Line source dispersion

CALINE3 (California Line Source Model) is a line source dispersion model tliat can be used to predict carbon monoxide concentrations near liighways and arterial streets given traffic emissions, site geometry, and meteorology. 

There are two main delivery methods for CBW agents Point source dispersal makes use of munitions, such as an artillery shell or missile warhead. Line source dispersal employs a sprayer system. The choice of one or the other depends on what is required for effective distribution of the chemical agent. 

The entire development on atmospheric dispersion lias been limited to eniissioiis from a "point" (e.g., stack) source. Altliough most dispersion applications involve point sources, in some instances tlie location of the emission can be more accurately described physically and niatlicmatically by either a line source or an area source. 

Here q is tlie source strengtli per unit distance (e.g., g/s-in). Note tliat tlie horizontal dispersion parameter Oy does not appear in tliis equation, since it is assumed tliat lateral dispersion from one segment of the line is compensated by dispersion in tlie opposite direction from adjacent segments. Also, y does not appear, since tlie concentration at a given x is tlie same for any value of y. Concentrations from infinite line sources, when tlie wind is not perpendicular to Uie line, can also be approximated. If tlie angle between the wind direction and line source is (f), we may write... 

BLP (Buoyant Line and Point Source Dispersion Model) is a Gaussian plume dispersion model associated witli aluminum reduction plants. 

To illustrate the application of the Monte Carlo method, we consider the problem of simulating the dispersion of material emitted from a continuous line source located between the ground and an inversion layer. A similar case has been considered by Runca et al. (1981). We assume that the mean wind u is constant and that the slender-plume approximation holds. The line source is located at a height h between the ground (z = 0) and an inversion layer (z = Zi). If the ground is perfectly reflecting, the analytical expression for the mean concentration is found by integrating the last entry of Table II over y from -< to -Hoo. The result can be expressed as... 

The quantities in the square brackets are just the ones known from equ. (4.19) with equ. (4.16). Due to the fixed value of pass it can be seen that for the evaluation of relative intensities the dispersion correction can be omitted. However, the transmission factor Tret(Ekin, pass) which describes the change of transmission caused by the retardation becomes very important in this case, see Fig. 4.16. It has to be determined experimentally, and in ideal cases it can be estimated on the basis of Liouville s theorem for optical systems (see Section 10.3.2). In the example shown in Fig. 4.16 the essential action of the retardation field is to change the brightness B in one dimension. (One has a one-dimensional problem because the lens produces focusing of the line source in one dimension only (for details see [GSa75]).) Following equ. (10.47) one gets (subscripts ( and r denote quantities before and after retardation)... 

One of the immediate applications of this model is to simulate advection and dispersion of contaminants in soil columns with low permeability and strong retention mechanisms. In these cases, the contaminant would not be expected to travel to the lowest layers of the soil profile very soon. In this chapter, results from two common contaminant-input conceptualizations were simulated. The first scenario consisted of a localized contaminant load (point source) located at the center of the topsoil column layer (point-source contaminant inputs may simulate localized leakages of chemicals on the surface of the earth). The second simulation consists of a linearly distributed contaminant load (line source) over the top surface of a soil column. Line sources are commonly used in groundwater contamination problems (e.g., see Mulligan and Ahlfeld, 2001). Additionally, a two-point source simulation is included for purposes of comparison. 

The transport associated with a line source of contaminant was also studied for the same data set (anisotropic media, isotropic dispersion). The model, besides providing numerical details of the simulation (maximum concentration value) also shows (Figure 3.10) the three-dimensional distribution of the contaminant for two cutting planes. The migration of the contaminant concentration for the line source has a wider distribution in the horizontal and transversal planes as shown in the figure. The contaminant concentration meets the CMC and CCC criteria just at 50%... 

The model was used to study the advection and dispersion of a trace contaminant load into a low-permeability soil column. An anisotropic case was simulated. The model estimated and showed the spatial distribution of the contaminant plume and visually depicted the concentration values in grayscale. The three-dimensional visualization provided by the model was shown to be very useful for identifying the extent and severity of the soil contamination due to the trace compound load under three different types of input load distribution (point source, line source, and two-point... 

Dispersion Models Based on Inert Pollutants. Atmospheric spreading of inert gaseous contaminant that is not absorbed at the ground has been described by the various Gaussian plume formulas. Many of the equations for concentration estimates originated with the work of Sutton (3). Subsequent applications of the formulas for point and line sources state the Gaussian plume as an assumption, but it has been rigorously shown to be an approximate solution to the transport equation with a constant diffusion coefficient and with certain boundary conditions (4). These restrictive conditions occur only for certain special situations in the atmosphere thus, these approximate solutions must be applied carefully. 

The nano-electrospray (nanoES) source is essentially a miniaturized version of the ES source. This technique allows very small amounts of sample to be ionized efficiently at nanoliters per minute flow rates and it involves loading sample volumes of 1-2 pi into a gold-coated capillary needle, which is introduced to the ion source. Alternatively for on-line nanoLC-MS experiments the end of the nanoLC column serves as the nanospray needle. The nanoES source disperses the liquid analyte entirely by electrostatic means [27] and does not require assistance such as solvent pumps or nebulizing gas. This improves sample desolvation and ionization and sample loading can be made to last 30 minutes or more. Also, the creation of nanodroplets means a high surface area to volume ratio allowing the efficient use of the sample without losses. Additionally, the introduction of the Z-spray ion source on some instruments has enabled an increase in sensitivity. In a Z-spray ion source, the analyte ions follow a Z-shaped trajectory between the inlet tube to the final skimmer which differs from the linear trajectory of a conventional inlet. This allows ions to be diverted from neutral molecules such as solvents and buffers, resulting in enhanced sensitivity. 

Meroney, R.N., Pavageau, M Rafailidis, S., and Schatzmann, M. (1996) Study of Line Source Characteristics for 2-d Physical Modelling of Pollutant Dispersion in Street Canyons,./. Wind Engineering Industrial Aerodynamics Vol. 62, 37-56. 

A more recent attempt to control aerosol particle size on target has been the use of aerodynamic dissemination and sprays as line sources. Thermal dissemination, wherein pyrotechnics are used to aerosolize the agent has been used particularly to generate fine, inhalable clouds of incapacitants. Dispersion considers the relative placement of the chemical agent munition upon or adjacent to a target immediately before dissemination so that the material is most efficiently used. 

To avoid spectral interferences when non-dispersive AFS instruments are used, line-like radiation sources are required. Spectral interferences using narrow line sources are uncommon, while when using continuum sources they are quite common. Corrections can be made by wavelength or amplitude modulation, which can be performed with filters. Different wavelengths are separated from each other by filters whose advantage is their low price and good spectral transmission. 

The spherical coordinate system with the coordinates r, 0, and (p is of course well suited for spherical sources. A sphere in a homogeneous medium disperses the current radially out in all directions. Because the surface area of a sphere is 4Tcr, the current density falls proportional to r. As we shall see, this is in contrast to a line source where the current density falls proportional to r (Table 6.1). Because the current spreads out in all directions, a fliree-dimensional (3D) analysis is necessary, but in a homogeneous medium any plane through the sphere center will show the same two-dimensional (2D) plot. 

Develop an order-of-magnitude solution for the dispersion of atmospheric pollutants. The most commonly used models of atmospheric dispersion from continuous sources are the Gaussian plume models. For an infinite-line source such as might be used to simulate automotive emissions on a freeway, the model takes the form... 

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