Support Center for Regulatory Atmospheric Modeling (SCRAM)

Air Quality Dispersion Modeling - Alternative Models

This page lists some known alternative models to the perferred/recommended models listed in the Guideline on Air Quality Models, Appendix W that can be used in regulatory applications with case-by-case justification to the Reviewing Authority (Section 3.2 of Appendix W). However, inclusion here does not confer any unique status relative to other alternative models that are being or will be developed in the future. The models in this section include ADAM, ADMS-3, AFTOX, ASPEN, DEGADIS, HGSYSTEM, HOTMAC/RAPTAD, HYROAD, ISC3, ISC-PRIME, OBODM, OZIPR, Panache, PLUVUEII, SCIPUFF, SDM, and SLAB.

Alternative Models and Documentation
Air Force Dispersion Assessment Model (ADAM) is a modified box and Gaussian dispersion model which incorporates thermodynamics, chemistry, heat transfer, aerosol loading, and dense gas effects. Release scenarios include continuous and instantaneous, area and point, pressurized and unpressurized, and liquid/vapor/two-phased options.
Model Code
Executables (ZIP)(271 K)
Model Documentation
Readme (TXT)(1 K)

Atmospheric Dispersion Modeling System (ADMS-3) is an advanced dispersion model for calculating concentrations of pollutants emitted both continuously from point, line, volume and area sources, or discretely from point sources. The model includes algorithms which take account of the following: effects of main site buiding; complex terrrain; wet deposition, gravitational settling and dry deposition; short term fluctuations in concentration; chemical reactions; radioactive decay and gamma-dose; plume rise as a function of distance; jets and directional releases; averaging time ranging from very short to annual; condensed plume visibility; meteorological preprocessor.

The modeling system is available at no cost in selected circumstances. Potential users should contact Dr. David Carruthers at "" for information on acquiring the ADMS-3 modeling system.

