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  • Writer's pictureTom Petersen

Emission Factors for Combustion Sources (Boilers and Generators)

Updated: May 10

So you know how much fuel your boiler used this month, but how do you know how much emissions it produced? The answer is the emission factor. For every combination of combustion source, fuel type and pollutant, the EPA gives us a corresponding emission factor that lets us do the math.

Since 1972 the EPA has published a comprehensive list of emission factors called AP-42. To find which emission factors apply to you, we recommend using WebFire, a searchable database. By finding the right Source Classification Code (SCC), which lists combinations of combustion source with fuel type, you can see the emission factor for every pollutant that source emits.

For example, the SCC for a 10-100 MMBTU boiler using natural gas is 10300602. Using this for a WebFire search results in 66 emission factors. Here are 2 emission factors for nitrogen oxides (NOx):

Control(s): If the source has any control devices installed. If not, use the UNCONTROLLED factor.

Emission Factor: E+02 means move the decimal point two places to the right. E-04 means move the decimal point 4 places to the left. Emission factor * MMCF gas burned = lbs of NOx emitted.

Quality: Grade assigned by the EPA to denote the accuracy of the emission factor.

Here are a few more common SCCs:

Boiler, # 2 Fuel Oil: 10300502

Generator, Diesel: 20300101

Generator, Natural Gas: 20300201

If you have any questions about emission factors or filing your annual emission statement in Pennsylvania, please contact EES at or call 215-704-1506.


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