AP 42 Compilation of Air Pollutant Emission Factors

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 includes stationary point and area source emission factors, and Volume II includes mobile source emission factors. Volume I is currently in its fifth edition and is available on the Internet. Volume II is no longer maintained as such, but roadway air dispersion models for estimating emissions from onroad vehicles and from non-road vehicles and mobile equipment are also available on the Internet.

In routine common usage, Volume I of the emission factor compilation is very often referred to as simply AP 42.

Introduction

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 equipment in the various refinery processing units as well as from the auxiliary steam-generating boilers, furnaces and engines, and Table 5.1.1 includes the pertinent emission factors. Table 5.1.2 includes 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 relief valves, piping valves, open-ended piping lines or drains, piping flanges, sample connections, and seals on pump and compressor shafts are discussed and included the report EPA-458/R-95-017, "Protocol for Equipment Leak Emission Estimates" which is included in the Chapter 5 section of AP 42. That report includes the emission factors developed by the EPA for petroleum refineries and for the synthetic organic chemical industry (SOCMI).

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 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 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 installer file along with a user manual, and the source code are available on the Internet.

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 other industrial categories besides the petroleum industry.

Estimating Air Emissions associated with Fossil Fuels and Stored Materials

The only emissions monitored are those associated with the burning of fossil fuels and the storage of some materials which generate toxic emissions. kWh are not monitored for emissions, and the discussion in this section does not address electricity.

There are three ways to monitor emissions of air contaminants:

* Annual or Biannual stack tests. This is a very expensive option.
* Continual Emissions Monitoring systems (CEM systems). This is also an expensive option.
* Parametric Monitoring, also known as AP42. This method converts fuel and electricity usage into emissions amounts using EPA emissions factors. This is the least expensive and most common method.
* The EPA usually will accept emissions data gathered using the AP42 method. However these emissions factors are averages and are based upon older less efficient equipment and may err on the high side. As a result some may choose alternative methods of tracking emissions. AP42 Emissions Factors for fossil fuels can be downloaded from the EPA website.

Estimating Air Emissions associated with Electricity Usage

The EPA does not offer AP42 factors that convert kWh into emissions. Although the generation of electricity is often associated with pollutants fouling the air, this is not always the case. Electricity generation using Nuclear, Solar, Wind and Hydro does not pollute the air at all. Depending upon the hour of the day, the electricity used by an office building may come from Coal and Natural Gas which foul the air, or Nuclear, Solar or Hydro, which do not.

There are a few lists of emissions factors that convert kWh into likely amounts of emissions. The Department of Energy offers emissions factors that convert electricity into emissions. However, the Leonardo Academy produced a more substantial list of emissions (CO2, VOCs, NOX, CO, SO2, PM10, Mercury, Cadmium and Lead) factors for the EPA in 1998, that Leonardo updates yearly using EPA Data. These emission factors are listed by State. Although there is no consensus on statewide emissions factors for electricity, reasonable estimates can be found using these factors.

From http://en.wikipedia.org/