NOTE

DATE: January 8, 2010

SUBJECT: Analysis of Ethanol Evaporative Permeation Effects Update

TO: RFS2 Docket EPA-HQ-OAR-2005-0161

FROM: David Hawkins, Assessment and Standards Division, OTAQ

This memorandum serves as an update to the data analysis of the ethanol effect on evaporative 

permeation.

Ethanol affects evaporative emissions from gasoline vehicles due to the increased volatility of 

Ethanol blends, the increased permeation of fuel vapors through tanks and hoses, and the 

increased vapor emissions due to the lower molecular weight of Ethanol. Each of these effects 

were modeled using the draft MOVES model, which separates permeation emissions from vapor 

venting emissions to allow better accounting for these different processes.

DATA USED

Permeation effects were developed from data available as of June 2009 from CRC E-65, E-65-3, 

E-77, E-77-2, and E-77-2b programs1, which measured evaporative emissions. The E-65 

programs used ten fuel systems that were removed from the vehicles and tested on E0, E5.7 and

E10 fuels. The E-77 programs used full vehicles, tested on E0, E10, and E20. An INNOVA 

sampler in E-77 was used to isolate and subtract refrigerant-134a and Methanol should they

contaminate the fuel permeation measurements. The canister was routed outside of the SHED, to 

ensure that measured emissions within the SHED were solely from permeation, rather than 

canister breakthrough. All of the E-77 vehicles underwent preliminary tests to ensure they did 

not contain any vapor leaks that would confound the results in the SHED. 

 

1

http://www.crcao.org/publications/emissions/index.html (E-77-2 and E-77-2b reports to be available Mid-2010)
Table 1. CRC E-65, E-65-3, E-77, E-77-2, and E-77-2b vehicles

Veh. No. Yr Make Model Evap Standard Program

10 1978 Oldsmobile Cutlass Pre-enhanced E-65

9 1985 Nissan Sentra Pre-enhanced E-65

8 1989 Ford Taurus GL Pre-enhanced E-65

7 1991 Honda Accord LX Pre-enhanced E-65

3 1992 Honda Accord Tier 0 E-77

10 1992 Toyota Camry Tier 0 E-77

6 1993 Chevrolet Caprice Classic Pre-enhanced E-65

5 1995 Ford Ranger Pre-enhanced E-65

9 1995 Plymouth Neon Tier 1 E-77

1 1996 Chevrolet S-10 Tier 1 E-77

6 1996 Chevrolet Cavalier Tier 1 E-77

7 1996 Chevrolet Cavalier Tier 1 E-77

8 1996 Ford Explorer Tier 1 E-77

202 1996 Ford Taurus Tier 1 E-77-2

216 1996 Ford Taurus Tier 1 E-77-2

4 1997 Chrysler Town & Country Pre-enhanced E-65

3 1999 Toyota Corolla ORVR E-65

4 1999 Dodge

Grand Caravan 

SE Tier 0 E-77

204 1999 Honda Accord Tier 1 E-77-2

2 2000 Toyota Tacoma Tier 1 E-77

2 2000 Honda Odyssey Enhanced E-65

220b 2000 Chevrolet Malibu Tier 1 E-77-2b

221b 2000 Mitsubishi Galant ES Tier 1 E-77-2b

1 2001 Toyota Tacoma Enhanced E-65

205 2001 Toyota Corolla Tier 1 E-77-2

207 2001 Dodge Caravan Tier 1 E-77-2

206b 2002 Nissan Altima Tier 2 E-77-2b

208b 2002 Chevrolet Trailblazer Tier 2 E-77-2b

11 2004 Ford Taurus E-65-3

12 2004 Chrysler Sebring E-65-3

211 2004 Toyota Camry LE Near Zero E-77-2

214 2004 Ford Escape Tier 2 E-77-2

215 2004 Toyota High Lander Tier 2 E-77-2

209b 2004 Chrysler Stratus Tier 2 E-77-2b

210b 2004 Chevrolet Impala Near Zero E-77-2b

213b 2004 Dodge Ram 1500 Near Zero E-77-2b

222b 2004 Ford Focus ZX3 Zero Evap E-77-2b

14 2005 Chevrolet Tahoe E-65-3

212 2006 Ford Taurus Near Zero E-77-2

5 2007 Ford Taurus Tier 2 E-77
ANALYSIS

There are several variables considered in determining the appropriate aggregation level for

permeation rate, including four evaporative model year groups defined by MOVES (pre-1977, 

1978-1995, 1996-2003, 2004 and later), two vehicle classes (car/truck), and three Ethanol 

volumes (E0, E5.7, E10). E15 and E20 were not analyzed for the RFS2 rule. Attempts to find 

an effect for each combination of these variable failed to be significant due to the relatively small 

amount of data; P-values of 0.6 or greater were calculated (Significance is generally accepted at 

p-values < 0.05). Data were then aggregated to determine significant effects; cars and trucks 

were aggregated, and E5.7 and E10 fuels are combined into a single “with ethanol” category to 

compare to E0 fuels. Likewise, model year 1996 and later (nominally representing evaporative 

enhanced vehicles) were combined to compare to pre-1996 vehicles. These steps decrease the 

resolution of the results but provide greater significance.

To determine the effect of the ethanol blend, the 65-105-65 F diurnal cycle test results from 

either 24-hour or 72-hour tests are used. The dataset was analyzed using the Mixed procedure in 

SAS 9 (Statistical Analysis System) to ensure significant (p < 0.05) differences between E0 and 

E5.7/E10 for both pre-enhanced and evaporative enhanced vehicles. Calculated p-values are 

<0.0001. The adjustment in MOVES2010 is the percent increase due to Ethanol in the fuel.

RESULTS

Table 2. Increase in emissions due to E5.7/E10 compared to E0 (gasoline)

Tech Group Percent increase 

due to ethanol

Pre-enhanced 66

Enhanced 113.8

Due to the evaporative enhanced phase in from 1996 to 1999 (20/40/90/100%), the two fuel 

adjustments are appropriately weighted for those model years. 

Table 3. Increase in emissions due to E5.7/E10 compared to E0 w/ phase-in (gasoline)

Model years (via 

fuelmygroupid in MOVES)

Percent increase 

due to ethanol

1995 and earlier 66

1996 75.5

19972000 107.1

2001 and later 113.8