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# AP 42 Air Pollutant Emission Factors

Atmospheric Science:

# AP 42 Air Pollutant Emission Factors

This article has been reviewed by the following Topic Editor: C Michael Hogan

The AP 42 Compilation of Air Pollutant Emission Factors, was first published by the U.S. Public Health Service in 1968. In 1972, it was revised and issued as the second edition by the U.S. Environmental Protection Agency (EPA). In 1985, the subsequent fourth edition was split into two volumes. Volume I covered air pollution emission factors for stationary point and area sources, and Volume II covered mobile source emission factors. Volume I is currently in its fifth edition and is available online at the website of the U.S. EPA.

Volume II is no longer maintained as such, but roadway air dispersion models for estimating emissions from onroad and offroad vehicles as well as from other mobile equipment are available online at the EPA's website.

In routine common usage, Volume I of the emission factor compilation is very often referred to as simply "AP 42". Print copies of AP 42 are no longer available.

## Introduction and Definitions

Air pollutant emission factors are representative values that attempt to relate the quantity of a pollutant released to the ambient air 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.

The equation for the estimation of emissions before emission reduction controls are applied is:

E = A × EF

and for emissions after reduction controls are applied:

E = A × EF × (1 – ER/100)

where:

E = emissions, in units of pollutant per unit of time

A = activity rate, in units of weight, volume, distance or duration per unit of time

EF = emission factor, in units of pollutant per unit of weight, volume, distance or duration

ER = overall emission reduction efficiency, in %

Emission factors are used by atmospheric dispersion modelers and others to determine the amount of air pollutants being emitted from sources within industrial facilities.

## Chapters in AP 42, Volume I, Fifth Edition

 Chapter 1: External Combustion Sources Chapter 2: Solid Waste Disposal Chapter 3: Stationary Internal Combustion Sources Chapter 4: Evaporation Loss Sources Chapter 5: Petroleum Industry Chapter 6: Organic Chemical Process Industry Chapter 7:  Liquid Storage Tanks Chapter 8: Inorganic Chemical Industry Chapter 9: Food and Agricultural Industries Chapter 10: Wood Products Industry Chapter 11: Mineral Products Industry Chapter 12: Metallurgical Industry Chapter 13: Miscellaneous Sources Chapter 14: Greenhouse Gas Biogenic Sources Chapter 15: Ordnance Detonation Appendix A: Miscellaneous Data & Conversion Factors Appendix B.1:  Particle Size Distribution Data and Sized Emission Factors for Selected Sources Appendix B.2: Generalized Particle Size Distributions Appendix C.1: Procedures for Sampling Surface/Bulk Dust Loading Appendix C.2: Procedures for Laboratory Analysis of Surface/Bulk Dust Loading Samples

Chapter 5, Section 5.1 "Petroleum Refining" discusses the air pollutant emissions from the various types of equipment used in the petroleum crude oil refineries as well as from their auxiliary steam-generating boilers, furnaces and engines, and Table 5.1.1 lists the pertinent emission factors. Table 5.1.2 lists the emission factors for the fugitive air pollutant emissions from the large wet cooling towers in refineries and from the oil/water separators used in treating refinery wastewater.

The fugitive air pollutant emission factors from over-pressure relief valves, piping, open-ended piping lines or drains, piping flanges, sample connections, and mechanical seals on pump and compressor shafts are also discussed and listed in Chapter 5.

In most cases, the emission factors in Chapter 5 are included for both uncontrolled conditions before emission reduction controls are implemented and controlled conditions after the specified emission reduction methods are implemented.

Chapter 7 "Liquid Storage Tanks" is devoted to the methodology for calculating the emissions losses from the six basic tank designs used for organic liquid storage: fixed roof (vertical and horizontal), external floating roof, domed external (or covered) floating roof, internal floating roof, variable vapor space, and pressure (low and high). The methodology in Chapter 7 was developed by the American Petroleum Institute (API) in collaboration with the EPA.

The EPA has developed a software program named "TANKS" which performs the Chapter 7 methodology for calculating emission losses from storage tanks. The program's installation file, along with a user manual and the source code, are available online at the EPA's website.

Chapters 5 and 7 discussed above are illustrative of the type of information contained in the other chapters of AP 42. It should also be noted that many of the fugitive emission factors in Chapter 5 and the emissions calculation methodology in Chapter 7 and the TANKS program also apply to many of the other industrial categories in AP-42 besides the petroleum industry.

## Citation

Milton Beychok (Lead Author);C Michael Hogan (Topic Editor) "AP 42 Air Pollutant Emission Factors". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth October 3, 2011; Last revised Date March 29, 2012; Retrieved May 21, 2013 <http://www.eoearth.org/article/AP_42_Compilation_of_Air_Pollutant_Emissions?topic=49479>

## The Author

I am a retired chemical engineer living with my wife in Newport Beach, California, USA. I spent the first part of my career (about 30 years) working in and designing petroleum refineries, petrochemical plants, natural gas treating plants and other industrial facilities in various locations worldwide. For the next 20 years or so, I was an independent consulting engineer in the environmental field ... impact studies, permitting, wastewater and air pollution emission studies. I am a graduate ... (Full Bio)