The AERMOD model has long had a non-default option to run in screening mode. In this mode, the calculations are performed with the plume centerline falling on top of each individual receptor.
One difficulty in running in screening mode is finding generic meteorological data. AERMET requires real surface and upper air observations, and this data may not contain all of the possible meteorological conditions that a modeler wants to test.
The U.S. EPA released AERSCREEN, the screening model based upon the AERMOD model, on March 2011. One component of the AERSCREEN release was the MAKEMET program. MAKEMET generates a matrix of meteorological conditions in the form of AERMOD-ready surface (*.SFC) and profile (*.PFL) files. The matrix is based on user-specified surface characteristics, ambient temperatures, anemometer height, and minimum wind conditions.
To take advantage of this powerful program, the new AERMOD View Version 7.3 includes the new MAKEMET Utility. This utility is available under the Tools | MAKEMET Utility menu option in AERMOD View and AERMET View.
The MAKETMET Utility
To create screening meteorological data files for AERMOD using the MAKEMET Utility, only a few parameters are needed:
Anemometer Parameters: To properly estimate potential wind speeds for the matrix, the user must specify the height above ground at which the wind is measured and the minimum wind speed. Default values are 10 meters and 0.5 meters/second, respectively.
Wind Direction Parameters: The output met data files (*.SFC and *.PFL) generated by MAKEMET can span as many (or as few) wind directions as desired. MAKEMET will calculate the precise wind directions to analyze from the parameters assigned here. The default settings use a 30° increment beginning at true north, so the matrix would use wind directions of 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, and 330. To analyze conditions from specific directions, adjust the parameters accordingly.
Temperature and Surface Parameters: Just like AERMET, MAKEMET requires surface characteristics (albedo, Bowen ratio, and surface roughness) to estimate planetary boundary layer conditions. Since these conditions can vary spatially and temporally, the MAKEMET Utility allows users to add as many different conditions as they need.
The example below uses two different sets of conditions – the first estimating a winter season and the second for summer. The temperature ranges are set for realistic seasonal values while the surface characteristics were estimated using the Land Use Type reference window.
Output Files: After all the above information is specified, click the Process button to run MAKEMET. Each MAKEMET run produces three files:
the surface met file (*.SFC),
the profile met file (*.PFL), and
a log file (*.log) which contains information summarizing the input data
AERMOD View - Screening Mode Option:
Once the screening met data files (*.SFC and *.PFL) are generated by the MAKEMET Utility, they can be used in AERMOD.
Step 1: Under AERMOD View’s Control Pathway window, Dispersion Options section, select the following options:
Run in Screening Mode, and
No Checks for Non-Sequential Met Data
Step 2: Go to the Met Pathway and specify the screening met data files (*.SFC and *.PFL).
Step: 3: After you run AERMOD, the model will perform screening calculations based on the condition matrix produced by MAKEMET.