Environmental phases

An obvious correlation between polar and alpine environments is the decrease in temperature with increasing latitude or elevation. This temperature change leads to a shift in environmental phase distribution equilibria - i.e. a chemical moves from the atmosphere to terrestrial surfaces, including direct deposition to surface waters, but also to snowpack and soils from which movement into surface and groundwater is possible. This process has been termed cold condensation but should more correctly be called cold-trapping because the contaminants are not actually condensing. 

Tracht change differs from change in Habitus in that it describes a change in the form of a crystal grown in an isotropic environmental phase through the combination of different faces and the relative sizes of respective faces. Therefore, Trachts are forms determined by the relative ratio of the normal growth rate R of the different crystal faces present on the surface of a growing crystal. The... 

Difference in the environmental phases. Since the interface roughness will be different for the same crystal species depending on whether the crystal was grown from the melt, solution, or vapor phases, different growth forms are expected for different environmental phases. This implies that the Tracht of the same crystal species will depend on the structure of the environmental phases, the degree of condensation, and the solute-solvent interaction. 

With regard to the attachment and detachment energies, the corners of a crystal or a rough interface that is constructed by kinks alone are sites where the process proceeds most quickly, whereas the low-index crystal faces, corresponding to smooth interfaces, represent the direction with the minimum rate of normal growth and dissolution. As a result, if a single crystalline sphere is dissolved in an isotropic environmental phase, a dissolution form bounded by both flat and curved crystal faces appears. This is called the dissolution form, which is not the same as the growth form. 

The two stones B and C show hitherto unknown features [18], as follows. There is a core portion with a square outline in cross-section and cuboid form in three dimensions, and all dislocation bundles with Burgers vector <100> generate from the surface of the core portion (Fig. 9.19). This implies that the core portion was formed somewhere else it was then trapped in a different environmental phase and acted as a seed under the new conditions, after which the major part of the crystal was formed. This was the first piece of evidence to prove the presence of seed crystals in the growth of natural diamond. 

The environmental phase is limited, for example in cells or organs. In other words, this situation is comparable to crystal growth in a partly closed vessel. 

We will address the distribution of organic compounds in the environment by looking at equilibrium partitioning of organic compounds between environmental phases, which include air, water, soil, and biota. Taking these phases pairwise, we can define the various physical and chemical properties that control the partition coefficients between these phases ... 

The goal of this chapter was to assess the influence of environmental phase partitioning and transport on the biogeochemical cycling and terrestrial reactivity of halogenated hydrocarbons. Whereas the global environmental behavior with... 

As polysaccharides tend to functionalize environmental phase space, for specification of polysaccharide dimensions, geometry and dynamics must be distinguished, although the transition is diffuse Whereas the dimensions of polysaccharide molecules in terms of sphere equivalent radii of mean excluded volume for macroscopic periods are up to maybe lOOnm only, dynamics of coherent supermolecular structures provide sphere equivalent radii that are more than one magnitude larger and enter the micrometer range. However, these structures are hidden if mass fractions are taken for illustration. Their identification typically needs sophisticated detection and specific scaling, for instance, photon correlation spectroscopy and representation of detected populations with respect to the square of coherent (occupied) volumes (Fig. 6C). 

The bioconcentration factor is the concentration of a chemical in a tissue per concentration of the chemical in water (generally adimensional) [Pavan, Netzeva et al, 2008]. This physical property characterizes the uptake of pollutants due to chemical partitioning from environmental phase (e.g., air or water) into an organic phase (e. g., lipids or proteins) through an exchange surface (e.g., gills of fish). 

One important group of input parameters is the compounds partition coefficients, Kxy, between the environmental phases present in the model (Eq. 3). 

Knowledge of the phase diagrams for compoimds of technical interest and of the environmental phases in contact with these compounds is the key for materials development and for the understanding of materials behavior in application. Not only can the thermal stability of particular phases be calculated by means of thermodynamic data, but suitable sintering procedmes can also easily be considered, and decomposition in aggressive media can be predicted. Generally recommended data books on binary and ternary systems are, e.g., those by Hansen [57], Elliott [58], Shunk [59], Mofatt [60, 61], Massalski [62], and Petzow and Effenberg [63]. Nowadays, the thermodynamic data of most of the important phases are available in publications or databases and can be readily used for thermochemical calculations. 

The descriptors obtained generally refer to the ground state of the molecules under gas-phase conditions, which may not correspond to the solvatized compounds or their transition states involved in interactions in environmental phases. Additionally, the currently used quantum-chemical descriptors do not contain any entropy terms. The different semi-empirical calculation schemes, such... 

