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.

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

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 N

EPAct NMOG Calculation Protocol

EPA-420-R-13-004

April 2013
N-1 

EPAct NMOG Calculation Protocol

19-Feb-2009 

The series of calculations shown here (Equations (1) through (6)) must be performed separately 

for each test phase (bag). The NMOG mass results can then be weighed in the usual way to form 

a test cycle composite emission rate. 

First we calculate corrected NMHC concentration for dilute exhaust (subscript e) and dilution air 

(subscript d) as follows: 

e e CH4 e MeOH e EtOH Pre OH e AcetHO AcetHOe NMHC = r4CHrFIDHC rEtOHrMeOH Pr rOH ⋅−⋅−⋅−⋅−⋅− (1)

d d CH4 d MeOH d EtOH Prd OH d AcetHO AcetHOd NMHC = r4CHrFIDHC rEtOHrMeOH Pr rOH ⋅−⋅−⋅−⋅−⋅− (2)

Note that these values are all as ppmC (so speciation results for EtOH, PrOH, and AcetHO 

reported in ppm of the particular chemical compound will need to be multiplied by 2 or 3 

depending on the number of C atoms in the compound). 

The following constant values shall be used for FID response factors: 

 rCH4 = 1.15 ppmC/ppmC (this program)

 rMeOH = 0.63 ppmC/ppmC (this program)

 rEtOH = 0.74 ppmC/ppmC (this program)

 rPrOH = 0.85 ppmC/ppmC (CARB)

 rFormHO = 0.00 ppmC/ppmC (various sources)

 rAcetHO = 0.51 ppmC/ppmC (this program)

Next, we must calculate the dilution factor to be used in generating the net NMHC concentration:

( )

( ) 4 2CO e NMHCe e MeOH4CH e Pr OHe EtOHe FormHOe AcetHOe e 10CO

z5.0y25.0x76.3y5.0x

x 100

DF − + +++++ + ⋅+





 





−+⋅++ ⋅

= (3)

The parameters x, y and z in Eq. (3) are coefficients taken from the chemical formula CxHyOz of 

a test fuel. The procedure to calculate their values is provided in Appendix 2. 

Once the DF is determined, we calculate the net NMHC concentration as follows:





 



 −⋅−= DF

1 NMHCconc NMHCe d 1NMHC (4)

Then we compute NMHCmass: 

6 NMHCmass Vmix DensityNMHC NMHCconc 10− ⋅= ⋅ ⋅ (5)
N-2 

Equations (4) and (5) must be repeated for each emission being considered. Vmix is the volume of 

dilute exhaust collected during a given phase of the test cycle, measured in standard cubic feet. 

Density is the calculated gas phase density of a particular species treated as a C1HyOz ideal gas. 

The following values of gas phase density shall be used: 

DensityNMHC = 16.334 g/ft3

DensityMeOH = 37.718 g/ft3

DensityEtOH = 27.115 g/ft3

DensityPrOH = 23.581 g/ft3

DensityFormHO = 35.345 g/ft3

DensityAcetHO = 25.929 g/ft3

To generate the NMOG figure, we need methanol, ethanol, 2-propanol, formaldehyde and 

acetaldehyde mass emissions as computed using Eq. (4) and (5) based on measured 

concentration values form the speciation results (as in Eq. (1) and (2)). 

Finally, then, NMOG mass emissions can be computed as follows: 

NMOGmass = NMHCmass + MeOHmass +EtOHmass +Pr OHmass + FormHOmass + AcetHOmass (6)

Once NMOGmass calculations have been completed for all three phases (cold transient (ct), 

stabilized (s) and hot transient (ht)) of the LA92 test cycle they, calculate the total weighted 

NMOG emissions using the following formula: 

































+

+

⋅+

+

+

⋅=

s

D ht D

mass.s

NMOG mass.ht NMOG

0.57

s

D ct D

mass.s

NMOG mass.ct NMOG

0.43

wm

NMOG (7)

For tests where there is no bag 2 or 3 speciation data, NMOG shall be computed assuming 

emission levels for oxygenated species in bags 2 and 3 are zero. 
N-3 

Attachment 1

Definitions

NMHCe – Concentration of NMHC in dilute exhaust sample, ppm C equivalent 

FIDHCe - Uncorrected concentration of HC in dilute exhaust sample as measured by the FID, 

ppm C equivalent

CH4e – Concentration of methane in dilute exhaust sample as measured, ppm C equivalent

MeOHe - Concentration of methanol in dilute exhaust sample as measured, ppm C equivalent

EtOHe - Concentration of ethanol in dilute exhaust sample as measured, ppm C equivalent

PrOHe - Concentration of 2-propanol in dilute exhaust sample as measured, ppm C equivalent

FormHOe - Concentration of formaldehyde in dilute exhaust sample as measured, ppm C 

equivalent

AcetHOe - Concentration of acetaldehyde in dilute exhaust sample as measured, ppm C 

equivalent

CO2e - Concentration of carbon dioxide in dilute exhaust sample as measured, percent

