Surface dust examples

Since the majority of the elements in surface dust arise from deposited aerosol and added soil it is not surprising to find strong linear relationships between the concentrations of the elements in an atmospheric dust and street or house dust. This is illustrated by the two examples given in Fig. 8 for remote house dust vs urban atmospheric dust and street dust vs rural atmospheric dust. As discussed above crustal/soil material is a major component of atmospheric dust and the soil based elements in the atmospheric dust are Al, Ca, Fe, Mg, Mn, Ni, K, Si and Ti. The elements As, Br, Cd, Cl, Co, Cu, Pb, Rb, Se, V, and Zn are, on the other hand, enriched in atmospheric dust. The same elemental distribution applies to surface dust, but in this case their concentrations (compared on a mass basis) are reduced presumably due to dilution with soil. However, the elements enriched in the atmosphere remain enriched in the surface dusts. 

Sample preparation for AFM analysis is relatively simple. Generally, a desired amount of sample is absorbed onto a smooth and clean substrate surface, for example, a freshly cleaved mica surface. For example, to prepare a food macromolecule sample for AFM imaging in air, the diluted macromolecule solution is disrupted by vortexing. Then, a small aliquot (tens of microliters) of vortexed solution is deposited onto a surface of freshly cleaved mica sheet by pipette. The mica surface is air dried before the AFM scan. A clean surrounding is required to avoid the interference of dust in the air. Molecular combing or fluid fixation may be applied to manipulate the molecule to get more information. 

The most frequently used methods for sampling indoor surface dust for SVOC/ POM analysis is simply to use dust from a vacuum cleaner dust bag, see for example, Krause, Chutsch and Englert (1989), or a special vacuum cleaner mouthpiece containing a filter, see for example, 0ie, Hersoug and Madsen (1997). Both the mouth-piece and the filter should be cleaned prior to use. It must be assured that the SVOCs and POMs of interest are quantitatively captured by the filter (e.g., phthalates are quantitatively captured by quartz fiber filters (Clausen and Wolkoffi 1997b)) and that the vacuum cleaner exhaust does not contaminate the samples with for example, phthalates. However, the vacuum cleaner sampling method is probably very dependent on the sampling conditions (e.g., carpet or hard floor... 

Figure 9. Example of surface dust and shelf mark staining on a nineteenth-century mans linen shirt that was folded neatly on a wooden shelf...

An important design criterion for filters is the filter area rating, by which is understood the volumetric flow rate of the dust-laden gas or air that can be effectively treated per unit area of filter surface, for example 100 m /hour per m. This ratio corresponds to the flow velocity of the gas admitted to the filter medium. 

The dusty gas stream arrives in the apparatus and is washed out by a liquid inducted into it or hits about its surface dust corpuscles leave from a gas stream owing to their collision with liquid drops. Scrubbers refer to the given group of wet-type collectors hollow and with a nozzle, high-speed turbulent dedusters, scrubbers of a percussion and others, for example. 

The second type is a stable dispersion, or foam. Separation can be extremely difficult in some cases. A pure two-component system of gas and liquid cannot produce dispersions of the second type. Stable foams can oe produced only when an additional substance is adsorbed at the liquid-surface interface. The substance adsorbed may be in true solution but with a chemical tendency to concentrate in the interface such as that of a surface-active agent, or it may be a finely divided sohd which concentrates in the interface because it is only poorly wetted by the liquid. Surfactants and proteins are examples of soluble materials, while dust particles and extraneous dirt including traces of nonmisci-ble liquids can be examples of poorly wetted materials. 

Common materials—such as textiles in the form of fibers or fabrics, foamed rubber, foamed plastics, thin sheets of plastic, paper, corrugated cardboard, combustible dusts, dry grass and twigs, and wood shavings—are all examples of materials with large sutface areas in relation to their volumes. In a well-estabhshed fire, materials with relatively small surface areas, such as chunks of coal or logs, burn readily. 

The water spraying method is most commonly used to reduce fugitive dusts emission by spraying water onto the exposed surface area, for example, along active travel paths, excavation areas, and truck boxes loaded with soils. 

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