Neutral gas dispersion modeling revised

  • Freddie Kootstra
  • Albert Pons Julia
  • Frank van het Veld
Conference paper


The first neutral gas dispersion models, which were developed in the late 70s and 80s, described the process of dispersion in a simplified way. In 1997 the 3rd release of the Yellow Book described an enhanced neutral gas dispersion model. This paper will present the main physical differences between the ‘old’ and ‘new’ dispersion model, as well as the problems encountered while extending the model’s capabilities for the use in safety studies. Generally, neutral gas dispersion is modeled as a Gaussian distribution in three dimensions (X, Y, and Z). The concentration at a certain downwind position (X, y, z) at time (t) is calculated as the product of the distribution functions (F x , F y , F z )) and a constant value that introduces the amount of released material. The distribution functions are dependent upon the release dimensions (b 0x , b 0y , b 0z ), the downwind position, the position of the cloud, and the dispersion parameters (σx, σy, σz). The ‘old’ model characterized atmospheric stability with a discrete dimensionless parameter (Pasquill class), and proposed simplified formulas for the distribution functions and for the dispersion parameters. The ‘new’ model contains more recent and realistic methods for characterizing the atmospheric stability, the calculation of the distribution functions and the dispersion parameters. The results of the ‘new’ neutral gas dispersion model have clearly improved upon the ‘old’ results. The outline of this paper is as follows: first a theoretical comparison of the ‘old’ and the ‘new’ neutral gas dispersion model will be presented, followed by a numerical comparison to illustrate the differences between the two models and validate the ‘new’ one


Reflection Coefficient Dispersion Model Dispersion Parameter Atmospheric Turbulence Toxic Dose 
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Copyright information

© Springer-Verlag London 2004

Authors and Affiliations

  • Freddie Kootstra
    • 1
  • Albert Pons Julia
    • 1
  • Frank van het Veld
    • 1
  1. 1.TNO Environment, Energy and Process Innovation, Department of Industrial SafetyNetherlands Organisation for Applied Scientific ResearchApeldoornThe Netherlands

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