Atmophiles

The ratio of anthropogenic emissions to total natural emissions is highest for the atmophilic elements Sn, Cu, Cd, Zn, As, Se, Mo, Hg, and Pb (Lantzy and Mackenzie, 1979). In the case of lead, atmospheric concentrations are primarily the consequence of the combustion of leaded gasoline. For many years, lead was used as a gasoline additive, in the form of an organometal compound, tetraethyl lead. When the fuel was... 

Banin et al. (1987) proposed a thin-horizon sampling approach to study the effects of traffic sources and atmospheric fallouts on soils in the arid zone of Israel. They pointed out that the large and systematic variability in the concentrations of the atmophile elements in the soil would be masked if a more conventional and less-detailed sampling scheme was used. The measured Pb concentration varied between 209 mg/kg in the top layer of an arid soil near the road in Israel and 66 mg/kg at a depth of 20 cm (Banin et al., 1987). If the profile had been sampled as one 0-20 cm horizon, the weighed average concentration observed would have been 76.3 mg/kg Pb. If it had been sampled in two 10-cm thick horizons, the concentrations would have been estimated to be 86.6 and 66 mg/kg in the top and bottom horizons, respectively (Banin et al., 1987). This distribution would strongly affect the bioavailability in arid soils. 

Banin A., Navrot J., Perl A. Thin-horizon sampling reveals highly localized concentrations of atmophile heavy metals in a forest soil. Sci Total Environ 1987 61 145-152. 

Note It is sometimes convenient to describe the element distribution between sulfides and oxides as chalcophiles (occurring in the Earth s crust as sulfides) and lithophiles (predominating as oxides and halides in the Earth s crust) (see Fig. 1.5). This geochemical classification includes also the siderophiles (remaining as metals or alloys, especially in the Earth s core) and the atmophiles (which occurs largely in volatile form in the atmosphere and dissolved in the oceans). 

Distinguish between the following terms lithophile, siderophile, chalcophile, atmophile. 

Goldschmidt s ideas on the primary distribution of the elements in the Earth have not been seriously challenged (see, however, Bums and Fyfe, 1966a). From studies of minerals in meteorites and phases from blast furnaces, Golschmidt classified the elements as siderophilic if they are inert (relative to iron) and enter the metallic phase, chalcophilic if they are concentrated in sulphides, lithophilic if they are concentrated in silicates and atmophilic if they are gaseous and are present in the atmosphere. Those elements enriched in organisms were also classed as biophilic. 

Atmophile elements, tending to occur in the uncombined state (e.g., N, Ar) ... 

Differentiated achondrites. They are achondrites that exhibit igneous textures or igneous textures modified by impact and/or thermal metamorphism, and that have compositions of lithophUe, siderophile, chalcophile, and atmophile elements that are highly fractionated from the ranges of chondritic materials. 

Primitive achondrites. They are achondrites that exhibit equilibrated, metamorphic textures, possibly modified by impact. Rare members have relict chondritic textures, but examples with classic, unequilibrated chondritic (i.e., type 3) textures are absent. They have compositions of lithophile, siderophile, chalcophile, and atmophile elements that are at most only moderately fractionated from the range of nebular materials. Some members may be quite fractionated, but the group as a whole is dominated by primitive materials. 

Support for loss of light gases from the atmosphere via hydrodynamic escape can be found in other atmophile isotopic systems. The Ne/ Ne ratio in the mantle is elevated... 

The atmophile elements hydrogen, carbon, nitrogen, and the rare gases are strongly depleted in the Earth compared to chondritic meteorites. Pepin (1989) concluded that it appears that simple veneer scenarios in which volatiles are supplied from sources resembling contemporaneous meteorite classes cannot explain the observed isotopic compositions. It is, therefore, often assumed that the isotopic compositions of these elements were affected by the process... 

Elements can also be classified according to their chemical behavior based on empirical observations from meteorites and systems in the Earth this leads to the following groups litho-phile, siderophile, chalcophile, or atmophile. The lithophile elements are ones that bond readily with oxygen and are concentrated in the silicate shell (crust and mantle) of the Earth. The siderophile elements readily bond with iron and are concentrated in the core. The chalcophile elements bond... 

In contrast, Zahnle et al. [116] argued tliat the present atmosphere of Titan was delivered by comets of low velocity at late accretion, ai d Uiat Titan has suffered less atmospheric erosion and has retained a higher fraction of incoming atmophiles. For a more-or-less solar composition comet, the most important C-and N-bearing products are likely CO and N2, witli small additional amounts of CO2, CH4, C2H2, and HCN. Most of the comet s N2 entered the atmosphere on Titan, where CO has been consumed by reaction with water to form CO2, CH4, and H2, the latter readily escaping into space. This alternative model for the formation of the present day atmosphere on Titan does not require conversion of N2 from NH3. 

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