For additional information on the ADMS-3 Modeling System please link to the Cambridge Environmental Research Consultants Website. Exit
AFTOX is a Gaussian dispersion model that will handle continuous or instantaneous liquid or gas elevated or surface releases from point or area sources. Output consists of concentration contour plots, concentration at a specified location, and maximum concentration at a given elevation and time.
Model Code and Documentation
Executable/Test Case/Readme (ZIP)(173 K)
User's Guide (ZIP)(26 K)
The Assessment System for Population Exposure Nationwide (ASPEN) consists of a dispersion and a mapping module. The dispersion module is a Gaussian formulation based on ISCST3 for estimating ambient annual average concentrations at a set of fixed receptors within the vicinity of the emission source. The mapping module produces a concentration at each census tract. Input data needed are emissions data, meteorological data and census tract data. The Emissions Modeling System for Hazardous Pollutants (EMS-HAP) is needed to process the emission inputs into the ASPEN model or the ISC3 model. The ASPEN model was used in estimating annual ambient concentrations for air toxics pollutant in the National Air Toxics Assessment (NATA) Study.
Model Code
ASPEN Modeling System (ZIP)(3.7 M)
Model Documentation
Descriptive Statement (PDF)(1 pg, 30 K)
User's Guide (PDF)(110 pp, 1.5 M, 2000)
The ASPEN model and the EMS-HAP Version 3.0 emission modeling system were used to estimate the ambient concentrations for the National-Scale Air Toxics Assessment for 1999. The 2005 results are available on the NATA website. The 1996 results using EMS-HAP Version 2.0 and the ASPEN model, are still available on the National Air Toxics Assessment (NATA) Archive Website.
DEGADIS simulates the atmospheric dispersion at ground-level of area source dense gas (or aerosol) clouds released with zero momentum into the atmospheric boundary layer over flat, level terrain. The model describes the dispersion processes which accompany the ensuing gravity-driven flow and entrainment of the gas into the boundary layer.
Model Code
Executables (ZIP)(3.2 M)
Source Code, NMAKE files, and Recompile Instructions (ZIP)(266 K)
Test Cases, Batch Files, and Results for Comparison (ZIP)(334 K)
Model Documentation
Readme (PDF)(12 pp, 60 K)
User's Guide (PDF)(419 pp, 9.6 M, 1989)
Evaluation of Dense Gas Simulation Models (PDF)(114 pp, 3.5 M, 1990)
Latest Model Change Bulletin (TXT)(1 K, 2012)
HGSYSTEM is a collection of computer programs designed to predict the source-term and subsequent dispersion of accidental chemical releases with an emphasis on denser-than-air (dense gas) behavior. Available from NTIS, Order Number PB96-501960.
HOTMAC is a 3-dimensional Eulerian model for weather forecasting; RAPTAD is a 3-dimensional Lagrangian random puff model for pollutant transport and diffusion. These models are used for prediction of transport and diffusion processes for complex terrain, coastal regions, urban areas, and around buildings where conventional models fail. Available from YSA Corporation.Exit
The HYbrid ROADway Model (HYROAD) integrates three historically individual modules that simulate the effects of traffic, emissions and dispersion. The traffic module is a microscale transportation model which simulates individual vehicle movement. The emission module uses speed distributions from the traffic module to determine composite emission factors; spatial and temporal distribution of emissions is based on the vehicle operation simulations. The model tracks vehicle speed and acceleration distributions by signal phase per 10-meter roadway segment for use in both emissions distribution and for induced flows and turbulence. The dispersion module uses a Lagrangian puff formulation, along with a gridded non-uniform wind and stability field derived from traffic module outputs, to describe near-roadway dispersion characteristics. HYROAD is designed to determine hourly concentrations of carbon monoxide (CO) or other gas-phase pollutants, particulate matter (PM) and air toxics - in consultation with appropriate Reviewing Authority - from vehicle emissions at receptor locations that occur within 500 meters of the roadway intersections.
Model Code and Documentation
Executable/Test Case/README (ZIP)(13.5 M)
Model Formulation (ZIP)(1.8 M)
User's Guide (ZIP) (1 M)
ISC3 is a steady-state Gaussian plume model which 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 deposition 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. The screening version of ISC3 is SCREEN3. ISC3 also uses the Emissions Modeling System for Hazardous Pollutants (EMS-HAP) to process an emission inventory for input into the model. The Building Profile Input Program (BPIP) and the Building Profile Input Program for PRIME (BPIPPRM) can also be used with ISC3 to correctly calculate building heights (bh) and projected building widths (pbw) for simple, multi-tiered, and groups of structures. For the status of ISC3 as a preferred model, please see the Note below.
Model Code
SHORT term (ISCST3) (ZIP)(1.7 M)
LONG term (ISCLT3) (ZIP)(390 K)
Model Documentation
User's Guide, Volume 1 with Addendum (PDF)(390 pp, 1.4 M, 1990)
User's Guide, Volume 2 with Addendum (PDF)(128 pp, 570 K, 1995)
Latest Model Change Bulletin for SHORT term (ISCST3) (TXT)(29 K, 2002)
Latest Model Change Bulletin for LONG term (ISCLT3) (TXT)(45 K, 1996)
Note: The promulgation package which establishes AERMOD as the preferred air dispersion model in the Agency's "Guideline on Air Quality Models" (Appendix W) in place of the ISC3 air dispersion model was signed by the Administrator of the US EPA on October 21. The package was then submitted to the Federal Register office and was published November 9, 2005.

This rule becomes effective December 9, 2005. Beginning one year after this date, the new model - AERMOD - should be used for appropriate application as replacement for ISC3. During this one-year period, protocols for modeling analyses based on ISC3 which are submitted in a timely manner may be approved at the discretion of the appropriate Reviewing Authority. Applicants are therefore encouraged to consult with the Reviewing Authority as soon as possible to assure acceptance during this period.
ISC-PRIME (Plume RIse Model Enhancements) is a model with building downwash incorporated into the Industrial Source Complex Short Term Model (ISCST3).
Model Code
Source Code (ZIP)(217 K)
Executables (ZIP) (639 K)
Model Documentation
README (TXT)(8 K, 2004)
User's Guide (PDF)(13 pp, 229 K, 1997)
Model Evaluation: ISCST3 and ISC-PRIME (PDF)(162 pp, 262 K, 1997) - Graphics are not included in document. Complete copy is available from NTIS. (See README for ordering information.)
Consequence Analysis - Available from NTIS (See README for ordering information.)
Consequence Analysis for Adoption of PRIME: an Advanced Building Downwash Model (PDF)(7 pp, 22 K, 1998) and Associated Tables (PDF)(3 pp, 24 K, 1998)
Consequences Analysis of Using ISC-PRIME over the Industrial Source Complex Short Term Model (PDF)(47 pp, 903 K, 1998)
Technical Papers
Development and Evaluation of the PRIME Plume Rise and Building Downwash Model (PDF)(5 pp, 19 K)
Project PRIME: Evaluation of Building Downwash Models Using Field and Wind Tunnel Data (PDF)(4 pp, 32 K)
Development and Evaluation of the PRIME Plume Rise and Building Downwash Model (PDF)(34 pp, 588 K)
Intended for use in evaluating the potential air quality impacts of the open burning and detonation (OB/OD) of obsolete munitions and solid propellants. OBODM uses cloud/plume rise dispersion, and deposition algorithms taken from existing models for instantaneous and quasi-continuous sources to predict the downwind transport and dispersion of pollutants released by OB/OD operations.
Model Code
Executable/Test Case (ZIP)(524 K, February 9. 2010)
Source Code (ZIP)(1 M)

