COORDINATING RESEARCH COUNCIL, INC. 

3650 MANSELL ROAD·SUITE 140·ALPHARETTA, GA 30022

CRC Report No. E-74b 

EFFECTS OF VAPOR PRESSURE, OXYGEN 

CONTENT, AND TEMPERATURE ON CO 

EXHAUST EMISSIONS 

May 2009 
The Coordinating Research Council, Inc. (CRC) is a non-profit corporation supported by 

the petroleum and automotive equipment industries. CRC operates through the 

committees made up of technical experts from industry and government who voluntarily 

participate. The four main areas of research within CRC are air pollution (atmospheric 

and engineering studies); aviation fuels, lubricants, and equipment performance, heavyduty vehicle fuels, lubricants, and equipment performance (e.g., diesel trucks); and lightduty vehicle fuels, lubricants, and equipment performance (e.g., passenger cars). CRC’s 

function is to provide the mechanism for joint research conducted by the two industries 

that will help in determining the optimum combination of petroleum products and 

automotive equipment. CRC’s work is limited to research that is mutually beneficial to 

the two industries involved, and all information is available to the public. 

CRC makes no warranty expressed or implied on the application of information contained 

in this report. In formulating and approving reports, the appropriate committee of the 

Coordinating Research Council, Inc. has not investigated or considered patents which 

may apply to the subject matter. Prospective users of the report are responsible for 

protecting themselves against liability for infringement of patents. 
Report No. SR2009-05-03

Effects of Vapor Pressure, 

Oxygen Content, and 

Temperature on CO Exhaust 

Emissions 

prepared for:

Coordinating Research Council

May 18, 2009

prepared by: 

Sierra Research, Inc. 

1801 J Street 

Sacramento, California 95811 

(916) 444-6666
Report No. SR2009-05-03 

Effects of Vapor Pressure, Oxygen Content, and Temperature on CO 

Exhaust Emissions

prepared for: 

Coordinating Research Council 

May 18, 2009 

Robert Crawford 

Rincon-Ranch Consulting 

Harold Haskew 

Harold Haskew & Associates 

Jeremy Heiken 

Dennis McClement 

James Lyons 

Sierra Research, Inc. 

1801 J Street 

Sacramento, CA 95811 

(916) 444-6666 
-iEffects of Vapor Pressure, Oxygen Content, and Temperature on CO 

Exhaust Emissions 

Table of Contents

Page

1. Executive Summary ........................................................................................................1

2. Introduction .....................................................................................................................6

3. Test Program ...................................................................................................................7

3.1 Test Vehicles ............................................................................................................7

3.2 Pretest Procedures ..................................................................................................10

3.3 Test Procedures ......................................................................................................10

3.4 Test Fuels ...............................................................................................................12

4. Data Analysis ................................................................................................................16

4.1 Overview of Experimental Design .........................................................................16

4.2 Vehicle Technology Groups ..................................................................................17

4.3 Test Fuels ...............................................................................................................18

4.4 Statistical Analysis Methodology ..........................................................................22

4.5 Analysis of Oxygenate Effects on CO Emissions..................................................23

4.6 Analysis of RVP Effects Between 7 and 9 psi at 75°F ..........................................28

4.7 Analysis of the Effect of Increasing RVP from 9 psi to 13 psi at 75°F .................33

4.8 Analysis of Impact of Increasing RVP from 9 psi to 13 psi at 50°F .....................36

5. STATISTICAL ANALYSIS and Development of Emission CorRection Factors .......42

5.1 Overview ................................................................................................................42

5.2 Methodology ..........................................................................................................42

5.3 Statistical Analysis Results (Primary) ...................................................................47

5.4 Alternative Statistical Analysis ..............................................................................62

5.5 Summary of Correction Factors Based on Primary Analysis ................................75

5.6 Comparison of Adjustment Factors to Those in MOBILE6.2 ...............................81

5.7 Comparison of RVP and Oxygenate Effects to Those of Previous Sierra Study ..85

6. COMPARISON OF MOBILE6.2 AND UPDATED CO ADJUSTMENT 

FACTORS..........................................................................................................................87

6.1 Methodology ..........................................................................................................87

6.2 Results ....................................................................................................................92

Appendix A – Sulfur Removal Protocol Used in Testing 

Appendix B – Additional Vehicle and Test Information and Emissions Data 
-iiList of Figures

Figure Page

Figure ES-1 2010 Winter On-Road CO Emission Inventory for Clark County, 

Nevada as a Function of Oxygenate Level ....................................................................3

Figure ES-2 Effects of Ethanol Content on Composite FTP Emissions in the E-74b 

Project ............................................................................................................................5

Figure 3-1 Fuel Ethanol, Vapor Pressure, and Temperature Combinations Tested .........15

Figure 4-1 Experimental Fuel Formulation for RVP and Oxygen Content ......................20

Figure 4-2 Oxygenate Effect by FTP Phase and Technology for RVP 9 Fuels at 

75°F ..............................................................................................................................27

Figure 4-3 Example of CO Emissions Trends with RVP at 75°F ....................................28

Figure 4-4 7 RVP Effect by FTP Phase and Technology at 75°F Compared to 9 

RVP Fuels ....................................................................................................................31

Figure 4-5 Oxygenate Effect by FTP Phase and Technology for RVP 7 to 9 Fuels 

at 75°F ..........................................................................................................................32

Figure 4-6 Impacts of 13 RVP Fuel by FTP Phase and Vehicle Group at 75°F 

Relative to 9 RVP Fuel ................................................................................................35

Figure 4-7 Oxygenate Effects by FTP Phase and Technology 9 to 13 RVP Fuels at 

75°F ..............................................................................................................................37

Figure 4-8 Effects of 13 RVP Fuel by FTP Phase and Technology at 50°F Relative 

to RVP 9 Fuels .............................................................................................................39

Figure 4-9 Oxygenate Effects by FTP Phase and Technology for 9 to 13 RVP Fuels 

at 50°F ..........................................................................................................................41

Figure 5-1 Group 1, Bag 1 CO Trends .............................................................................76

Figure 5-2 Group 1, Bag 2 CO Trends .............................................................................77

Figure 5-3 Group 1, Bag 3 CO Trends .............................................................................77

Figure 5-4 Group 4, Bag 1 CO Trends .............................................................................78

Figure 5-5 Group 4, Bag 2 CO Trends .............................................................................78

Figure 5-6 Group 4, Bag 3 CO Trends .............................................................................79

Figure 6-1 Las Vegas Typical Winter Day Diurnal Profiles ............................................88

Figure 6-2 Winter On-Road CO Emission Inventory for Clark County, Nevada 9 

RVP Gasoline...............................................................................................................93

Figure 6-3 2010 Winter On-Road CO Emission Inventory for Clark County, 

Nevada as a Function of RVP ......................................................................................94

Figure 6-4 2010 Winter On-Road CO Emission Inventory for Clark County, 

Nevada as a Function of Oxygenate Level ..................................................................94
-iiiList of Tables

Table Page

Table ES-1 Summary of Statistically Significant Relationshipsa Observed Between 

FTP Composite Emissions and Test Variables ..............................................................2

Table 3-1 Test Vehicle Descriptions...................................................................................8

Table 3-2 Test Vehicle Emission Certification Classes ......................................................9

Table 3-3 Original Fuel Blending Targets ........................................................................12

Table 3-4 Fuel Properties (Average from sponsors) .........................................................13

Table 3-5 Additional Fuel Properties (from Haltermann) ................................................14

Table 4-1 Average Emission Rates by Technology Group (g/mile)..................................18

Table 4-2 Effect of Fuel Oxygen Content on CO Emissions ............................................25

Table 4-3 Effect of Low Gasoline RVP on CO Emissions ...............................................29

Table 4-4 Effect of High Gasoline RVP on CO Emissions ..............................................34

Table 4-5 Effect of High Gasoline RVP on CO Emissions ..............................................38

Table 5-1 Model Summary for CO FTP Composite .........................................................50

Table 5-2 Model Summary for CO FTP Bag 1.................................................................51

Table 5-3 Model Summary for CO FTP Bag 2.................................................................52

Table 5-4 Model Summary for CO FTP Bag 3.................................................................53

Table 5-5 Model Summary for THC FTP Composite ......................................................54

Table 5-6 Model Summary for THC FTP Bag 1 ..............................................................55

Table 5-7 Model Summary for THC FTP Bag 2 ..............................................................56

Table 5-8 Model Summary for THC FTP Bag 3 ..............................................................57

Table 5-9 Model Summary for NOx FTP Composite ......................................................58

Table 5-10 Model Summary for NOx FTP Bag 1 ............................................................59

Table 5-11 Model Summary for NOx FTP Bag 2 ............................................................60

Table 5-12 Model Summary for NOx FTP Bag 3 ............................................................61

Table 5-13 Alternative Model for CO FTP Composite ....................................................63

Table 5-14 Alternative Model for CO FTP Bag 1 ............................................................64

Table 5-15 Alternative Model for CO FTP Bag 2 ............................................................65

Table 5-16 Alternative Model for CO FTP Bag 3 ............................................................66

Table 5-17 Alternative Model for HC FTP Composite ....................................................67

Table 5-18 Alternative Model for HC FTP Bag 1 ............................................................68

Table 5-19 Alternative Model for HC FTP Bag 2 ............................................................69

Table 5-20 Alternative Model for HC FTP Bag 3 ............................................................70

Table 5-21 Alternative Model for NOx FTP Composite ..................................................71

Table 5-22 Alternative Model for NOx FTP Bag 1 ..........................................................72

Table 5-23 Alternative Model for NOx FTP Bag 2 ..........................................................73
-ivTable 5-24 Alternative Model for NOx FTP Bag 3 ..........................................................74

Table 5-25 Correction Factor Coefficients for FTP CO Emissions ...................................75

Table 5-26 Estimated Effects of Design Variables on FTP CO Emissions 

(Compared to Design Variable Conditions Stated, Percent) .......................................75

Table 5-27 Correction Factor Coefficients for FTP THC Emissions ...............................79

Table 5-28 Estimated Effects of Design Variables on FTP THC Emissions ....................80

Table 5-29 Correction Factor Coefficients for FTP NOx Emissions ................................81

Table 5-30 Estimated Effects of Design Variables on FTP NOx Emissions ....................81

Table 5-31 Comparison of CO Adjustment Factors to MOBILE6.2 Factors ...................82

Table 5-32 Comparison of THC Adjustment Factors to MOBILE6.2 Factors.................83

Table 5-33 Comparison of NOx Adjustment Factors to MOBILE6.2 Factors .................84

Table 5-34 Comparison of RVP and Temperature Adjustment Equation 

Coefficients for FTP Composite Exhaust CO Emissions ............................................86

Table 5-35 Estimated Impact of Reducing RVP from 11.7 to 9.0 psi on FTP 

Composite CO Emissions ............................................................................................86

Table 6-1 Wintertime Gasoline Fuel Requirements for Clark County .............................89

Table 6-2 Winter 2006 Gasoline Parameters ...................................................................89

Table 6-3 Comparison of Las Vegas Winter On-Road CO Inventory Based on 

MOBILE6.2 and Updated Adjustment Factors (tons per day) ....................................93

Table 6-4 Comparison of E-74b and MOBILE6.2 Emission Rates FTP Composite 

CO Exhaust Emissions at Standard Conditions (grams per mile) ...............................96
-1- 

1. EXECUTIVE SUMMARY 

In response to the Clean Air Act Amendments of 1990, both Phoenix, Arizona and Las 

Vegas, Nevada areas were designated as being in nonattainment with the National 

Ambient Air Quality Standard (NAAQS) for carbon monoxide (CO). Both areas 

implemented regulations requiring winter gasolines to contain 3.5 percent oxygen by 

weight and limiting Reid Vapor Pressure (RVP) to 9 psi in order to reduce CO emissions 

from on-road motor vehicles. However, the regulations also created fuel property 

requirements that differed from those in place throughout the rest of the southwest, 

including California, and this tended to reduce the flexibility of the fuel supply and 

distribution system to provide gasoline in Phoenix and Las Vegas during the winter. 

Despite the fact that ambient CO concentrations have not exceeded the NAAQS in either 

area for a number of years, both areas continue to enforce these fuel regulations. One 

reason why the regulations remain in place is that the U.S. Environmental Protection 

Agency (EPA)’s MOBILE6.2 emission factor model predicts that the elimination of the 

oxygenate requirements and RVP restrictions will result in large increases in CO 

emissions from on-road mobile sources. 

In 2003, Sierra Research (Sierra) reviewed the adjustment methodology used in 

MOBILE6, a predecessor to MOBILE6.2, to account for the impacts of oxygenate and 

RVP on CO emissions under winter conditions.*

 Sierra found that the oxygenate 

adjustment methodology had been recently updated using data from 1988 and later 

model-year vehicles certified to Tier 1 exhaust emission standards and concluded that it 

was reasonable. In contrast, Sierra found that the RVP methodology was originally 

developed for use in the now outdated MOBILE4 and MOBILE5 models using data 

acquired from early 1980s model-year vehicles and that it appeared to overpredict the 

increase in CO emissions associated with an increase in RVP relative to alternative 

correction factors developed by Sierra that included more recent data. The oxygenate and 

RVP adjustment methodologies that Sierra reviewed in MOBILE6 have been carried over 

by U.S. EPA into MOBILE6.2. 

Since the last time either the U.S. EPA oxygenate and RVP adjustment methodologies 

were revisited by the agency and Sierra’s 2003 study, vehicles certified to much more 

stringent exhaust and evaporative emission control standards have entered the fleet in 

large numbers and their populations will continue to expand. Given this, and the fact that 

the U.S. EPA methodologies generally rely on data from older vehicles, the Coordinating 

Research Council (referred to here as Sponsors) funded the E-74b vehicle testing 

 

*

Heirigs, P.L., and Lyons, J.M, “Review of Current and Future CO Emissions from On-Road Vehicles in 

Selected Western Areas,” Sierra Research Report No. SR03-01-01, January 28, 2003. 
-2- 

program. The E-74b program was designed primarily to evaluate the effects of RVP and 

oxygenate content on exhaust CO emissions under conditions similar to those found in 

the Phoenix and Las Vegas areas during the winter on recent model-year vehicles. 

Therefore, test vehicles selected for the E-74b program were certified to Tier 1 and more 

stringent exhaust emission standards and both enhanced and so-called “zero” evaporative 

emissions standards. Similarly, the test fuel matrix included fuels with RVP levels 

varying from 9 to 13.3 psi and oxygenate content ranging from zero to 3.5 weight 

percent, and emissions testing was performed at both 75°F and 50°F. In addition to the 

RVP and oxygenate matrix, an E20 test fuel was included in the test fuel matrix to 

examine the emission effects of increasing gasoline ethanol content beyond the current 

E10 limit. 

A complete statistical analysis of the vehicle emissions and fuel property data was 

conducted. The results of this analysis revealed statistically significant relationships 

between test variables and CO, THC, and NOx emissions. These relationships are 

summarized in Table ES-1 in terms of the directional change in the test variable and the 

directional impact on emissions. Note that the same directional changes in primary test 

variables are also applicable to the four combinations of test variables. 

