AERMOD Tech Guide

Gaussian Plume Air Dispersion Model

4.1.1 Wind Speed Profiling in the Interface

At least one wind speed measurement is required for each simulation with AERMOD. The AERMOD profile equation for wind speed is:

Equation (28)

For the CBL, the m’s are evaluated using eq. (7) with zref replaced by z, and during stable conditions they are calculated as follows (Van Ulden and Holtslag, 1985):

Equation (29)

For small z/L (<<1), eq. (29) reduces to the well-known m form given in eq. (19),with ßm = 5; in eq. (29) the effective constant ßm in the small z/L limit is 4.93. m m

However, for large z/L (>1) and heights as great as 200 meters in the SBL, the m given by eq. (29) is found to fit wind observations much better than the m given by eq.(19) (see van Ulden m and Holtslog, 1985).

Figure 2 and Figure 3 show the form of the wind profiles used by AERMOD. In order to produce these figures, and others which follow, we constructed two typical cases, one each for the CBL and the SBL. For the CBL we assumed that zi =1000m, L=-10m and zo =0.1 (_zo =.0001zi and L=-.01zi ). For the SBL we assumed that zi =100m, L=10m and zo =0.1m

Figure 2

Figure 2: Wind speed profile, for both CBL and SBL, in the region below 7Zo

Figure 3

Figure 3: Wind speed profile, for both CBL and SBL, in the region above 7Zo