For criteria air pollutants and precursors, the emissions trends are based on the triennial National Emissions Inventory data, with some interim year data included for non-triennial years. The methods and interim-year approaches are described on the “Development of Data” tab included with the data provided on the Air Pollutant Emissions Trends Data page. This page also links to a “Trends Procedural Documentation” page that includes the methods used for older inventory periods (1900-1984 and 1985-1999).

For greenhouse gas emissions, you can find greenhouse gas inventory trends methods from the latest “Inventory of U.S. Greenhouse Gas Emissions and Sinks,” which is available on the National Greenhouse Gas Emissions page.