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demonstration of applicability each time they are used.
Emissions and Dispersion Modeling System (EDMS) - The EDMS (Reference 57) is the EPA
and FAA preferred guideline model to calculate emissions and model dispersion at airports.
EDMS is jointly developed by the FAA and the USAF. The model includes an emissions
inventory section, which was described in Section Three of this document, and a dispersion
modeling section. The heart of the dispersion model is the Gaussian dispersion equation, which
takes an emission rate from a source and calculates one hour concentrations of key criteria
pollutants in the air at each receptor location.
In addition to the source activity, the dispersion portion of the model requires input on source
coordinates and the hourly variation of emissions (using operational profiles). The program
allows the user to import weather data files from the National Climatic Data Center and also
allows the user to create their own weather files. In running the model for dispersion, the user is
allowed the flexibility of choosing a weather file as well as a range of weather hours within that
file. During run execution, a progress meter displays the run status.
34
Line source algorithms are used for aircraft, APU, and vehicle roadway operations. GSE activity
and stationary sources are treated as point sources. Vehicle parking lots are treated as area
sources. The ability to toggle sources in and out of a given study allows for enhanced analysis
capabilities when running dispersion. EDMS also incorporates a graphical view of the airport or
air base, plotting runways, runway queues, aircraft gates, roadways, parking lots, stationary
sources, and receptors in relation to each other.
The output of the dispersion section of EDMS is the hourly averaged concentration of pollutants
at each receptor for the chosen duration of weather hours. Concentrations averaged over 3, 8, and
24 hour periods also are given for comparison with NAAQS.
CAL3QHC - CAL3QHC is the EPA recommended model for analyzing CO impacts at roadway
intersections and is available on EPA’s Support Center for Regulatory Air Models Bulletin
Board System (SCRAM) (Reference 83). The model combines the EPA model for estimating the
concentrations of nonreactive pollutants from highway traffic, CALINE3 (Reference 4), with a
traffic model to calculate delays and queues that occur at signalized intersections. It can be used
in a screening or refined mode. The latest version of the MOBILE model should be used for
emissions input to CAL3QHC. The EPA user’s guide to the model is User’s Guide for
CAL3QHC Version 2: A Modeling Methodology for Predicting Pollutant Concentrations near
Roadway Intersections (Reference 86), also available on SCRAM. For EPA guidance on a
methodology for evaluating air quality impacts at one or more roadway intersections where
vehicle traffic will cause or contribute to increased emissions of carbon monoxide (CO) see
EPA’s Guideline For Modeling Carbon Monoxide From Roadway Intersections.
Industrial Source Complex Model (ISC3) - ISC3 is an EPA preferred model for assessing
pollutant concentrations from a wide variety of sources associated with an industrial source
complex. It is a steady-state Gaussian plume model that can account for: settling and dry
deposition of particles; downwash; area, line, and volume sources; plume rise as a function of
downwind distance; and separation of point sources. ISC3 operates in both long-term and shortterm
modes. ISC3 is appropriate for the following applications: industrial source complexes,
rural or urban areas, flat or rolling terrain, transport distances less than 50 kilometers, 1-hour to
annual averaging times, and continuous toxic air emissions. The model is available on EPA’s
Support Center for Regulatory Air Models Bulletin Board System (SCRAM) (Reference 83). The
basis ISC3 model is valid for simple terrain (i.e., terrain does not rise above the stack height).
Variations on the ISC3 model exist for special situations, such as complex terrain.
A variety of other dispersion models have been developed for use in regulatory applications
ranging from highways to stack sources to regional ozone modeling. Most are based on some
form of the basic Gaussian approximation, although some of the more recent models use
sophisticated numerical modeling techniques to simulate more complex phenomena. Some of
these models are labor-intensive; for example, the Urban Airshed Model requires the user to
input hourly emissions of all sources within the region of interest. Table 2 presents a list of other
EPA-preferred models. The table shows that much of the model development and application
activity has focused on stacks as emission sources, with comparatively little emphasis on
　
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