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Factor development:

Optional emissions mass adjustment factor for evaporative emissions testing using California test fuel containing 10% 

ethanol

February 21, 2012

Authored by: California Air Resources Board Staff

I. California Evaporative Emission Test Procedure diurnal mass equation derived for an ethanol containing fuel:

Edi = EHCd + (OEHCEEeOH)(EEeOH) Main equation

The “10-6” factor of the test procedure equation is not in the “main equation” above since MEtOH is expressed in g in lieu of μg just for the 

purpose of developing this factor.

Where:

EHCd = 2.97(P)(V)×10−4

T {�PPECfid� − ra(PPEC EeOH)}

To simplify the calculation, initial concentrations assumed to be zero.

ra = the FID response factor to ethanol

OEHCEEeOH = available HC mass of an ethanol molecule (assuming a hydrocarbon H: C ratio of 2.3: 1)

total mass of an ethanol molecule

Hydrocarbon H:C (hydrogen to carbon) ratio obtained from 40 CFR 86.143-96

OEHCEEeOH = 28.66

46.07

OMHCEEtOH = 0.62
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EEeOH = (CEeOH)(EWEeOH)(P)(V)

(R)(T)

CCEeOH = 2(CEeOH) (Concentration in terms of carbon)

PPEC EeOH = 106 × (CC EeOH) (PPM concentration in terms of carbon)

CEeOH = PPMC EtOH

2×106

EEeOH = (PPEC EeOH)(EWEeOH)(P)(V)

(R)(T)(2)(106)

EWEeOH = 46.07 grams

mole

R = .0481 (inHg)(ft3)

(mole)(°R)

EEeOH = (P)(V)

(T) (. 000479)(PPEC EeOH)

Combine sub-components into main equation:

Edi = (P)(V)

T {(. 000297)(PPECfid) − (ra)(. 000297)(PPEC EeOH) + (.62)(. 000479)(PPEC EeOH)}

Edi = (P)(V)

T �(. 000297)(PPECfid) − (ra)(. 000297)(PPEC EeOH) + (. 000297)(PPEC EeOH)�

<V> Edi = (P)(V)

T (. 000297)�(PPECfid) − (ra)(PPEC EeOH) + (PPEC EeOH)�

Edi = (P)(V)

T (. 000297)[(PPECfid) − (ra − 1)(PPEC EeOH)] HC + Ethanol direct accounting
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II. California Evaporative Emission Test Procedure diurnal mass equation derived for FID response only:

Edi FID only = (P)(V)

T (. 000297)(PPECfid) Ethanol FID response only

III. Obtain mass adjustment factor from percent difference: (Mdi) versus (Mdi FID only):

Express PPMC EtOH in terms of PPMCfid to eliminate a variable in Mdi.

To do this, use ethanol to hydrocarbon ratio:

From <V>:

Edi =

(P)(V)

T (. 000297)�(PPECfid) − (ra)(PPEC EeOH)� (mass non-ethanol HC component)

+ (P)(V)

T (. 000297)(PPEC EeOH) (mass ethanol component, HC equivalent)

rEeOH = mass ethanol component, HC equivalent

mass non − ethanol HC component

<W> rEeOH =

(P)(V)

T {(.000297)(PPMC EtOH)}

(P)(V)

T (.000297)�(PPMCfid)−(ra)(PPMC EtOH)� (emissions ethanol ratio)

(rEeOH)(PPECfid) − (rEeOH)(ra)(PPEC EeOH) = PPEC EeOH

(rEeOH)(PPECfid) = PPEC EeOH + (rEeOH)(ra)(PPEC EeOH)

PPEC EeOH{1 + (rEeOH)(ra)} = (rEeOH)(PPECfid)
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<X> PPEC EeOH = (rEtOH)(PPMCfid)

{1+(rEtOH)(ra)}

<X> subbed into “HC + Ethanol direct accounting”:

Edi simplified = (P)(V)

T (. 000297) �(PPECfid) − (ra − 1) (rEeOH)(PPECfid)

{1 + (rEeOH)(ra)}

�

Edi simplified = (P)(V)

T (. 000297)(PPECfid) �1 − (ra − 1) (rEeOH)

{1 + (rEeOH)(ra)}

�

Percent difference: (Mdi simplified) versus (Mdi FID only):

%diff =

(P)(V)

T (. 000297)(PPECfid) �1 − (ra − 1) (rEeOH)

{1 + (rEeOH)(ra)}

� − (P)(V)

T �(. 000297)(PPECfid)�

(P)(V)

T �(. 000297)(PPECfid)�

× 100%

%diff =

�1 − (ra − 1) (rEeOH)

{1 + (rEeOH)(ra)}

� − 1

1

× 100%

%diff = −(ra − 1) (rEeOH)

{1 + (rEeOH)(ra)}

× 100%

%diff = (1 − ra) (rEeOH)

1 + (rEeOH)(ra)

× 100%
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This represents how much greater the reported diurnal mass would be if determined by subtracting out the FID response to ethanol and then 

adding on actual ethanol, versus just calculating reported mass from the FID response only.

