Greenhouse gas emissions calculations

This method may be used to develop an editable spreadsheet containing detailed emissions calculations of greenhouse gas (GHG) emissions for each GHG-emitting process at your facility. Each step in your calculation(s) needs to be clear and easy to follow.

Include the following information with your calculations:

  • AQ Facility ID No. – Include your Air Quality (AQ) facility Identification Number (ID No.). This is the first eight digits of the permit number for all permits issued under the operating permit program. If your facility has never been issued a permit under this program, do not include at this time.
  • AQ File No. – Include your AQ File Number, if known. This number can be found in the “cc” section of correspondence from the MPCA. If you do not know this, or can’t find it, do not include it at this time.
  • Facility name – Include your facility name.
  • Emission unit ID(s) – Include the identification number of each emission unit. Obtain this number from your Form GI-05B, or the appropriate form related to the permit you are applying for, or your existing permit. If you are applying for a registration permit Option D, just provide a description of the emission unit.
  • Stack/Vent designation number(s) – Include the designation number of the stack(s) or vent(s) through which the unit will exhaust into the atmosphere. Obtain these numbers from Form GI-04, or the appropriate form related to the permit you are applying for, or your existing permit. If you are applying for a registration permit Option D, just provide a description of the control equipment.
  • Control equipment Include a description of the type of control equipment. Use either the identifying number from Form GI-05A, or the appropriate form related to the permit you are applying for, or your existing permit. If none, indicate no control equipment. If you are applying for a registration permit Option D, just provide a description of the control equipment.
  • Source of emission factors – Indicate the sources of your emission factors. Possible sources include the Climate Registry, EPA’s web page on climate change and GHG emissions,  40 CFR Part 98, those listed on the Emissions Calculations page, and those described in Minn. R. 7005.0100, subp. 10. If the emission factor is from AP-42, cite the exact section or table used. If emission factor is from some other source, attach a photocopy of the information used, or provide an exact internet address, so the information can be verified.
  • Formula/Equation – The formula and/or equation needs to be available in each spreadsheet cell for which there is a calculation (for example, Steps 3, 4, 5, 7, 8, 9, 10, and 11 below.)
  • Operating limitations – Describe in detail any permit limits you plan to take to restrict your potential-to-emit (fuel type and/or usage, hours of operation, bottlenecks, etc. - see Proposing Synthetic Minor Permit Limits). Describe the limiting factors, cite any rules that apply (e.g., Standards of Performance for Stationary Sources (NSPS, 40 CFR part pt. 60), Best Available Control Technology [BACT]). The associated limit must be used to calculate your potential-to-emit after permit limits in Step 9. If you used vendor certification or stack test data to limit your potential-to-emit, the factor you used will become your permit limit. Include all proposed limits on Form CD-01, and anywhere else as instructed in the application forms.

Emissions calculation instructions

Follow these steps for calculating your GHG emissions for each GHG-emitting operation at your facility. Except as specifically directed below, each column of your spreadsheet will probably correlate to each step indicated below. Additional columns can and should be included in the spreadsheet to indicate additional steps or information specific to your operation.

Step 1. Pollutant 

Include each of the following pollutants as applicable.

  • CO2 = carbon dioxide
  • CH4 = methane
  • N2O = nitrous oxide
  • HFC = hydrofluorocarbons
  • PFC = perfluorocarbons
  • SF6 = sulfur hexafluoride
  • CO2e = carbon dioxide equivalent

Step 2. Emission factor

Document the emission factor for each pollutant except CO2e (there is no “emission factor” for CO2e, that will be dealt with later); HFCs and PFCs are each reported as the total of several individual compounds. The individual HFCs and PFCs that are to be reported are listed in Table A-1 of Subpart A of 40 CFR Part 98. For HFCs and PFCs, document the emission factor for each individual compound. Remember to use uncontrolled emission factors, and include the applicable units. Include the source of the emission factors used.  

Step 3. Global warming potential

List the “global warming potential” (GWP) of each pollutant except CO2e (there is no GWP for CO2e, the GWPs are used later to calculate CO2e). The GWP for each of the other pollutants (including for each of the individual HFCs and PFCs) are found in Table A-1 of Subpart A of 40 CFR Part 98.

