Emission Factors
Emission factors are numbers which when multiplied by an activity and corrected by a control efficiency resulting in a calculated emission for an air pollutant. Emission factors are single numbers for non-storage tank equipment and complex formulas for calculation of volatile organic compounds from storage tanks. Storage tank calculations are highly complex because of factors influencing the storage tank (i.e., product stored, location, meteorological factors, etc.).
Emission factors are developed from source test data. The emission factor information can be determined based on testing done on a facility's piece of equipment or from other information. DNR established a protocol for using emission factor information based on the source of the information:
- Emission factors developed by the facility through emission testing or some other scientific means.
- Emission factors developed by the United States Environmental Protection Agency based on testing data completed on similar operations in the United States.
- Emission factors developed by material balances and through engineering judgement.
Emission factors are assigned to pieces of equipment through an eight digit code known as the Source Classification Code (SCC). For DNR calculations of emissions the SCC must be correct or the emission factor assigned to the activity will result in an incorrect air emission calculation.
DNR has defined specific emission factors for specific business sectors based on discussions with industrial groups. These specific emission factors were developed to ensure air emissions were calculated consistently across the state. Emission factor agreements are used to calculate emissions for nonmetallic mining equipment and hot mix asphalt equipment.
Air Pollutant Emissions Calculated
DNR calculates the emission totals for the following pollutants:
- PM
- particulate matter
- PM10
- inhalable particulate
- SO2
- sulfur dioxide
- NOX
- nitrogen oxides
- CO
- carbon monoxide
- ROG
- reactive organic gases
(DNR also calculates emissions for some hazardous air pollutatants based on data supplied by the United States Environmental Protection Agency.)
Emission Calculation Formula
For most emission sources the following equation is used:
E=(Q*EF*(1-C/100))
where
E = Calculated emissions in tons per year.
Q = Actual annual throughput.
EF = Emission factor. The emission factors are either supplied by USEPA
or derived from a stack test or engineering calculation. In some cases,
the sulfur percent and/or the ash content will multiply the emission factor.
C = Collector efficiency, in percent. This is the combination of the capture
efficiency and the control efficiency. To calculate C, multiply the capture
efficiency by the control efficiency and divide by 100.
Emission Factor Information
Emission factors are used to calculate the air emissions from a process throughput or fuel use. The emission factor is multiplied by the process throughput or fuel use to determine the uncontrolled air emissions from a process. After the uncontrolled emission is calculated it is then adjusted to a control efficiency of a control device provided the process is linked to the control device and the control device removes the specific air pollutant. There are three main sources of emission factors:
- USEPA document AP-42, Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources, 5th Edition, USEPA-OAQPS, January 1995 (with subsequent supplements). The electronic version of the emission factors in this document is contained in the FIRE database. You may download this information for free from the USEPA CHIEF (exit DNR).
- Stack test data approved by the Department.
- Engineering calculations approved by the Department.
Source Classification Codes
SCC is an acronym that stands for Source Classification Code. A SCC is an eight digit number developed by USEPA. This eight digit number is assigned to a process. For example, the SCC for a traveling grate (overfeed) stoker is 10100201. The SCC represents this process numerically in any database that deals with a traveling grate (overfeed) stoker. Presently, there are about 9,600 SCCs established by USEPA.
But why are they important? As stated in the question regarding the calculation of emissions one of the terms used in emission calculations is the emission factor. The emission factor for each pollutant is assigned to a specific SCC. If the SCC is incorrect then the assigned emission factor is incorrect and the resulting emission calculation is wrong. You may download SCC information from the USEPA CHIEF WebFIRE web site (exit DNR).
The majority of air emission factors are used to calculate sulfur dioxide, nitrogen oxides, carbon monoxide, reactive organic gases, and particulate matter. How are hazardous air pollutant emissions calculated?
When an applicable hazardous air pollutant emission factor exists, it is used to calculate hazardous air pollutant emissions. As in years past, when emission factors do not exist for a hazardous air pollutant, the company representative should enter the amount of the hazardous pollutant directly into the ARS software program at the process level in the 'Reported' tab.
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