Qualitative approach In the summer of 1956, experimental observations in Nebraska resulted in Frank Pasquill suggesting categories of atmospheric stability that could be identified from easily available information (Pasquill, 1961). These categories are very important and are used in many of the simpler models for atmospheric dispersion. The Pasquill approach uses the letters A to F to describe stabilities: A is extremely unstable, B is moderately unstable, C is slightly unstable, D is neutral, E is slightly stable and F is moderately stable. The approach depends on knowing the surface wind speed at 10 m altitude and assessing the amount of solar radiation (or insolation) in
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