Jump to main content or area navigation.

Contact Us

Modeling and Inventories

AP-42:  Compilation of Air Pollutant Emission Factors

Historically, EPA has produced the report "Compilation of Air Pollutant Emission Factors." "Volume I: Stationary Point and Area Sources" is available from EPA's Office of Air Quality Planning and Standards. This document includes emission factors for "fugitive dust" on roadways. AP-42 section 13.2.1 contains emission factors for paved roads; unpaved road emission factors are in section 13.2.2.

"Volume II: Mobile Sources" (commonly referred to as "AP-42") is no longer maintained. More current mobile source emission factors are available using the Office of Transportation and Air Quality (OTAQ) mobile source models.

However, for reference purposes, we continue to post parts of the most recent mobile sources AP-42 on this web page. In particular, Appendix H is still useful in documenting the emission factors produced by MOBILE5, and in some cases carried over into MOBILE6 without additional documentation.


In its first edition (1978), Volume II of AP-42 contained all available information about mobile source emission factors, including the source code listing of the MOBILE1 highway vehicle emission factor model. As EPA's understanding of the many parameters influencing in-use vehicle emission levels increased, it was no longer feasible to provide complete listings of all emission factors in AP-42 Vol. II. The last complete update to AP-42 Volume II (4th Edition, 1989; Supplement A, 1991) included in Section I extensive background information and documentation about the highway vehicle emission factor model (at that time, MOBILE5), and included hundreds of tables presenting of both values used in the model and "look-up tables" of emission factors produced by the model for various conditions.

Section II provided emission factor information, in the form of look-up tables, for a wide range of off-road mobile sources (including agricultural equipment, construction equipment, lawn and garden equipment, aircraft and aircraft engines, locomotives, marine vessels, and miscellaneous types of equipment). Much of the information presented in Section II had not been updated since it was first compiled in the 1970s, and so did not reflect changes in technology that took place even in the absence of emission standards and other regulatory requirements.

Both Section I and Section II of AP-42 Volume 2 have been superseded by more recent EPA work. Information provided below is for historical reference only.

top of page

Highway Vehicles

NOTE: You will need Adobe Acrobat Reader, available as a free download, to view some of the files on this page. See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.

In the early 1990s, OTAQ began to develop a 5th edition of AP-42 Volume II, based on the MOBILE5 highway vehicle emission factor model. The following sections of the planned 5th edition of AP-42 Vol. II were completed and posted on the web:

  • Appendix G: Sample Calculation of Motor Vehicle Emissions
  • Appendix H: Highway Mobile Source Emission Factor Tables
  • Appendix I: Emission Sensitivity Tables -- All Vehicles Combined
  • Appendix J: Emission Sensitivity Tables -- By Vehicle Type
  • Appendix K: Emission Sensitivity Tables -- Air Conditioning and Extra Loads

Appendix G: Sample Calculation of Motor Vehicle Emissions (PDF) (115K)

Appendix H:  Highway Mobile Source Emission Factor Tables

Appendix G describes the major steps used in MOBILE5 to calculate average in-use emissions for the specific case of exhaust hydrocarbons (HC) from light-duty gas vehicles. Appendix H consists of several hundred tables that document many of the values used within the MOBILE emission factor model, as well as providing highway vehicle emission factors calculated under a range of conditions (e.g., by calendar year, at various ambient temperatures and average speeds). Appendices I and J provide tables of HC, carbon monoxide (CO), and oxides of nitrogen (NOx) emission factors, for all vehicles (fleetwide composite emission factors) and by vehicle type respectively, over a range of calendar years, operating mode fractions, and ambient temperatures. Appendix K provides tables of emission factors for light-duty gas vehicles and trucks illustrating the impact of differing levels of assumed vehicle air conditioning use and of carrying extra loads (500 lb extra load, and trailer towing). All of these appendices were structured very similarly to the previous versions presented in Supplement A to AP-42 Vol. II (January 1991).

As work continued on updating this document, it became apparent that the complexity of the MOBILE model had increased to such an extent that is was no longer feasible to provide documentation of the model in this format. At the same time, plans were being implemented for the next major update of the model, MOBILE6. As part of the MOBILE6 development process, OTAQ began planning for a more thorough and methodical review of all aspects of the new model, with all technical documentation of the model being posted on our web site (go to https://www.epa.gov/otaq/mobile.htm for more information about MOBILE6). MOBILE6 has since been superseded by more recent models.

However, at this time EPA is leaving these parts of AP-42 (Appendixes G-K) posted on the web. In particular, Appendix H is still useful in documenting the emission factors produced by MOBILE5, and in some cases carried over into MOBILE6 without additional documentation. Aspects of emission factor estimation which are still the same in MOBILE6 as in MOBILE5 include (but are not limited to):

  • speed correction factors for heavy-duty vehicles,
  • most temperature correction factors
  • fuel volatility (Reid vapor pressure) effects on exhaust emissions
  • tampering rates and associated emission offsets
  • humidity correction for NOx emission factors.

top of page

Nonroad Mobile Sources

There are a tremendous variety of engines and equipment types that together comprise nonroad mobile sources. Among these are agricultural equipment (e.g, tractors, combines), construction equipment (e.g., dozers, cranes), lawn and garden equipment (e.g., lawnmowers, string trimmers, chain saws), aircraft and aircraft engines, locomotives, marine vessels (both commercial and recreational), and various miscellaneous types of equipment (e.g., forklifts, airport ground support equipment).

The emission factors presented in tables in Section II of AP-42 Volume II for nonroad sources dated mostly from testing and other work performed in the 1970s. These Section II emission factors are not currently available electronically. Instead, those interested in nonroad emissions should refer to the EPA’s NONROAD model.

The NONROAD model does not include aircraft and aircraft engines, locomotives, or commercial marine vessels. Updated information on aircraft and aircraft engine emissions is provided by the Federal Aviation Administration (FAA)'s Office of Environment and Energy through the Emissions and Dispersion Modeling System (EDMS). For more information and to obtain this model, go to http://www.faa.gov/about/office_org/headquarters_offices/aep/models/edms_model/; this can also be accessed from https://www.epa.gov/otaq/aviation.htm within the OTAQ web site. Note that the use of the FAA's EDMS is required for general conformity determinations. Updated information on emissions from locomotives is available in an EPA fact sheet Emission Factors for Locomotives (PDF) (9 pp, 370K, EPA-420-F-09-025, April 2009). Information on estimating emission inventories from commercial marine vessels is available here.

Additional Resource Information

EPA-MOBILENEWS Listserv:  Full description and subscription information  

top of page

This page is maintained by EPA's Office of Transportation and Air Quality (OTAQ).
For more: About Us | Get E-mail Updates | Browse the A to Z Subject Index.

Jump to main content.