Plume elevation

The Assessment of SO2 Emitted into Atmosphere Table 2 Plume elevation (AH) depending on wind speeds... 

Elastic scattering is also the basis for Hdar, in which a laser pulse is propagated into a telescope s field of view, and the return signal is collected for detection and in some cases spectral analysis (14,196). The azimuth and elevation of the scatterers (from the orientation of the telescope), their column density (from the intensity), range (from the temporal delay), and velocity (from Doppler shifts) can be deterrnined. Such accurate, rapid three-dimensional spatial information about target species is useful in monitoring air mass movements and plume transport, and for tracking aerosols and pollutants (197). 

One of the effects of wind speed is to dilute continuously released pollutants at the point of emission. Whether a source is at the surface or elevated, this dilution takes place in the direction of plume transport. Figure 19-2 shows this effect of wind speed for an elevated source with an emission of 6 mass units per second. For a wind speed of 6 m s", there is 1 unit between the vertical parallel planes 1 m apart. When the wind is slowed to 2 m s there are 3 units between those same vertical parallel planes 1 m apart. Note that this dilution by the wind takes place at the point of emission. Because of this, wind speeds used in estimating plume dispersion are generally estimated at stack top. 

If the receptor is within an area source, or if emission rates do not vary markedly from one area source to another over most of the simulation area, the narrow-plume hypothesis can be used to consider only the variation in emission rates from each area source in the alongwind direction. Calculations are made as if from a series of infinite crosswind line sources whose emission rate is assigned from the area source emission rate directly upwind of the receptor at the distance of the line source. The ATDL model (22) accomplishes this for ground-level area sources. The RAM model (8) does this for ground-level or elevated area sources. 

The Offshore and Coastal Dispersion (OCD) model (26) was developed to simulate plume dispersion and transport from offshore point sources to receptors on land or water. The model estimates the overwater dispersion by use of wind fluctuation statistics in the horizontal and the vertical measured at the overwater point of release. Lacking these measurements the model can make overwater estimates of dispersion using the temperature difference between water and air. Changes taking place in the dispersion are considered at the shoreline and at any points where elevated terrain is encountered. 

These meteorological parameters, with the possible exception of the mean wind speed and direction, are not generally available for inclusion in calculations. Even wind speed measurements, which are usually taken at 20 ft above grade, must be corrected to the release point elevation. The correction applied to the wind speed depends on the turbulence of the air. The wind speed is the key determinant of the convection of pollutant in a plume. 

It is known that the vertical distribution of diffusing particles from an elevated point source is a function of the standard deviation of the vertical wind direction at the release point. The standard deviations of the vertical and horizontal wind directions are related to the standard deviations of particle concentrations in the vertical and horizontal directions within the plume itself. This is equivalent to saying that fluctuations in stack top conditions control the distribution of pollutant in the plume. Furthermore, it is known that the plume pollutant distributions follow a familiar Gaussian diffusion equation. 

One major item remains before we can apply the dispersion methodology to elevated emission sources, namely plume height elevation or rise. Once the plume rise has been determined, diffusion analyses based on the classical Gaussian diffusion model may be used to determine the ground-level concentration of the pollutant. Comparison with the applicable standards may then be made to demonstrate compliance with a legal discharge standard. 

Wilson, D. J., J. E. Fackrell, and A. C. Robins. 1982a. Concentration fluctuations in an elevated plume A diffusion-dissipation approximation. Atmospheric Environ. 16(ll) 2581-2589. 

Figure34.12 Mixing forced draft with induced. The overloaded forced-draft tower with excess plume results in elevated wet bulb at air inlets on new tower. Removing the forced draft and adding one more cell to the induced draft resolved the problem...

Elevated Plumes can be trapped either above or below the base of the inversion and held in a horizontal plane. Again, these can be brought down to ground level by eddies. This process is known as fumigation and can result in short-term high-level concentrations. 

A recirculation system extracts contaminated groundwater from the site, adds to or amends the extracted water ex situ, and reinjects the activated water to the subsurface, generally upgradient of the contaminated zone. As an alternative, extraction and injection are performed at different elevations in a single well, creating vertical circulation. A groundwater recirculation configuration may be used to provide containment of a plume or to allow the addition of amendments in a more controlled environment. 

Dc is the characteristic source dimension for continuous releases of dense gases (length), q0 is the initial plume volume flux for dense gas dispersion (volume/time), and u is the wind speed at 10 m elevation (length/time). 

Properties are assumed uniform across the plume at any elevation, z. This is called a top-hat profile as compared to the more empirically correct Gaussian profile given in Equation (10.1). 

No further action may be preferable to natural attenuation in certain instances. Very low risk situations may be better served by no further action since it eliminates the need for continued monitoring and further documentation. Sites with low levels of contaminants or nondiscemible plumes may be better candidates for no further action. Furthermore, very minor releases of hydrocarbons to the subsurface may not be sufficient to support bioremediation. Alternatively, sites with elevated levels of contaminants in nonpotable aquifers may be better addressed through conduct of a risk assessment. 

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