When applying the AERMET meteorological processor (EPA, 2004a) to prepare the

meteorological data for the AERMOD model (EPA, 2004b), the user must determine appropriate

values for three surface characteristics: surface roughness length {zo}, albedo {r}, and Bowen

ratio {Bo}. The surface roughness length is related to the height of obstacles to the wind flow

and is, in principle, the height at which the mean horizontal wind speed is zero based on a

logarithmic profile. The surface roughness length influences the surface shear stress and is an

important factor in determining the magnitude of mechanical turbulence and the stability of the

boundary layer. The albedo is the fraction of total incident solar radiation reflected by the

surface back to space without absorption. The daytime Bowen ratio, an indicator of surface

moisture, is the ratio of sensible heat flux to latent heat flux and is used for determining

planetary boundary layer parameters for convective conditions driven by the surface sensible

heat flux. This section provides recommendations regarding several issues associated with

determining appropriate surface characteristics for AERMOD modeling applications.


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