Table ES-1 

Summary of Statistically Significant Relationshipsa

 Observed Between FTP 

Composite Emissions and Test Variables 

Variables CO THC NOx 

Temperature (decreasing from 75°F) +b + + 

Oxygen Content (increasing from 0 wt%) -c - + 

RVP (increasing from 9 psi) + + 

Temperature and Oxygen Content + 

RVP and Oxygen Content 

RVP and Temperature - 

Oxygen Content Squared + a

At 95% or greater confidence level. 

b

+ Indicates increasing emissions. 

c

- Indicates decreasing emissions. 

Based on the results of the statistical analysis, updated adjustments for RVP, oxygenate 

and temperature impacts under moderate winter conditions were developed from the 

E-74b data. These updated adjustments were substituted for those used in MOBILE6.2, 

and the impacts of this substitution were evaluated on the wintertime CO inventory for 
-3- 

the Las Vegas area.* The results of this evaluation indicate that, for late-model vehicles 

operating under wintertime conditions, MOBILE6.2 currently: 

1. Overestimates CO emissions; 

2. Underestimates the impact of increasing oxygenate content in reducing CO 

emissions; and 

3. Overestimates the impact of increasing RVP in increasing CO emissions. 

The magnitude of the differences between the current MOBILE6.2 adjustments and those 

developed based on the data collected in this project can be seen in Figure ES-1. 

Figure ES-1 

2010 Winter On-Road CO Emission Inventory for Clark County, Nevada as a 

Function of Oxygenate Level 

200

250

300

350

400

450

500

550

600

650

700

200

250

300

350

400

450

500

550

600

650

700

0 2.7 3.5 0 2.7 3.5

CO TPDCO TPD

% OXYGEN                                            % OXYGEN

2010 MOBILE 6.2                  2010Updated Adjustments

9 RVP

11.7 RVP

13.3 RVP

 

*

The Las Vegas area was selected for this comparison for several reasons. First, it, along with the Phoenix, 

Arizona area, represents one of the two major urban areas where regulations requiring winter gasoline to 

contain 3.5 percent oxygen by weight and limiting RVP to 9 psi were implemented in order to reduce CO 

emissions from on-road vehicles. Next, because limited project resources precluded comparisons in both 

areas, it was selected over Phoenix due to the availability of the emission inventory data required to 

perform the comparison. 
-4- 

Figure ES-1 shows the 2010 winter CO emission inventory for Clark County (Las 

Vegas), Nevada as a function of RVP and fuel oxygen content estimated using 

MOBILE6.2 with the existing oxygen, RVP and temperature adjustment factors and 

those developed under this study. The general overestimation of CO emissions by 

MOBILE6.2 relative to the results of this study can be seen by the displacement of the 

constant RVP lines on the right and left sides of the figure. Most notably, with the 

updated adjustment factors, even the highest estimated CO emissions under the 13.3 RVP 

and no oxygen case are lower than those estimated by MOBILE6.2 for the lowest CO 

emissions case at 9 RVP and 3.7 weight percent oxygen. 

Next, as can be seen by the space between the constant RVP lines, for an RVP increase 

from 9 to 13.3 psi the updated adjustment factors predict an increase in CO emissions of 

about 15%, which is less than one-half of the 35% increase currently predicted by 

MOBILE6.2. Finally, as can also be seen from the slopes of the constant RVP lines as 

oxygenate content is increased, the updated adjustment factors predict a much greater 

reduction in CO emissions with increasing oxygenate content than that currently 

predicted by MOBILE6.2. Moving from 9 RVP and no oxygen to 9 RVP and 3.5 percent 

oxygen by weight, the updated adjustments show about a 23% reduction in the CO 

inventory. Using MOBILE6.2, this same change in oxygen content would be estimated 

to reduce the CO inventory by only about 8%. Overall, the results of this study show that 

(1) CO emissions in Las Vegas are considerably lower than estimated by MOBILE6.2; 

(2) removal of the RVP limit in Las Vegas would have a smaller effect in terms of the 

percentage increase in CO emissions than predicted by MOBILE6.2; and (3) elimination 

of the winter oxygenate requirements in Las Vegas would have a larger effect, again in 

terms of the percentage increase in CO emissions, than predicted by MOBILE6.2. 

Although CO emissions in the Phoenix area were not explicitly evaluated, similar 

findings would be made using the updated adjustments developed from the E-74b data. 

As noted above, in addition to allowing for the evaluation of the RVP and oxygen 

adjustment factors under winter conditions in the Las Vegas and Phoenix areas, the data 

collected during the E-74b test program provide insight with respect to another important 

question—the effect of increasing the ethanol content of gasoline above 10% by volume 

on exhaust emissions. This was possible because of the inclusion of an E20 test fuel in 

the test fuel matrix. However, the results may be confounded to some degree because of 

variation in the distillation properties of the E20 test fuel relative to the other test fuels in 

the project. 

Figure ES-2 shows the estimated change in exhaust emissions of total hydrocarbons 

(THC), CO, and oxides of nitrogen (NOx) as a function of oxygen content at 75°F and 9 

RVP. As shown in the figure, analysis of emissions data from the late-model vehicles 

tested in the E-74b project indicates that increasing ethanol (and therefore oxygen) 

content leads to reduced exhaust emissions of THC and CO and increased emissions of 

NOx. For THC and NOx, the relationships between changes in emissions and ethanol 

content found in the E74b data are linear. In contrast, for CO the relationship is nonlinear, with diminishing changes in CO emissions resulting from increasing the amount 

of ethanol added. 
-5- 

Figure ES-2 

Effects of Ethanol Content on Composite FTP Emissions in the E-74b Project 

### 
-6- 

2. INTRODUCTION 

The effects caused by changes in gasoline RVP and oxygen content on exhaust emissions 

have been of concern for quite some time and adjustments to account for these effects 

were incorporated into the U.S. EPA’s MOBILE series of emission factor models during 

the 1980s and 1990s. In general, the MOBILE adjustments for RVP and oxygenate 

effects are based on older model-year vehicles and have not been updated with data 

obtained from newer model-year vehicles certified to more stringent exhaust and 

evaporative emissions standards. As a consequence of these MOBILE adjustments, 

Phoenix, Arizona and Las Vegas, Nevada areas implemented regulations requiring winter 

gasolines to contain 3.5 percent oxygen by weight and limiting Reid Vapor Pressure to 9 

psi in order to reduce CO emissions from on-road motor vehicles. As noted previously, 

these regulations also created fuel property requirements that differed from those in place 

throughout the rest of the southwest, including California, and this tended to reduce the 

flexibility of the fuel supply and distribution system to provide gasoline in Phoenix and 

Las Vegas during the winter. 

 

Given the above, the Coordinating Research Council (referred to here as Sponsors) 

funded the E-74b vehicle testing program designed primarily to evaluate the effects of 

RVP and oxygenate content on exhaust CO emissions under conditions similar to those 

experienced in the Las Vegas and Phoenix areas during winter months. Given their 

prevalence in the in-use vehicle fleet, this testing focused on recent model-year vehicles 

certified to Tier 1 and more stringent exhaust emission standards and both enhanced and 

so-called “zero” evaporative emissions standards. This project involved vehicle testing, a 

complete statistical analysis of the data, and the development of updated adjustment 

factors for RVP and oxygenate effects on exhaust emissions. In addition, because an E20 

fuel was added to the test fuel matrix, the results of the E-74b project provide insight into 

the exhaust emission impacts that would be associated with an increase in the allowable 

ethanol content of gasoline beyond the current limit of ten percent by volume. 

The subsequent sections of this report describe the test program, data analysis, statistical 

analysis and development of adjustments, and evaluation of the updated RVP and 

oxygenate adjustments on the wintertime CO emission inventory in the Las Vegas area. 

The catalyst sulfur removal protocol used in the project is presented in Appendix A and 

all vehicle test data collected during the project are presented in Appendix B. Finally, an 

assessment of test-to-test variability in the E-74b project is presented in Appendix C. 

### 
-7- 

3. TEST PROGRAM 

3.1 Test Vehicles

Detailed vehicle fleet specifications were provided by the sponsors of the E-74b program. 

The vehicle definition included make, model year, engine size, and exhaust and 

evaporative emission certification classes. The vehicles tested exactly met the requested 

vehicle specifications. 

Test vehicles were purchased from local Arizona dealers and private parties specifically 

for use in this program. They were selected to include representative high sales volume 

samples based on emission control system/manufacturer/engine size categories. 

Accumulated odometer mileages were appropriate for the model year procured, ranging 

from 28,000 miles to 104,000 miles. The vehicle model years ranged from 1994 to 2006. 

A detailed under hood visual inspection was performed prior to purchase. Vehicles that 

had been modified, or that showed signs of extensive damage and repair, were not to be 

procured. In particular, the catalytic converter and engine emission control systems were 

inspected to ensure they were intact, and that their apparent age and condition were 

appropriate for the candidate vehicle. The operation of the vehicle’s brakes and 

transmission was verified to ensure testability. Table 3-1 describes the test vehicles in 

the program. Table 3-2 provides additional detail regarding the certification standards 

applicable to the test vehicles selected. 

As shown in Table 3-2, the test vehicles were certified to either federal Tier 1, National 

Low Emission Vehicle (NLEV), or Tier 2 exhaust emission standards. In addition, most 

of the vehicles were certified as being in compliance with the federal Cold Temperature 

CO requirements. With respect to evaporative emissions, test vehicles were certified to 

either the pre-enhanced (e.g., one-hour diurnal), enhanced, or near-zero emission 

standards. 
-8- 

Table 3-1 

Test Vehicle Descriptions 

Veh No MY Make Model Type Trans Displacement (l) Odometer Ta

001 1994 Chevrolet Lumina PC Auto 3.1 81,512 002 1996 Ford Taurus PC Auto 3.0 86,538 003 1995 Jeep Cherokee LDT Man/5 4.0 98,668 004 1999 Honda Accord PC Auto 2.3 100,414 005 2001 Toyota Corolla PC Auto 1.8 92,047 006 2002 Nissan Altima PC Auto 2.5 104,712 007 2001 Dodge Caravan LDT Auto 3.3 92,740 008 2002 Chevrolet Trail Blazer LDT Auto 4.2 58,618 009 2004 Dodge Stratus PC Auto 2.4 63,184 010 2004 Chevrolet Impala PC Auto 3.4 57,604 011 2004 Toyota Camry PC Auto 3.0 42,592 012 2006 Ford Taurus PC Auto 3.0 28,354 013 2004 Dodge Ram 1500 SLT LDT Auto 4.7 96,119 014 2004 Ford Escape LDT Auto 3.0 40,188 015 2004 Toyota Highlander LDT Auto 3.3 88,693 
-9- 

Table 3-2 

Test Vehicle Emission Certification Classes 

Veh No Model Year Make Exhaust Standard 

Standards a 

(g/mile) 

Cold CO Standards 

(g/mile) E

001 1994 Chevrolet Tier 1 LDV .31/4.2/.6 N/A 002 1996 Ford Tier 1 LDV .31/4.2/.7 10.0 003 1995 Jeep Tier 1 LDT2 .40/5.5/0.97 N/A 004 1999 Honda NLEV LEV .09/4.2/.3 10.0 E005 2001 Toyota NLEV LEV .09/4.2/.3 10.0 E006 2002 Nissan NLEV ULEV .055/2.1/.3 10.0 E007 2001 Dodge NLEV LEV LDT2 .13/5.5/.5 12.5 E008 2002 Chevrolet NLEV LEV LDT2 .13/5.5/.5 12.5 E009 2004 Dodge Tier 2 Bin 5 .09/4.2/.07 10.0 E010 2004 Chevrolet Tier 2 Bin 5 .09/4.2/.07 10.0 E011 2004 Toyota Tier 2 Bin 9 .09/4.2/.30 10.0 N012 2006 Ford Tier 2 Bin 5 .09/4.2/.07 10.0 N013 2004 Dodge Tier 2 Bin 10 LDT .23/6.4/.60 12.5 E014 2004 Ford Tier 2 Bin 9 .09/4.2/.30 10.0 N015 2004 Toyota Tier 2 Bin 5 .09/4.2/.07 10.0 N

a Standards are given as NMHC/CO/NOx 
-10- 

3.2 Pretest Procedures

All exhaust emission testing in this project was performed using the U.S. EPA’s standard 

“Federal Test Procedure” (FTP). An FTP exhaust emission test was performed to assess 

vehicle condition upon arrival at the testing laboratory. The results were reviewed with 

Harold Haskew and Associates before continuing. The in-use compliance of the vehicles 

with their very stringent certification standards was notable. No emissions-related repairs 

were required prior to testing. 

The fuel tank temperatures encountered during vehicle operation strongly influence the 

rate of fuel vapor generation. Emission testing is performed on a chassis dynamometer. 

Left uncontrolled, fuel tank temperatures occurring during dynamometer operation can be 

unrepresentatively high or low. Exhaust emission CO levels encountered with Tier 0 

vehicles were believed to be influenced by fuel vapors purged by the engine from the 

evaporative emission control canister. The temperature of the gasoline during FTP 

testing in this program was therefore monitored and controlled. 

An on-road fuel tank temperature profile appropriate for FTP testing at 50° and 75°F was 

measured. Each test vehicle was instrumented with external fuel tank thermocouples, 

drained and filled to 40% tank capacity, preconditioned with one LA4 road equivalent, 

and soaked overnight. The vehicle was then operated on the road through the equivalent 

of the dynamometer FTP cycle while fuel tank temperatures were monitored. These 

temperature data were used to develop fuel temperature targets for use during 

dynamometer emission testing. 

A special preconditioning cycle was performed before the first test fuel cycle to minimize 

the effect of residual catalyst sulfur deposits resulting from operation with uncontrolled 

commercial fuels. A description of the sulfur preconditioning is provided in Appendix A. 

Individual random test orders were created for each vehicle prior to the start of testing. 

The various combinations of fuel RVP, ethanol level, and ambient temperatures were 

performed in the predetermined order. The detailed test results, provided in Appendix B, 

include the run number for the individual tests. 

3.3 Test Procedures

Vehicles received extensive preconditioning prior to each test. The preconditioning 

served to normalize both the exhaust emission control adaptive learning function and fuel 

carryover effects in the evaporative emission control charcoal canister. 

Vehicle preconditioning began with canister normalization. The canister received a 300 

bed volume purge with room air at a nominal flow rate of 0.4 cfm. The vehicle 

evaporative service port (or a tee installed for the purpose) was used for the purge. One 

liter of the fuel type to be used for the emission test was then placed in a sealed container. 

The container was mounted on a laboratory digital scale. Nitrogen was bubbled through 
-11- 

the fuel, and the saturated vapor was directed to the service port and canister of the 

vehicle being tested. Canister loading continued until the weight of the fuel sample had 

been reduced by an amount equal to 25% of the vehicle canister capacity. For example, a 

canister with a 120-gram working capacity was loaded with 30 grams of fuel vapor. The 

rate of nitrogen flow was controlled to maintain a nominal rate of fuel weight change of 

40 grams/hour. Rates were adjusted to maintain a purge/load cycle within a two-hour 

limit. 

