Procedures for the Development of Emissions Factors from Stationary Sources
Procedures for the Development of Emissions Factors from Stationary Sources (pdf) January 2023
Appendix F: Source Classification Codes for Source Categories Containing 15 or Fewer Sources (pdf) November 2021
The report presents an introduction to emissions factors and provides the historical background for how and why the EPA has developed recommended emissions factors for stationary emissions units or processes. It also describes the approach and new procedures that EPA will follow when developing new or revising existing recommended emissions factors. Please note that we have made a minor change to the emission factor quality rating scale. Previous versions of AP-42 used the term 'poorly' to describe the lowest emission factor representativeness rating. While poorly representative factors are potentially less representative than other emission factors, they are not necessarily less accurate. In most cases, the poorly representative factors are based on a smaller number of emissions test data points which lowers the representativeness score. The data being used may also have lower quality ratings due to a lack of supporting documentation. Therefore, the lowest emission factor representativeness is now labeled as 'minimally' because this more accurately conveys that there is value in using the emission factor for estimates, but that the data used to develop the factors is less robust than other factors.
Included is an overview of EPA’s interactive emissions factors database, WebFIRE, and a discussion of the role the Electronic Reporting Tool (ERT) plays in submitting emissions test data to EPA. Finally, this document provides an overview of the data review and public participation process that the EPA should follow when developing new or revised recommended emissions factors.