Pasquill scheme

III-l. The dispersion of toxic gases is, to a high degree, site specific and toxicity is dependent on the chemical composition. However, for a preliminary evaluation, the values given in Table III-l may be used [III-l], These values are based on the Pasquill scheme (i.e. no buoyancy or heavy gas effect), with a short duration intake of air to the control room, and on the following assumptions, which also provide some conditions for their applicability ... 

Pasquill (11) advocated the use of fluctuation measurements for dispersion estimates but provided a scheme "for use in the likely absence of special measurements of wind structure, there was clearly a need for broad estimates" of dispersion "in terms of routine meteorological data" (p. 367). The first element is a scheme which includes the important effects of thermal stratification to yield broad categories of stability. The necessary parameters for the scheme consist of wind speed, insolation, and cloudiness, which are basically obtainable from routine observations (Table 19-3). 

The Monin-Obukhov length L is not a parameter that is routinely measured. Recognizing the need for a readily usable way to define atmospheric stability based on routine observations, Pasquill (1961) proposed a discrete atmospheric stability classification scheme that was later modified by Turner (1969). The scheme relies on observations of near-surface (10 m) wind, solar radiation, and cloudiness. If these... 

Frank Pasquill proposed his scheme in 1958 in a written note which he didn t consider worth publishing. Subsequently his method was acknowledged so useful that it was universally adopted. 

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