Vapor phase movement

Roy WR, Griffin RA. 1987. Vapor-phase movement of organic solvents in the imsaturated zone. Environmental Institute for Waste Management Studies. University of Alabama. Open file report no. 16. 

Hg (25 C) (corrected for a tn.p. of 68 C) and a literature vapor pressure of 1.8 X 10 mm Hg (25 C). In order for the mesostemic effect to be seen, a minimum vapor pressure is essential as well as the compound needing to be a least moderately lipophilic. As such, it should accumulate on the surface of a hydrophilic layer and be readily available for vapor phase movement much like the vaporization off of a water surface is enhanced by lipophilic compounds as observed in measurements of the Henry constant. 

A number of theories have been put forth to explain the mechanism of polytype formation (30—36), such as the generation of steps by screw dislocations on single-crystal surfaces that could account for the large number of polytypes formed (30,35,36). The growth of crystals via the vapor phase is beheved to occur by surface nucleation and ledge movement by face specific reactions (37). The soHd-state transformation from one polytype to another is beheved to occur by a layer-displacement mechanism (38) caused by nucleation and expansion of stacking faults in close-packed double layers of Si and C. 

Other environmental properties of interest are those that govern movement of chemicals, for these properties can influence not only the possibility of human exposure but also the lifetime and fate of the chemical. Clearly, if a nitrosamine is formed in, or introduced into, the soil and stays there, it presents little threat to man, and its lifetime will depend on the chemical or microbiological properties of the soil. If it should move to the surface and volatilize into the atmosphere, on the other hand, there will exist the possibility of human exposure via inhalation and also the possibility of vapor-phase photodecomposition. If a nitrosamine were to leach from soil into water, it could perhaps be consumed in drinking water alternatively, exposure of the aqueous solution to sunlight could provide another opportunity for photodecomposition. 

For vapor to move in the unsaturated zone, the soil formations must be sufficiently dry to permit the interconnection of air passages among the soil pores. Vapor concentration and vapor flow govern its movement. Vapor can move by diffusion from areas of higher concentration to areas of lower concentration and ultimately to the atmosphere. Therefore, the transportation of the vapor phase of gasoline components in the unsaturated zone can pose a significant health and safety threat because of inhalation and explosion potential. 

In the upper unsaturated zone (above the capillary fringe), multiphase movement and transformation are typical. Vapor-phase gasoline becomes more important gasoline adsorption by soil, dissolution in pore water, and free product in the pore space can also be significant. 

Membranes act as a semipermeable barrier between two phases to create a separation by controlling the rate of movement of species across the membrane. The separation can involve two gas (vapor) phases, two liquid phases or a vapor and a liquid phase. The feed mixture is separated into a retentate, which is the part of the feed that does not pass through the membrane, and a permeate, which is that part of the feed that passes through the membrane. The driving force for separation using a membrane is partial pressure in the case of a gas or vapor and concentration in the case of a liquid. Differences in partial pressure and concentration across the membrane are usually created by the imposition of a pressure differential across the membrane. However, driving force for liquid separations can be also created by the use of a solvent on the permeate side of the membrane to create a concentration difference, or an electrical field when the solute is ionic. 

Because mirex is a very hydrophobic compound with a low vapor pressure, atmospheric transport is unlikely (Hoff et al. 1992). These authors reported detecting mirex in only 5 of 143 samples at a maximum and mean concentration of 22 pg/m and 0.35 pg/m, respectively. Based on a vapor pressure of <3x10 mm Hg at 25 °C, mirex is expected to exist mainly in the particulate phase with a small proportion existing in the vapor phase in the ambient atmosphere (IARC 1979c). A mass balance approach to the movement of mirex within Lake Ontario indicates that 5% of the total input of mirex to the lake can be attributed to atmospheric deposition compared with 72% of benzo(a)pyrene (Arimoto 1989). 

Peterson MS, Lion LW, Shoemaker CA (1988) Influence of vapor phase sorption and diffusion on the fate of trichloroethylene in an unsaturated aquifer system. Environ Sci Technol 22 571-578 Petersen LW, Moldrup P, El-Farhan YH, Jacobsen OH, Yamaguchi Y, Rolston DE (1995) The effect of moisture and soil texture on the adsorption of organic vapors. J Environ Qual 24 752-759 Pignatello JJ (1989) Sorption dynamics of organic compounds in soils and sediments. In Sawhney BL, Brown K (eds) Reactions and movement of organic chemicals in soils. Soil Sci Soc Amer Spec Publ 22 45- 81... 

A loss of water from plant shoots—indeed, sometimes even an uptake — occurs at cell-air interfaces. As we would expect, the chemical potential of water in cells compared with that in the adjacent air determines the direction for net water movement at such locations. Thus we must obtain an expression for the water potential in a vapor phase and then relate this P to for the liquid phases in a cell. We will specifically consider the factors influencing the water potential at the plant cell-air interface, namely, in the cell wall. We will find that vFcel1 wal1 is dominated by a negative hydrostatic pressure resulting from surface tension effects in the cell wall pores. 

Ice samples have a main dispersion induced by reorientation of the water molecules and proton conduction with movement of the point defects. Here, we discuss values of the relaxation time r of the main dispersion of ice samples reported in the literature and measured by the present authors. For convenience in experimental measurements, we define two classification of ice sample as bulk ice and ice particle aggregates corresponding to two types of growth, liquid phase growth and vapor phase growth. 

The presence of a solute causes vapor-pressure lowering of a solvent. If the solute is nonvolatile (nonevaporating), the solution has a lower vapor pressure than the pure solvent does. (Review vapor pressure in Chapter 7.) From a molecular view, the solute particles at the surface of the liquid inhibit the movement of solvent molecules from going into the vapor phase, but do not inhibit solvent molecules in the vapor phase from returning to the liquid phase, so the rate of evaporation is lower than the rate of condensation until there are fewer solvent molecules in the vapor phase. For solving problems, the vapor pressure of any component (call it A) in the solution. Pa, is related to the vapor pressure of the pure substance, P, by Raoult s law ... 

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