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IIOAC - Integrated Indoor-Outdoor Air Calculator

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What does IIOAC Do?

IIOAC is a tool based on EPA’s AERMOD for use in assessing releases to air and exposure potential for new and existing chemicals. A key feature of the tool is the grouping of inputs to define emission scenarios. An emission scenario is a collection of releases featuring one or multiple source types, each with different temporal patterns and emission rates. For each emission scenario, the tool provides outputs such as air concentrations, particle deposition, and human exposure doses for receptors at different distances for each source type.

IIOAC allows the user to choose  different source types (point/stack, fugitive, area), meteorological stations and local land cover, release durations, particle/vapor scenarios, and urban or rural settings. Modeling defaults are described  in the IIOAC User Guide. For example, there are 14 meteorological stations with pre-processed meteorology data. Releases may occur through facility (stack, incinerator, and fugitive), area soil, and area water sources. Daily-averaged and annual-averaged air concentrations are used to estimate chemical exposure doses. IIOAC was developed to process multiple scenarios from multiple sources at once; the tool allows for intermittent releases and variation in meteorological conditions to account for potential variability in exposure conditions.

How Does IIOAC Work?

OPPT designed the Integrated Indoor-Outdoor Air Calculator (IIOAC) as a user-friendly Excel-based tool to estimate indoor and outdoor air concentrations and particle deposition at different distances from sources that release chemical substances to the air. IIOAC allows OPPT to  quickly estimate air concentrations from multiple sources and multiple air releases. The tool uses pre-run results from a suite of AERMOD dispersion scenarios run in a variety of meteorological and land-use settings.


Refer to this Getting Started Guide for instructions on how to download and use IIOAC

Software Requirements

Excel 2010 or later is required to use IIOAC.

Peer Review of AERMOD

EPA provides recommendations for regulatory applications of air dispersion modeling in its Guidelines on Air Quality Models (Appendix W). AERMOD is EPA’s recommended air dispersion model and has been subject to peer review and model evaluation.

Download and Install IIOAC

Download the IIOAC model
Please read the IIOAC Questions/Answers before contacting the EPA with questions.
The IIOAC User’s Guide  provides additional information on air dispersion modeling, modeling inputs, and approaches used to develop IIOAC.

Terms and conditions of use

  • Permission is granted for individuals to download and use the software on their personal and business computers. Users may not alter, modify, merge, adapt, or prepare derivative works from the software.
  • Professional judgment is needed to determine adequacy and applicability of the models and methods provided in IIOAC

EPA Technical Contact:

Eva Wong, U.S. EPA
U.S. Environmental Protection Agency
Office of Pollution Prevention and Toxic
Risk Assessment Division (7403M)
1200 Pennsylvania Avenue, N.W.
Washington, DC 20460