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Air Quality Emission Factor

Definition Overview How do I develop local emission factors?


An air quality emission factor is the relationship between the amount of pollution produced and the amount of raw material processed or number of product units produced.

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AQ Modeling flowchart

An emission factor is a representative value that relates 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 emission factor is used to calculate the total emission from a source as an input for the emission inventory. The general U.S. EPA equation for emission estimation is:

E = A x EF x (1-ER/100) where: E = emissions A = activity rate EF = emission factor ER = overall emission reduction efficiency, %

General emission factors are available to the public. However, variations in the conditions at a given facility, such as the raw materials used, temperature of combustion, and emission controls, can significantly effect the emissions at an individual location. Whenever possible, the development of local emission factors is highly desirable.

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How do I develop local emission factors?

For information on the Compilation of Air Pollutant Emission Factors, AP-42, you may access EPA's documentation at http://www.epa.gov/ttn/chief/ap42/index.html.


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