Atmospheric contamination, turbulent dispersion

Volatilization (also referred to as vaporization or evaporation) is the conversion of a chemical from the sohd or hquid phase to a gas or vapor phase. The partitioning of a volatile compound in the subsurface environment comprises two distinct patterns volatilization of contaminant molecules (from the liquid, sohd, or adsorbed phase) and dispersion of the resulting vapors in the subsurface gas phase or the overlying atmosphere by diffusive and turbulent mixing. Even though the two processes are fundamentally different and controlled by different chemical and environmental factors, they are not wholly independent under natural conditions only by integrating their effects can volatilization be characterized. 

Eq. 7.2, where is then the eddy diffusion coefficient (Taylor and Spencer 1990). The height of the turbulent zone, within the atmospheric boundary layer, is orders of magnitude greater than that of the laminar flow layer, and dispersion of contaminant vapors in the turbulent zone is relatively rapid. 

This paper is mainly a general review of turbulent atmospheric flows through canopy flows and the various mathematical and computational modelling approaches that are available. The review which is mostly non-mathematical in its presentations, is particularly relevant to urban areas because of the urgency of developing methods for dealing with accidental releases in urban areas. The dispersion of contaminants flow studies is also included in this review. We focus on dispersion from localised sources released suddenly, or over longer periods. 

Therefore, a superadiabatic situation (Fig. 6-4), is favourable to the instability of the turbulent movements of the atmosphere and therefore it is favourable to an effective dispersion of contaminants. On the other hand, an underadiabatic situation is stable and unfavourable to dispersion (Fig. 6-5). 

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