The vehicle was then drained and refueled with as-received tank fuel to 40% capacity 

with the fuel specified for the upcoming test. The vehicle was operated over three cycles 

of a 7.6-mile road course. The operation included mixed city street and expressway 

driving, with an average speed similar to the dynamometer LA4 cycle used for FTP 

testing. The vehicle was then parked in the laboratory at a nominal temperature of 75°F. 

A final drain and 40% fill with the same fuel was performed. The dynamometer test cell 

and soak area were set at the temperature specified for the upcoming test. The final LA4 

preconditioning was performed and the vehicle was placed in the controlled temperature 

soak area. 

Soak time between the end of the preconditioning and the start of the FTP was 

maintained between 18 and 22 hours. At the end of the soak period, the vehicle was 

transferred to the emission test cell. An FTP test was performed in accordance with new 

vehicle certification procedures. Enhancements included use of an INNOVA analyzer to 

measure ethanol in the exhaust and second-by-second emissions measurements before 

and after the catalytic converter. The cell temperature was set at 50° or 75°F, as specified 

in the randomized testing schedule. Emissions of CO, THC, non-methane hydrocarbons 

(NMHC), NOx, and carbon dioxide (CO2) were measured and reported in grams and 

grams/mile. The ethanol component of the hydrocarbon emissions was handled as 

specified in the California Air Resources Board (CARB) procedures* cited in the federal 

regulations. 

Fuel temperatures were controlled during the final LA4 and FTP tests. The temperature 

rise observed during the initial road test would be applied to the ambient temperatures 

maintained during each test on a vehicle. An 8°F fuel temperature rise observed during 

the initial road LA4 would translate to a rise from 50° to 58°F during a 50°F 

dynamometer test. Under-vehicle air flow was adjusted to maintain the fuel temperature 

profile observed during road operation. 

Data from each preconditioning and test series were carefully reviewed for completeness 

and conformance to all quality specifications. The test vehicle would be scheduled for 

the next randomly selected test in the series following test acceptance. 

 

*

California Non-Methane Organic Gas Test Procedures, July 12, 1991, amended July 30, 2002, California 

Air Resources Board, Monitoring and Laboratory Division. 

http://www.arb.ca.gov/msprog/levprog/cleandoc/clean_nmogtps_final.pdf
-12- 

3.4 Test Fuels

The test fuels were specifically prepared for this program. The RVP of the finished fuels 

was targeted at levels of 7.0, 9.0, and 13.0 psi. Ethanol contents of E0, E10, and E20 

were specified. The base stocks for the E10 and E20 fuels were intended to yield 

appropriate RVP and other properties following addition of the ethanol. 

The fuels were prepared by Haltermann Products of Channelview, Texas. The average 

inspection properties of winter-grade conventional gasoline blended with ethanol, as 

reported in the 2002-2003 Northrop Grumman (formally NIPER) gasoline survey,* were 

supplied as targets. Table 3-3 displays the survey results. Initially only two batches of 

fuel were to be tested, and all properties, except RVP, were to be “closely matched.” 

Both fuels were to contain 10% ethanol. The program was later expanded to include 

seven different combinations of fuel RVP and ethanol content. As a result, the fuel 

properties at the highest RVP and highest ethanol contents were no longer as “close” as 

those of the lower RVP and ethanol fuels. 

The fuels were to be blended from standard refinery streams. Samples of the finished 

fuels were analyzed by several of the test sponsors. Table 3-4 displays the results of the 

analyses performed by the sponsors. Table 3-5 displays additional analysis performed by 

the fuel blender. 

Table 3-3 

Original Fuel Blending Targets 

Property Limits Test Method 

Gravity, °API Report ASTM D 287 

DVPE 9.0, 13.0 ASTM D 5191 

T10 Varies w/DVPE ASTM D 86 

T50 158-168 F ASTM D 86 

T90 315-325 F ASTM D 86 

FBP < 437 F ASTM D 86 

RON 91-95 ASTM D 2699 

MON 83-87 ASTM D 2700 

(R+M)/2 87-91 

Aromatics 21-25 vol% ASTM D 1319 (Vol %), or D 5580 (Wt %) 

Benzene 0.9-1.1 vol % ASTM D 5580 or D 3606 

Olefins 7-11 vol% ASTM D 1319 (Vol %), or D 6550 (Wt %) 

Sulfur 25-30 ppm ASTM D 2622 

Ethanol 10 vol% ASTM D 4815 

 

*

“Motor Gasolines, Winter 2002-03,” Cheryl Dickson, August 2003, Northrop Grumman, Bartlesville, OK, 

NGMS-230 PPS 2003/3 
-13- 

Table 3-4 

Fuel Properties (Average from sponsors) 

Inspection Units Fuel 6 Fuel 3 Fuel 5 Fuel 7 Fuel 1 Fue

API Gravity °API 60.2 63.3 64.1 58.5 58.8 59Relative Density 60/60°F 0.7381 0.7262 0.7231 0.7447 0.7435 0.73DVPE psi 6.95 9.10 12.76 7.30 8.79 13.Oxygenates--D4815 MTBE vol % 0.00 0.00 0.00 0.00 0.00 0.0ETBE vol % 0.00 0.00 0.00 0.00 0.00 0.0EtOH vol % 0.00 0.00 0.00 9.54 9.42 9.0Oxygen wt % 0.00 0.00 0.00 3.53 3.49 3.3HC Composition Aromatics vol % 22.1 23.4 24.2 24.4 23.6 22Olefins vol % 8.0 9.6 9.5 8.8 9.6 9.Saturates vol % 70.0 67.1 66.4 57.3 57.5 59D86 Distillation IBP °F 99.9 88.8 82.0 104.0 97.2 8310% °F 142.4 122.4 106.4 133.0 125.1 10750% °F 197.9 191.0 189.1 195.0 189.8 16590% °F 313.6 316.5 316.3 317.0 319.0 322EP °F 361.0 353.7 353.7 360.0 357.2 352Recovery vol % 97.8 97.6 96.6 97.8 97.9 96Residue vol % 1.3 1.6 1.3 1.0 1.1 1.Loss vol % 1.0 0.8 2.1 1.2 1.0 1.Drivability Index - 1120.7 1073.2 1043.2 1101.5 1075.9 979
-14- 

Table 3-5 

Additional Fuel Properties (from Haltermann) 

Inspection Units Fuel 6 Fuel 3 Fuel 5 Fuel 7 Fuel 1 Fue

DVPE psi 6.95 9.10 12.76 7.30 8.79 13.EtOH vol % 0.00 0.00 0.00 9.54 9.42 9.0Sulfur Content ppm 29 28 26 27 29 27 Benzene vol % 0.90 1.00 1.00 1.00 1.00 0.9Research Octane Number 93.2 94.4 94.6 94.0 92.9 94 Motor Octane Number 83.8 84.5 83.5 83.8 84.1 83(R+M)/2 88.5 89.5 89.0 88.9 88.5 88Benzene vol % 0.89 1.05 1.05 1.06 1.10 0.9C/H Ratio 6.200 6.196 6.170 6.092 6.106 6.1Net Heat of Combustion btu/lb 18,703 18,733 18,758 18,016 17,973 18,0Oxygen wt. % 0.008 0 0 3.396 3.609 3.4C+H wt. % 99.99 100.00 100.00 96.60 96.39 96.H wt. % 13.89 13.90 13.95 13.62 13.56 13.C wt. % 86.10 86.10 86.05 82.98 82.83 83.Net Heat of Combustion D3338 Btu/lb 18,573 18,592 18,580 18,514 18,516 18,5
-15- 

Fuels were produced at three vapor pressure levels (7.0, 9.0, and 13.0 psi) with three 

levels of ethanol (0%, 10%, and 20%). The E0 and E10 fuels were produced at all three 

vapor pressure levels. The E20 fuel was produced only at the 9.0 psi level. 

Tests were performed at two temperatures (50° and 75°F) with each of the 9.0 psi and 

13.0 psi fuels. The 7.0 psi fuels were tested only at 75°F. Figure 3-1 summarizes the 

combinations included in the test program. 

Figure 3-1 

Fuel Ethanol, Vapor Pressure, and Temperature Combinations Tested 

### 

50°F

75°F

E0 E10 E20

7.0 psi

9.0 psi

13.0 psi

R

V

P

Temperature

Ethanol
-16- 

4. DATA ANALYSIS 

4.1 Overview of Experimental Design

As was shown in Figure 3-1, the test program included 12 combinations of RVP (3 

levels), ethanol content (3 levels), and ambient temperature (2 levels). The design is 

unbalanced because only 12 of the possible 18 combinations of three variables were 

tested. 

To obtain the greatest insight into the effects of RVP, oxygenate, and ambient 

temperature, the analysis in this section considers the dataset as if it involved the four 

individual experiments outlined below. 

 An experiment on the effect of oxygenate (ethanol content) conducted at a 

temperature of 75°F and at RVP 9. This experiment consists of the three test 

points E0, E10, and E20 in the background plane of the experimental matrix 

shown in Figure 3-1 at RVP 9. The emissions effect of varying oxygenate levels 

can be directly observed in this subset of the program test data. 

 An experiment on the effect of low RVP at FTP conditions of 75°F. This 

experiment consists of the five test points in the background plane spanning E0, 

E10, and E20, and RVP 7 and 9 fuels. This experiment combines the effect of 

RVP 7 fuel (compared to a baseline of RVP 9 fuel), with two non-zero levels of 

oxygenate. As a result, the oxygenate effect must be controlled for in order to 

observe the emissions effect of low RVP fuel. 

 An experiment on the effects of high RVP at FTP conditions of 75°F. This 

experiment consists of the five data points in the background plane spanning E0, 

E10, and E20, and RVP 9 and 13 fuels. Because this experiment also combines 

oxygenate with RVP effects, statistical controls must be employed to observe the 

emissions effect of high RVP fuel. 

 A final experiment on the effects of high RVP at an ambient temperature of 50°F. 

This experiment consists of the five data points in the foreground plane spanning 

E0, E10, and E20, and RVP 9 and 13 fuels. After appropriate controls for the 

effect of oxygenate at low temperature, the effect of RVP at lower ambient 

temperatures can be observed in this experiment. 
-17- 

The benefit of this approach is that the major trends in the data can be easily seen and 

understood without relying on complex statistical models to infer the trends. In addition, 

the only variable for which statistical control is required is that of added oxygen content 

in the experiments dealing with RVP effects. This control can be easily implemented in 

simple statistical models that are unlikely to risk misfitting the data. The results of the 

individual analyses are then combined in Section 5 in a complete statistical analysis of 

the data and the estimation of correction factor equations for use in the MOBILE model. 

4.2 Vehicle Technology Groups

The first step in the data analysis involved dividing the test vehicles into four groups 

based on the sophistication of their emission control technology: 

1. Group 1 – Test vehicles No. 1, No. 2, and No. 3. This group includes the oldest 

vehicles, certified to Tier 1 exhaust emission standards. Two of the vehicles 

(Nos. 1 and 3) were not certified to enhanced evaporative emission or to cold CO 

standards. 

2. Group 2 – Test vehicles No. 4 through No. 8. These vehicles were certified to 

NLEV exhaust emission, enhanced evaporative emission, and cold CO standards. 

3. Group 3 – Test vehicles Nos. 9, 10, and 13. This group consists of three vehicles 

certified to Tier 2 exhaust emission, enhanced evaporative emission, and cold CO 

standards. 

4. Group 4 – Test vehicles Nos. 11, 12, 14, and 15. This group consists of four 

vehicles certified to Tier 2 exhaust, near-zero evaporative emission, and cold CO 

standards. 

In addition to the above, all of the vehicles in Groups 2 through 4 were equipped with onboard refueling vapor recovery systems. 

The average FTP composite and bag emission rates by technology group are shown in 

Table 4-1. 

Many of the vehicles in Groups 3 and 4 had emission levels, particularly for Bag 3, that 

were reported as zero because they fell below the minimum detectable levels of the 

emission analyzers when recorded to two decimal places. In order to include these data 

in the statistical analysis where logarithmic models were used for the dependent emission 

variable, a de minimus emission level of one-half of the smallest non-zero measurement 

recorded for the pollutant was substituted for zero readings. At such low levels, the 

difference in logarithms of emissions can be subject to large fluctuations due to small 

values in the denominator. Thus, it should come as no surprise that estimating emission 

effects with high statistical confidence is sometimes problematic for these vehicles. 
-18- 

Table 4-1 

Average Emission Rates by Technology Group (g/mile) 

(At 75°F, RVP = 9 psi, E0 fuel) 

Group 1 Group 2 Group 3 Group 4 

NMHC CO NOx NMHC CO NOx NMHC CO NOx NMHC CO NOx 

FTP 0.39 4.88 0.94 0.08 1.31 0.17 0.07 0.68 0.05 0.04 0.23 0.05 

Bag 1 0.89 9.13 1.56 0.27 2.97 0.47 0.22 2.37 0.18 0.14 1.03 0.13 

Bag 2 0.21 1.56 0.56 0.03 0.83 0.05 0.04 0.26 0.01 0.02 0.01 0.03 

Bag 3 0.34 0.89 1.19 0.04 0.96 0.18 0.03 0.19 0.02 0.02 0.06 0.04 

4.3 Test Fuels

As shown previously in Table 3-4, the T50 temperatures for Fuels 2 and 4 differed 

markedly from those of the other test fuels. The other test fuels were controlled to have 

T50 values within the range 189°F to 198°F, while Fuels 2 and 4 had T50 values 24°F 

and 30°F below this range, respectively. Further, review of Summer and Winter Alliance 

of Automobile Manufacturers (AAM) Fuel Survey Data indicated that the T50 values of 

these fuels were substantially lower than the lowest values observed in commercial 

California gasolines. This raised a concern in light of the findings of the CRC E-67 

study* regarding emission impacts associated with T50 itself and with interactions 

between T50 and ethanol content. 

In regard to T50 and ethanol content, the CRC E-67 study observed that ethanol content 

and T50 interacted in such a way that, at high levels of T50 (above 220°F), raising 

ethanol content to high levels was associated with increased CO emissions, an effect not 

seen at lower T50 levels. However, the high T50 level in the CRC E-67 study was well 

above the values in the test fuels for this project. In addition, the CRC E-67 study noted 

the presence of diminishing returns in the overall effect of ethanol content on CO 

emissions, such that the reduction in CO emissions due to oxygenation was primarily 

observed at low to mid levels, with little or no incremental benefit observed at high 

levels. This finding guided the conduct of this analysis and led to the characterization of 

a non-linear oxygenate effect for CO emissions. 

In regard to the representativeness of Fuels 2 and 4, a Principal Components Analysis 

(PCA) was conducted on the fuel property data to gain insight on whether the low T50 

values were anomalies or merely represented blending effects associated with meeting 

the experimental targets for RVP. PCA is a useful tool in many real-world problems 

 

*

Durbin, T.D., et al., “Effects of Ethanol and Volatility Parameters on Exhaust Emissions,” CRC Project 

No. E-67. College of Engineering – Center for Environmental Research and Technology, University of 

California, Riverside. January 2006. 
-19- 

where variables display a high degree of correlation among themselves. When the 

correlations are inherent—i.e., result from the underlying physical reality—PCA can 

yield valuable insight to the causal factors at work in the data. PCA decomposes the 

correlation matrix describing the linear relationships among the variables into 

eigenvectors that represent the distinct patterns by which the variables covary in the data. 

