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     In addition to the mass mean diameters (microns), particle densities (gm/cm3), and the mass fractions for each particle size category being modeled, the dry deposition model also requires surface roughness length (cm), friction velocity (m/s), and Monin-Obukhov length (m).  The surface roughness length is specified by the user, and the meteorological preprocessor (PCRAMMET or MPRM) calculates the friction velocity and Monin-Obukhov length for input to the model.

     The lowest few meters of the atmosphere can be divided into two layers: a fully turbulent region where vertical fluxes are nearly constant, and the thin quasi‑laminar sublayer.  The resistance to transport through the turbulent, constant flux layer is the aerodynamic resistance.  It is usually assumed that the eddy diffusivity for mass transfer within this layer is similar to that for heat.  The atmospheric resistance formulation is based on Byun and Dennis (1995):

stable (L > 0):

unstable (L < 0):

where,    u*   =the surface friction velocity (cm/s),

          k    =the von Karman constant (0.4),

          z    =the height above ground (m),

          L    =the Monin-Obukhov length (m),

          zd   =deposition reference height (m), and

          zo   =the surface roughness length (m).

The coefficients used in the atmospheric resistance formulation are those suggested by Dyer (1974).  A minimum value for L of 1.0m is used for rural locations.  Recommended minimum values for urban areas are provided in the user's guides for the meteorological preprocessor programs PCRAMMET and MPRM.

 

 

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

 

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