Introduction to the ISC Model
Marti Blad
NAU College of Engineering
Model Overview
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The Industrial Source Complex (ISC)
model version 3--key regulatory model
developed by EPA
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Gaussian plume model appropriate for
complex mixture of sources
Chemical reactions can only be treated in
rudimentary way, thus…
Model best applied to non-reactive pollutants
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Model Overview
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Short-term and long-term versions of ISC3 model
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Differ in averaging times available for data output
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Short-term model also has more sophisticated capabilities for
estimating effects of terrain and deposition
ISC-PRIME
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ISC-AERMOD
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Plume Rise Model Enhancements
Based on more-sophisticated treatment of boundary layer
dynamics than possible with Gaussian plume model
GUI Courtesy of Lakes Environmental
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Applications
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ISCST3 Model widely used by EPA, state and
local environmental agencies
Models effects of various pollution sources
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Model can calculate average concentrations over time
periods of an hour to a year
Appropriate modeling uses include
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Demonstrating sufficiency of proposed State Implementation
Plans (SIPs) for criteria air pollutants
Predicting air quality impact of new regulated sources
Supporting assessment of health impacts of air toxics
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History
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Several revisions to model, each adding
new capabilities (without changing
Gaussian plume assumptions at heart of
model)
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ISCST3 has new
Algorithms for wet and dry deposition
 Way of simulating area sources
 Method for simulating complex terrain
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How To Get the Model
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Primary source for most up-to-date model
is EPA’s Support Center for Regulatory Air
Quality Models (SCRAM) website
www.epa.gov/ttn/scram
Site includes compiled, executable version
of model for running on Microsoft
Windows operating system
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How to Get the Model (cont.)
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EPA version not particularly user-friendly
No graphical interface--everything done
with input/output files
More user-friendly interfaces designed by
several private vendors
To locate, Web search “ISCST3”
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ISC Model outline
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Screens with multiple tabs for multiple inputs
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Control Pathway
Source Pathway
Receptor Pathway
Meteorology Pathway
Terrain Grid Pathway
Output Pathway
See each piece now in detail
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Pathways in detail
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Control Pathway
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Dispersion options, specify pollutant,
averaging times, terrain height options
Source characteristics
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Source type: point, volume, open pit
source release parameters
Variable emission rate: season, month, hour
Variables for deposition, settling & removal
Variable source groups: single, combined
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Pathways in detail (cont.)
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Receptor Pathway
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Network of gridded receptors
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Cartesian & polar
Where to calculate concentrations
Specify discrete receptor location
Flagpole
 Elevated receptors: terrain above stack base
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Plant boundary distances
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Pathways in detail (cont.)
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Meteorology
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Specify met data input files
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Station location and other indicators
Anemometer height
Wind speed categories
Wind profile exponents
Vertical temperature gradients
Data time period to process
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Pathways in detail (cont.)
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Terrain Grid
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Used to calculate dry depletion in elevated or
complex terrain
Output Pathway
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Summary of high values by receptor
For each averaging period and source group
 Overall maximum values
 Find all occurrences over threshold value
 Plot files
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Site Maps for Modeling
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One degree DEMs
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http://edcwww.cr.usgs.gov/glis/hyper/guide/1_dgr_
dem
7.5 degree DEMs
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http://edcwww.cr.usgs.gov
Format notation
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DXF. = autoCAD
DLG. = USGS digital line graph
LULC.= USGS land use and land coverage
BMP.= Bitmap images
SHP. = ArcView shapefiles
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Dispersion Coefficients
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Met Data Needed for the ISCST3
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Surface Roughness
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Noontime Albedo
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Albedo Values for Model Inputs
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Daytime Bowen Ratios by Land Use
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Parameters not Frequently Seen
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Anthropogenic heat flux
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Surface heating caused by humans
Rural = 0.0 Watts/m2
Urban (large) = 20 Watts/m2
Rammet View has many inside program
Fraction of net radiation absorbed @ ground
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Rural = 0.15
Urban = 0.27
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Other Dispersion Models
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Models-3 CMAQ
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Will provide more advanced chemistry for reactive
pollutants
Plume within grid to more realistically simulate
dispersion at multiple scales
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