Finally, to complete the description of eq. (79), the surface portion of vertical dispersion (F

zgs)in the SBL, is calculated from Venkatram (1992) as

For the direct and indirect sources in the CBL, the ambient portion of the vertical dispersion

(Fza of eq. (75)) is denoted as Fzaj (j = 1, 2) to distinguish between updrafts and downdrafts. Fzaj is

composed of an elevated (F

zej) and surface (Fzg) portion and is given bywhere the elevated portion (F

zej) is obtained from Weil et al. (1997)as

where F

wjis a parameter in the bi-Gaussian pdf (eq.(53)).The expression α ( ) is designed to be 1.0 above the surface layer

b p i=Min0.6 + 4H z, 1.0(

Hp> 0.1zi) and to otherwise match Venkatram’s (1992) result for vertical dispersion from asurface source in a neutral boundary layer.

For the CBL, the vertical dispersion from a source within the surface layer (

Hp{x} < 0.1zi) isparameterized by

where

bc =0.5,u*is the friction velocity, andLis the Monin-Obukhov length; above the surfacelayer (

Hp> 0.1zi), Fzgis assumed to equal zero. In the limit of a surface release (Hp =0), theparameterization of eq. (87) follows the form suggested by Venkatram (1992) for vertical

dispersion in the unstable surface layer; i.e., . The parameterization is designed ( ) σ

z∝u u x L*~ 2 2

to: 1) agree with Venkatram’s result in the limit of a surface release, 2) provide good agreement

between the modeled and observed concentrations from the Prairie Grass experiment (Paine et al.,

2001), and 3) decrease with source height in the surface layer and ultimately vanish for above the

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castellano: DISPER CUSTIC DESCAR RADIA italiano:

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

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