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Unformatted text preview: Notes on Gaussian Plume Dispersion Modeling 1. Pasquill Stability Class To facilitate predicting the effect of atmospheric stability on pollutant dispersion, F. Pasquill proposed a relatively simple scheme that permits the classification of stability based on readily observed parameters. His framework is still widely used in air pollution transport modeling. Pasquills system defines six stability classes based on three observable characteristics: - intensity of incoming solar radiation (daytime) - near-surface wind speed - extent of cloud cover The six classes are given letter designations A-F. The meaning and the corresponding lapse rate are summarized in the following table: stability class T/ z (K/100 m) A (extremely unstable) < 1.9 B (moderately unstable) 1.9 to 1.7 C (slightly unstable) 1.7 to 1.5 D (neutral) 1.5 to 0.5 E (slightly stable) 0.5 to 1.5 F (moderately stable) > 1.5 Recall the adiabatic lapse rate = T/ z = 1 K / 100 m (midpoint of stability class D). Incoming solar radiation, I, is classified as strong, moderate, or slight, based on the following power levels (recall that the solar constant is 1353 W m-2 ): - strong I > 700 W m 2- moderate 350 I 700 W m 2- slight I < 350 W m 2 The stability class under daytime conditions is determined from the intensity of incoming radiation and the wind speed according to the following chart....
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- Fall '09