AERMOD Tech Guide

Gaussian Plume Air Dispersion Model

8.1.2 Directionally and/or Monthly Varying Surface Characteristics

Noon time albedo (r ' ); Bowen ratio (Bo ); roughness length (zo ) - For AERMET, the user can specify monthly variations of three surface characteristics for up to 12 upwind direction sectors. These include: the albedo (r), which is the fraction of radiation reflected by the surface; the Bowen ratio (Bo), which is the ratio of the sensible heat flux to the evaporation heat flux; and the surface roughness length (zo) , which is the height above the ground at which the horizontal wind velocity is typically zero. The user will be guided by look-up tables (in the AERMET user's guide) of typical values for these three variables for a variety of seasons and land use types.