 illustrates the wide range of particle diameters potentially present in the ambient atmosphere. A typical size distribution of ambient particles is shown in Fig. 2-3. The distribution of number, surface, and mass can occur over different diameters for the same aerosol. Variation in chemical composition as a function of particle diameter has also been observed, as shown in Table 4-3. 

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 chemical composition of PM10 shows a considerable conformity in these countries. Always, secondary inorganic aerosols (SIA) are the major constituent ( 40%) followed by the carbonaceous compounds ( 25%). Contributions of sea salt and mineral dust vary between 10% and 15% depending on presence and distance of respective sources. The unidentified mass is some 15% indicating that the composition of PM10 in this region is fairly well known. 

Atmospheric particles in the troposphere are composed of a complex mixture of highly water-soluble inorganic salts, insoluble mineral dust, and carbonaceous material (which includes organic compounds plus elemental carbon) (Jacobson et al., 2000). Studies in which the chemical composition has been determined as a function of particle size demonstrate a correlation between the chemical composition and the size mode of atmospheric aerosols (Meszaros et al., 1997 Krivacsy and Molnar, 1998 Alves et al.,2000 Maenhaut et al.,2002 Smolik et al., 2003 Samara andVoutsa, 2005). 

Aerosols Solid particulate matter Liquid particulates Dust, smoke Fumes, oil mists, polymeric reaction products. Airborne particulate matter varies widely in its physical and chemical composition, source and particle size. 

The coarse mode is largely composed of primary particles generated by mechanical pro-ce.sses such as soil dust raised by llie wind and/or vehicular traffic and construction activities. Coarse particles arc also emitted in gu.ses from industrial sources such as coal combustion and smelting. The coarse mode often peaks at about lO/tin. The chemical composition of the coarse mode is for the most part the sum of the chemical components of the primary aerosol emissions. However, there may be some contributions from gas-to-particle conversion, such as ammonium nitrate, as discussed below. 

The sources and chemical compositions of the fine and coarse urban particles are different. Coarse particles are generated by mechanical processes and consist of soil dust, seasalt, fly ash, tire wear particles, and so on. Aitken and accumulation mode particles contain primary particles from combustion sources and secondary aerosol material (sulfate, nitrate, ammonium, secondary organics) formed by chemical reactions resulting in gas-to-particle conversion (see Chapters 10 and 14). 

Sea spray, volcanic eruptions, soil dust, as well as some industries (cement manufacturing) produce the so called primary aerosols, i.e. the material is emitted directly in particulate state (Klockow, 1982), and they are both line and coarse. Secondary aerosols are produced in the atmosphere usually by eondensation after emission from high temperature sources, and they are fine as a rule. Considering the difference in the chemical composition it is recognized that the major components of the fine aerosols are toxie substances of anthropogenic origin such as As, Cd, Pb, Se, Zn etc. while the course aerosols are enriched in elements like Ca, Fe, Si coming from erosion, sea aerosols and other natural sources. 

Because of the manifold partiele formation processes, the chemical composition of submicrometer eontinental aerosol particles is rather complex. The major constituents of these partieles are usually sulfates, nitrates, soot, organic compounds, and soil dust. Sulfates are derived mainly from anthropogenic SO2, ni-... 

With emission source chemical signatures and corresponding aerosol or rainwater sample measurements PLS can be used Co calculate a chemical element mass balance (CEB). Exact emission profiles for the copper smelter and for a power plant located further upwind were not available for calculation of source contributions to Western Washington rainwater composition. This type of calculation Is more difficult for rainwater Chan for aerosol samples due Co atmospheric gas to particle conversion of sulfur and nitrogen species and due Co variations In scavenging efficiencies among species. Gatz (14) has applied Che CEB to rainwater samples and discussed Che effect of variable solubility on the evaluation of Che soil or road dust factor. 

The concentration of metals in atmospheric aerosols and rainwater (Table 7.1) is therefore a function of their sources. This includes both the occurrence of the metals in combustion processes and their volatility, as well as their occurrence in crustal dust and seawater. As a result of this, the size distribution of different metals is very different and depends on the balance of these sources. For a particular metal this distinction is similar in most global locations (Table 7.2), although some variability does occur as wind speed and distance from source exert an influence on the particle size distribution spectrum (Slinn, 1983). Once in the atmosphere particles can change size and composition to some extent by condensation of water vapour, by coagulation with other particles, by chemical reaction, or by activation (when supersaturated) to become cloud or fog droplets (Andreae et al., 1986 Arimoto et al., 1997 Seinfeld and Pandis, 1998). 

There have been many measurements of the elemental composition of urban aerosols stimulated by the need for large databases in aerosol source apportionment (discussed in a later section). Table 13.2 compares concentrations in the fine and coarse fractions for various U.S. cities. The results show remarkable similarities in the order of magnitude of the concentrations from city to city for each element. Soil dust is a major component of the coarse fraction as indicated by the strong enrichment in aluminum and silicon in every city. The coarse fraction is much less active chemically both with respect to its mechanisms of formation and as a site for reaction, compared to the fine fraction discussed next. 

Owing to their chemical, thermal, and mechanical resistance, carbon fibers are an ideal material for highly durable composites. Compared to steel, they are four times Ughter at similar strength, which in addition is preserved up to temperatures of more than 2000 °C. Certain threads, ribbons, and fabrics are made from pure carbon fibers, as well as there are carbon-reinforced plastics which are employed to manufacture, for example, components of aircrafts or cars, sporting devices, implants, or filters for dusts and aerosols. 

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