Elements atmophile

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. 

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. 

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... 

Lithophile elements are those which have a preference for a silicate host, whereas chalcophile elements have an affinity for sulfur and so will most frequently be found in sulfides. Siderophile elements are those which will partition preferentially into a metallic iron phase and so are enriched in the Earth s core and in iron meteorites. Atmophile elements prefer the gaseous phases of the Earth atmosphere. This classification is discussed more fully in Chapter 2, Section 2.3.2. 

The atmophile elements (H, C, N, noble gases) condense at and below the condensation temperature of water (liquid or ice). Liquid water or water ice condenses at the temperature where the partial pressure of water vapour equals the vapour pressure over liquid water or water ice. The condensation curve for water (liquid or ice) is... 

The most important of the atmophile elements is hydrogen, which is the most abundant element in solar composition material. Hydrogen s dominance controls the chemistry of solar composition material. With the exception of helium, which is non-reactive, hydrogen is about 1,000 times as abundant as all other elements combined. Thus, hydrogen-bearing gases (hydrides) are major or important gases at chemical equilibrium for many elements. A few examples are H2O, CH4 (at low temperatures), NH3 (at low temperatures), H2S, HF, HC1, and HBr. 

Later the concept of atmophiles, elements tending to go to the atmosphere, was introduced. Examples of elements belonging to the different groups are given in Table 4.4. 

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