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
- 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)
- 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.
AP 42, Fifth Edition
Compilation of Air Pollutant Emission Factors,
Volume 1: Stationary Point and Area Sources
Table of Contents, AP 42, Volume I, Fifth Edition
|Cover page and Contents
||Cover page, detailed Table of Contents, Publications in Series,
Insertion Instructions, and Key Word Index (PDF 128K). This is current through the Fifth Edition, Supplement C of AP 42. For sections and chapters added after November 1997, see the chapter web pages below.
||Introduction to AP 42, Volume I, Fifth Edition - January 1995 (PDF
||External Combustion Sources
||Solid Waste Disposal
||Stationary Internal Combustion Sources
||Evaporation Loss Sources
||Organic Chemical Process Industry
||Liquid Storage Tanks
||Inorganic Chemical Industry
||Food and Agricultural Industries
||Wood Products Industry
||Mineral Products Industry
||Greenhouse Gas Biogenic Sources
||Miscellaneous Data & Conversion
Factors -- September 1985 (PDF 103K)
Distribution Data and Sized Emission Factors for Selected Sources
-- October 1986 (PDF 2M)
Size Distributions -- September 1996 (PDF 137K)
||Procedures for Sampling
Surface/Bulk Dust Loading -- July 1993 (PDF 65K)
||Procedures for Laboratory
Analysis of Surface/Bulk Dust Loading Samples -- July
1993 (PDF 42K)
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 FAQs
Answers to frequently asked questions about AP 42
Draft Sections Under Review - no drafts are currently under review
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.
Jump to main content.