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 casebycase 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, ADMS3, AFTOX, ASPEN, BLP, CALPUFF, DEGADIS, HGSYSTEM, HOTMAC/RAPTAD, HYROAD, ISC3, ISCPRIME, OBODM, OZIPR, Panache, PLUVUEII, SCIPUFF, SDM, and SLAB.
Alternative Models and Documentation 

ADAM 
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/twophased options. 
Model Code 
Executables (ZIP)(271 K) 
Model Documentation 
Readme (TXT)(1 K) 
ADMS3 
Atmospheric Dispersion Modeling System (ADMS3) 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 gammadose; 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 "David.Carruthers@cerc.co.uk" for information on acquiring the ADMS3 modeling system. For additional information on the ADMS3 Modeling System please link to the Cambridge Environmental Research Consultants Website. Exit

AFTOX 
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) 
ASPEN 
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 (EMSHAP) 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 EMSHAP Version 3.0 emission modeling system were used to estimate the ambient concentrations for the NationalScale Air Toxics Assessment for 1999. The 2005 results are available on the NATA website. The 1996 results using EMSHAP Version 2.0 and the ASPEN model, are still available on the National Air Toxics Assessment (NATA) Archive Website.

BLP 
BLP is a Gaussian plume dispersion model designed to handle unique modeling problems associated with aluminum reduction plants, and other industrial sources where plume rise and downwash effects from stationary line sources are important. 
Model Code 
Code/Executable/Test Cases/Postprocessors (ZIP)(231 K) 
Model Documentation 
User's Guide (PDF)(206 pp, 5.8 M, 1980) User's Guide Addendum (PDF)(17 pp, 505 K, 1991) Model Change Bulletin (TXT)(1 K, 1999) 
CALPUFF Modeling System 
CALPUFF is a multilayer, multispecies nonsteadystate puff dispersion model that simulates the effects of time and spacevarying meteorological conditions on pollution transport, transformation and removal. CALPUFF can be applied on scales of tens to hundreds of kilometers. It includes algorithms for subgrid scale effects (such as terrain impingement), as well as, longer range effects (such as pollutant removal due to wet scavenging and dry deposition, chemical transformation, and visibility effects of particulate matter concentrations). From April 2003 until January 2017, CALPUFF was the EPA preferred model for longrange transport for the purposes of assessing NAAQS and/or PSD increments. With the 2017 revisions to the Guideline on Air Quality Models (Appendix W to 40 CFR Part 51), the EPA has established in Section 4.2(c)(ii) a screening approach for longrange transport assessments for NAAQS and PSD increments. This screening approach will streamline the time and resources necessary to conduct such analyses and provides a technically credible and appropriately flexible way to use CALPUFF or other Lagrangian models as a screening technique. With the establishment of the screening approach for longrange transport, CALPUFF was delisted as an EPA preferred model in the 2017 revised Guideline. Should a cumulative impact analysis for NAAQS and/or PSD increments be necessary beyond 50 km, the selection and use of an alternative model shall occur in agreement with the appropriate reviewing authority and approval by the EPA Regional Office based on the requirements of Appendix W, Section 3.2. 
Model Code 
The files associated with this system, e.g., executables/source code, preprocessors, associated utilities, test cases, selected meteorological data sets and documentation can be found on Exponent's website through the model component links below. Support documents related to CALPUFF can also be found on this website. Upon entering the Exponent website, you will see the CALPUFF Model listing on the lefthand panel. To access the system code, click on "DOWNLOAD", then click on "Skip Registration" if you do not want to register. The most recent EPAApproved version of the CALPUFF Modeling System includes:
For every update of the "EPAApproved" version of the CALPUFF Modeling System, a consequence analysis is performed by USEPA using an update protocol that identifies what model changes have been made and their implications based on the analysis results. This analysis compares the base CALPUFF Modeling System (i.e., current version) with the beta (i.e., proposed updated version). 
Support Documents 
Previous SCRAM Website CALPUFF Modeling System Posting Reference (PDF)(4 pp, 40 K, 2018)
Summary of Update Process (PPT)(40 pp, 3.5 M, 2005)
A Comparison of CALPUFF with ISC3 (PDF)(50 pp, 1 M, 1998)
Application of CALMET/CALPUFF and MESOPUFF II to Compare Regulatory Design Concentrations for a Typical LongRange Transport Analysis (PDF)(88 pp, 486 K, 2002)
Peer Review of Calmet/Calpuff Modeling System (PDF)(40 pp, 1 M, 1998) Note: Part of Appendix F and all of Appendix G are unavailable in electronic form.
Response to Peer Review Comments of Calmet/Calpuff Modeling System (PDF)(5 pp, 16 K, 1998)
Technical Issues Related to CALPUFF Nearfield Applications (PDF)(16 pp, 145 K, 2008)

DEGADIS 
DEGADIS simulates the atmospheric dispersion at groundlevel 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 gravitydriven 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 
HGSYSTEM is a collection of computer programs designed to predict the sourceterm and subsequent dispersion of accidental chemical releases with an emphasis on denserthanair (dense gas) behavior. Available from NTIS, Order Number PB96501960. 
HOTMAC/RAPTAD 
HOTMAC is a 3dimensional Eulerian model for weather forecasting; RAPTAD is a 3dimensional 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 
HYROAD 
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 10meter 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 nonuniform wind and stability field derived from traffic module outputs, to describe nearroadway dispersion characteristics. HYROAD is designed to determine hourly concentrations of carbon monoxide (CO) or other gasphase 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 
ISC3 is a steadystate 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 longterm and shortterm modes. The screening version of ISC3 is SCREEN3. ISC3 also uses the Emissions Modeling System for Hazardous Pollutants (EMSHAP) 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, multitiered, 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 oneyear 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. 
ISCPRIME 
ISCPRIME (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 ISCPRIME (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 ISCPRIME 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) 
OBODM 
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 quasicontinuous 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 
OZIPR is a onedimensional 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 CitySpecific 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 
Panache is an Eulerian (and Lagrangian for particulate matter), 3dimensional finite volume fluid mechanics model designed to simulate continuous and shortterm pollutant dispersion in the atmosphere, in simple or complex terrain. Available from Transoft US. Inc. Exit 
PLUVUEII 
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) 
SCIPUFF 
Secondorder Closure Integrated PUFF Model (SCIPUFF) is a Lagrangian puff dispersion model that uses a collection of Gaussian puffs to predict threedimensional, timedependent 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) 
SDM 
Shoreline Dispersion Model (SDM) is a multiplepoint 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) 
SLAB 
The SLAB model treats denserthanair releases by solving the onedimensional 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) 