Introduction to the ISC Model

1
Introduction to the ISC Model

2
Outline

• Model Overview
• Applications
• History
• How to Get the Model
• Input Data Requirements
• Model Tutorial
• Future Directions for Dispersion Models

3
Model Overview

• The Industrial Source Complex (ISC) model version
  3 is a key regulatory model developed by EPA.
• It is a Gaussian plume model appropriate for a
  complex mixture of sources.
• Chemical reactions can only be treated in a very
  rudimentary way, thus the model is best applied
  to non-reactive pollutants.

4
Model Overview

• There are short-term and long-term versions of
  the ISC3 model.
• They differ in the averaging times available for
  data output.
• The short term model also has more sophisticated
  capabilities for estimating the effects of
  terrain and deposition.
• We will focus on the short-term model in this
  workshop (ISCST3).

5
Applications

• The ISCST3 Model is widely used by the EPA, and
  state and local environmental agencies to model
  the effects of a variety of pollution sources.
• The model can calculate average concentrations
  over time periods ranging from an hour to a year.
• Appropriate uses include
• Modeling to demonstrate sufficiency of proposed
  State Implementation Plans (SIPs) for criteria
  air pollutants.
• Modeling to predict air quality impact of new
  regulated sources.
• Modeling to support assessment of health impacts
  of air toxics.

6
History

• The ISC model has gone through several revisions,
  each of which has added new capabilities (without
  changing the Gaussian plume assumptions at the
  heart of the model).
• ISCST3 has new algorithms for wet and dry
  deposition, a new way of simulating area sources
  and a new method for simulating complex terrain.

7
How to Get the Model

• The primary source for the most up-to-date model
  is the EPAs Support Center for Regulatory Air
  Quality Models (SCRAM) website
  www.epa.gov/ttn/scram
• This site includes an already compiled executable
  version of the model for running on a Microsoft
  Windows computer operating system.

8
How to Get the Model

• It also contains all the original Fortran
  computer code that can (with some difficulty) be
  compiled to work on other computer operating
  systems.
• Note that the current version of the model
  requires the use of the Lahey Fortran compiler.

9
How to Get the Model

• Note that the EPA version of the model is not
  designed to be particularly user-friendly. There
  is no graphical interface, so everything is done
  with input and output files.
• More user friendly interfaces for the models have
  been designed by a number of private vendors. To
  find one, just do an internet search for ISCST3.

10
Input Data Requirements

• Source Characteristics
• Source type, stack height, emission rate, stack
  gas temperature, etc.
• Meteorology
• Temperature, wind speed, wind direction, Pasquill
  stability class.

11
Input Data Requirements

• Receptor grid
• Tells the model where in the model domain to
  calculate concentrations.
• Other model options
• Urban or rural
• Terrain
• Averaging time

12
ISCST3 Tutorial

• Section 2 of the ISC3 Users Guide, Volume 1
• www.epa.gov/scram001/userg/regmod/isc3v1.pdf
• Provides an introduction to the most frequently
  used options in ISCST3
• Simulation is of emission of a non-reactive
  pollutant from a single, isolated stack in a
  rural area.

13
ISCST3 Tutorial

• Focuses on teaching the new user how to apply the
  keyword/parameter approach to defining options in
  the model
• Input parameters are divided into six areas
• Overall job control options
• Information on the source(s)
• Receptor locations
• Meterology data
• Terrain grid
• Output options

14
ISCST3 Tutorial

• Goals for this exercise
• Get comfortable manipulating input/output files.
• Learn how to set up the input file correctly and
  run ISCST3.
• Become familiar with some of the key options
  available in the model and how to change these.
• Lets go the lab and do some modeling!

15
Future Directions for Dispersion Models

• ISC-AERMOD
• Based on a more sophisticated treatment of
  boundary layer dynamics than is possible with a
  Gaussian plume model.
• Models-3 CMAQ
• Will provide more advanced chemistry for reactive
  pollutants.
• Plume within a grid to more realistically
  simulate dispersion at multiple scales.