By the mid-to-late 1980's, a substantial scientific base on the PBL and new dispersion

approaches existed for revamping regulatory dispersion models, but this did not occur. In a

review of existing or proposed regulatory models developed prior to 1984, Smith (1984) reported

that the techniques were many years behind the state-of-the-art and yielded predictions that did

not agree well with observations. Similar findings were reported by Hayes and Moore (1986),

who summarized 15 model evaluation studies. The need for a comprehensive overhaul of EPA's

basic regulatory models was clearly recognized. This need, including a summary of background

information and recommendations, was the focus of an AMS/EPA Workshop on Updating


Applied Diffusion Models held 24-27 January 1984 in Clearwater, Florida (see Weil (1985) and

other review papers in the November 1985 issue of the Journal of Climate and Applied


In February 1991, the U.S. EPA in conjunction with the AMS held a workshop for state and

EPA regional meteorologists on the parameterization of PBL turbulence and state-of-the-art

dispersion modeling. One of the outcomes of the workshop was the formation of AERMIC. As

noted above, the expressed purpose of the AERMIC activity was to build upon the earlier model

developments and to provide a state-of-the-art dispersion model for regulatory applications. The

early efforts of the AERMIC group are described by Weil (1992). In going through the design

process and in considering the nature of present regulatory models, AERMIC’s goal expanded

from its early form. In addition to improved parameterization of PBL turbulence, other problems

such as plume interaction with terrain, surface releases, building downwash and urban

dispersion were recognized as needing attention.


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