AERMOD Tech Guide

Gaussian Plume Air Dispersion Model

4. AERMOD's Meteorological Interface

AERMOD interface, a set of routines within AERMOD, uses similarity relationships with the boundary layer parameters, the measured meteorological data, and other site-specific information provided by AERMET to compute vertical profiles of: 1) wind direction, 2) wind speed, 3) temperature, 4) vertical potential temperature gradient, 5) vertical turbulence (w ) and w 6) horizontal turbulence (v ).

For any one of these six variables (or parameters), the interface (in constructing the rofile) compares each height at which a meteorological variable must be calculated with the heights at which observations were made and if it is below the lowest measurement or above the highest measurement (or in some cases there is no data at all), the interface computes an appropriate value from selected PBL similarity profiling relationships. If data are available both above and below a given height, an interpolation is performed which is based on both the measured data and the shape of the computed profile (see the Appendix for a complete description of this procedure). This overall profiling approach simultaneously takes advantage of the information contained in both the measurements and parameterizations from similarity formulas. As will be discussed, at least one level of measured wind speed, wind direction, and temperature is required. However, turbulence can be parameterized without any direct turbulence measurements.

In AERMOD, the mixing height zi , has an expanded role in comparison to how it is used in ISC3. In AERMOD the mixing height is used as an elevated reflecting/penetrating surface, an important scaling height, and enters in the w* determination eq. (10). zi is defined as follows:

Equation (27)

Since algorithms used for profiling differ in the SBL and CBL, the INTERFACE must determine the stability of the PBL; this is accomplished by examining the sign of L. If L < 0 then the PBL is considered to be convective (CBL) by AERMOD. If L > 0 then the PBL is stable (SBL).

The following sections provide a comprehensive description of the algorithms used to generate profiles of the boundary layer meteorology and how AERMOD uses the profiles to extract pertinent layer-averaged meteorology for the transport and dispersion calculations.