Glossary:Emissions Factor

The emission factor describes typical methane emissions per unit of activity of a component or part of the gas system (e.g. valve, pipeline section) or from an event and can have units like [kg/km], [kg/event] or [kg/equipment].

(Note - this is not an exhaustive list, the emission factor is linked to the activity factor and expressed in a numerical value consistent with the activity factor)

A representative value that attempts to relate 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 a 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 an 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).

Emissions factors have long been the fundamental tool in developing national, regional, state, and local emissions inventories for air quality management decisions and in developing emissions control strategies. More recently, emissions factors have been applied in determining site-specific applicability and emissions limitations in operating permits by federal, state, local, and tribal agencies, consultants, and industry.

The general equation for emissions estimation is:

E = A x EF x (1-ER/100)

where:

• E = emissions;
• A = activity rate;
• EF = emission factor, and
• ER =overall emission reduction efficiency

See also:

EF