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

Air pollution dispersion terminology

Air pollution dispersion terminology includes the words and technical terms that have a special meaning to those who work in the field of air pollution dispersion modeling...

emission factor

Emission factor

An emission intensity is the average emission rate of a given pollutant from a given source relative to the intensity of a specific activity; for example grams of carbon dioxide released per megajoule of energy produced, or the ratio of greenhouse gas emissions produced to GDP...

s, and Volume II includes mobile source

Air pollution dispersion terminology

Air pollution dispersion terminology includes the words and technical terms that have a special meaning to those who work in the field of air pollution dispersion modeling...

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 Volume II is no longer maintained as such, but roadway air dispersion models for estimating emissions from onroad vehicles and from non-road vehicles and mobile equipment are also available on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

Pollutant

A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...

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

Air pollution

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....

. 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

Atmospheric dispersion modeling

Atmospheric dispersion modeling is the mathematical simulation of how air pollutants disperse in the ambient atmosphere. It is performed with computer programs that solve the mathematical equations and algorithms which simulate the pollutant dispersion...

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 tower

Cooling tower

Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...

s in refineries

Oil refinery

An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...

and from the oil/water separators used in treating refinery wastewater

Wastewater

Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

.

The fugitive air pollutant emission factors from relief valves

Safety valve

A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....

, piping valves, open-ended piping lines or drains, piping flange

Flange

A flange is an external or internal ridge, or rim , for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel...

s, sample connections, and seals on pump

Pump

A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

and compressor

Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

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

American Petroleum Institute

The American Petroleum Institute, commonly referred to as API, is the largest U.S trade association for the oil and natural gas industry...

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, NO_x, 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 .

Conversion of Carbon Dioxide metric tons to KWH for the purpose of calculating avoided units of carbon dioxide emissions.
7.18 x 10-4 metric tons CO₂ / kWh http://www.epa.gov/cleanenergy/energy-resources/refs.html

Other sources of emission factors

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