wherezPG = 0.46 m (Prairie Grass release height), and z MAX[z z ] . To insure that " does max PG = ;
not become unrealistically large for surface releases,z is not allowed below zPG (i.e., 0.46 m). In
the SBL,z = hes; in the CBL z = hs; for penetrated sources, z = hep. . As " becomes small for
large release heights,Fya would tend to grow linearly with downwind distance.
22.214.171.124Vertical Dispersion from Ambient Turbulence
For sources in the SBL (and for sources in the CBL that are emitted directly into the stable
layer above the mixed layer), the ambient portion of the vertical dispersion (Fzas) is composed of
an elevated (Fzes) and near-surface (Fzgs) component. For hes < zi simple interpolation provides a
smooth transition between the two components.
Forhes $ zi Fzas is set equal to Fzes. The expressions for calculating hes are found in Section 5.6.2.
It should be noted, for sources in the SBL, thatFzas is the specific form of the ambient portion of
the vertical dispersion (i.e.,Fza in eq. (75)).
In the SBL, the elevated portion of the vertical dispersion follows the form of eq. (76):
whereFwT is the vertical turbulence due to the mechanical mixing (Cimorelli et al., 2004).
As with the lateral component, the Lagrangian time scale (TLzs) for the vertical turbulence can
be written in the form (Venkatram et al. 1984)
The length scalel is an interpolation between the limiting length scales for neutral conditions,
l h, and stable conditions :
wherel h and . Under very stable conditions or at large heights, l n es = 0.36 l N s wT = 0 27 . ~σ
approachesls. When conditions are near neutral, N is very small, and l approaches ln.
By combining eqs. (80), (81), and (82) we find the following expression that is used by
AERMOD to computeFzes, the elevated portion of the vertical dispersion for the stable source:
n951 - n952 - n953 - n954 - n955 - n956 - n957 - n958 - n959 - n960 - n961 - n962 - n963 - n964 - n965 - n966 - n967 - n968 - n969 - n970 - n971 - n972 - n973 - n974 - n975 - n976 - n977 - n978 - n979 - n980 - n881 - n982 - n983 - n984 - n985 - n986 - n987 - n988 - n989 - n990 - n991 - n992 - n993 - n994 - n995 - n996 - n997 - n998 - n999 - n1000
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