Parameters Affecting Atmospheric Dispersion

A wide variety of parameters affect atmospheric dispersion of toxic materials ... 

Parameters Affecting Atmospheric Dispersion The parameters important to atmospheric dispersion can be divided roughly into three categories contaminant source atmospheric and terrain properties and contaminant interaction with the atmosphere. 

Parameters Affeeting Gas Dispersion A wide variety of parameters affect the dispersion of gases. These include (1) wind speed, (2) atmospheric stability, (3) local terrain characteristics, (4) height of the release above the ground, (5) release geometry, i.e. from a point, line, or area source, ( momentum of the material released, and (7) buoyancy of the material released. 

In most real-world applications for which the controlhng meteorological parameters are measured from a tower, conditions are reasonably steady and horizontally homogeneous (less than 50%) variation from the spatial and temporal average dirring the experiment) and no exceptional circimistances exist that could affect the atmospheric dispersive capacity in ways not accoimted for by the model, accmacy within a factor of 2 can be ejqrected. 

The provisions to monitor site related parameters affected by seismic, atmospheric, water and groundwater related, demographic, industrial and transport related developments should be described in this section. This may be used to provide necessary information for emergency operator actions in response to external events, to support the periodic safety review at the site, to develop dispersion modelling for radioactive material and as confirmation of the completeness of the set of site specific hazards taken into account. 

It is apparent from equations 3.2.4-3.2.7 that the determination of the concentration field is dependent on the values of the Gaussian dispersion parameters a, (or Oy in the fully coupled puff model). Drawing on the fundamental result provided by Taylor (1923), it would be expected that these parameters would relate directly to the statistics of the components of the fluctuating element of the flow velocity. In a neutral atmosphere, the factors affecting these components can be explored by considering the fundamental equations of fluid motion in an incompressible fluid (for airflows less than 70% of the speed of sound, airflows can reasonably be modeled as incompressible) when the temperature of the atmosphere varies with elevation, the fluid must be modeled as compressible (in other words, the density is treated as a variable). The set of equations governing the flow of an incompressible Newtonian fluid at any point at any instant is as follows ... 

In the case of point sources, available dispersion models are typically based on assumption of a Gaussian distribution. The relative complexity and reliability of Gaussian distribution models are affected by parameters such as turbulence although modifications can be made to account for complex atmospherics. Reliability of the Gaussian approach is relatively satisfactory for distances up to about 100 km from the stationary source. Seinfeld and Pandis (1998) have published a comprehensive treatment of Gaussian... 

As seen, the boundary conditions, especially the atmospheric conditions, affect directly the dispersion however, in most cases the exact values of the parameters that characterized the conditions are not known and approximate values are used to perform the consequences analyses. In this sensitivity analysis the effects of variations in the wind speed, ambient temperature, atmospheric pressure and ground roughness on predicted concentrations are analyzed. 

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