MEMORANDUM

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

FROM: Aron Butler, staff engineer, OAR/OTAQ/ASD

SUBJECT: Summary of recent findings for fuel effects of a 10% ethanol blend on light duty 

exhaust emissions

DATE: January 29, 2010

Background

Section 1506 of the Energy Policy Act of 2005 requires EPA to produce an updated fuel effects 

model representing the 2007 light-duty gasoline fleet, including determination of the emissions 

impacts of increased renewable fuel use. Pursuant to this goal, our office, with support from the 

Department of Energy Office of Energy Efficiency and Renewable Energy, has undertaken a 

study to examine the effects of five fuel properties (ethanol, aromatics, vapor pressure, and two 

distillation parameters: T50 and T90) on exhaust emissions from light-duty vehicles meeting the 

latest federal emission regulations (known as the Tier 2 program). The initial phase was a pilot 

study of the effects of ethanol, done using a typical base conventional gasoline (0% ethanol, or 

E0) and a typical 10% ethanol blend (E10) between May 2008 and January 2009.

This memo specifically addresses effects of E10 relative to E0 on emissions of hydrocarbons (as 

NMHC) and nitrogen oxides (NOx) as suggested by the pilot study. Previous studies had 

suggested E10 blends produced different emission behavior for these pollutants in newer vs. 

older technology vehicles.1 Data from this pilot study provides further such evidence, which we 

feel is sufficient to guide decisions related to inventory modeling.

2

 Other pollutants not covered 

by this memo (such as CO and air toxics) are being modeled assuming similar behavior for 

newer and older vehicles, consistent with recent data.

1,2

The full fuel effects study, involving 31 fuels, is expected to be completed by mid-2010, and its 

results may supersede the findings described here. Emission behavior of other pollutants not 

covered here will be described in reports related to the full study, and in subsequent rulemaking 

actions that use those results.

Methods

The emissions testing used 19 vehicles covering a mix of passenger cars and light trucks,

representing vehicles with high sales volumes. The test vehicle fleet is shown in Table 1. Two 

test fuels were produced containing 0% and 10% ethanol by volume, with other properties being 

 

1

 For more detailed discussion of emissions data sources, see Section 3.1 of the RFS1 RIA, EPA-420-R-07-004, 

available at http://www.epa.gov/otaq/renewablefuels/420r07004chap3.pdf.

2

 For more detailed discussion of inventory modeling for the final rulemaking, see Section 3.1 of the RFS2 RIA, 

EPA-420-R-10-006, available at http://www.epa.gov/otaq/renewablefuels/.
similar to what would typically be found at commercial filling stations. These fuel properties are 

given in Table 2.

The vehicles were tested at 75°F and 50°F using the LA92 test cycle, with each fuel being tested

twice (two replicates). Fuels were tested in ascending order of ethanol blend level. A speed 

versus time trace of the LA92 test cycle is shown in Figure 1. The three phases of the test cycle 

are designed to allow separation of start-up emissions (when the engine and catalyst are 

relatively cold) from fully-warmed-up driving (when operation of emission controls has 

stabilized). For purposes of estimating emission inventories, the phases are typically weighted 

together to form a single, composite emission factor (in grams per mile) to represent average 

driving patterns.

Results

The resulting emissions data were analyzed using a mixed model approach, with the fixed effect 

parameter being ethanol content. Emission measurements were transformed using the natural 

logarithm before input into the model, which is a standard practice in analysis of this type of data

in order to mitigate issues with data variability and skew. Results shown in Table 3 indicate that 

a 10% ethanol blend (E10) did not have a statistically significant effect (at a p = 0.05 level) on 

NMHC or NOx emissions relative to gasoline containing no ethanol (E0) at either test 

temperature. The p-value refers to the significance level of the statistical comparison. In most 

scientific studies of physical phenomena, a result (such as a difference between two treatments) 

is accepted as true or valid only if the significance level is p = 0.05 or less, suggesting relative 

safety from accepting a result which may have occurred only by chance. Since none of the 

emission comparisons evaluated here had p-values at 0.05 or below, we interpret this to mean

there is no difference in emissions between the E0 and E10 fuels.

Figure 3 depicts the data after removal of outliers, with calculated means and 95% confidence

intervals. The confidence interval describes the range in which the true mean of all such 

emission results would fall with 95% likelihood, which gives an indication of the precision of the 

calculated mean value shown.
Table 1. Test vehicle fleet summary.

MAKE BRAND MODEL (all 2008 model year) ENGINE

Chrysler Dodge Caliber 2.4L I4

Chrysler Dodge/Chrysler Caravan/Town&Country 3.3L V6

Chrysler Jeep Liberty 3.7L V6

Ford Ford Focus 2.0L I4

Ford Ford 500/Taurus/Freestyle 3.0L V6

Ford Ford F150 5.4L V6

Ford Ford/Mercury Explorer/Mountaineer 4.0L V6

GM Buick/GMC/Saturn Enclave/Acadia/Outlook 3.6L V6

GM Chevrolet Cobalt/HHR 2.4L I4

GM Chevrolet Impala 3.5L V6

GM Chevrolet/GMC Avalanche/Silverado 5.3L V8

Honda Honda Civic 1.8L I4

Honda Honda Accord 2.4L I4

Honda Honda Odyssey 3.5L V6

Nissan Nissan Altima 2.5L I4

Toyota Toyota Corolla 1.8L I4

Toyota Toyota Camry 2.4L I4

Toyota Toyota Sienna 3.3L V6

Toyota Toyota Tundra 4.0L V6

Table 2. Test fuel property summary.

E0 E10

Ethanol vol % D5599 <0.1 9.35

T50 °F D86 215 209

T90 °F D86 324 319

RVP psi D5191 9.17 9.05

Aromatics vol % D1319 29.3 22.9

Olefins vol % D1319 6.4 5.7

Benzene vol % D3606 0.48 0.49

Sulfur ppm D5453 23 23

RON - D2699 93.4 93.7

MON - D2700 83.5 84.9

(R+M)/2 - - 88.5 89.3

Parameter Units Method

Test Fuel

Table 3. Summary of Statistical Analysis of Emission Tests.

Emission Test Temperature Percent Difference P-value*

(deg.F) (E10 vs. E0)

NOx (composite result) 50 -12.87 0.64

NOx (composite result) 75 -7.59 0.94

NMHC (composite result) 50 -3.93 0.97

NMHC (composite result) 75 -12.96 0.09

*P-value refers to the significance level of the statistical comparison. In most studies of physical phenomena, a result is 

accepted as true or valid only if the significance level is p = 0.05 or less, suggesting relative safety from accepting a 

result which may have occurred only by chance. We interpret this to mean no significant differences were found, and 

thus no emission difference between E0 and E10 fuels.
Figure 1. LA92 test cycle.

0

10

20

30

40

50

60

70

80

0 200 400 600 800 1000 1200 1400 1600

Time (seconds)

Speed (mph)

Phase 1 

300s 

1.19mi

Phase 2 

1135s 

8.63mi

Phase 3 

300s 

1.19mi

Figure 2. NMHC Composite Means (Blue Dots) and 95% 

Confidence Intervals (Vertical Lines) after outlier removal.

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

50_E0 50_E10 75_E0 75_E10

Temperature (50, 75) and EtOH Level (E0, E10)

g

p

e

r

m

i
Figure 3. NOx Composite Means (Blue Dots) and 95% 

Confidence Intervals (Vertical Lines) after outlier removal.

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

50_E0 50_E10 75_E0 75_E10

Temperature (50, 75) and EtOH Level (E0, E10)

g

p

e

r

m

i