above

zim. Therefore, whether the plume is above or belowzim, the region of low turbulence above

zimwill have an appropriate effect on the concentration distribution within the mixing layer.When the plume buoyancy carries the rising plume into the relatively non-turbulent layer

above

zim, the reflecting surface is still placed at 2.15 Fzsabove the effective plume height becausethere will be plume spread due to plume buoyancy and downward mixing is still important.

Therefore, in the SBL, plume material is assumed to reflect off an elevated surface which is

defined as:

where F

zsin eq. (68) is determined from equations found in Section 5.5.1.2 with FwTanduevaluated at

hes; not as an effective parameter. It is important to note thatzieffdepends ondownwind distance since F

zsis distance dependent. In fact, as eq. (68) suggests, this effectivereflecting surface is only folding back the extreme tail of the upward distribution. Also, if the

height of the receptor

zr$zieffthen the effective reflecting surface is not considered. Thisapproach is also implemented for the penetrated source. For the penetrated and injected sources

zieffis calculated using eq. (68) with Fzsandhesreplaced by Fzpandheprespectively.5.4

Treatment of Lateral Plume MeanderIn AERMOD we include the effect that lower-frequency, non-diffusing eddies (i.e., meander)

have on plume concentration. Meander (or the slow lateral back and forth shifting of the plume)

decreases the likelihood of seeing a coherent plume after long travel times. This effect on plume

concentration could best be modeled with a particle trajectory model, since these models estimate

the concentration at a receptor by counting the number of times a particle is seen in the receptor

volume. However, as a simple steady state model, AERMOD is not capable of producing such

information. AERMOD accounts for meander by interpolating between two concentration limits:

the coherent plume limit (which assumes that the wind direction is distributed about a welldefined

mean direction with variations due solely to lateral turbulence) and the random plume

limit, (which assumes an equal probability of any wind direction).

For the coherent plume, the horizontal distribution function (

FyC) has the familiar Gaussianform:

where F

yis the lateral dispersion parameter (see Section 5.5). For the random plume limit, thewind direction (and plume material) is uniformly distributed through an angle of 2B

.Therefore,the horizontal distribution function

FyRtakes the simple form:

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

castellano: DISPER CUSTIC DESCAR RADIA italiano:

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

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