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 This website is no longer updated and links to external websites and some internal pages may not work.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

What sources make up the Sectors or Tiers used in the emissions data summaries?

Tier 1 and Sector categories are assigned by source classification codes (SCCs) that are the most specific processes available in the NEI.  The latest SCC list with the Tier 1 and Sector assignments can be downloaded from the EPA SCC website in Comma Separate Values (CSV) format.