The vectors themselves form an orthogonal basis and provide an independent 

(uncorrelated) set of variables that can be used as an alternative expression of the data. 

What is usually seen in PCA is that most of the variance in the data is explained by a 

small subset of eigenvectors, so that a reduction in the dimensionality of the problem is 

achieved. It is not uncommon for 3 to 5 vector variables to represent 90% or more of the 

variation present in a dataset that contains 10 or more variables. 

In this case, PCA revealed four primary eigenvectors that represent 96% of the variation 

in the fuels. Vectors 1 and 2 represent the blending methods used to form the 

experimental fuels and can be explained as follows: 

 Vector 1 (49% of the variation in fuels): An oxygenation index representing the 

blending of EtOH along with associated effects, including a tendency to increase 

RVP. This blending strategy appears to substitute aromatics and olefins for 

saturates in oxygenated fuels, possibly as a strategy to offset the direct RVP effect 

of added EtOH and to maintain target RVP levels. 

 Vector 2 (27% of the variation in fuels): An RVP index representing the 

reformulation of the base fuel to meet varying RVP targets, including a tendency 

for increased RVP to be associated with lower specific gravities and lower T10 

distillation points. This blending strategy appears to raise RVP primarily by 

selecting lighter components within each of the hydrocarbon classes, so that the 

overall mix of aromatics, olefins, and saturates is relatively unchanged. 

Together, Vector 1 and 2 account for 76% of the total variation in fuels. The two 

additional eigenvectors (Vectors 3 and 4) appear to represent final blending steps taken to 

control research octane number (RON) and motor octane number (MON), respectively, to 

near-constant levels. 

Figure 4-1 diagrams the relationships between RVP and oxygen content in the 

experimental fuels as revealed by PCA. In the figure, each experimental fuel has been 

scored*

 to determine the extent to which it expresses the characteristics described by 

Vectors 1 and 2. A shift in the base RVP level is seen as a movement predominantly up 

and to the right on the formulation diagram, as seen between Fuels 3 and 5. A change in 

 

*

The scoring process is similar to computation of an index value from known properties to assess a 

characteristic in the absence of direct measurement. As an example, Diesel fuel can be scored for cetane 

quality using the ASTM cetane index method as an alternative to the actual measurement of cetane in a test 

engine. 
-20- 

Figure 4-1 

Experimental Fuel Formulation for RVP and Oxygen Content 

Fuel 1:

E10 RVP 9

Fuel 2:

E10 RVP 13

Fuel 3:

E0 RVP 9

Fuel 4: E20 RVP 9

Fuel 5:

E0 RVP 13

Fuel 6:

E0 RVP 7 Fuel 7:

E10 RVP 7

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0

Vector 2 Score: RVP Index

Vector 1 Score: Oxygenation Index

Oxygenation

Oxygenation

Oxygenation

Summer v.

Winter

RVP Change

the oxygenation level is seen as a movement down and predominantly to the right, as 

seen between Fuels 3, 1, and 4.*

In this diagram, neither Fuel 2 (RVP 13) nor Fuel 4 (RVP 9) appears to be anomalous, in 

that each creates nearly parallel fuel reformulation lines representing the blending to 

increase oxygenation. What is distinctive is that Fuels 2 and 4 are the rightmost fuels in 

the diagram, and most strongly express the fuel reformulation represented by Vector 1. 

This vector represents not only fuel oxygen content, but also associated changes in the 

hydrocarbon composition of fuels with resulting effects on specific gravity and the 

distillation curve. Vector 1 is strongly correlated with T50 (r = -0.89), and it should be 

no surprise that Fuels 2 and 4, with the highest Vector 1 scores, have the lowest T50 

values. 

Whether the two fuels in question are fully representative of gasolines in the market, we 

conclude that they are logical outcomes of the blending strategies used to create the 

experimental fuels and should be retained in the analysis. A larger issue is whether the 

T50 effects that occurred in the blending of Fuels 2 and 4 are representative of those 

observed in commercial gasolines at these RVP and oxygenate levels. There is, 

unfortunately, no definitive answer to this question, particularly for E20 blends where 

standardized fuel specifications do not exist. 

 

*

Fuels 6 and 7, which are not of direct concern here as their T50 values do not differ significantly, also 

show that oxygenation leads predominantly to movement down and to the right, while RVP reductions lead 

to movement down and to the left. 
-21- 

The depression of T50 in Fuels 2 and 4 below the range of the other fuels has significant 

consequences for the interpretation of the data generated in this project. If the lower T50 

level of these fuels leads to an emission effect in its own right, then Fuels 2 and 4 

confound that T50 effect to some degree with effects of oxygenate content and RVP. 

Confounding means that two or more variables are correlated to such an extent that it 

becomes difficult or impossible to separate their individual contributions. 

In this dataset, the consequences of confounding are as follows: 

 Fuel 4 is the only test fuel containing more than 10% ethanol. If Fuel 4 were 

removed from the dataset, the analysis would necessarily be restricted to the range 

of E0 to E10. By retaining Fuel 4, the analysis can assess whether the emissions 

effect due to the higher oxygen content is in proportion to that observed at lower 

levels, but it cannot determine whether the result is due to higher oxygen levels or 

to a much lower T50 or to some combination of the two effects.

 Fuel 2 is one of two test fuels at RVP 13 and the only such test fuel that also 

contained oxygen. Removing Fuel 2 from the dataset would leave the analysis 

dependent on only one test fuel for the determination of RVP effects and would 

make it impossible to test whether there was an interaction between increased 

RVP and oxygen content. By retaining Fuel 4, the analysis can test for the 

presence of an interaction between RVP and oxygen content, although it cannot 

determine the extent to which such an interaction is caused by RVP and Oxygen

or by T50 or by a combination of the variables.

In addition, estimates of the effect of RVP itself and in interaction with ambient 

temperature will be partially confounded by emissions effects caused by T50. Such 

partial confounding is termed aliasing and occurs in regression analysis when the 

coefficient estimated for a variable such as RVP is changed in value by the inclusion of 

effects actually caused by another variable (such as T50), which is correlated with the 

predictor but not included in the regression model. The presence of aliasing means that 

the coefficient does not estimate the effect associated with the predictor alone. As a 

result, the coefficient estimate is biased with respect to the true (but unknown) value. 

The depression of T50 values in two of the test fuels poses a major problem in the 

analysis due to the confounding with design effects and the potential for aliasing to 

change estimated coefficient values. 

It was determined that there was no potential for separating the imbedded T50 effect by 

the application of statistical controls. This is because T50 is exactly confounded with the 

high oxygenation level (E20) and with the interaction between RVP and oxygen content 

at the E10 level.*

 Instead, the analysis was conducted twice in order to attempt to assess 

the import of the T50 effects. 

 

*

The confounded terms are the quadratic term in OxPct, which represents the extent to which emissions of 

the E20 fuel differ from what would be expected from extrapolating the E10 effect to E20, and the term 

RVP · OxPct. 
-22- 

 The first (and primary) analysis used data for all of the test fuels and regression 

terms formed from the variables T, RVP, OxPct, and their two-way interactions. 

This analysis contains an embedded T50 effect of the kind introduced by Fuels 2 

and 4 and ascribes those effects to terms involving RVP and OxPct. Its results 

can be used reliably and without bias to the extent that T50 depression is 

generally observed in fuels blended to these RVP and oxygenate levels. 

 A second (sensitivity) analysis in which the two terms that are exactly confounded 

by T50 are dropped from consideration and replaced by a term measuring the T50 

depression below a reference level of 190°F. This analysis contains an explicit 

T50 effect, but it will ascribe to T50 any incremental effects that are related to the 

E20 oxygen level or to the interaction between RVP and oxygen content (at the 

E10 level). Its results serve to bracket quantitatively the limitations of the first 

analysis and of predictions based on it. It may prove possible to use the results of 

this sensitivity analysis to adjust predictions (at least approximately) if T50 

depression does not occur in fuels blended to the RVP and oxygenate levels 

reflected in Fuels 2 and 4. 

4.4 Statistical Analysis Methodology

As discussed above, the test program data can be viewed as a series of experiments in 

which selected fuels and tests examine the response of the test vehicles to changes in fuel 

oxygen content and RVP at test temperatures of 75°F and 50°F. The analyses of these 

individual experiments are presented below. In general, the methodology involved fitting 

simple statistical models to subsets of the data to estimate the effects of oxygenation and 

RVP on CO emissions. Only CO emissions are examined in this stage, because the 

objective of the test program was to evaluate oxygenate, RVP, and temperature effects on 

CO emissions. Questions related to the presence and magnitude of emission effects by 

FTP phase and by vehicle technology group are considered, and estimated emission 

changes are presented in both tabular and graphical form. 

Based on the trends established in these individual analyses, an overall model is 

formulated for emission adjustment factors as a function of ambient temperature, RVP, 

and fuel oxygen content. A complete statistical analysis, including the development of 

the new correction factor equations for CO, NOx, and HC emissions by FTP phase, is 

presented in Section 5. 

The analysis reported here was conducted using the general linear models procedure 

(PROC GLM) of the Statistical Analysis System (SAS) to fit general linear models 

involving temperature, RVP, and oxygen content to exhaust emissions. In some 

instances, an alternative SAS regression package (PROC REG) was used when it was 

desired to produce datasets containing residuals, predicted values, and confidence limits. 

Conventional regression techniques were used to fit and evaluate models in order to test 

the statistical significance of differing formulations and to conduct tests on whether terms 
-23- 

differed significantly by technology group or vehicle type. The logarithm of exhaust 

emissions was used in all cases as the dependent variable. 

Because the purpose of the analysis is to measure the response of vehicles to temperature, 

RVP, and oxygen content, a statistical technique known as absorption was used to 

remove the effect of varying emissions levels by vehicle. This technique is numerically 

equivalent to including dummy variables in the model to represent the mean emission 

levels of N-1 vehicles, but it is generally easier to specify such models using absorption. 

If emissions data on vehicles with varying emission levels are pooled for analysis without 

absorption or the use of dummy variables, the estimated response coefficients will often 

be dominated by the vehicles with the highest emissions levels. That is, in cases where 

the response is proportional to a base emission level, high emission vehicles will tend to 

show large responses and will create an upward bias in the response coefficients that are 

estimated. 

Unlike the fitting of dummy variables, absorption removes the effect of varying emission 

levels by first normalizing all data (both dependent and independent variables) to remove 

the corresponding mean values for each vehicle. That is, log emissions ln(E) is replaced 

by the logarithm of the emissions ratio ln(E/E0) relative to the mean emissions level E0

for the vehicle, ambient temperature is replaced by the deviation of temperature from the 

average temperature for each vehicle, and RVP and oxygen content are similarly replaced 

by their deviations from the mean. As a result, the data are cast in the form of deviations 

from a reference point for each vehicle that has been removed from the data. When the 

resulting normalized data are pooled in the analysis, each vehicle is given equal weight in 

estimating the response coefficients. This choice of reference point (the mean values) is 

mathematically equivalent to any other choice of reference point, such as the vehicle 

emission level at FTP conditions. 

The varying emission levels of the individual vehicles are by far the largest contributor to 

the total variance in the data. PROC GLM counts this contribution to the sum of squares 

reduction in computing the regression R2 statistic, as does PROC REG count the sum of 

squares reduction due to dummy variables for vehicles. As a result, all of the regression 

models fit in this analysis approach or exceed R2 values of 0.90. R2 is at best a simplistic 

measure of goodness-of-fit in regression modeling and, in this case, where all R2 values 

are very high, it is of little utility. As a result, R2 statistics are not reported in the 

discussion of the statistical results. 

4.5 Analysis of Oxygenate Effects on CO Emissions

The starting point for the analysis is the examination of oxygenate effects on CO 

emissions. Tests at FTP conditions of 75°F and RVP 9 on Fuels 3, 1, and 4 (E0, E10, and 

E20, respectively) were selected to isolate the effect of oxygenation from changes in RVP 

or ambient temperature. While the fuels are described by their nominal ethanol content, 

the actual measured oxygen content is used as the independent variable. Values given as 

“percent CO reductions per percent” refer to percent oxygen content. 
-24- 

For reference, the MOBILE6.2 adjustment factors for Tier 1 and later vehicles use these 

values: 

 Normal emitters: no effect from oxygenate. 

 High emitters: -5.3 percent per percent oxygen. 

None of the vehicles in this project would be classified as high emitters (defined as CO 

emissions exceeding 3 times the 50,000 mile CO standard), with Vehicle 2 being closest 

to a high emitter at 2 times the 50,000 mile standard. As a result, the analysis can 

determine the emissions effect of oxygenation for normal emitters only. 

The analysis of oxygenate effects uses a log emissions model to estimate the sensitivity 

of CO emissions to oxygen content by vehicle technology group and FTP test phase. The 

regression model is of the mathematical form: 

 ln[CO · (OxPct)/CO0] = C1 · OxPct (Eq. 4-1) 

where OxPct is the oxygen content stated as a weight percent (not decimal fraction). The 

model assumes a linear response of CO emissions to oxygen content, and CO0 is the CO 

emissions at FTP conditions of 75°F, RVP 9, and E0. The model is fit in log space as a 

simple equation of the form Y = A + B · OxPct, and the reference emissions level CO0 is 

computed from the regression intercept A. 

The results of the analysis are summarized in Table 4-2, which shows the estimated 

coefficient C1, along with standard errors and significance levels, and two measures of 

the oxygenate effect: 

 The estimated reduction in CO emissions at 3.7 percent oxygen content typical of 

E10 gasoline; and 

 The estimated percent change in CO emissions per percent oxygen content. 

Estimates reported with prob>|t| of 0.05 or less are statistically significant at a 95 percent 

confidence level or better, while estimates with prob>|t| in the range 0.10 to 0.05 can be 

accepted as being statistically significant at reduced confidence levels (in the range of 90 

to 95 percent). 

As seen clearly in Table 4-2, an oxygenate effect is present in all technology groups and 

FTP phases, with CO emissions declining with increasing oxygen content. The 

magnitude of the effect is also relatively consistent (within the error of the estimates) 

across technology groups and FTP phases, with CO emissions being reduced in most 

instances by 5 to 9% per percent oxygen content. The observed oxygenate effect is 
-25- 

Table 4-2 

Effect of Fuel Oxygen Content on CO Emissions 

(FTP Conditions of 75°F, RVP 9) 

Vehicle 

Group N 

FTP 

Phase 

lnCO Model 

(E0, E10, E20) CO Benefit 

For E10 

Percent CO 

Change per 

C1 Std Err Prob >|t| % Oxygen

All 15 

Composite -0.072 0.012 0.0001 -23% -6% 

Bag 1 -0.054 0.009 0.0001 -18% -5% 

Bag 2 -0.198 0.052 0.0003 -52% -14% 

Bag 3 -0.084 0.042 0.0497 -27% -7% 

1 3 

Composite -0.079 0.022 0.0037 -25% -7% 

Bag 1 -0.064 0.014 0.0006 -21% -6% 

Bag 2 -0.117 0.027 0.0012 -35% -10% 

Bag 3 -0.049 0.032 0.1608 -16% -4% 

2 5 

Composite -0.076 0.024 0.0054 -25% -7% 

Bag 1 -0.044 0.011 0.0010 -15% -4% 

Bag 2 -0.248 0.102 0.0244 -60% -16% 

Bag 3 -0.099 0.040 0.0218 -31% -8% 

3 3 

Composite -0.047 0.008 0.0001 -16% -4% 

Bag 1 -0.043 0.012 0.0035 -15% -4% 

Bag 2 -0.103 0.052 0.0747 -32% -9% 

Bag 3 -0.065 0.045 0.1796 -21% -6% 

4 4 

Composite -0.080 0.029 0.0137 -26% -7% 

Bag 1 -0.068 0.027 0.0232 -22% -6% 

Bag 2 -0.267 0.145 0.0828 -63% -17% 

Bag 3 -0.107 0.148 0.4795 -33% -9% 

generally as large as, or larger than, the -5.3% per percent oxygen effect used in 

MOBILE6.2 for high emitters, and it obviously exceeds the MOBILE6.2 assumption of 

no effect for normal emitters. 

