The infinite series term in Equation (1‑50) accounts for the effects of the restriction on vertical plume growth at the top of the mixing layer. As shown by Figure 1‑3, the method of image sources is used to account for multiple reflections of the plume from the ground surface and at the top of the mixed layer. It should be noted that, if the effective stack height, he, exceeds the mixing height, zi, the plume is assumed to fully penetrate the elevated inversion and the ground‑level concentration is set equal to zero.
Equation (1‑50) assumes that the mixing height in rural and urban areas is known for all stability categories. As explained below, the meteorological preprocessor program uses mixing heights derived from twice‑daily mixing heights calculated using the Holzworth (1972) procedures. The ISC models currently assume unlimited vertical mixing under stable conditions, and therefore delete the infinite series term in Equation (1‑50) for the E and F stability categories.
The Vertical Term defined by Equation (1‑50) changes the form of the vertical concentration distribution from Gaussian to rectangular (i.e., a uniform concentration within the surface mixing layer) at long downwind distances. Consequently, in order to reduce computational time without a loss of accuracy, Equation (1‑50) is changed to the form:
at downwind distances where the σz/zi ratio is greater than or equal to 1.6.
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APLICACIONES castellano: DIS CUS DES RAD english: DIS CUS DES RAD
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