# Emissions Factors & AP 42, Compilation of Air Pollutant Emission Factors

### 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).

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. These factors are usually expressed as the weight of pollutant divided by a unit weight, volume, distance, or duration of the activity emitting the pollutant (e.g., kilograms of particulate emitted per megagram of coal burned). Such factors facilitate estimation of emissions from various sources of air pollution. In most cases, these factors are simply averages of all available data of acceptable quality, and are generally assumed to be representative of long-term averages for all facilities in the source category (i.e., a population average).

The general equation for emissions estimation is:

E = A x EF x (1-ER/100)

where:

• E = emissions;
• A = activity rate;
• EF = emission factor, and
• ER =overall emission reduction efficiency, %

AP-42, Compilation of Air Pollutant Emission Factors , has been published since 1972 as the primary compilation of EPA's emission factor information. It contains emission factors and process information for more than 200 air pollution source categories. A source category is a specific industry sector or group of similar emitting sources. The emission factors have been developed and compiled from source test data, material balance studies, and engineering estimates. The Fifth Edition of AP-42 was published in January 1995. Since then EPA has published supplements and updates to the fifteen chapters available in Volume I, Stationary Point and Area Sources. The latest emissions factors are available below on this website. Use the AP 42 Chapter webpage links below to access the document by chapter.

WebFIRE: Access to these emissions factors and other EPA reviewed stationary point and area source factors is also available from the WebFIRE application. WebFIRE provides fast and complete access to the Agency’s air emissions factors information.

For information about emissions factors from highway vehicles and nonroad mobile sources, visit the Office of Transportation and Air Quality web site.

Emissions Factors Procedures
Procedures for the Development of Emissions Factors from Stationary Sources. This page includes both the existing procedures and the review draft for the proposed new procedures.

Chapter & Section Description Comments Requested by: Proposed But Not Finalized After the comment period, can I use a draft section? (TXT 1K) Section 2.4 Municipal Solid Waste Landfills May 5, 2009 Section 4.12 Manufacture of Rubber Products February 2, 2009 Chapter 15 Ordnance Detonation December 7, 2009
 AP 42, Fifth Edition Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources

Proposed and final rules related to emissions factors
October 14, 2009  - The Emissions Factors Program Improvements - Advanced notice of proposed rulemaking is available on the www.regulations.gov website , and the EPA's OAR and Policy Guidance Recent Additons webpage (PDF 290K). The comment period ended December 14, 2009.

AP 42 listing of supplements and updates.
Supplements A through F (1996 - 2000)
Updates 2001 to 2011

Older editions of AP-42, Volume 1
This information is available for historical purposes only. For the most recent emissions factors, supported by the EPA, please see the table of contents above.

For current information on AP 42 updates and the activities of the Measurement Policy Group, you can subscribe to the CHIEF Listserv.