The atmospheric dispersion of releases

This appendix describes four simple programs for calculating the atmospheric dispersion of releases on the basis of the formulae of Chapter 6. 

As noted at the beginning of Appendix 2, for historical reasons some of the measurement units 

The programs are written in Visual Basic for Applications (VBA) for execution in Microsoft Excel . They can be downloaded from the companion website (Files DISPERSION 1, DISPERSION2, FUMIGATION 1, FUMIGATION2). 

The Microsoft Excel cells for the input data and output results are (examples)  

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The dilution in air due to the atmospheric dispersion of radioactive aerosols resulting from a release of radioactive material was modelled for positions along the centre line of the plume using the diffusion equation with a top hat distribution to account for the directional fluctuations in crosswinds ... 

Kaiser, C. D. (1979). Examples of the Successful Application of a Simple Model for the Atmospheric Dispersion of Dense, Cold Vapors to the Accidental Release of Anhydrous Ammonia from Pressurized Containers. United Kingdom Atomic Energy Authority Safety and Reliability Directorate, Pub. SRD R150. 

Ellis, J., 2003. Use of atmospheric models in response to the Chernobyl disaster, in Tracking and Predicting the Atmospheric Dispersion of Hazardous Material Releases, National Research Council. National Academies Press, Washington DC... 

National Research Council (NRC). 2003. Tracking and predicting the atmospheric dispersion of hazardous material releases—Implications for homeland security. National Academies Press, Washington, DC. 

The 3D finite volume code ADREA-HF was developed for the computation of the atmospheric dispersion of heavy gas clouds in complex terrain. It contains a one-equation turbulence submodel taking account of two-phase processes [3]. The code has been applied to ammonia, propane, chlorine, and also buoyant releases. It has recently been tested against the BAM hydrogen release experiments. The calculational results for one of the trials are given in Fig. 8-8 showing the hydrogen dispersion near buildings [111]. 

Gas Dispersion. This group of models describes the atmospheric dispersion of clouds of gases and gas/aerosol mixtures. The objective of these models is to estimate the variation of concentration in air of the released material as a function of time and distance from release location. Further information can be found in CCPS (1995a). 

We evaluated the atmospheric dispersion of ammonia released in a major chemical accident near the town of lonava in central Lithuania. The course of the accident has been briefly described by Kletz (1991). More detailed reports have been prepared by the Lithuanian State Committee for Environmental Protection (1989) and by Andersson (1991). For a more complete description of this study, the reader is referred to Kukkonen et al. (1993). 

Entrainment The suspension of liquid as an aerosol in the atmospheric dispersion of a two-phase release or the aspiration of air into a jet discharge. 

Validating the final experimental protocol was accomplished by running a model study in which Nd was released into the atmosphere from a 100-MW coal utility boiler. Samples were collected at 13 locations, all of which were 20 km from the source. Experimental results were compared with predictions determined by the rate at which the tracer was released and the known dispersion of the emissions. 

ApSimon, H. M., and WUson, J. J, N., Modeling atmospheric dispersal of the Chernobyl release across Europe. Boundary-Layer Meteorol. 41, 123-133 (1987). 

Meteorology plays an important role in determining the height to which pollutants rise and disperse. Wind speed, wind shear and turbulent eddy currents influence the interaction between the plume and surroimding atmosphere. Ambient temperatures affect the buoyancy of a plume. However, in order to make equations of a mathematical model solvable, the plume rise is assumed to be only a function of the emission conditions of release, and many other effects are considered insignificant. 

Atmospheric dispersion of any rupture disc discharges would result in a vapor cloud with gas concentrations above the lower explosive limit. Thus, such releases must be avoided, and other mitigation procedures should be used. However, as an additional check on the situation, mapping of the potential gas cloud versus the plant layout was conducted with the conclusion that no ignition sources were likely to be present in the region where the vapor cloud would be flammable. 

Elevated stacks to aid atmospheric dispersion of the vapor releases. 

Man contributes to the Se cycle through his industrial activity and his use of fertilisers (see Chapter 9). During the combustion of coal and oil (Fig. 1.3) some selenium is released to the atmosphere, dispersed and returned to the earth mainly in rain. The full extent of Man s influence has, however, yet to be evaluated. 

The atmospheric dispersion is modeled by a modified Gaussian plume equation which estimates the average dispersion of the contaminants released from the source in each wind direction. The Gaussian model of a plume dispersion accounts for the gaseous contaminant transport from the source area to a downwind receptor and is represented by the equation of Pasquill as modified by Gifford (Chacki, 2000) ... 

At synthesis these are grouped in spatial deposits with sizes of around 100 nm, similar to Dahlia, Fig. 9c. This comes from the fact that the quantity of carbon atoms released by the laser pulse is large and the energy of the separate atoms is likewise significant, as a result these are dispersed in all directions and traverse a long path. The large work pressure obstructs the speedy dispersal of the atoms and facilitates deposit formation. The form of the SWNH deposit is also dependent on the nature of the atmospheric ambient. When the work gas is He or N2 the spherical assembly with a budlike shape bud[ k.Q nanohoms) is predominant 70-80 %, while for an Ar work gas ambient 95 % of the formation resembles the dahlia flower (42), (43). Their structure has fewer defects than that of the bud iike nanohoms. 

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