Step 4. Mass emission rate

For each pollutant except CO2e, calculate the Mass Emission Rate in lb/hr. Calculate the emission rate by using this method:

  • Mass Emission rate (lb/hr) = Emission factor (lb/unit) x capacity (unit/hr)

Step 5. Maximum uncontrolled emissions

For each pollutant except CO2e, calculate the Maximum uncontrolled mass emissions of each pollutant by using the following method:

  • Maximum uncontrolled mass emissions (tons/yr) = mass emission rate (lb/hr) x 8760 (hrs/yr) x 0.0005 (tons/lb)

Step 6. Maximum uncontrolled carbon dioxide equivalent

(This should be a continuation of the column used in Step 5)

In addition to the mass emission rate of each green house gas, calculated in Step 5, you need to calculate the “carbon dioxide equivalent,” or CO2e, of the greenhouse gases as a group. To do this, multiply the maximum uncontrolled mass emission rate (in tons per year, as calculated in Step 5) of each greenhouse gas (CO2, CH4, N2O, SF6, each individual PFC, and each individual HFC) by its GWP.  Then add them together to get CO2e in tons/year:

  • Max uncontrolled CO2e (tons/yr) = [1 x uncontrolled CO2 (tons/yr)] + [25 x uncontrolled CH4 (tons/yr)] + [298 x uncontrolled N2O (tons/yr)] + [22800 x uncontrolled SF6 (tons/yr)] + [GWPPFCn x uncontrolled PFCn (tons/yr)] + [GWPPFCn x uncontrolled HFCn (tons/yr)]

Step 7. Pollution control efficiency

Indicate the pollution control efficiency. The pollution control efficiency is the product of the capture efficiency and the destruction/collection efficiency indicated on Form GI-05A (or other similar form, depending on the type of permit you are applying for), or in your existing permit. Document this number here, and if you are applying for a new individual permit or an amendment to an existing individual permit, remember to include on Form CD-05 a plan to demonstrate and maintain the destruction/collection efficiency. The efficiency should be expressed for each pollutant. If there is no control for a particular pollutant, indicate “zero” as the control efficiency. Do not enter a pollution control efficiency for CO2e.

Step 8. Maximum controlled mass emission rate [lb/hr]

This is the maximum controlled mass emissions rate in lb/hr required in the first column of item 3e on Form GI-07. This calculation applies to the GHG components (CO2, CH4, N2O, etc), not to CO2e. Calculate the controlled mass emissions by using the following method:

  • Max. controlled mass emission rate [lb/hr] = Mass emission rate (lb/hr) x (100 – Pollution control efficiency) ÷ 100

Step 9. Maximum controlled mass emissions

Calculate the Maximum Controlled Mass Emissions in tons/year, for each pollutant except CO2e. Use this method for the calculation:

  • Max. controlled mass emissions [tons/year] = Maximum Controlled Mass Emissions (tons/year) x (100 – Pollution control efficiency) ÷ 100.

Step 10. Maximum controlled carbon dioxide equivalent [tons/year]

(This should be a continuation of the column used in Step 9)

Calculate the maximum controlled CO2e by multiplying the individual controlled mass emission rates (calculated in Step 9) of each individual greenhouse gas by its global warming potential, then adding them together

  • Max controlled CO2e (tons/yr) = [1 x controlled CO2 (tons/yr)] + [25 x controlled CH4 (tons/yr)] + [298 x controlled N2O (tons/yr)] + [22800 x controlled SF6 (tons/yr)] + [GWPPFCn x controlled PFCn (tons/yr)] + [GWPHFCn x controlled HFCn (tons/yr)]

Step 11. Actual emissions

If this is an existing unit and historical records exist, calculate actual emissions using the average of the previous two calendar years of usage data (last 12 months if doing calculations for Registration Permit Option D). Report actual emissions in tons/year.

To calculate actual emissions using the above equations, substitute actual operating parameters and/or hours per year operated for the maximum capacities to get mass emissions (CO2, CH4, N2O, SF6, HFCs, and PFCs) in tons per year. Then, as described in Step 10, multiply these calculated actual mass emissions by the appropriate GWP for each pollutant, and add them together to get CO2e.

Step 12. Limited controlled mass and CO2e emissions

(Skip this item if you are working on calculations for a Registration Permit Option D.) 

The limited controlled emissions are calculated by taking into account all limitations on operation of the source you are proposing to comply with in this application. These limitations include limits on hours of operation, or on the amount of material used. You start the calculation of limited controlled emissions by repeating the calculation of emission rate [starting with Step 4] but taking into account the limits you propose. This is the limited controlled emissions in tons per year in the right column of item 3e on Form GI-07.

If an emission unit is subject to an emission limitation specified in 40 CFR pt. 60, 40 CFR pt. 61, 40 CFR pt. 63 or Minn. R. ch. 7011, you must show this requirement in the calculation of limited controlled emissions and take this into account in calculating the limited controlled emissions. If you choose to propose to comply with more a stringent limit, you should state this clearly and show the resulting allowed emissions in this calculation.