IMPROVING THE EFFECT OF ATMOSPHERIC STABILITY CLASS FOR DISPERSION MODELING

Recent guidelines released by the U.S. EPA define a worst-case scenari o as a release under stable atmospheric conditions defined as Pasquil- Gifford stability class F. Unfortunately, very few tests at F stabilit y hare been available heretofore to provide a basis for models. Recent test data with propane releases by the German research organization T UV provide a set of 60 experiments conducted specifically to define th e effects of atmospheric stability class on dispersion. Of these 25 te sts were at F stability. A comparable number were at each other stabil ity class A through E. In addition 23 tests were at wind speeds under 1.5 m/s in stable atmospheres. This paper reports on adjustments made to our models based on these new data by reducing the originally-postu lated sensitivity to stability class. In spite of considerable scatter in the TUV data, particularly between two different types of propane analyzers, the model allows us to extract information by averaging ove r the tests.