TABLE 1: %diff data determined from ethanol/hydrocarbon ratios (rEtOH) from different vehicles

Vehicle: Fuel tank 

matl:

rEtOH: %diff For

ra = .69: 

(%)

Zero-evap 2004 MY Focus Metal .09 3

Near-zero 2004 MY Impala Plastic .11 3

Near-zero 2006 MY Taurus Metal .21 6

Near-zero 2004 MY Camry Plastic .26 7

Near-zero 2004 MY Ram 1500 Plastic .16 4

rEtOH (emissions ethanol ratio) values in Table 1 were determined using E-77-2b & E-77-2 3-day diurnal speciation data, tested with 7psi E10

fuel. Appendix 1 contains a spreadsheet detailing this calculation and shows the exact data which was used.

ra (FID response factor to ethanol) values in Table 1 originate from ARB FID data, with an average value of .69. This data set is shown in 

Appendix 2.

The percent difference equation obtained above can be applied as follows to create an emissions mass adjustment factor for ethanol

(EMAF) for vehicles tested with a fuel with similar characteristics to the E10 fuel used in the development of this factor. EMAF can be 

multiplied by the FID response only mass emissions to account for ethanol mass emissions without separately measuring for ethanol in the 

emissions:

Emissions mass adjustment factor for ethanol = EMAF = 1 +

%diff

100%

EMAF = 1.08, based upon worst case rEtOH (emissions ethanol ratio, HC equivalent) = .26 and average ra (FID response factor to ethanol) = 

.69, and a +.01 (added onto 1.07) compliance margin to account for small sample size.

Edi adjuseed = Edi FID only × EEEE

Edi adjuseed = Edi FID only × 1.08
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Appendix 1: Evaporative Emissions Mass Adjustment Factor (EMAF) Calculation

Evaporative emissions mass:

Vehicle: MY:

Evap 

Standard:

Data 

source:

Vehicle

number:

Mass 

EtOH: 

(mg)

Mass 

EtOH, HC 

Equiv: 

(mg)

Total 

evap 

mass HC: 

(mg)

Mass nonethanol 

HC (mg):

EtOH 

fraction: rEtOH:

EMAF 

w/ ra 

= .77:

EMAF 

w/ ra = 

.56:

EMAF 

w/ ra = 

.69:

Focus 2004

zero 

evap E-77-2b 222b 37.91 23.50 287.6 264.10 0.13 0.09 1.02 1.04 1.03

Ram 

1500 2004 near zero E-77-2b 213b 395.89 245.45 1769.4 1523.95 0.22 0.16 1.03 1.07 1.04

Impala 2004 near zero E-77-2b 210b 189.14 117.27 1192.5 1075.23 0.16 0.11 1.02 1.05 1.03

Camry 2004 near zero E-77-2 211 202.11 125.31 611.9 486.59 0.33 0.26 1.05 1.10 1.07

Taurus 2006 near zero E-77-2 212 101.32 62.82 360.79 297.97 0.28 0.21 1.04 1.08 1.06

ra:

ra is the FID ethanol response 

factor

0.77 max

0.56 min

0.69 avg

EtOH fraction is the mass proportion of ethanol in the total evaporative emissions

rEtOH is the mass of the ethanol component HC equivalent divided by the mass of the non-ethanol HC component in the evaporative 

emissions

Mass EtOH and total evap mass data came from the Coordinating Research Council reports referred to in the "Data source" column above
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1.01

1.02

1.03

1.04

1.05

1.06

1.07

1.08

1.09

1.10

1.11

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

E

M

A

F

EtOH ratio

EMAF: Evaporative Emissions Mass Adjustment Factor for 

Ethanol

ra = .77

ra = .56

ra = .69

Focus

Impala Taurus Near 

Zero

Camry 

Near Zero

EEEE = {1 + (1 − ra) × (reee)

1 + (reee) ra

}

Ram 

1500 

Near 

Zero
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Appendix 2: Ethanol Response Factor (ra) Data From ARB FID Machines

FID EQUIP_ID ETHANOL_ra CALIB_DATE

1 0.6572 1/1/1997

1 0.6572 10/1/1997

1 0.6572 10/1/1998

1 0.6572 6/1/2001

1 0.7556 2/27/2002

1 0.7556 5/27/2002

2 0.734 1/1/2000

2 0.734 4/16/2002

2 0.7398 8/22/2003

3 0.598 1/1/1997

3 0.598 10/1/1997

3 0.598 8/2/2001

3 0.607 5/22/2002

3 0.7598 8/22/2003

4 0.7465 1/1/1997

4 0.7465 10/1/1997

4 0.7465 8/1/2001

4 0.763 7/16/2003

5 0.5591 1/1/1997

5 0.5591 7/1/1997

5 0.5591 10/1/1997

6 0.7591 8/28/2003

7 0.757 5/28/2002

VVT1 0.771668 7/14/2011 Average EtOH ra 0.69

VVT2 0.771881 7/20/2011 Max EtOH ra 0.77

VVT3 0.764846 7/25/2011 Min EtOH ra 0.56