Emission factor

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Emission factor
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An emission factor is a numerical value that represents the amount of a specific pollutant emitted into the air per unit of activity or process. It is typically used to estimate the emissions from a facility or source based on the amount of fuel consumed or other activity data. Emission factors can be expressed in units of mass per unit of activity, such as grams per mile or pounds per hour. They are used in air quality modeling and emission inventories to estimate the total emissions from a particular source or group of sources.

Examples of emission factors

Here are a few examples of emission factors:

  • CO2 emission factor for coal combustion : It ranges between 0.94 to 0.98 pounds of CO2 per pound of coal.
  • NOx emission factor for natural gas combustion : It ranges between 0.03 to 0.06 pounds of NOx per million Btu of natural gas.
  • SO2 emission factor for oil combustion : It ranges between 0.05 to 0.10 pounds of SO2 per million Btu of oil.
  • PM2.5 emission factor for gasoline vehicle : It ranges between 0.0002 to 0.0005 grams per mile traveled.
  • VOC emission factor for paint manufacturing : It ranges between 0.02 to 0.1 pounds of VOC per gallon of paint produced.

These are just examples, and actual emission factors can vary widely depending on the specific source, process, and location. It's important to use the correct emission factors for the specific source or process being considered. Additionally, emission factors can change over time as technology and regulations evolve.

Calculation of emission factors

Emission factors are usually determined through laboratory testing or by using data from similar sources. The general formula for calculating an emission factor is:

Emission Factor (EF) = (Emissions (E) / Activity Data (A))


  • Emissions (E) is the amount of a specific pollutant emitted into the air, typically measured in mass units such as grams or pounds.
  • Activity Data (A) is the data that represents the activity or process that is associated with the emissions, such as fuel consumption, production rate, or distance traveled.

For example, if a coal-fired power plant emits 1,000 pounds of sulfur dioxide (SO2) per day and consumes 10,000 tons of coal per day, the emission factor for SO2 would be:

EF (SO2) = (1,000 pounds / 10,000 tons) = 0.1 pounds of SO2 per ton of coal

It is also possible to calculate emission factors for specific processes, such as combustion in boilers, vehicles, and industrial processes, as well as for specific pollutants, such as NOx, CO2, and particulate matter.

It's worth to mention that the EFs are not always constant, they can vary depending on the type of fuel, process and location, it's important to use the right EF for the right source.

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