EPAct/V2/E-89: Assessing the Effect 

of Five Gasoline Properties on Exhaust 

Emissions from Light-Duty Vehicles 

Certified to Tier 2 Standards 

Final Report on Program Design and 


Data Collection
 

Appendix P
 

Derivation of FID Response Factors for 


Oxygenated Emission Species
 

Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

National Renewable Energy Laboratory 

U.S. Department of Energy 

Coordinating Research Council 

NOTICE 

This technical report does not necessarily represent final EPA decisions or 


positions. It is intended to present technical analysis of issues using data 


that are currently available. The purpose in the release of such reports is to 


facilitate the exchange of technical information and to inform the public of 


technical developments.
 

EPA-420-R-13-004 

April 2013 
 

 

 

 

 

 

 

 

 

 

Exhaust hydrocarbons were measured in this program using a flame ionization detector (FID), 

which is calibrated to count carbon ions produced during complete combustion of propane. The 

FID has good linearity of response over a wide range of molecular sizes and concentrations of 

hydrocarbons, however, due to its principles of operation the instrument’s response to some 

compounds can deviate significantly from unity. Methane and oxygenated species are examples 

of compounds that are known to have response factors different from 1.0. Since these responses 

are used in calculation of NMOG results, and the test fuels included several ethanol blends, it is 

important to account for these differences. 

Typical response factors (RFs) are found in the literature, but can vary between labs depending 

on instrument models and calibrations. Therefore, prior to the start of Phase 3, SwRI performed 

measurements of RFs for methane, methanol, ethanol, and acetaldehyde (formaldehyde’s RF was 

assumed to be zero). To ensure the results would be as accurate and relevant as possible for this 

dataset, RFs were measured on the same site where the emission tests would take place, and at 

concentrations as close as practical to the level occurring during the actual tests. The 

measurement process involved diluting known span bottle gases (concentrations between 49-200 

ppm) using a calibrated Horiba 500-step divider. 

After some initial trials using different gas divider ranges, the factors used for the program were 

derived by averaging several measurements made between approximately 1-10 ppm, as shown in 

the table on the next page. Final values used in the NMOG calculations and their sources are as 

follows: 

rCH4 = 1.15 ppmC/ppmC (measured in this program) 

rMeOH = 0.63 ppmC/ppmC (measured in this program) 

rEtOH = 0.74 ppmC/ppmC (measured in this program) 

rPrOH = 0.85 ppmC/ppmC (taken from ARB documents) 

rFormHO = 0.00 ppmC/ppmC (multiple sources) 

rAcetHO = 0.51 ppmC/ppmC (measured in this program) 

P-1
 
 

 

 

 

 

 

Mixture Actual* (ppmC) Measured (ppmC) Response Average 

Methane / Air 

(90.4 ppm source) 

13.56 

4.52 

1.81 

15.49 

5.21 

2.09 

1.14 

1.15 

1.16 

0.90 1.04 1.15 1.15 

Ethanol / N2 

(98.0 ppm source) 

9.80 

4.90 

0.98 

7.19 

3.61 

0.73 

0.73 

0.74 

0.75 0.74 

Acetaldehyde / N2 

(200.0 ppm source) 

10.00 

4.00 

2.00 

5.14 

2.05 

1.03 

0.51 

0.51 

0.51 

1.20 0.62 0.52 0.51 

Methanol / N2 

(49.9 ppm source) 

9.97 

4.99 

2.49 

6.06 

3.15 

1.60 

0.61 

0.63 

0.64 0.63 

*“Actual” refers to the concentration calculated by taking the source bottle concentration divided by the gas divider 

setting. 

P-2