The oxygenate effect is statistically significant for the FTP Composite, Bag 1, and Bag 2 

tests, both overall (all vehicles) and in all technology groups, in spite of low CO emission 

levels for Groups 1 and 2 and very low CO emission levels for Groups 3 and 4. For Bag 

3, the effect is statistically significant overall and for Group 2 vehicles. The effect 

appears to be present in other technology groups, but fails the test of statistical 

significance in those groups at conventionally accepted levels of statistical significance. 

Figure 4-2 presents bar charts by FTP phase and vehicle technology group that are 

similarly scaled on the vertical axis to facilitate a visual comparison of the trends. The 

bars are shown below the zero line to emphasize that the oxygenate effect reduces CO 

emissions. Error bars (vertical lines) are shown in the graphs as  1 standard errors (σ); 
-26- 

the 95 percent confidence limits would be twice as wide. An approximate test of the 

significance of observed differences can be based on these 1 σ error bars: two estimates 

are not significantly different if their 1 σ error bars overlap. 

As seen in Figure 4-2, the oxygenate effect is smaller (in percentage terms) in Bag 1 than 

in Bag 2. The Bag 1 to Bag 2 difference is statistically significant, and this is true in all 

four technology groups. The effect in Bag 3 appears to be intermediate in size between 

Bags 1 and 2, but the error bars are generally large enough that it is not statistically 

different from the Bag 1 effect. 

The oxygenate effect is very consistent across technology groups. Depending on the FTP 

phase, the graphs may suggest that the Group 4 vehicles have a somewhat smaller effect 

than other technology groups. However, formal tests for the existence of technologyrelated differences find no evidence that the oxygenate effect (by Phase) differs among 

the four primary technology groups, among exhaust or evaporative technology groups, or 

between passenger cars (PC) and light-duty trucks (LDT). The oxygenate effect appears 

to be homogenous with respect to vehicle technology, in spite of the progressively lower 

levels of CO emissions of newer vehicles. 

The key conclusions of this analysis are that the data indicate clearly a substantial 

oxygenate effect in late-model motor vehicles (at least at the FTP conditions of 75°F and 

RVP 9), and that its magnitude appears to be consistent across the vehicle technology 

groups. The oxygenate effect varies by FTP phase, ranging from about -5% per percent 

oxygen in Bag 1, to -14% per percent oxygen in Bag 2, and to -7% per percent oxygen in 

Bag 3. As will be seen in the following sections, the emissions data obtained with the 

oxygenated fuels used in the RVP testing at both 50°F and 75°F support these 

conclusions. 
-27- 

Figure 4-2 

Oxygenate Effect by FTP Phase and Technology 

for RVP 9 Fuels at 75°F 

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Composite

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 1

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 2

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 3
-28- 

4.6 Analysis of RVP Effects Between 7 and 9 psi at 75°F

A previous study of RVP effects on CO emissions based on CRC research* using vehicle 

certification data concluded, “Fuel volatility increases between 7 RVP and 9 RVP have 

little effect on CO emissions at 75°F. This is consistent with the MOBILE6 model, 

because the MOBILE model predicts CO increases only at volatilities above 9 RVP.” As 

suggested by Figure 4-3, and supported by the analysis in this section, the data from this 

project are consistent with the conclusion of the earlier study. It is possible that a small 

CO emissions increase occurs between 7 and 9 RVP, but the magnitude of such increase 

(if it exists) is small compared to the normal variation in the test data. The data from this 

project show no statistically significant evidence that CO emissions increase between 7 

and 9 RVP. 

Figure 4-3 

Example of CO Emissions Trends with RVP at 75°F 

FTP Composite CO

(All Vehicles)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

5 7 9 11 13 15

RVP

CO Emissions (gm/mi)

E0 E10 E20

Note: The error bars are  1 standard error ranges. 

An analysis was conducted of CO emission changes between 7 and 9 RVP using five 

fuels tested at 75°F, including Fuels 6 (E0) and 7 (E10) and Fuels 3 (E0), 1 (E10), and 4 

(E20). The analysis uses a log emissions model to estimate the sensitivity of CO 

emissions to RVP changes by vehicle technology group and FTP test phase at 75°F: 

 ln[CO · (RVP)/CO0] = CRVP · (RVP – 9) + C1 · OxPct (Eq. 4-2) 

 

*

Examination of Temperature and RVP Effects on CO Emissions in EPA’s Certification Database. Final 

Report CRC Project No. E-74a. Prepared by Air Improvement Research, Inc., Novi, Michigan. April 2005. 
-29- 

where RVP is in units of psi and OxPct is the fuel oxygen content as a weight percent 

(not decimal fraction).* CO0 is the CO emissions at FTP conditions of 75°F, RVP 9, and 

E0. This model assumes a linear response of CO emissions to variation in RVP at a 

constant ambient temperature of 75°F. The actual measured RVP value is used as the 

independent variable, not the nominal RVP level planned in the experimental design. 

The OxPct term is included as a control for the oxygenate effect in three of the fuels. 

While the oxygenate effects are displayed graphically, the estimated C1 coefficients are 

not tabulated. 

Table 4-3 summarizes the effect of increasing RVP from 7 to 9 at 75°F and E0. In 

general, the analysis is unable to detect a meaningful effect on CO emissions with an 

acceptable degree of statistical confidence. For Groups 1 and 2, the analysis estimates a 

small CO emission decrease at 7 RVP in some cases, ranging from reductions of 7 to 

perhaps as much 20%. In other cases, however, the analysis estimates a CO emission 

increase, and none of the estimates reach a conventionally accepted level of statistical 

significance. For Groups 1 and 2, only two of the estimates could be considered weakly 

Table 4-3 

Effect of Low Gasoline RVP on CO Emissions 

(FTP Conditions of 75°F) 

Vehicle 

Group N 

FTP 

Phase 

lnCO Model 

(RVP 7-9, E0, E10, E20) 

CO Benefit 

For RVP 7 

CRVP Std Err Prob >|t| Gasoline

All 15 

Composite 0.018 0.027 0.51 7% 

Bag 1 -0.019 0.024 0.41 -7% 

Bag 2 0.321 0.145 0.03 262% 

Bag 3 -0.110 0.122 0.37 -35% 

1 3 

Composite -0.017 0.043 0.70 -7% 

Bag 1 -0.062 0.033 0.09 -22% 

Bag 2 0.071 0.088 0.44 33% 

Bag 3 -0.051 0.038 0.22 -18% 

2 5 

Composite 0.086 0.046 0.08 41% 

Bag 1 0.000 0.030 0.99 0% 

Bag 2 0.756 0.343 0.04 1961% 

Bag 3 0.085 0.082 0.31 41% 

3 3 

Composite 0.000 0.029 0.99 not measurable 

Bag 1 0.000 0.032 0.99 not measurable 

Bag 2 0.066 0.129 0.62 not measurable 

Bag 3 -0.007 0.123 0.96 not measurable 

4 4 

Composite -0.027 0.078 0.73 not measurable 

Bag 1 -0.026 0.075 0.73 not measurable 

Bag 2 0.157 0.311 0.62 not measurable 

Bag 3 -0.474 0.443 0.30 not measurable 

 

*

As before, the model is fit in log space as a simple equation of the form Y = A + B · OxPct, and the 

reference emissions level CO0 is computed from the regression intercept A. 
-30- 

significant (Group 1 Bag 1, and Group 2 Composite). For Groups 3 and 4, the 

confidence level of the estimates is so low that the CO benefit is reported as being not 

measurable. Only the estimate for Group 2 Bag 2 reaches the 95% confidence level in 

significance, and this result gives an implausibly large emissions effect. (This result is 

also responsible for the Bag 2 estimate for all vehicles showing a comparably large and 

implausible emissions effect.) 

A review of the individual test data strongly suggests that one vehicle is primarily 

responsible for this outcome, although no formal outlier test was performed given the 

exploratory nature of the analysis in this section. Vehicle 7 produced CO emissions of 

0.82 g/mile when tested at FTP conditions (RVP 9, E0) and 0.09 g/mile and 0.00 g/mile 

when tested on E10 and E20 fuels at 9 RVP. Both of its tests at 7 RVP reported CO 

emissions of 0.00 g/mile. As a result, the change from 7 to 9 to RVP (at zero oxygen 

content) is associated with a 100% reduction in CO emissions. Other vehicles showed 

CO emission changes ranging from -18% to +19% in the same circumstances. It is 

unknown whether the specific test results for Vehicle 7 represent a marked sensitivity to 

RVP (and fuel oxygenation) or reflect a change in vehicle condition after the baseline test 

on Fuel 3. However, it is clear that the apparent response to reduced RVP is not 

characteristic of the other vehicles. The implausible result for Group 2 Bag 2 has been 

discounted for the purposes of this section, but Vehicle 7 has been retained in the dataset. 

In the analysis of the following section, Vehicle 7 is shown to have a response to RVP 7 

fuel that is both statistically significant and different from the responses of other vehicles, 

which fail to reach the threshold of statistically significance. 

In all other respects, there is no evidence in the dataset that RVP changes between 7 and 

9 RVP have statistically significant effects on CO emissions at 75°F, although the 

presence of an RVP effect smaller than the normal test variation cannot be ruled out. 

This conclusion is true whether vehicles are pooled to increase the sample size for 

analysis or divided into technologically homogenous groups. These trends are illustrated 

in the bar charts of Figure 4-4, which is individually scaled on the vertical axis to display 

the estimates for each FTP phase. Error bars (vertical lines) represent  1 standard error 

(σ); the 95% confidence limit of the estimates would be twice as wide. Two estimates are 

not significantly different if their 1 σ error bars overlap (approximately). 

On the other hand, the dataset indicates the presence of an oxygenate effect for 7 and 9 

RVP fuels in each FTP phase and vehicle technology group. The observed oxygenate 

effect at 7 RVP varies in magnitude by FTP phase and is present across all technology 

groups (if not always statistically significant). These trends are illustrated in the bar 

charts of Figure 4-5, which is scaled on the vertical axis to facilitate a visual comparison 

of the trends. Error bars (vertical lines) are shown as  1 standard error (σ); the 95 

percent confidence limit of the estimates would be twice as wide. Two estimates are not 

significantly different if their 1 σ error bars overlap (approximately). 
-31- 

Figure 4-4 

7 RVP Effect by FTP Phase and Technology 

at 75°F Compared to 9 RVP Fuels 

-15%

-10%

-5%

0%

5%

10%

15%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Composite

-12%

-10%

-8%

-6%

-4%

-2%

0%

2%

4%

6%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 1

-50%

-40%

-30%

-20%

-10%

0%

10%

20%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 3

-40%

-20%

0%

20%

40%

60%

80%

100%

120%

140%

All Group 1 Group 2 Grpup 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 2
-32- 

Figure 4-5 

Oxygenate Effect by FTP Phase and Technology 

for RVP 7 to 9 Fuels at 75°F 

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Composite

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 1

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 3

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Grpup 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 2
-33- 

4.7 Analysis of the Effect of Increasing RVP from 9 psi to 13 psi at 75°F 

Another RVP analysis was conducted at 75°F using the test data for the three Fuels 3, 1, 

and 4 (E0, E10, E20, respectively) at 9 RVP and the two Fuels 5 and 2 (E0 and E10, 

respectively) at 13 RVP. The analysis uses the log emissions model described previously 

to estimate the sensitivity of CO emissions to RVP changes by vehicle technology group 

and FTP test phase. The model is of the form: 

 ln[CO · (RVP)/CO0] = CRVP · (RVP – 9) + C1 · OxPct (Eq. 4-3) 

where RVP is in units of psi and OxPct is a wt percent oxygen content (not decimal 

fraction).*

 CO0 is again the CO emissions at FTP conditions of 75°F, 9 RVP, and E0. As 

before, the actual measured RVP value is used as the independent variable, and the OxPct 

term is included as a control for the oxygenate effect in three of the fuels. 

The results of the analysis show that as RVP increases from 9 psi to 13 psi, increases in 

CO emissions are observed. In addition, the data again demonstrate the presence of a 

oxygenate effect in all FTP Phases and for all vehicle technology groups. 

For reference, MOBILE6.2 CO uses the following factors to adjust CO emissions for 

RVP levels about 9 psi for vehicles certified to Tier 1 and more stringent standards: 

Bag 1: +4.2 percent per psi 

Bag 2: +30.0 percent per psi 

Bag 3: +26.1 percent per psi 

Table 4-4 summarizes the results of the analysis. For Groups 1 and 2, increasing RVP 

from 9 to 13 at 75°F consistently increases CO emissions by amounts on the order of 5% 

per psi in Bag 1, 10 to 35% per psi in Bag 2, and 15 to 20% in Bag 3. These estimated 

RVP effects are comparable in magnitude to those assumed in MOBILE6.2 for Bag 1, but 

are somewhat smaller in magnitude than the MOBILE6.2 effects for Bags 2 and 3. The 

RVP effects are statistically significant at the 95 percent confidence level (or better) for 

Group 1 vehicles, but are both smaller and of weaker significance for Group 2 vehicles. 

For Groups 3 and 4, the estimated RVP effect is always smaller than for Groups 1 and 2 

and is of inconsistent algebraic sign (positive and negative), with the one exception of the 

Bag 2 effect in Group 4. All of the estimated effects display such poor statistical 

significance that they are reported as not measurable. The best level of significance 

achieved in any bag for Groups 3 and 4 could still occur by chance with a probability of 

nearly 1 in 3 (28%). No one vehicle (or subset of vehicles) appears to be responsible for 

this outcome. Instead, the variance in the data is simply large enough that, at the low 

emission levels of these vehicles, there is no statistical significance to the estimated 

effects. 