Model Documentation
README1 (TXT)(1 K)  - install directions for version 1.3.24
README2 (TXT)(12 K) - errata and update by dates for version 1.3.24
User's Guide: Volume 1 (PDF)(196 pp, 460 K, 1998)
User's Guide: Volume 2 (PDF)(58 pp, 328 K, 1998)
User's Guide: Volume 3 (PDF)(24 pp, 40 K, 1997) - dated recompile instructions
OZIPR is a one-dimensional photochemical box model that is an alternative version of the OZIP model that deals with air toxic pollutants.
Model Code
Code/Executable/Test Inputs (ZIP)(907 K)
Model Documentation
README (TXT)(2 K, 2005)
User's Guide (PDF)(43 pp, 183 K)
Guidance Document (PDF)(120 pp, 4 M, 1989) - Procedures for applying City-Specific EKMA.
Support Document (PDF)(78 pp, 3 M, 1999) - Also available from NTIS (TXT)(19 K)
Appendix A (PDF)(17 pp, 126 K)
Appendix B (PDF)(241 pp, 438 K)
Appendix C (PDF)(241 pp, 437 K)
Appendix D (PDF)(61 pp, 114 K)
Appendix E (PDF)(25 pp, 70 K)
Appendix F (PDF)(4 pp, 35 K)
Panache is an Eulerian (and Lagrangian for particulate matter), 3-dimensional finite volume fluid mechanics model designed to simulate continuous and short-term pollutant dispersion in the atmosphere, in simple or complex terrain. Available from Transoft US. Inc.  Exit
A model used for estimating visual range reduction and atmospheric discoloration caused by plumes resulting from the emissions of particles, nitrogen oxides, and sulfur oxides from a single source. The model predicts the transport, dispersion, chemical reactions, optical effects and surface deposition of point or area source emissions.
Model Code
Code/Executable/Test Case (ZIP)(782 K)
Model Documentation
User's Guide (PDF)(116 pp, 4 M, 1992)
User's Guide - Addendum (PDF)(24 pp, 900 K, 1996)
Latest Model Change Bulletin (TXT)(5 K)
Second-order Closure Integrated PUFF Model (SCIPUFF) is a Lagrangian puff dispersion model that uses a collection of Gaussian puffs to predict three-dimensional, time-dependent pollutant concentrations. In addition to the average concentration value, SCIPUFF provides a prediction of the statistical variance in the concentration field resulting from the random fluctuations in the wind field.
Model Documentation
Model Overview (PDF)(5 pp, 18 K)
Shoreline Dispersion Model (SDM) is a multiple-point Gaussian dispersion model that can be used to determine ground level concentrations from tall stationary point source emissions near a shoreline.
Model Code
Code/Executable/Test Case (ZIP)(328 K)
Model Documentation
User's Guide (PDF)(222 pp, 4.7 M, 1988)
Latest Model Change Bulletin (TXT)(2 K)
The SLAB model treats denser-than-air releases by solving the one-dimensional equations of momentum, conservation of mass, species, and energy, and the equation of state. SLAB handles release scenarios including ground level and elevated jets, liquid pool evaporation, and instantaneous volume sources.
Model Code
Code/Executable/Test Case (ZIP)(111 K)
Model Documentation
Model User's Guide (PDF)(150 pp, 6.2 M, 1990)
Evaluation of Dense Gas Simulation Models (PDF)(114 pp, 3.5 M, 1990)

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