Despite the obvious differences between the spheres, many of the processes and mechanisms that control chemical fate are common to all of them. In all spheres, transport can occur by advection and diffusion, and marty of the chemical reactions are similar in the various spheres. One reason for the similarities is that the environmental spheres are composites of the same principal phases. The most important of these environmental phases are... 

The exact chemical composition of virtually any natural environmental phase thus remains elusive. Many natural phases periodically undergo further changes in time (e.g., as a function of season or over longer time periods). Some phases, such as algae blooms or a seasonal snow cover, even have only a temporary existence. 

FIGURE 4 Chemical transfer processes between environmental phases can lead to the cycling of chemicals on different time scales. 

The two above formrrlatiorts of mass preservation differ only with respect to the size of the control voltrme. Because in the latter case the system is of an tmspecified, infinitesimal size, each term is expressed as amormt per rmit time per unit volume. The term 9C/9t expresses the change of a chemical s concentration at one specific point in space in an environmental phase, which can be brought about by transport of chemical to or from that point, or by formation or degradation of that chemical at that point. Expres-siorts for describing these transport and transformation processes will be presented below in Sections III and IV... 

The distribution of chemical between environmental phases is at the core of understanding enviromnental fate. Examples of environmental phase distribntions are those between air and water, between atmospheric particles and the gas phase, between plants and air, between soil and air, between suspended matter and the dissolved phase in water, and between groundwater and snbsnrface solids. On a fundamental level, the distribntion behavior of a chemical determines where a chemical is residing in the environment. It further influences the natnre and extent of the transport and transformation processes it will experience. The distribution of a chemical between gas phase and particle phase in the atmosphere not only determines by which mechanism and how fast the chemical is being deposited to the Earth s sitrface, bnt also further determines the type and rate of reactions that it will experience in the atmosphere. A chemical in a water body experiences very different behavior depending on whether it is dissolved in water or whether it sorbs to colloidal or sohd matter suspended in the water colimm. Similarly, the mobility and reactivity of a contaminant in the snbsnrface enviromnent depend strongly on its distribution between water and solids. 

Environmental phase distributions of elements or inorganic chemicals usually involve different chemical species and therefore speciation reactions. For example, different species of an element such as mercury have different vapor pressure and solubility. Elemental mercury, Hg(0), is fairly volatile and only sparingly soluble in water, whereas oxidized Hg(II) complexes are much less volatile but more water soluble. The distribution of mercury among the phases of air, water, and solid will thus depend on its speciation, which in turn is influenced by variable conditions of the environment, including pH, redox conditions, and the presence of other chemical species. This is approached quantitatively using equilibrium reaction constants for the various speciation reactions and illustrated using distribution diagrams that delineate the major prevalent species as a function of pH or pE, or both. 

By measuring concentration ratios, environmental phase distributions for chemicals can be empirically determined and characterized, both in the field and the laboratoiy. Examples are sorption coefficients Kd between water and soil or sediment solids or coefficients Kp describing the distribution between the gas phase and atmospheric particulate matter. Going beyond such empirical descriptions requires the derivation of relationships of general validity that allow the quantitative description of phase distributions involving environmental chemicals or enviromnental phases for which no such empirical data exist. 

Some environmental phase distributions closely resemble distributions involving pure or chemically well-defined phases. For example, the equilibrium distribution between the gas and aqueous phase is a well-defined characteristic of a chemical, described by Henry s law constant or the air-water partition coefficient Kaw- Further, the influence of properties of the water phase such as the... 

Many environmental phase equilibria— in particular, those involving a phase transition to the gas phase— are strongly influenced by temperatirre. Higher temperatirres favor partitioning into the gas phase, whereas sorption to solid surfaces and dissolution in aqueous and oiganic phases are enhanced at lower temperatures. Environmental temperature differences on both a spatial and temporal scale can thus result in variations in environmental partitioning. Gas-particle equihbria are shifted toward the particle phase under cold atmospheric conditions. Diurnal and seasonal cycles in the atmospheric deposition and evaporation of environmental chemicals of intermediate volatility have been observed and explained by the temperature influence on partitioning. 

FIGURE 6 Phase distribution equilibria involving pure phases with importance for describing environmental phase partitioning. Kaw, air-water partition coefficient Kow, octanol-water partition coefficient Kqa, octanol-air partition coefficient Pl, (supercooled) liquid vapor pressure Cw and Co, saturation solubility in water and octanol, respectively yw and yo, activity coefficient in water and octanol, respectively. 

TABLE I One-Parameter LFERs Used To Describe Important Environmental Phase Distribution Equiiibria ... 

They ignore much of the variability of environmental phases. For example, not all variability mKo among various soils and sediments is explained by the organic matter content, nor is all the variability in plant-air partitioning explained by the lipid content of the plant tissue. 

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