Transport and transformation

Air pollution can be considered to have three components sources, transport and transformations in the atmosphere, and receptors. The source emits airborne substances that, when released, are transported through the atmosphere. Some of the substances interact with sunlight or chemical species in the atmosphere and are transformed. Pollutants that are emitted directiy to the atmosphere are called primary pollutants pollutants that are formed in the atmosphere as a result of transformations are called secondary pollutants. The reactants that undergo transformation are referred to as precursors. An example of a secondary pollutant is O, and its precursors are NMHC and nitrogen oxides, NO, a combination of nitric oxide [10102-43-9] NO, and NO2. The receptor is the person, animal, plant, material, or ecosystem affected by the emissions. 

Transport and Transformation. Once emitted into the atmosphere, the fate of a particular poUutant depends upon the stabihty of the atmosphere, which determines the concentration of the species, the stabihty of the poUutant in the atmosphere, which determines the persistence of the substance. Transport depends upon the stabUity of the atmosphere which, in turn, depends upon the ventilation. The stabUity of a poUutant depends on the presence or absence of clouds, fog, or precipitation the poUutant s solubUity in water and reactivity with other atmospheric constituents (which may be a function of temperature) the concentrations of other atmospheric constituents the poUutant s stabUity in the presence of sunlight and the deposition velocity of the poUutant. 

Regardless of the source, the resultant oil slicks are essentially surface phenomena that are affected by several transportation and transformation processes. With respect to transportation, the principal agent for the movement of slicks is the wind, but length scales are important. Whereas small (i.e. relative to the slick size) weather systems, such as thunderstorms, tend to disperse the slick, cyclonic systems can move the slick essentially intact. Advection of a slick is also affected by waves and currents. To a more limited extent, diffusion can also act to transport the oil. 

FIGURE 7.15 Transport and transformation of toxic chemicals in soil environments (left) and water environments... 

It has been recognized for some time that fluids in motion, such as the atmosphere or the ocean, disperse added materials. This properly has been exploited by engineers in a variety of ways, such as the use of smoke stacks for boiler furnaces and ocean ontfalls for the release of treated wastewaters. It is now known that dilution is seldom the solution to an enviromnental problem the dispersed pollutants may accumulate to undesirable levels in certain niches in an ecosystem, be transformed by biological and photochemical processes to other pollntants, or have nnanticipated health or ecological effects even at highly dilute concentrations. It is therefore necessary to rmderstand the transport and transformation of chemicals in the natural environment and through the trophic chain ctrlminating in man. 

Two main hazards associated with chemicals are toxicity and flammability. Toxicity measurements in model species and their interpretation are largely the province of life scientists. Chemical engineers can provide assistance in helping life scientists extrapolate their resrrlts in the assessment of chemical hazards. Chemical engineers have the theoretical tools to make important contributions to modehng the transport and transformation of chemical species in the body—from the entry of species into the body to their action at the rrltimate site where they exert their toxic effect. Chemical engineers are also more likely than life scientists to appreciate... 

Jury WA, Winer AM, Spencer WF, et al. 1987b. Transport and transformation of organic chemicals in the soil-air-water ecosystem. Rev Environ Contam Toxicol 99 119-164. 

Bassingthwaighte JB, Wang CY, Chan IS. Blood-tissue exchange via transport and transformation by capillary endothelial cells. Circ Res 1989 65 997-1020. 

From the time when it was shovm that micro flow reactors can provide valuable contributions to organic chemistry, it was obvious to develop them further and their workflow towards modern screening techniques [20]. It was especially the finding of high reaction rates, the capability to transport and transform minute sample volumes and the first integration of analytics that paved the way to a parallelization of micro flow processing. These benefits were combined with the ease of automation of a micro flow system. By this means, the potential of on-line analysis of the reactions can be fully exploited. 

USEPA] US Enviromnental Protection Agency. 2002. Proceedings and summary report, workshop on the fate, transport, and transformation of mercury in aquatic and terrestrial environments. EPA/USGS workshop 2001 May 8-10 West Pahn Beach, FL, USA. USEPA Office of Research and Development. EPA/625/R-02/005. 171 p. 

The chemical, physical and biological properties of a substance in conjunction with the environmental characteristics of an area, result in physical, chemical, and biological processes associated with the transport and transformation of the substance in soil and groundwater. These processes are shortly described in the following sections, along with some representative mathematical methods or models employed in the literature. Information is mainly obtained from Bonazountas and Fiksel (3j. 

