UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

 OFFICE OF 

AIR AND RADIATION

June 10, 2010

MEMORANDUM

SUBJECT: Example Workbook Calculating the Error of the Mass-Balance Approach in

Estimating Fluorinated GHG Emissions from Fluorinated GHG Production

FROM: Deborah Ottinger

Climate Change Division

TO: The Record

Under the proposed rule for Mandatory Reporting of Greenhouse Gases: Additional Sources of 

Fluorinated GHGs, facilities interested in pursuing the mass-balance approach to estimate their 

fluorinated GHG emissions from fluorinated GHG production would have to be able to 

demonstrate that their process measurements and calculations passed an error test (75 FR 18652, 

April 12, 2010). Calculations for the test are included in the proposed rule. The workbook 

entitled “Example Mass Balance Error Calculation.xls” illustrates how the error calculation 

might work with one well-known production process. 

This workbook was developed as a "proof of concept," not an actual calculation tool. If EPA 

finalizes the error test for the mass-balance approach, the Agency will provide a more userfriendly tool that will include instructions and background. Nevertheless, by working through 

the spreadsheets and referring to the corresponding equations in the proposed subpart L 

regulatory text, one can see how the error test could be implemented.

There are four spreadsheets in the workbook. The first two contain the calculations of interest 

for the two reactants (one spreadsheet per reactant). The third and fourth provide background on 

the reaction and ensure that the masses will actually balance. A facility wouldn't need the third 

spreadsheet to calculate the error for an actual process because the relevant values would be 

measured rather than calculated.

To see how the first two spreadsheets work, spreadsheet users should refer to the equations in the 

proposed regulatory text whose numbers appear in the heading of each group of columns. In 

general, the equations appear in the sheet in the order that a facility would solve them to 

calculate its emissions. Within each equation, the columns on the left side are the inputs, and the 

last column is the output. The values that are calculated using the mass-balance equations (and 

error propagation equations) appear in purple. (Since the spreadsheet is just a model, it also 
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calculates some of the input values that appear in black, but they would be measured in an actual 

process.) The calculations proceed from left to right and down. The outputs of some equations 

are used as the inputs for the next, both for the emissions calculation and for the error 

calculation. 

The values for the percentages of products and by-products in various streams are hypothetical. 

Users of the spreadsheet can adjust these, but they should take care to ensure that they are 

accounting for all masses and flows (e.g., make sure the percentages of the by-product going to 

the various process streams don't add up to more than 100%). 

One important note: the spreadsheet uses the example of HCFC-22 with HFC-23 as the byproduct because this is a widely known reaction. The workbook calculates both HCFC-22 

emissions (the product) and HFC-23 emissions (the by-product). However, HCFC-22 

production is actually covered by subpart O rather than subpart L, and only the HFC-23 

emissions, not the HCFC-22 emissions, are covered by subpart O. Nevertheless, the basic math 

and logic should be the same for the processes covered by subpart L.