Pasquill-Gifford curves

As an alternative to estimating empirical equations. Seinfeld (1986) presents equations that are equivalent to the Pasquill-Gifford curves, as well as several other empirical models. An example of an empirical model presented as a set of formulae is that recommended by Briggs (Gifford, 1976), shown in Table 4-7. 

The most widely used ay and ct- correlations based on the Pasquill stability classes have been those developed by Gifford (1961). The correlations, commonly referred to as the Pasquill-Gifford curves, appear in Figures 18.4 and 18.5. 

FIGURE 18.4 Correlations for crv based on the Pasquill stability classes A to F (Gifford 1961). These are the so-called Pasquill-Gifford curves. 

To make an estimate of oy, or the stabiUty class must first be determined. The two typing techniques of Pasquill-Gifford and Turner discussed previously can be used. Then a series of curves or formulas are referenced to find values for Oy and as a function of stability class, downwind distance, and averaging time. For the values of Ty and 7 that follow, averaging time should be considered to be 1 hr. 

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