To illustrate the model a steady state solution is given which would apply to the lake after prolonged steady exposure to water emission of 10 mol/h and atmospheric input from air of 5.3 ng/m3. The solution is given in Figure 2B in the form of fugacities, concentrations and transport and transformation process rates. 

To address media-specific problems, single-media models for air, surface water, groundwater and soil pollution have been developed and used by different disciplines. Although these models generally provide detailed description of the pollutant distribution in space and time and incorporate mass transfer from other media as boundary conditions, they are not capable of characterizing the total environmental impact of a pollutant release. Multimedia models have been, therefore, developed to predict the concentration of chemicals in multiple environmental media simultaneously with consideration of chemical transport and transformation within and among media [1],... 

The current version of CalTOX (CalTOX4) is an eight-compartment regional and dynamic multimedia fugacity model. CalTOX comprises a multimedia transport and transformation model, multi-pathway exposure scenario models, and add-ins to quantify and evaluate variability and uncertainty. To conduct the sensitivity and uncertainty analyses, all input parameter values are given as distributions, described in terms of mean values and a coefficient of variation, instead of point estimates or plausible upper values. 

Fate and exposure analyses. The multimedia transport and transformation model is a dynamic model that can be used to assess time-varying concentrations of contaminants that are placed in soil layers at a time-zero concentration or contaminants released continuously to air, soil, or water. This model is used for determining the distribution of a chemical in the environmental compartments. An overview of the partitioning among the liquid, solid and/or gas phases of individual compartments is presented in Fig. 7. The exposure model encompasses... 

McKone TE (1993) CalTOX, A multi-media total-exposure model for hazardous wastes sites. Part II. The dynamic multi-media transport and transformation model. A report prepared for the State of California, Department Toxic Substances Control by the Lawrence Livermore National Laboratory No. UCRL-CR 111456PtII, Livermore... 

Four mass balance equations can be written, one for each medium, resulting in a total of four unknown fugacities, enabling simple algebraic solution as shown in Table 1.5.9. From the four fugacities, the concentration, amounts and rates of all transport and transformation processes can be deduced, yielding a complete mass balance. 

Phase Properties, Compositions, and Transport and Transformation Rates ... 

Volatilization Volatilization and biodegradation may be dominant transport and transformation processes for styrene in water calculated volatilization t,/2 = 3 h from a river 1-m deep with a current speed of 1.0 m/s and wind velocity of 3 m/s (Howard 1989) ... 

Southworth, R.G. (1977) Transport and transformations of anthracene in natural waters. In Aquatic Toxicology. ASTM ATP 667, Marking, L.L., Kimerle, R.A., Editors, American Society for Testing and Materials, pp. 359-380, Philadelphia. 

Southworth, G.R. 1979. Transport and transformation of anthracene in natural waters. Pages 359-380 in L.L. Marking and R.A. Kimerle (eds.). Aquatic Toxicology. ASTM STP-667. American Society for Testing and Materials, Philadelphia, PA. 

Su Yin, Yuan Xinzhong, Ceng Guangming, Li Huimeng and Li Lian. 2008. Study on influence factors of transportant and transformations of Pb in soil-plant system. Journal of Anhui Agricultural Sciences, 36(16), 6953-6955. (in Chinese). 

The simple kinetics for uptake of soluble substrate of the bacteria in a biofilm is traditionally described by a combination of mass transport across the water/biofilm interface, transport in the biofilm itself and the corresponding relevant biotransformations. Transport through the stagnant water layer at the biofilm surface is described by Fick s first law of diffusion. Fick s second law of diffusion and Michaelis-Menten (Monod) kinetics are used for describing the combined transport and transformations in the biofilm itself (Williamson... 

Most pigmented systems are considered viscoelastic. At low shear rates and slow deformation, these systems are largely viscous. As the rate of deformation or shear rate increases, however, the viscous response cannot keep up, and the elasticity of the material increases. There is a certain amount of emphasis on viscoelastic behavior in connection with pigment dispersion as well as ink transportation and transformation processes in high-speed printing machines (see below). Under periodic strain, a viscoelastic material will behave as an elastic solid if the time scale of the experiment approaches the time required for the system to respond, i.e., the relaxation time. Elastic response can be visualized as a failure of the material to flow quickly enough to keep up with extremely short and fast stress/strain periods. 

Woodburn KB, Rao PSC, Fukui M, Nkedi-Kizza P (1986) In Macalady DL (ed) Transport and transformations of organic contaminants. J Contaminant Hydrol 1 277... 

Brown BD, Rolston DE. 1980. Transport and transformation of methyl bromide in soils. Soil Science 130 68-75. 

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