scope:

Introduction

The Gaussian puff model proceeds from the idea that the atmospheric pollutants emitted from a Single point source in a short period of time form a small puff which grows in size with time and is transported fur¬ ther by the wind in the process. This dispersion is to be independent of whether yet other sources are present or whether the same source previously or subsequently emits further or whether yet other substances are released in addition. Consequently, only the release of a single type of substance from a Single source needs to be discussed here, because more complicated situations can be described within the frame¬ work of this model approach by simple superimposition.

This disposes of all effects which are based on the physical or chemical mutual interaction of the substances emitted, or on the effect on the transport characteristics of the ambient atmosphere (e.g. thermal lift, effects of heavy gases, nonlinear chemical reactions). However, thermal lift can be treated parametrically (see Section 5.3).

The concentration distribution inside a puff has in every direction the form of a Gaussian bell-shaped curve, and here the extent can differ in the horizontal and vertical. This form is suggested by the fact that the diffusion equation with constant coefficients for a punctiform initial distribution is solved precisely by the (three-dimensional) Gaussian curve, and the ex¬ tent increases in a way proportional to the Square root of the time (see Appendix A).

It is not possible using this model approach to give a faithfully detailed description of the dispersion prop¬ erties of the atmosphere (wind profile, diflferent diffusivity) which vary with the height above ground; they can be acquired only as an average over the vertical extent of the puff.