Pollutants transport mechanisms

The second pollutant transport mechanism can act more globally. Wind currents can lift localized pollutants up out of the PEL and into the free troposphere. The meteorological conditions off the east coasts of North America and Asia, in particular, can drive this form of transport. Once in the free troposphere, strong winds such as the jet streams can move pollutants for long distances without significant dilution or removal [60]. 

We begin by reviewing the regulatory driving force in the United States for air pollution abatement. To appreciate the objectives of our Federal air pollution control regulations, an understanding of the fate and transport mechanisms in the environment is important. Hence, some general discussions on the behavior of pollutants in the atmosphere are included in this chapter. 

First order parameters affecting dispersion stem from meteorological conditions. These, as much as any other consideration, determine how a stack is to be designed for air pollution control purposes. Since the operant transport mechanisms are determined by the micro-meteorological conditions, any attempt to predict ground-level pollutant concentrations is dependent on a reasonable estimate of the convective and dispersive potential of the local air. The following are meteorological conditions which need to be determined ... 

In the present compilation of the distribution and pharmacokinetic data of a dozen xenobiotics studied in the dogfish shark, this species yielded excellent data consistent with what we know from similar studies on terrestrial mammals. The data from the shark occasionaly provided information not available in other animals. Major transport parameters in this fish were shown to be similar to those found in mammals. This aquatic organism handles lipid-soluble pollutants by sequestering them in its fatty liver. Together with a previous summary (23) we have now studied about three dozen xenobiotics in this species. Because of its ease of handling, low cost, abundance, predictive value of transport mechanisms, and well-developed pharmacokinetics, the dogfish shark is an ideal fish species to use as a model to study aquatic pollutants. 

When the rates of sorption or desorption processes are known, environmental fate modeling can provide an educated estimate and prediction on the accessibility and bioavailability of a target pollutant to a specific transport mechanism in the environment. Hence, the present chapter is an attempt to assess fate (i.e., in terms of pollutant mobility using predictive sorption or desorption coefficients) as well as effects (i. e., in terms of bioavailability) of various pollutants and to correlate these observations for development of predictive relationships. 

Such methods are used in more fundamental studies to elucidate the soil chemistry, to determine the structure and composition of soil components and to improve understanding of the processes in the soil that control the mobilisation and retention of nutrient and toxicant elements in soil as well as to illuminate their transport mechanisms. They are, therefore, more important for the soil physical chemist than the functionally defined procedures that are the main concern of the agronomist. Both methods are of major interest to the environmental scientist particularly in the study of the fate of environmental pollutants. Many of the extractants intended to target particular species are also used in a functional speciation role. 

An in-depth description of the electrochemical treatment of organic-polluted wastewater in which the concentration profiles of every compound in the electrochemical cell are calculated is particularly difficult, as it would lead to a very complex mathematical system. This complex situation arises since the concentration of every compound depends on the time and on the distance to the electrode surface, and that the particular concentration of every species for a given case depends on three different mass-transport mechanisms diffusion, convection, and migration. 

On-line passive multi-tracer pollutant transport and deposition mechanisms are included in HIRLAM-Tracer (Chenevez et al. 2004)... 

The investigation of air flows, turbulence, heat exchange, and pollutant transport within residential urban areas have become important in recent years because of the ecological reasons and the elaboration of measures for a better urban comfort and countermeasures to possible terrorist s attacks. There are several scientific programs running by the USA and European Union towards a better understanding of relevant physical mechanisms and forecasts for the urban climate of some test cities, see Chapters 2 and 9. 

There are different patterns of distribution of the inventories of pollutants in the basins of the central and southwestern Baltic Sea, probably caused by the differences in the transport mechanisms and geochemical behavior of the components. However, most of the components show arelatively uniform distribution of the inventories (e.g., PCBs, Fig. 14.21). It means that the anthropogenic amount of these contaminants deposited in the basins varies only in narrow ranges. Independent of the location of possible sources, these contaminants were widespread and distributed over the whole area before deposition. 

However, a series of additional mechanisms are superimposed on the general scheme above, which can significantly control, impede or enhance subsurface pollutant transport ... 

Tha transport mechanisms of molecular diffusion and mass carried by eddy motion are again assumed edditive although the contribution of the molecular diffusivity term is quite small except in the region nenr a wall where eddy motion is limited. The eddy diffusivity is directly applicable to problems snch as the dispersion of particles or species (pollutants) from a souree into a homogeneously turbulent air stream in which there is little shear stress. The theories developed by Taylor.36 which have been confirmed by a number of experimental investigations, can describe these phenomena. Of more interest in chemical engineering applications is mass transfer from a turbolent fluid to a surface or an interface. In this instance, turbulent motion may he damped oni as the interface is approached aed the contributions of both molecolar and eddy diffusion processes must he considered. To accomplish this. 9ome description of the velocity profile as the interface is approached must be available. 

In the research of resources and environment, such as geological storage of nuclear wastes, landfill of refuse and intrusion of saline water, transport of pollutant along with groundwater in fractured media has become one of the hotspots in recent years. This research becomes very difficult due to complexity of fractured media themselves. Solute transport in single fracture system is the basis of studying the solute transport mechanism in fractured media, and can help people to better understand the convection - diffusion mechanism of solute in fractures. 

In electrokinetic processes, there are two major transport mechanisms electromigration and electro-osmosis. Generally, in an electrical field, electromigration causes cationic metals such as cadmium, zinc, lead, nickel, and copper to move from the anode toward the cathode in electro-osmosis, the direction of movement of the pore water is toward the cathode when the zeta potential of the soil surface is negative. This can result in an enhanced removal of metals because the direction of transport of the ions in both mechanisms is the same. However, the direction of electromigration for anionic pollutants is toward the anode and that for electroosmosis is from anode to cathode, as stated previously. The opposite direction of movement means that the removal rate of anionic pollutants could be reduced. 

In 1996, as part of the Superfund Innovative Technology Evaluation (SITE) Program, the United States Environmental Protection Agency (USEPA) demonstrated the ISEE system at the SNL chemical waste landfill site in Albuquerque, New Mexico (USEPA, 1998). The ISEE system was developed by SNL for removing hexavalent chromium from unsaturated soil. This was a cutting edge, since most of the laboratory-scale studies were carried out in saturated soil samples. In a saturated sample, the contact of the interstitial fluid with the solid particles is more effective and aids in the extraction and transportation of pollutants. The two primary transport mechanisms in electrokinetics (electromigration and electroosmosis) require a liquid medium (water), but in the unsaturated soil zone, the lack of water in the interstices makes the solubilization and transportation of the heavy metals precipitated or adsorbed on the solid particles surface more difficult. 

Liao, C.M., C.M. Lin, L.J. Jou, et al. 2007. Linking valve closure behavior and sodium transport mechanism in freshwater clam Corbicula ftuminea in response to copper. Environ Pollut. 147 656-667. 

Electrokinetic remediation involves the installation of electrodes into multiple wells within a contaminated zone, followed by the application of a low electric potential. Ideally, the contaminants migrate toward the electrodes due to different transport mechanisms, and, upon reaching the wells, contaminant-laden liquids are extracted and treated. Although implementation is simple, the geochemical processes that occur within soils during electrokinetic remediation are complex and dependent on system variables such as soil type, pollutant type, treatment time, electrolyte solution, and applied voltage. 

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