 

*

As before, the model is fit in log space as a simple equation of the form Y = A + B · OxPct, and the 

reference emissions level CO0 is computed from the regression intercept A. 
-34- 

Table 4-4 

Effect of High Gasoline RVP on CO Emissions 

(FTP Conditions of 75°F) 

Vehicle 

Group N 

FTP 

Phase 

lnCO Model 

(RVP 9-13, E0-E20) 

CO Impact 

of 13 RVP 

Gasoline 

Percent CO 

Change per 

CRVP Std Err Prob >|t| Psi 

All 15 

Composite 0.062 0.015 0.000 28% 6.4% 

Bag 1 0.024 0.012 0.054 10% 2.5% 

Bag 2 0.146 0.073 0.052 79% 15.7% 

Bag 3 0.053 0.061 0.385 24% 5.5% 

1 3 

Composite 0.080 0.021 0.003 38% 8.3% 

Bag 1 0.041 0.016 0.026 18% 4.2% 

Bag 2 0.085 0.031 0.021 41% 8.9% 

Bag 3 0.113 0.033 0.007 57% 12.0% 

2 5 

Composite 0.099 0.028 0.002 49% 10.4% 

Bag 1 0.017 0.016 0.320 7% 1.7% 

Bag 2 0.221 0.141 0.134 142% 24.8% 

Bag 3 0.140 0.049 0.010 75% 15.0% 

3 3 

Composite 0.005 0.011 0.688 not measurable 

Bag 1 -0.006 0.018 0.725 not measurable 

Bag 2 0.035 0.078 0.662 not measurable 

Bag 3 -0.039 0.067 0.572 not measurable 

4 4 

Composite 0.046 0.041 0.280 not measurable 

Bag 1 0.044 0.039 0.272 not measurable 

Bag 2 0.180 0.209 0.403 not measurable 

Bag 3 -0.031 0.220 0.891 not measurable 

Figure 4-6 shows the trend in RVP effects by FTP phase and technology group in the 

format used in prior sections to facilitate the visual comparison of trends by FTP phase 

and vehicle technology group. Error bars (vertical lines) are shown as  1 standard errors 

(σ); the 95 percent confidence limit of the estimates would be twice as wide. Two 

estimates are not significantly different if their 1 σ error bars overlap (approximately). 

The key conclusions to draw for increasing RVP from 9 to 13 psi at 75°F are as follows: 

 A statistically significant RVP effect exists in Groups 1 and 2. This is of 

comparable size (or perhaps somewhat smaller, depending on FTP phase) to the 

effect assumed in MOBILE6.2 An effect may not exist in Groups 3 and 4, or it 

may be too small to detect with acceptable statistical significance. 

 For Groups 1 and 2, the RVP effect is smaller in Bag 1 than in Bag 2. The Bag 3 

effect appears to be intermediate in magnitude, but may not be significantly 

different from the values in the other Phases. 
-35- 

Figure 4-6 

Impacts of 13 RVP Fuel by FTP Phase and Vehicle Group 

at 75°F Relative to 9 RVP Fuel 

0%

2%

4%

6%

8%

10%

12%

14%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Composite

0%

1%

2%

3%

4%

5%

6%

7%

8%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 1

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 3

0%

5%

10%

15%

20%

25%

30%

35%

40%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag2
-36- 

Formal tests for differences by technology indicate that Groups 1 and 2 can be combined 

for the estimation of RVP effects. The formal tests find no evidence that RVP effects at 

75°F differ by evaporative control technology or between PCs and LDTs for vehicles in 

Groups 1 and 2. 

Figure 4-7 shows the effect of fuel oxygenation on CO emissions that was estimated in 

conjunction with the RVP effect. The sizes of the effect by FTP phase are similar (within 

the error bars of the data) to those seen in 9 RVP fuels in the prior analysis. Formal tests 

for whether the RVP effect varies by technology indicate that no such differences can be 

detected, whether by exhaust or evaporative control technology or between PC and LDT. 

4.8 Analysis of Impact of Increasing RVP from 9 psi to 13 psi at 50°F 

The effect of RVP and oxygen content at 50°F was assessed using a regression model of 

the form found in Eq. 4-3. However, the CO0 term in the equation is now measured 

relative to CO emissions at 50°F, 9 RVP, and E0. Put another way, the underlying effect 

of cold ambient temperature on CO emissions is incorporated in the baseline CO value. 

Table 4-5 summarizes the results of the RVP analysis at 50°F. There is evidence that 

increasing RVP from 9 to 13 psi reduces CO emissions in Bag 1. This effect is highly 

significant when all vehicles are grouped together, and the RVP coefficient has a 

consistent (negative) sign in all technology groups, even when not statistically 

significant. 

In the other FTP phases, increasing RVP from 9 to 13 at 50°F may have small upward 

effects on CO emissions, but the result is at best of weak statistical significance. Groups 

3 and 4 show directionally similar results, of similar or smaller magnitude, but the results 

fail to reach an acceptable level of statistical significance. An effect may well be present, 

but it may be difficult to detect at the low emission levels of these vehicles. 
-37- 

Figure 4-7 

Oxygenate Effects by FTP Phase and Technology 

9 to 13 RVP Fuels at 75°F 

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Composite

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 1

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 3

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 2
-38- 

Table 4-5 

Effect of High Gasoline RVP on CO Emissions 

(Cold-Ambient Temperature of 50°F) 

Vehicle 

Group N 

FTP 

Phase 

lnCO Model 

(RVP 9-13, E0-E20) 

CO Impact 

of 13 RVP 

Gasoline 

Percent CO 

Change per 

CRVP Std Err Prob >|t| psi 

All 15 

Composite -0.026 0.016 0.107 -10% -2.6% 

Bag 1 -0.020 0.018 0.009 -8% -2.0% 

Bag 2 0.038 0.038 0.374 16% 3.9% 

Bag 3 0.032 0.072 0.663 13% 3.2% 

1 3 

Composite 0.004 0.024 0.873 2% 0.4% 

Bag 1 -0.008 0.023 0.732 -3% -0.8% 

Bag 2 0.075 0.034 0.050 35% 7.8% 

Bag 3 0.007 0.025 0.778 3% 0.7% 

2 5 

Composite -0.016 0.022 0.472 -6% -1.6% 

Bag 1 -0.070 0.018 0.001 -24% -6.7% 

Bag 2 0.043 0.065 0.519 19% 4.4% 

Bag 3 0.040 0.024 0.115 17% 4.0% 

3 3 

Composite -0.032 0.023 0.195 -12% -3.1% 

Bag 1 -0.048 0.027 0.104 -17% -4.7% 

Bag 2 0.036 0.053 0.503 16% 3.7% 

Bag 3 0.067 0.077 0.405 31% 6.9% 

4 4 

Composite -0.056 0.047 0.252 -20% -5.5% 

Bag 1 -0.074 0.056 0.209 -25% -7.1% 

Bag 2 0.005 0.135 0.971 2% 0.5% 

Bag 3 0.013 0.275 0.962 5% 1.3% 

Figure 4-8 shows the trend in RVP effects by FTP phase and technology group. Error 

bars (vertical lines) are shown as  1 standard errors (σ); the 95 percent confidence limit 

of the estimates would be twice as wide. Two estimates are not significantly different if 

their 1 σ error bars overlap (approximately). 

The key conclusions drawn from the RVP analysis at 50°F are as follows: 

 There is clearly a reduction in Bag 1 CO emissions at low temperature resulting 

from increasing RVP to 13 psi. The effect appears to exist in all technology 

groups, although it cannot be estimated in three of them with acceptable statistical 

significance. 

 There appears to be a consistent, but small, adverse effect on CO emissions in 

Bags 2 and 3, but it is too small to estimate with any degree of statistical 

significance using the 50°F subset of the data. 
-39- 

Figure 4-8 

Effects of 13 RVP Fuel by FTP Phase and Technology 

at 50°F Relative to RVP 9 Fuels 

 

FTP Composite

-12.0%

-10.0%

-8.0%

-6.0%

-4.0%

-2.0%

0.0%

2.0%

4.0%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 2

0%

2%

4%

6%

8%

10%

12%

14%

16%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 3

0%

5%

10%

15%

20%

25%

30%

35%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi)

FTP Bag 1

-14%

-12%

-10%

-8%

-6%

-4%

-2%

0%

2%

4%

All Group 1 Group 2 Group 3 Group 4

RVP Effect (Percent per psi) 
-40- 

As noted previously, Section 5 presents the results of a complete statistical analysis of the 

test data and uses the results of the analysis to estimate RVP correction equations as a 

function of ambient temperature; these correction equations account for the likely 

presence of a small RVP effect at 50°F. 

Figure 4-9 shows the effect of fuel oxygenation on CO emissions that was estimated in 

conjunction with the RVP effect. The sizes of the effect by FTP phase are directionally 

consistent with those seen in previous sections, but of generally smaller magnitude at 

50°F than at 75°F. The oxygenate effect again appears to be present and relatively 

consistent across all technology groups. 
-41- 

Figure 4-9 

Oxygenate Effects by FTP Phase and Technology 

for 9 to 13 RVP Fuels at 50°F 

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Composite

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 1

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 3

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

All Group 1 Group 2 Group 3 Group 4

Oxygen Benefit (Percent per %)

FTP Bag 2

### 
-42- 

5. STATISTICAL ANALYSIS AND DEVELOPMENT OF EMISSION 

CORRECTION FACTORS 

5.1 Overview

This section presents a statistical analysis of the E-74b THC, CO, and NOx emissions 

data. The results of the analysis are presented in detail and then summarized in the form 

of correction factor equations for use at temperatures below 75°. While subsets of the 

data were examined in Section 4, the analysis discussed in this section is based on all of 

the fuels tested in the E74-b program, with RVP values ranging from 7 to 13 psi and 

oxygen content ranging from E0 to E20. However, not all combinations of temperature, 

RVP, and oxygen content were tested. The E20 oxygenation level was tested only for 

RVP 9 fuels (but at both 50°F and 75°F), while the RVP 7 fuels (at E0 and E10) were 

tested only at 75°F. 

As described below, the statistical analysis has been conducted twice to address the 

potential impacts of variation in T50 in test fuels 2 and 4 relative to the other test fuels. 

The primary analysis presented in Section 5.3 is based on the E-74b design variables: 

temperature, RVP, and oxygen content. This formulation of the analysis will include, in 

the coefficients estimated for the RVP and oxygen terms, the emission effects (if any) 

caused by variations in T50 for test fuels 2 and 4. The second analysis, described in 

Section 5.4, was conducted to test the sensitivity of the primary results by including a T50

term in models that are otherwise similar, except for the statistically confounded terms 

that must be excluded. 

Lastly, the development of the correction factor equations is described and the results are 

compared with the correction factors incorporated into MOBILE6.2 and with correction 

factors previously developed by Sierra.* 

5.2 Methodology

5.2.1 Mathematical Formulation

The effects of ambient temperature, RVP, and oxygen content on emissions are 

represented in MOBILE6.2 in the form of equations that adjust emission factors at FTP 

conditions to reflect emission rates at non-FTP conditions. For temperatures above 75°F, 

 

*

Heirigs, P.L., and Lyons, J.M, “Review of Current and Future CO Emissions from On-Road Vehicles in 

Selected Western Areas,” Sierra Research Report No. SR03-01-01, January 28, 2003. 
-43- 

the MOBILE6.2 correction factor equations take the form of a statistical response 

surface, including linear terms in temperature, RVP, and oxygen content and a number of 

their two-way interactions. A simplified form is implemented for temperatures below 

75°F. 

The statistical analysis conducted here uses the most complete, second-order response 

surface in the design variables temperature, RVP, and oxygen content that can be 

estimated for the data, including all linear terms, all two-way interactions, and a quadratic 

term in oxygen content (the only variable tested at three levels). This formulation is very 

similar to that used in MOBILE6.2 for temperatures above 75°F. 

The mathematical form of the general second-order response surface used here is given in 

Eq. 5-1: 

ln E = ln E0 + CT · T + CT,O2 · T · OxPct 

 + CRVP-L · RVPL 

 + CRVP-H · RVPH + CRVP-H,T · RVPH · T + CRVP,O2 · RVP OxPct 

 + C1,O2 · OxPct + C2,O2 · OxPct2 (Eq. 5-1) 

where: T = T - 75°F 

 RVPL = min(0, RVP – 9 psi) 

 RVPH = max(0, RVP – 9 psi) 

 RVP = RVP – 9 psi 

 OxPct = Oxygen content (as a weight percent, not decimal fraction) 

This formulation provides separate slopes for the effect of RVP below and above 9 psi to 

accommodate the evidence that RVP effects differ between these regimes. One regime is 

that of RVP values between 7 and 9 psi in which vehicles must demonstrate compliance 

with federal and California certification standards. Vehicle performance in this regime is 

constrained by the certification process. The second regime is that of RVP values above 

9 psi, in which vehicle certification does not directly constrain vehicle performance. In 

this regime, fuels are formulated on a seasonal basis (primarily for winter) with RVP 

levels selected to achieve satisfactory vehicle startup and driveability. 

RVP values below 9 psi are measured by the variable RVPL, which is zero for fuels with 

RVP above 9 psi. The RVPL slope is included in the statistical models to provide a test 

for whether emissions differ between 7 and 9 psi. The slope is retained in all models 

without regard to statistical significance to distinguish emissions between the two 

regimes. The earlier CRC E74-a program demonstrated that there is no statistically 

significant difference in vehicle certification emissions between 7 and 9 psi, and the 

exploratory analysis in the preceding section showed that there is no statistically 

significant difference in in-use vehicle CO emissions in the current program. The a 

priori hypothesis is that the RVPL slope will fail to be statistically significant. 
-44- 

RVP values above 9 psi are measured by the variable RVPH, which is zero for fuels with 

RVP below 9 psi. The RVPH slope is included in the model to measure the extent to 

which RVP values in excess of 9 psi have an effect on vehicle emissions compared to 

emissions at the RVP = 9 psi value used for certification. Based on prior research, the a 

priori hypothesis is that higher fuel volatility will, in some cases, have an adverse effect 

on HC and CO emissions at 75°F, but may have no effect, or possibly a beneficial effect, 

at colder temperatures. NOx emissions effects are expected to counter the HC/CO trends. 

The response surface is linear with respect to T, RVPL, and RVPH. It includes all twoway interaction terms between the variables that can be tested, including interactions 

between T and RVPH, RVP and OxPct, and T and OxPct. Because oxygen content was 

tested at three levels, a non-linear response surface is fit with respect to OxPct, from 

which the potential for changes in oxygenate response rates over the range from E0 to 

E20 can be evaluated. The interaction terms T · OxPct and T · RVPH represent the 

potential for the oxygen and RVP effects to differ between 50°F and 75°F. The term 

RVP · OxPct represents the potential interaction of RVP and OxPct, such that the 

observed emissions change differs from what would be expected from the two variables 

alone. 

The functional form of Eq. 5-1 measures temperature and RVP as departures from the 

FTP conditions (75°F, RVP = 9 psi, 0% oxygen content), so that the intercept term E0

estimates emissions at FTP conditions. Because the emissions intercept term is vehiclespecific, and is either absorbed (removed from the analysis) or specified as dummy 

variables, it is of no direct interest in the understanding of emissions changes relative to 

FTP conditions. Therefore, intercept terms are not reported in the results of the analysis. 

These key trends described in Section 4 for CO are incorporated, along with 

corresponding trends for HC and NOx, in the statistical analysis and the updated 

correction factor equations developed here: 

 A widespread oxygenate effect in which CO emissions are reduced with 

increasing gasoline oxygen content by an amount that varies by FTP phase but is 

relatively consistent in size across technology groups. This effect may show 

evidence of diminishing returns for CO, in which the marginal benefit of further 

oxygenation decreases as oxygen content rises. 

