Emissions Factors & AP 42, Compilation of Air Pollutant Emission Factors
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).
E = A x EF x (1-ER/100)
- 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.
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.
Draft Sections Under Review
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 below.
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.
|Draft Sections Under Review|
|After the comment period, can I use a draft section? (TXT 1K)|
|Chapter & Section||Description||Comments Requested by:|
|Section 2.4||Municipal Solid Waste Landfills||May 5, 2009|
|Section 4.12||Manufacture of Rubber Products||February 2, 2009|
|Section 5.1||Petroleum Refining||August 19, 2014|
|Section 8.13||Sulfur Recovery||August 19, 2014|
|Section 13.5||Industrial Flares||August 19, 2014|
|Chapter 15||Ordnance Detonation||December 7, 2009|
For current information on AP 42 updates and the activities of the Measurement Policy Group, you can subscribe to the CHIEF Listserv.