1.3.4 Area and Open Pit Source Emissions

 

     For area and open pit source emissions, Equation (1‑65) is changed to the form:

 

where K, D, Vd, and vd are defined in Equations (1‑1), (1‑54), (1‑65), and (1-80).  The parameter Q is the total mass per unit area emitted over the time period τ for which deposition is calculated.  The area source integral is estimated as described in Section 1.2.3.

 

1.4 THE ISC SHORT‑TERM WET DEPOSITION MODEL

 

     A scavenging ratio approach is used to model the deposition of gases and particles through wet removal.  In this approach, the flux of material to the surface through wet deposition (Fw) is the product of a scavenging ratio times the concentration, integrated in the vertical:

 

where the scavenging ratio (Λ) has units of s-1.  The concentration value is calculated using Equation (1-1).  Since the precipitation is assumed to initiate above the plume height, a wet deposition flux is calculated even if the plume height exceeds the mixing height.  Across the plume, the total flux to the surface must equal the mass lost from the plume so that

 

Solving this equation for Q(x), the source depletion relationship is obtained as follows:

 

where t = x/u is the plume travel time in seconds.  As with dry deposition (Section 1.3), the ratio Q(x)/Qo is computed as a wet depletion factor, which is applied to the flux term in Equation (1-89).  The wet depletion calculation is also optional.  Not considering the effects of wet depletion will result in conservative estimates of both concentration and deposition, since material deposited on the surface is not removed from the plume.

 

 

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