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     For large travel-times, hed in Equation (1-53) can become less than zero.  However, the tilted plume approximation is not a valid approach in this region.  Therefore, a minimum value of zero is imposed on hed.  In effect, this limits the settling of the plume centerline, although the deposition velocity continues to account for gravitational settling near the surface.  The effect of gravitational settling beyond the plume touchdown point (where hed = 0) is to modify the vertical structure of the plume, which is accounted for by modifying the vertical dispersion parameter (σz).

     The process of adjusting the vertical profile to reflect loss of plume mass near the surface is illustrated in Figures 1-6 and 1-7.  At a distance far enough downwind that the plume size in the vertical has grown larger than the height of the plume, significant corrections to the concentration profile may be needed to represent the removal of material from the plume due to deposition.  Figure 1-6 displays a depletion factor FQ, and the corresponding profile correction factor P(z) for a distance at which σz is 1.5 times the plume height.  The depletion factor is constant with height, whereas the profile correction shows that most of the material is lost from the lower portion of the plume.  Figure 1-7 compares the vertical profile of concentration both with and without deposition and the corresponding depletion of material from the plume.  The depleted plume profile is computed using Equation (1-54). 

 

 

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  APLICACIONES castellano: DIS CUS DES  RAD   english: DIS CUS DES RAD  

 

 português: DIS CUS DES RAD   italiano:   DIS CUS  DES RAD

 

français:  DIS CUS DES RAD