 Little or no effect on CO emissions at 75°F for fuel RVP values below 9 psi. 

 An effect of increasing CO emissions with gasoline RVP between 9 and 13 psi 

that is substantially larger at 75°F than at 50°F. The effect varies by FTP phase 

and by vehicle technology group. However, the effect is restricted to RVP values 

in excess of 9 psi, based on the absence of statistically significant evidence for 

emission effects at 7 psi. 

 For cold ambient temperatures (50°F), there is evidence that increasing gasoline 

RVP to 13 psi causes a reduction in CO emissions during Bag 1. This “cold-
-45- 

temperature benefit” is not detected in the other FTP phases or for the other 

pollutants. This effect is represented in the analysis as an RVP · T interaction that 

reverses sign and becomes an emissions benefit at temperatures below 75°F. 

 In addition to these fuel effects, the adjustment factor analysis estimates coldtemperature emissions offsets by FTP phase for the testing at 50°F. 

5.2.2 Conduct of the Analysis

5.5.2.1 Overall Fleet – The analysis was conducted in a standardized sequence for each 

of the 12 analysis cells formed from the intersection of pollutant (CO, HC, NOx) and 

FTP test phase (Composite, Bag 1, Bag 2, Bag 3). To begin the analysis for each cell, the 

full response surface was estimated using ordinary least squares regression analysis 

applied to the data for all vehicles. Its key results (coefficient estimates and p values) are 

reported under the heading Full Model in the tables found in Section 5.3. As will be 

seen, the second-order response surface is over-specified in general—meaning that it 

contains more terms than are needed to represent the trends in the data. Because many of 

the terms have correlations of non-negligible size, there is a tendency for the terms in the 

Full Model to show poor or no statistical significance. Thus, there is a need to reduce the 

model to include only those terms that represent meaningful and statistically significant 

effects. 

The second stage of the analysis involved the use of stepwise regression techniques to 

choose among the terms in Eq. 5-1 to find those that are statistically significant. Both 

forward- and backward-selection techniques were used. In forward selection, one starts 

with a model containing only the intercept and RVPL terms; the terms with strongest 

statistical significance are then added one by one until no remaining term achieves at 

least p=0.10. In backward selection, all terms are initially introduced in the model, and 

those terms not achieving p=0.10 are removed one by one until all terms remaining 

achieve at least p=0.10. In this, the RVPL term is required to remain in the model. 

Because stepwise regression cannot be counted on to always find the “best” choice of 

terms, the results of the two selection methods were compared and judgment was applied 

in the instances where the methods disagreed. The results of the final models are 

reported in the tables under the heading Reduced Model. 

An Outlier Assessment was conducted based on the residuals from the Reduced Model. 

In this assessment, the observed value for each emissions test was compared to the 99% 

confidence limits for the value predicted by the regression model. A “good” data point 

has 1 chance in 100 of lying outside the prediction confidence limits merely by chance, 

and in a data set of 180 tests it is likely that a few tests will do so in each instance. The 

tests flagged as potential outliers by this method were then examined to determine if they 

should be excluded from the data. Only tests substantially outside the confidence limits 

and appearing to diverge from the predicted trends would be excluded. After other 

adjustments made to the data to include certain vehicles or categories of tests (identified 

below), no individual tests were excluded on this basis as outliers. 
-46- 

5.2.2.2 Technology Groups – A second round of analysis was conducted to identify terms 

that take on different values in one or more of the four vehicle technology groups. 

Stepwise regression techniques were again used to select among an enlarged pool of 

model terms, including all of the individual terms shown in Eq. 5-1 plus additional terms 

that allowed the coefficients to differ in any of the four groups. The form of the Reduced 

Model, the form and statistical significance of terms in the technology-based models 

selected by stepwise regression, and analyst judgment were combined to select final 

Technology Models reported in the tables. No statistically significant differences were 

found for any of the four technology Groups individually, perhaps due to the small 

sample of vehicles in each group, but it was determined that effects sometimes displayed 

statistical differences when divided into two groups (Groups 1 and 2 combined, and 

Groups 3 and 4 combined). However, the analysis more often finds a technologically 

uniform response, at least when measured on a percentage basis and within the sample 

size limits of the dataset. 

Given the form selected for the final Technology Models, the outlier analysis was 

repeated for individual tests, and a further analysis of residuals was conducted to 

determine if the emissions response to T, RVP, RVP · T, or OxPct varied to a statistically 

significant extent with respect to any of the following distinctions: 

 By the four vehicle technology groups; 

 By the three exhaust technology groups; 

 By the three evaporative technology groups; 

 By PC and LDT groups; or 

 By individual vehicle. 

The further residual analyses employed the F test to determine if there was sufficient 

evidence to conclude that one or more of the several (to many) levels in each distinction 

were different from the rest. Statistically significant differences were investigated, 

leading either to decisions to adjust the statistical models or to exclude divergent data 

until such differences were resolved. The adjustments are discussed below. 

1. The FTP Bag 3 CO emissions of many vehicles are reported as 0.00 gm/mi, as a 

consequence of the inherently low emission levels of new vehicles that employ 

sophisticated exhaust and evaporative emission controls. Although the emission 

readings were reset to a de minimus level of 0.005 to permit inclusion in the log 

models, the response coefficients estimated for the Tier 2 Groups in the 

technology analysis were often weak and sometimes counter-intuitive. A decision 

was made to exclude all data points with FTP Bag 3 CO = 0.00 gm/mi from the 

Bag 3 CO analysis, reducing the number of total data points to N = 156. Bag 3 

CO emissions are so low for vehicles in Groups 3 and 4 that it is doubtful whether 

temperature or RVP effects would be large enough to be meaningful in inventory 

analysis, if they could be detected with statistical significance in a larger dataset 

of vehicle testing. 
-47- 

2. The analysis of FTP Bag 2 CO emissions demonstrated that Vehicle 7 (2001 

Dodge Caravan) had a distinctive response to RVP 7 fuels, as had been noted in 

the exploratory analysis of the prior section, in which its Bag 2 CO emissions 

were measured as 0.00 gm/mi on both RVP fuels. Rather than exclude the two 

Vehicle 7 tests from the dataset, a separate term was introduced to allow a 

different RVPL response for this vehicle alone. 

3. The analysis of FTP Bag 1 THC emissions indicated that the performance of 

Vehicle 11 (2004 Toyota Camry) was consistently different from that of other 

vehicles. Specifically, it had higher THC emissions at 50°F (by 25%, p=0.00) and 

higher emissions at 50°F on RVP 13 fuel (by 29%, p=0.03) in comparison to 

other Tier 2 vehicles under comparable conditions. Because the results suggest 

the possibility of engine or emission controls operating improperly at cold start 

under low ambient temperature, the data for this vehicle were dropped entirely 

from the analysis of the FTP Composite and Bag 1. The vehicle’s data were 

retained for Bags 2 and 3, for which there was no indication of a significant 

difference compared to other vehicles. 

4. FTP Bag 1 NOx emissions were found to vary significantly between PCs and 

LDTs with respect to the response to RVP (p=0.03) and to the interaction of RVP 

and temperature (p=0.03). A final technology model was fit to capture this 

difference in the correction factor equations. It shows that PC NOx emissions 

have no measurable sensitivity to RVP in FTP Bag 1, but that LDT NOx 

emissions are increased by a statistically significant amount when using high RVP 

fuel. Although FTP Composite emissions are computed from the bag-specific 

emissions, the PC/LDT difference for Bag 1 NOx is not detected with statistical 

confidence in FTP Composite NOx emissions. 

Except for the adjustments itemized above, no other deletions were made for outliers. In 

general, the data points identified by the outlier test most often lie at low emission values, 

where they are flagged as potential outliers because they show large percentage 

differences from the log-emissions regression line. However, even large percentage 

differences applied to a very small emissions estimate may amount to no more than a few 

tenths of 1 gm/mi and, therefore, are not of substantive concern. 

5.3 Statistical Analysis Results (Primary)

The results of the statistical analysis are reported in Tables 5-1 through 5-12, in a format 

that should be easily understood from the preceding discussion of the analysis 

methodology. The analysis reported in this section is the primary statistical analysis, in 

which only design effects are included in the model formulation. As explained 

previously, the presence of a much lower T50 temperature in two of the test fuels causes 

the analysis to face the problem of statistical confounding. The results of a sensitivity 

analysis are presented in Section 5.4 as an alternative to this primary analysis. 
-48- 

5.3.1 FTP Composite CO Emissions

The results of the statistical analysis for FTP Composite CO (Table 5-1) are briefly 

described to ensure understanding of the results shown in Tables 5-1 through 5-12. The 

coefficient values given in the tables pertain to the Eq. 5 model of log emissions; the 

corresponding percentage effect on emissions can be calculated as exp(coefficient)-1. 

A first round of analysis examined the data as a whole, without consideration of 

technology differences. The Full Model section of the table reports the results for the fit 

of the complete second-order response surface. Of the eight possible terms (excluding 

the intercept), there is no evidence that the effect of oxygen content on Composite CO 

emissions varies with temperature (the interaction term T · OxPct). Further, there is no 

evidence that RVP values below 9 psi have an effect on Composite CO (the RVP term) or 

that the effect of oxygen content varies with respect to RVP (the RVP · OxPct term). All 

other terms are statistically significant at acceptable confidence levels or better. 

The Reduced Model reports the results for the statistically significant effects once the T · 

OxPct and RVP · OxPct interaction terms are omitted. The RVP term is retained in the 

Reduced Model, even though it lacks statistical significance, to distinguish emission 

levels between the two RVP regimes. As shown for the outlier assessment, only three 

tests lie outside the 99% confidence intervals for the predictions of the reduced model. 

The number of such tests is only slightly greater than the 1.8 tests that would be expected 

in a sample of N=180 tests. After inspection of a graphical display of the data, no points 

were excluded as outliers. 

The Technology Model section of the table reports the results of a second round of 

analysis to determine whether any of the terms in Eq. 5-1 vary by vehicle technology 

group. In the analysis, each term (including terms not found to be statistically significant 

in the first round of analysis) is tested for inclusion in the model in seven different forms: 

 As a uniform coefficient applicable to all vehicles; 

 As coefficients that differ in one or more of the four vehicle technology groups; 

and 

 As coefficients that differ between two composite groups consisting of Groups 1 

and 2 combined (Tier 1/NLEV) and Groups 3 and 4 combined (the two Tier 2 

Groups). 

The technology model is then built from the terms that are found to fit the data with an 

acceptable level of statistical significance (p=0.10 or better). Correction factor equations 

for use in MOBILE6.2 are derived from the technology models, as will be summarized in 

Section 5.5. 

 

For FTP Composite CO, the technology analysis finds that the T and RVP effects and the 

RVP · T interaction differ between the composite Groups 1 and 2 and the composite 

Groups 3 and 4 to a statistically significant degree. Groups 3 and 4 (vehicles certified to 

Tier 2 exhaust emission standards) have a slightly larger temperature sensitivity (on a 
-49- 

percentage basis), but they have a substantially smaller RVP response and a smaller 

RVP · T interaction term. 

The oxygenate effect is found to be uniform across all technology groups and of the same 

size at both 50°F and 75°F ambient temperatures and at all three RVP levels. The data 

clearly indicate that the CO emissions benefit of oxygenated gasoline is subject to 

diminishing returns as the oxygen content increases beyond E10. The quadratic form (C1

+ C2) · OxPct is shown to be statistically significant at the p=0.01 level or better. The 

maximum point (the point of maximum CO benefit) is computed by the formula: 

 OxPctmax = -C1 / (2 · C2) (Eq. 5-2) 

For the values C1 and C2 estimated here, the maximum benefit is reached at an oxygen 

content of 6.9% or E18.8. The emissions benefit of oxygenation is subject to 

significantly diminished returns as oxygen content is increased beyond E10. At the E10 

level oxygenation is estimated to reduce FTP Composite CO emissions by 26%, but 

increasing oxygenation to E18.8 extends the CO reduction to only 30%. 

Although the quadratic form changes direction beyond the maximum point, the analysis 

does not provide a definitive answer on the trend of emissions with oxygen content 

beyond the maximum point—i.e., whether emissions are constant beyond the maximum 

or turn back up to follow the trend of reduced benefit (increased emissions) that is 

predicted by the quadratic beyond the maximum point. Further, no information is 

available in the E74-b data for oxygen content beyond that of E20. What is clear is that 

oxygenation of gasoline is subject to diminishing returns as the oxygen content is 

increased and that oxygenation of gasoline beyond the maximum point is not likely to 

carry appreciable incremental emissions benefit. As a practical matter, the estimated 

maximum benefit should be held constant at higher oxygenation levels in applying the 

results of this analysis. 

Because only Fuel 4 was blended with an oxygenate level of E20, the observed nonlinearity in the oxygenate effect is dependent on the emission performance of Fuel 4. As 

indicated in Section 4, Fuel 4 was blended with a T50 level some 30°F below the range of 

the five closely controlled fuels, so that the observed non-linearity of the oxygenate effect 

may be due, in whole or in part, to the low T50 temperature of Fuel 4. 

