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Basic Emissions Factors Information

Emissions factors have long been the fundamental tool in developing national, regional, state, and local emissions inventories for air quality management decisions and in developing emissions control strategies. More recently, emissions factors have been applied in determining site-specific applicability and emissions limitations in operating permits by federal, state, local, and tribal agencies, consultants, and industry. These users have requested guidance on the use of emissions factors and other emissions quantification tools (e.g., emissions testing and monitoring, mass balance techniques) in developing permits that are practical in their enforcement. As a result, you will find in the Emissions Factors and Policy Applications Center (EFPAC) the following:

  • Details about reassessments, development plans, and activities that advance the emissions factors development and documentation program, and
  • Clarifications and options that promote the use of improved emissions quantification tools including guidance on the appropriate uses of emissions factors for implementing the air programs (e.g., flexible and standard operating permits, performance track, improved monitoring, regulatory and incentives programs).

Emissions Factors Uncertainty

Uncertainty is dependent on the kind of emissions released, the number of tests used to determine the emissions factor, the appropriate decision level (or percentile) within the distribution range, and the number of similar emissions units within a specific area. EPA released a draft review for public comment on April 24, 2007.

Since the posting of the Draft Emission Factor Uncertainty Assessment for comment on April 24, 2007, we have received numerous inquiries from interested stakeholders questioning whether the Agency intends to include the effect of uncertainty on a source's applicable emission-related requirements, or whether states or local authorities need to apply the effect of uncertainty to determine area compliance with NAAQS standards. As originally stated in the Draft Assessment, we do not attempt to evaluate or provide guidance on the application of emissions factor uncertainty in making environmental decisions. Moreover, any such decisions would be made only after a formal notice and comment rulemaking process. However, EPA did not intend any change in current practices that would warrant rulemaking. Rather, our intent is to educate sources and regulators about the accuracy of emission factors and to improve such accuracy through the incorporation of the results of direct emissions testing into the estimation of future emission factors.

Emissions Factors and Policy Application Center Highlights
These are highlight items and other Measurement Policy Group activities involving emission monitoring and other quantification protocols.

CHIEF Listserv
The CHIEF Listserv will notify you about new emissions factors, conferences, updates to software tools and any new additions to the Emissions Factors and Policy Applications Center.

Emissions Factors Procedures
The purpose of this document is to describe the specific tasks involved in the development of air pollution emissions factors and their subsequent incorporation into EPA's web-based Factor Information and REtrieval (WebFIRE) system.

Emissions Factors, AP 42
An emissions factor is a representative value that attempts to relate the quantity of a pollutant released to the atmosphere with an activity associated with the release of that pollutant. In this webpage you will find:
  • An Introduction to Emissions Factors Volume I
  • Chapters and Appendixes by Topic for Volume I
  • Notices of Chapter and/or Sections under Review
  • Procedures for Preparing Emissions Factors Documents
  • Emissions Factors Supplements
  • A section of Frequently Asked Questions (FAQs)
  • Older Editions of Emissions Factors Volume I

Web version of FIRE

The FIRE (Factor Information REtrieval System) application web site provides fast and complete access to the Agency's air emissions factors information. Web FIRE will replace the software application, FIRE version 6.25 and the MS Access version of the database. An Internet version of FIRE will allow more frequent updates and easier access.

Emissions Factors Software and Tools
On this webpage you will find software and tools such as the:
  • TANKS is a desktop software program that estimates volatile organic compound (VOC) and hazardous air pollutant (HAP) emissions from fixed- and floating-roof storage tanks.
  • Other emissions tools, such as SPECIATE and WATER9.

Locating and Estimating Reports

This report series, titled Locating and Estimating Air Toxic Emissions from Sources of (source category or substance) characterizes the source categories for which emissions of a toxic substance have been identified. AP 42, Compilation of Air Pollutant Emission Factors and the FIRE database should be checked for more current emissions factors.

Emissions Factors, Related Resources
These resources contain information developed by the US EPA or by outside parties which have undergone limited EPA and external review and are felt to be potentially useful, but which are not contained in AP 42. They should be used with discretion.

CHIEF Publications and Archive
On this webpage you will find EPA documents and software related to emissions factors and the CHIEF (Clearinghouse for Inventories & Emissions Factors) Archive Database. The archive is a collection of older reports and software manuals, as well as references and background reports cited in the Compilation of Air Pollutant Emission Factors, AP-42, Volume I: Stationary Point & Area Sources. Most of the material is in a scanned PDF format.

| Office of Air Quality Planning & Standards | Technology Transfer Network |
| Clearinghouse for Inventories & Emissions Factors |

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