Algorithms and Environmental Engineering - Mathematics and Statistics for the Environment - page 95

• CTDMPLUS (Complex Terrain Dispersion Model Plus Algorithms for Unstable Situations)
is a refined point-source Gaussian air quality model for use in all stability conditions for
complex terrain (i.e., terrain exceeding the height of the stack being modeled as contrasted
with simple terrain, which is defined as an area where terrain features are all lower in
elevation than the top of the stack of the source). The model contains, in its entirety, the
technology of CTDM for stable and neutral conditions.
• ISC3 (Industrial Source Complex Model) is a steady-state Gaussian plume model that can
be used to assess pollutant concentrations from a wide variety of sources associated with
an industrial complex. This model can account for the following: settling and dry deposi-
tion of particles; downwash; point, area, line, and volume sources; plume rise as a function
of downwind distance; separation of point sources; and limited terrain adjustment. ISC3
operates in both long-term and short-term modes.
• OCD (Offshore and Coastal Dispersion Model) is a straight-line Gaussian model devel-
oped to determine the impact of offshore emissions from point, area, or line sources on the
air quality of coastal regions. OCD incorporates overwater plume transport and dispersion
as well as changes that occur as the plume crosses the shoreline. Hourly meteorological
data are needed from both offshore and onshore locations.
4.7 SCREENING TOOLS
Screening tools are relatively simple analysis techniques to determine if a given source is likely to
pose a threat to air quality. Concentration estimates from screening techniques precede a refined
modeling analysis and are conservative. Following are some of the screening tools available:
• CAL3QHC/CAL3QHCR (CALINE3 with queuing and hot-spot calculations) is a
CALINE3-based CO model with a traffic model to calculate delays and queues that occur
at signalized intersections; CAL3QHCR requires local meteorological data.
• COMPLEX 1 is a multiple point-source screening technique with terrain adjustment that
incorporates the plume impaction algorithm of the VALLEY model.
• CTSCREEN (Complex Terrain Screening model) is a Gaussian plume dispersion model
designed as a screening technique for regulatory application to plume impaction assess-
ments in complex terrain. CTSCREEN is a screening version of the CTDMPLUS model.
• LONGZ is a steady-state Gaussian plume formulation for both urban and rural areas in flat
or complex terrain to calculate long-term (seasonal and/or annual) ground-level ambient
air concentrations attributable to emissions from up to 14,000 arbitrarily placed sources
(stack, buildings, and area sources).
• SCREEN3 is a single-source Gaussian plume model that provides maximum ground-level
concentrations for point, area, flare, and volume sources, as well as concentrations in
the cavity zone and concentrations due to inversion break-up and shoreline fumigation.
SCREEN3 is a screening version of the ISC3 model.
• SHORTZ is a steady-state bivariate Gaussian plume formulation model for both urban and
rural areas in flat or complex terrain to calculate ground-level ambient air concentrations.
It can calculate 1-hr, 2-hr, 3-hr, etc., average concentrations due to emissions from stacks,
buildings, and area sources for up to 300 arbitrarily placed sources.
• VALLEY is a steady-state, complex-terrain, univariate Gaussian plume dispersion algo-
rithm designed for estimating either 24-hour or annual concentrations resulting from emis-
sions from up to 50 (total) point and area sources.
• VISCREEN calculates the potential impact of a plume of specified emissions for specific
transport and dispersion conditions.