COe - Concentration of carbon monoxide in dilute exhaust sample as measured, ppm

rCH4 - FID response to methane, ppmC/ppmC

rMeOH - FID response to methanol, ppmC/ppmC

rEtOH - FID response to ethanol, ppmC/ppmC

rPrOH - FID response to 2-propanol, ppmC/ppmC

rFormHO - FID response to formaldehyde, ppmC/ppmC

rAcetHO - FID response to acetaldehyde, ppmC/ppmC

NMHCd - NMHC concentration in dilution air, ppm C equivalent

FIDHCd - Uncorrected HC concentration in dilution air sample as measured by the FID, ppm C 

equivalent

CH4d - Concentration of methane in dilution air sample as measured, ppm C equivalent

MeOHd - Concentration of methanol in dilution air sample as measured, ppm C equivalent

EtOHd - Concentration of ethanol in dilution air sample as measured, ppm C equivalent

PrOHd - Concentration of 2-propanol in dilution air sample as measured, ppm C equivalent

FormHOd - Concentration of formaldehyde in dilution air sample as measured, ppm C equivalent

AcetHOd - Concentration of acetaldehyde in dilution air sample as measured, ppm C equivalent

DF - Dilution factor

x - Carbon-to-carbon ratio in formula CxHyOz determined as in Appendix 2 for the fuel used (by 

definition x=1)

y - Hydrogen-to-carbon ratio in formula CxHyOz determined as in Appendix 2 for the fuel used 

z - Oxygen-to-carbon ratio in formula CxHyOz determined as in Appendix 2 for the fuel used 

X – Carbon mass fraction of the fuel 

Y – Hydrogen mass fraction of the fuel 

Z – Oxygen mass fraction of the fuel 

NMHCconc – Concentration of NMHC in dilute exhaust sample corrected for background, ppm C 

equivalent 

MeOHconc - Concentration of methanol in dilute exhaust sample corrected for background, ppm 

C equivalent 
N-4 

EtOHconc - Concentration of ethanol in dilute exhaust sample corrected for background, ppm C 

equivalent

PrOHconc - Concentration of 2-propanol in dilute exhaust sample corrected for background, ppm 

C equivalent

FormHOconc - Concentration of formaldehyde in dilute exhaust sample corrected for background, 

ppm C equivalent

AcetHOconc - Concentration of acetaldehyde in dilute exhaust sample corrected for background, 

ppm C equivalent

Vmix - Volume of dilute exhaust collected during a given phase of the test cycle, scf 

DensityNMHC – Density of NMHC treated as a C1Hy ideal gas at standard conditions of 293.16oK 

and 760 mm Hg, g/ft3

DensityMeOH - Density of methanol treated as a C1HyOz ideal gas at standard conditions of 

293.16o

K and 760 mm Hg, g/ft3

DensityEtOH - Density of ethanol treated as a C1HyOz ideal gas at standard conditions of 293.16oK 

and 760 mm Hg, g/ft3

DensityPrOH - Density of 2-propanol treated as a C1HyOz ideal gas at standard conditions of 

293.16o

K and 760 mm Hg, g/ft3

DensityFormHO - Density of formaldehyde treated as a C1HyOz ideal gas at standard conditions of 

293.16o

K and 760 mm Hg,ft3

DensityAcetHO - Density of acetaldehyde treated as a C1HyOz ideal gas at standard conditions of 

293.16oK and 760 mm Hg, g/ft3

MNMHC - Molecular mass of NMHC treated as a C1Hy, g/mole, calculated according to the 

formula provided in Appendix 3 

NMOGmass - NMOG mass, g/test phase 

NMHCmass - NMHC mass, g/test phase

MeOHmass - Methanol mass, g/test phase 

EtOHmass - Ethanol mass, g/test phase 

PrOHmass - 2-propanol mass, g/test phase 

FormHOmass - Formaldehyde mass, g/test phase

AcetHOmass - Acetaldehyde mass, g/test phase

NMOGwm – Weighted NMOG emissions, g/mile

NMOGmass.ct - NMOG mass emitted during the cold transient phase of the test cycle, g/test phase

NMOGmass.s - NMOG mass emitted during the stabilized phase of the test cycle, g/test phase 

NMOGmass.ht - NMOG mass emitted during the hot transient phase of the test cycle, g/test phase

Dct - Distance driven by the test vehicle on a chassis dynamometer during the cold transient 

phase of the LA92 test cycle, miles 

Ds - Distance driven by the test vehicle on a chassis dynamometer during the stabilized phase of 

the LA92 test cycle, miles

Dht - Distance driven by the test vehicle on a chassis dynamometer during the hot transient phase 

of the LA92 test cycle, miles
K-5 

Attachment 2

Calculation of x, y and z Coefficients in Formula CxHyOz Using Fuel C, H and O Content Data

The carbon-to-carbon ratio x in formula CxHyOz by definition equals 1. The hydrogen-to-carbon 

and oxygen-to-carbon ratios y and z, respectively, can be calculated using the following 

equations: 

 

12.011

X

1.008

Y

y = (A2.1) and 

12.011

X

15.999

Z

z = (A2.2) where: 

X – Carbon mass fraction of the fuel

Y – Hydrogen mass fraction of the fuel

Z – Oxygen mass fraction of the fuel

The values of X, Y and Z will be provided by the EPA for all fuels tested in the EPAct Program.