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 This website is no longer updated and links to external websites and some internal pages may not work.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

Microenvironment Tracker (MicroTrac) Factsheet

MicroTrac is a model developed by EPA that uses GPS data to estimate time of day and duration that people spend in different microenvironments, such as indoors and outdoors at home, work, school, and inside vehicles. Using MicroTrac can improve exposure assessments for health studies by helping air pollution scientists determine location and physical activity of study participants prior to adverse health effects.

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