Natural Dusts

Studies of atmospheric particles show that their distribution is often birno-dal i.e., the particles are made up of rwo separate fractions, one with fine and one with coarse particles (Fig. 9.1). The coarse particles, from about 2.5 pm upward, are made up of natural dust from the effect of wind, erosion, plants, volcanoes, etc. The finer fraction is made up of particles smaller than 2.5 pm and consists primarily of particles from human activity, combustion, traffic, and processes. 

Complexity of cometaiy and other natural dusts and aerosols stimulated several approaches to solve the scattering problem through experimental simulation. 

Our study has provided us with a set of conelusions of general value, applieable to the inversion of the light-scattering data for a variety of natural dusts and aerosols, and with some specific conclusions for cometaiy dust. 

Based on this analysis, the major sources of trace metals in PM2.5 at the urban sites included in this study are, natural dust resuspension processes (indicated by th presence of mineral elements such as Fe and Mn), industrial emissions (Cu, As, Cd, Pb, Mo and Sn), fossil fuel refining and/or burning processes (Ni, V, Se) and traffic related emissions (Ba, Sr Sb, Zn). The mineral component comprises 55-65% of the trace metal concentrations in PM2.5 in urban areas and above 70% at rural sites. The contribution of the anthropogenic sources depends on the human... 

Germany, sampled during Winter 2002. For comparison are also shown the isotopic composition of natural dust (O) [48], isotopic composition of incinerator dust ( ) [167,182], and aerosols composition from Southern Germany ( ) [179]. (b) Diagram Pb/ Pb vs. Pb/ Pb for wine samples (+) [183], also shown in the shaded zone natural dust (O) isotopic composition. 

Winkler, E, M, 1977, Natural dust and acid rain. Water Air Soil Poll, 7 295-302,... 

Naturally dust particles may also be detached when the resultant of the detaching forces is greater than that of the forces resisting detachment. 

C. Insoluble in water, soluble in organic solvents. Flavone occurs naturally as dust on the flowers and leaves of primulas. It has been prepared from o-hydroxyacetophenone and benzaldehyde. 

The soil that accumulates on fabrics is generally of an oily nature and contains particles of dust, soot, and the like. Thus soil may be either a solid, a... 

Selenium and tellurium occur naturally in sulphide ores, usually as an impurity in the sulphide of a heavy metal. They are recovered from the flue dust produced when the heavy metal sulphide is roasted. 

Rhenium does not occur free in nature or as a compound in a distinct mineral species. It is, however, widely spread throughout the earth s crust to the extent of about 0.001 ppm. Commercial rhenium in the U.S. today is obtained from molybdenum roaster-flue dusts obtained from copper-sulfide ores mined in the vicinity of Miami, Arizona, and elsewhere in Arizona and Utah. 

Except for siUca and natural abrasives containing free siUca, the abrasive materials used today are classified by NIOSH as nuisance dust materials and have relatively high permissable dust levels (55). The OSHA TWA allowable total dust level for aluminum oxide, siUcon carbide, boron carbide, ceria, and other nuisance dusts is 10 mg/m. SiUca, in contrast, is quite toxic as a respkable dust for cristobaUte [14464-46-1] and tridymite [15468-32-3] the allowable TWA level drops to 0.05 mg/m and the TWA for quartz [14808-60-7] is set at 0.1 mg/m. Any abrasive that contains free siUca in excess of 1% should be treated as a potential health hazard if it is in the form of respkable dust. Dust masks are requked for those exposed to such materials (see Industrial hygene). 

The pH of rainwater in equUibrium with atmospheric CO2 is 5.6, a value frequendy cited as the natural background pH. However, in the presence of other naturaUy occurring species such as SO2,, NH, organic acids, sea salt, and alkaline cmstal dust, the natural values of unpoUuted rainwater vary... 

The toxicity of these fluoroaluminates is mainly as inorganic fluorides. The ACGIH adopted (1992—1993) values for fluorides as F is TLV 2.5 mg/m. The oral toxicity in laboratory animal tests is reported to be LD q rat 2.15 mg/kg (41). Because of the fine nature of the products they can also be sources of chronic toxicity effects as dusts. 

Eactory Mutual Engineering Corp. 1151 Boston-Providence Turnpike Norwood, Mass. 02062 Standards for safety equipment, safeguards for flammable Hquids, gases, dusts, industrial ovens, dryers, and for protection of buddings from wind and other natural ha2ards. 

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