An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Support Center for Regulatory Atmospheric Modeling (SCRAM)

Air Modeling - Guidance for Air Toxics Modeling

This section provides miscellaneous guidance documents other than permit modeling or State Implementation Plan (SIP) attainment demonstrations.  

Air Toxics Modeling Guidance

Guidance for Dispersion Modeling in Urban Areas
Guidance Documentation
Dispersion Modeling of Toxic Pollutants in Urban Areas and Appendices (PDF)(288 pp, 10 MB, 07-01-1999, 454-R-99-021)

Application Documentation
Example Application of Modeling Toxic Air Pollutants in Urban Areas (PDF)(111 pp, 6 MB, 06-01-2002, 454-R-02-003)

Also available from NTIS (PB# PB2002-108218). In preparing this document, it was necessary to revise and update the techniques described in Dispersion Modeling of Toxics Pollutants in Urban Areas (ZIP)(268 K, 06-30-1999) and incorporate techniques developed in A Simplified Approach for Estimating Secondary Production of Hazardous Air Pollutants (HAPS) Using the OZIPR Model (PDF)(78 pp, 3 MB, 12-01-1999, 454_R-99-054)

Other Toxics Guidance

Guidance on Hazardous/Toxic Air Releases (ZIP)(2 MB, 06-18-1993) - Includes 5 documents.
Volume V - Procedures for Air Modeling of Superfund Sites (ZIP)(246 K, 02-07-1995)
National Specialty Workshop on Technical Tools for Air Toxics Assessment Final Report (ZIP)(159 K, 10-27-1997)
Air Toxics Risk Assessment Reference Library (ATRA) - Link to reference library for conducting air toxics analyses at the facility and community-scale.