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 www.epa.gov. 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 This website is no longer updated and links to external websites and some internal pages may not work.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 »

Guide to Selected Algorithms, Distributions, and Databases Used in Exposure Models Developed By the Office of Air Quality Planning and Standards

This report and the appendices provide a detailed description of the components of the models pNEM, APEX, and HAPEM together with an explanation of the model's role within the source exposure model.

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.