Pasquill stability categories

Fig. 20-1. Concentration of an air pollutant at the point of maximum ground-level concentration as a function of wind speed and Pasquill stability category (A-F).

Doty, S. R., Wallace, B. L., and Holzworth, G. C., "A Climatological Analysis of Pasquill Stability Categories Based on STAR Summaries." National Climatic Center, Environmental Data Service, National Oceanic and Atmospheric Administration, Asheville, NC, 1976. 

Relationship of Pasquill Stability Categories to Ranges of the Parameter a ... 

FIGURE 4-25a Standard deviations of mass distribution in a Gaussian plume, cry and az, given as a function of both distance downwind from a point source and Pasquill stability categories. Dispersion coefficient as used in this figure means the standard deviation of the plume width or height [L] rather than a Fickian coefficient [L2/T], (From Atmospheric Chemistry and Physics of Air Pollution, by J. H. Seinfeld. Copyright 1986, John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.)... 

To calculate downwind concentrations, use Eq. [4-16]. From Table 4-6, a wind speed of 4.5 m/sec corresponds to Pasquill stability category C during the winter when insolation is low. By using Fig. 4-25, at a downwind distance of 8 km, cry is approximately 700 m and crz is approximately 400 m. Note thaty = 0 directly downwind and z = 0 at ground level. First, estimate Q/u ... 

From Table 4-6, the Pasquill stability category is D. Turbulent intensity in the vertical direction can be calculated from Eq. [4-21] ... 

To calculate it. and cry, use Eq. [4-22], together with estimates of fz and fy obtained using the appropriate formulae from Table 4-8. For rural conditions and Pasquill stability category D ... 

The correlations for ay and az in the previous subsection require knowledge of atmospheric variables that may not be available. In that case, one needs correlations for a, and [Pg.864]

Fig. 2.5 Lead in air versus distance from motorway. Lines are labelled with Pasquill stability categories, [7]. Experimental measurements o, Little and Wiffen [11] Bevan et al...

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