5.3.2 Summary of Statistical Analysis Results

Tables 5-1 through 5-12 summarize the results of the primary statistical analysis. With 

one exception, the technology models summarized in the tables are the final models from 

which the correction factor equations were developed. For FTP Bag 1 NOx, the test data 

show a clear difference in the RVPH and RVPH · T response between passenger cars 

(PCs) and light-duty trucks (LDTs). An expanded model was fit for the purpose of 

estimating PC and LDT correction factors, and its coefficients are tabulated in Section 

5.4. All terms in the model achieve p=0.05 values or better. 
-50- 

Table 5-1 

Model Summary for CO FTP Composite 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) -0.01857 0.00 

T · OxPct 0.00006 0.93 

 RVPL (RVP-9) 0.00013 1.00 

 RVPH (RVP-9) 0.07946 0.00 

RVPH · T 0.00370 0.00 

RVP · OxPct -0.00360 0.60 

 OxPct -0.09466 0.00 

OxPct · OxPct 0.00640 0.09 

Reduced Model

 T (T-75) -0.01879 0.00 

 RVPL (RVP-9) 0.00001 1.00 

 RVPH (RVP-9) 0.07271 0.00 

RVP · T 0.00373 0.00 

 OxPct -0.10337 0.00 

OxPct · OxPct 0.00746 0.02 

Outlier Assessment

 Tests with p<0.01 a 3 

 Tests Excluded none 

Technology Model

T Groups 1+2 -0.01315 0.00 

 Groups 3+4 -0.02519 0.00 

RVPL (RVP-9) All -0.00025 0.99 

RVPH Groups 1+2 0.10843 0.00 

 Groups 3+4 0.03396 0.12 

RVP · T Groups 1+2 0.00474 0.00 

 Groups 3+4 0.00276 0.03 

OxPct -0.10312 0.00 

OxPct · OxPct b 0.00743 0.01 

a

 Expected tests with p<0.01 = 1.8 

b Asymptote for OxPct = 6.9% or E18.8 
-51- 

Table 5-2 

Model Summary for CO FTP Bag 1 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) -0.02751 0.00 

T · OxPct 0.00035 0.57 

 RVPL (RVP-9) -0.03644 0.31 

 RVPH (RVP-9) 0.05231 0.01 

RVPH · T 0.00315 0.00 

RVP · OxPct -0.00717 0.25 

 OxPct -0.09410 0.00 

OxPct · OxPct 0.00754 0.03 

Reduced Model

 T (T-75) -0.02623 0.00 

 RVPL (RVP-9) -0.02974 0.39 

 RVPH (RVP-9) 0.03591 0.02 

RVP · T 0.00299 0.00 

 OxPct -0.11536 0.00 

 OxPct · OxPct 0.00950 0.00 

Outlier Assessment

 Tests with p<0.01 a 4 

 Tests Excluded none 

Technology Model

T Groups 1+2 -0.02377 0.00 

 Groups 3+4 -0.02896 0.00 

RVPL (RVP-9) All -0.02967 0.38 

RVPH Groups 1+2 0.03599 0.02 

 Groups 3+4 Same 

RVP · T Groups 1+2 0.00300 0.00 

 Groups 3+4 Same 

OxPct -0.11523 0.00 

OxPct · OxPct b 0.00949 0.00 a

 Expected tests with p<0.01 = 1.8 

b Asymptote for OxPct = 6.3% or E16.9 
-52- 

Table 5-3 

Model Summary for CO FTP Bag 2 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) 0.01718 0.20 

 T · OxPct -0.00473 0.07 

 RVPL (RVP-9) 0.33022 0.03 

 RVPH (RVP-9) 0.13600 0.11 

 RVPH · T -0.00486 0.20 

 RVP · OxPct 0.00041 0.99 

 OxPct -0.10208 0.35 

 OxPct · OxPct -0.00514 0.72 

Reduced Model

 T (T-75) -- -- 

 RVPL (RVP-9) 0.03584 0.74 

 dVeh07 · RVPL 3.32832 0.00 

 RVPH (RVP-9) 0.16848 0.00 

 RVPH · T 0.00705 0.00 

 OxPct -0.08735 0.00 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 6 

 Tests Excluded none 

Technology Model

T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

RVPL (RVP-9) All 0.03584 0.74 

dVeh07 · RVPL 3.32832 0.00 

RVPH Groups 1+2 0.16848 0.00 

 Groups 3+4 Same 

RVP · T Groups 1+2 0.00705 0.00 

 Groups 3+4 Same 

OxPct -0.08735 0.00 

OxPct · OxPct n/a a

 Expected tests with p<0.01 = 1.8 
-53- 

Table 5-4 

Model Summary for CO FTP Bag 3 

(N = 156, excluding Tests with COBag3 = 0.000)

Coefficient Prob > |t| 

Full Model

 Intercept -- -- 

 T (T-75) 0.00307 0.66 

 T · OxPct 0.00022 0.87 

 RVPL (RVP-9) 0.02292 0.76 

 RVPH (RVP-9) 0.10408 0.02 

 RVPH · T 0.00138 0.49 

 RVP · OxPct -0.01126 0.40 

 OxPct -0.10838 0.05 

 OxPct · OxPct 0.00905 0.22 

Reduced Model

 T (T-75) -- -- 

 RVPL (RVP-9) 0.00248 0.97 

 RVPH (RVP-9) 0.06640 0.01 

 RVP · T -- -- 

 OxPct -0.13783 0.00 

 OxPct · OxPct 0.01191 0.06 

Outlier Assessment

 Tests with p<0.01a 4 

 Tests Excluded none 

Technology Model

T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

RVPL (RVP-9) All 0.02253 0.71 

RVPH Groups 1+2 0.14635 0.00 

 Groups 3+4 None 

RVPH · T Groups 1+2 0.00527 0.00 

 Groups 3+4 None 

OxPct -0.13279 0.00 

OxPct · OxPct b 0.01105 0.06 a

 Expected tests with p<0.01 = 1.6 

b Asymptote for OxPct = 6.0% or E16.2 
-54- 

Table 5-5 

Model Summary for THC FTP Composite 

(N = 168, excluding Vehicle 11)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) -0.01164 0.00 

 T · OxPct -0.00058 0.11 

 RVPL (RVP-9) 0.00022 0.99 

 RVPH (RVP-9) 0.01679 0.15 

 RVPH · T 0.00059 0.26 

 RVP · OxPct -0.00075 0.83 

 OxPct -0.02045 0.18 

 OxPct · OxPct 0.00006 0.98 

Reduced Model

 T (T-75) -0.01026 0.00 

 T · OxPct -0.00071 0.04 

 RVPL (RVP-9) 0.01840 0.29 

 RVPH (RVP-9) -- -- 

 RVPH · T -- -- 

 OxPct -0.02281 0.00 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 3 

 Tests Excluded none 

Technology Model

T Groups 1+2 -0.00812 0.00 

 Groups 3+4 -0.01301 0.00 

T · OxPct -0.00072 0.03 

RVPL (RVP-9) All 0.01850 0.27 

RVPH Groups 1+2 -- -- 

 Groups 3+4 -- -- 

RVPH · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct -0.02279 0.00 a

 Expected tests with p<0.01 = 1.7 
-55- 

Table 5-6 

Model Summary for THC FTP Bag 1 

(N = 168, excluding Vehicle 11)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) -0.01760 0.00 

 T · OxPct -0.00074 0.08 

 RVPL (RVP-9) -0.00613 0.80 

 RVPH (RVP-9) 0.01549 0.25 

 RVPH · T 0.00080 0.19 

 RVP · OxPct -0.00087 0.83 

 OxPct -0.02842 0.11 

 OxPct · OxPct 0.00069 0.76 

Reduced Model

 T (T-75) -0.01579 0.00 

 T · OxPct -0.00092 0.02 

 RVPL (RVP-9) 0.00909 0.65 

 RVPH (RVP-9) -- -- 

 RVPH · T -- -- 

 OxPct -0.02634 0.00 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 4 

 Tests Excluded None 

Technology Model

T Groups 1+2 -0.01379 0.00 

 Groups 3+4 -0.01835 0.00 

T · OxPct -0.00092 0.02 

RVPL (RVP-9) 0.00919 0.64 

RVPH Groups 1+2 -- -- 

 Groups 3+4 -- -- 

RVP · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct -0.02633 0.00 a

 Expected tests with p<0.01 = 1.7 
-56- 

Table 5-7 

Model Summary for THC FTP Bag 2 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) 0.00410 0.23 

 T · OxPct -0.00079 0.24 

 RVPL (RVP-9) 0.02665 0.49 

 RVPH (RVP-9) 0.00926 0.97 

 RVPH · T -0.00086 0.38 

 RVP · OxPct 0.00177 0.79 

 OxPct 0.02271 0.42 

 OxPct · OxPct -0.00510 0.16 

Reduced Model

 T (T-75) -- -- 

 T · OxPct -- -- 

 RVPL (RVP-9) 0.02654 0.37 

 RVPH (RVP-9) -- -- 

 RVPH · T -- -- 

 OxPct 

 OxPct · OxPct 

Outlier Assessment

 Tests with p<0.01 a 1 

 Tests Excluded None 

Technology Model

T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

T · OxPct -- -- 

RVPL (RVP-9) All -0.00258 0.93 

RVPH Groups 1+2 0.06932 0.00 

Groups 3+4 0.00230 0.02 

RVP · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct -- -- a

 Expected tests with p<0.01 = 1.8 
-57- 

Table 5-8 

Model Summary for THC FTP Bag 3 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) 0.00613 0.02 

 T · OxPct -0.00072 0.17 

 RVPL (RVP-9) 0.00241 0.93 

 RVPH (RVP-9) 0.02259 0.18 

 RVPH · T -0.00020 0.79 

 RVP · OxPct -0.00448 0.38 

 OxPct -0.00362 0.87 

 OxPct · OxPct -0.00135 0.63 

Reduced Model

 T (T-75) 0.00387 0.01 

 T · OxPct -- -- 

 RVPL (RVP-9) -0.00662 0.81 

 RVPH (RVP-9) 0.01942 0.03 

 RVPH · T -- -- 

 OxPct -- -- 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 2 

 Tests Excluded none 

Technology Model

T Groups 1+2 0.00039 0.01 

 Groups 3+4 same 

RVPL (RVP-9) -0.00662 0.81 

RVPH Groups 1+2 0.01942 0.03 

 Groups 3+4 same 

RVP · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct -- -- a

 Expected tests with p<0.01 = 1.8 
-58- 

Table 5-9 

Model Summary for NOx FTP Composite 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) -0.00397 0.16 

 T · OxPct -0.00069 0.22 

 RVPL (RVP-9) -0.01120 0.73 

 RVPH (RVP-9) 0.03777 0.04 

 RVPH · T -0.00026 0.75 

 RVP · OxPct -0.00411 0.46 

 OxPct 0.01520 0.52 

 OxPct · OxPct 0.00056 0.85 

Reduced Model

 T (T-75) -0.00644 0.00 

 T · OxPct -- -- 

 RVPL (RVP-9) -0.01831 0.53 

 RVPH (RVP-9) 0.03134 0.00 

 RVPH · T -- -- 

 OxPct 0.02362 0.00 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 3 

 Tests Excluded none 

Technology Model

T Groups 1+2 -0.00691 0.00 

 Groups 3+4 -0.00594 0.01 

RVPL (RVP-9) All -0.01834 0.53 

RVPH Groups 1+2 0.03135 0.00 

 Groups 3+4 same 

RVPH · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct 0.02361 0.00 a

 Expected tests with p<0.01 = 1.8 
-59- 

Table 5-10 

Model Summary for NOx FTP Bag 1 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) -0.00696 0.00 

 T · OxPct -0.00060 0.21 

 RVPL (RVP-9) -0.01051 0.70 

 RVPH (RVP-9) 0.00833 0.58 

 RVPH · T -0.00061 0.37 

 RVP · OxPct 0.00216 0.64 

 OxPct -0.00651 0.74 

 OxPct · OxPct 0.00235 0.36 

Reduced Model

 T (T-75) -0.00974 0.00 

 T · OxPct -- -- 

 RVPL (RVP-9) -0.02198 0.38 

 RVPH (RVP-9) 0.01855 0.03 

 RVPH · T -- -- 

 OxPct 0.01670 0.00 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 2 

 Tests Excluded none 

Technology Model

T Groups 1+2 -0.01046 0.00 

 Groups 3+4 -0.00896 0.00 

RVPL (RVP-9) All -0.02204 0.38 

RVPH Groups 1+2 0.01857 0.03 

 Groups 3+4 Same 

RVPH· · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct 0.01669 0.00 a

 Expected tests with p<0.01 = 1.8 
-60- 

Table 5-11 

Model Summary for NOx FTP Bag 2 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) -0.00514 0.52 

 T · OxPct 0.00031 0.84 

 RVPL (RVP-9) -0.12002 0.18 

 RVPH (RVP-9) 0.16090 0.00 

 RVPH · T 0.00191 0.40 

 RVP · OxPct -0.03218 0.04 

 OxPct 0.04019 0.54 

 OxPct · OxPct 0.00191 0.82 

Reduced Model

 T (T-75) -- -- 

 T · OxPct -- -- 

 RVPL (RVP-9) -0.08755 0.26 

 RVPH (RVP-9) 0.14026 0.00 

 RVPH · OxPct -0.03448 0.01 

 OxPct 0.05243 0.01 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 2 

 Tests Excluded none 

Technology Model

T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

RVPL (RVP-9) All -0.07059 0.37 

RVPH Groups 1+2 0.06209 0.03 

 Groups 3+4 Same 

RVPH · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct 0.03110 0.01 a

 Expected tests with p<0.01 = 1.8 
-61- 

Table 5-12 

Model Summary for NOx FTP Bag 3 

(N=180, 15 Vehicles)

 Coefficient Prob>|t| 

Full Model

 Intercept -- -- 

 T (T-75) 0.00669 0.22 

 T · OxPct -0.00202 0.06 

 RVPL (RVP-9) -0.01100 0.86 

 RVPH (RVP-9) 0.05348 0.12 

 RVPH · T -0.00011 0.94 

 RVP · OxPct -0.00726 0.50 

 OxPct 0.05997 0.18 

 OxPct · OxPct -0.00605 0.30 

Reduced Model

 T (T-75) -- -- 

 T · OxPct -- -- 

 RVPL (RVP-9) -0.03790 0.47 

 RVPH (RVP-9) 0.04520 0.02 

 RVPH · T -- -- 

 OxPct 0.03620 0.00 

 OxPct · OxPct -- -- 

Outlier Assessment

 Tests with p<0.01 a 4 

 Tests Excluded none 

Technology Model

T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

RVPL (RVP-9) All -0.03790 0.47 

RVPH Groups 1+2 0.04520 0.02 

 Groups 3+4 same 

RVPH · T Groups 1+2 -- -- 

 Groups 3+4 -- -- 

OxPct 0.03620 0.00 a

 Expected tests with p<0.01 = 1.5 
-62- 

5.4 Alternative Statistical Analysis

To assess the uncertainty introduced by the confounding of T50 variations with the design 

effects of RVP and oxygenation, an alternative statistical analysis was conducted in 

which the terms RVP·OxPct and OxPct2

 (i.e., the terms that are confounded with the 

variation in T50) were dropped from consideration and a T50 term was introduced. This 

change in formulation of the statistical model shifts part of the explanation of emission 

changes away from RVP and OxPct to the T50 term. 

The mathematical form used in the alternative statistical analysis is given in Eq. 5-3: 

 ln E = ln E0 + CT · T + CT,O2 · T · OxPct 

 + CRVP-L· RVPL 

 + CRVP-H · RVPH + CRVP-H,T · RVPH · T + CRVP,O2 · RVP · OxPct 

 + C1,O2 · OxPct + C2,O2 · OxPct2 (Eq. 5-3) 

where: T = T - 75°F 

 RVPL = min(0, RVP – 9 psi) 

 RVPH = max(0, RVP – 9 psi) 

 RVP = RVP – 9 psi 

 OxPct = Oxygen content (as a weight percent, not decimal fraction) 

 dT50 = T50 - 190°F 

The alternative statistical analysis was conducted in a manner similar to that described 

above, but without repeating the analysis to select statistically significant terms in each 

case, so that the alternative models are comparable to the primary models except for the 

changes introduced by the dT50 term. As with the primary analysis, a Full Model was 

initially estimated using the alternative formulation given above. Then, a Reduced Model

was estimated by including a dT50 term with the subset of terms in Eq. 5-3 that were 

included in the models of the primary analysis. The dT50 term is retained in the Reduced 

Model, even though it is not statistically significant at accepted levels, to show the effect 

on the coefficients estimated for other terms and to demonstrate the weakness of the dT50

term itself. A Technology Model was estimated in a similar manner, retaining the 

technology distinctions and terms used in the primary analysis. 

Tables 5-13 through 5-24 compile the statistical results of the alternative analysis in 

comparison to the primary analysis. Inclusion of the dT50 term has the effect of reducing 

the coefficient estimated for the RVPH effect, while leaving the coefficients of the 

temperature effect and the RVP · T interaction largely unchanged. The oxygenation 

effect is now represented by a linear slope for the emissions change between E0 and E20, 

while the deviation of emissions at E20 from the linear trend is included in the dT50 term. 

The statistical weakness of the dT50 term suggests that the design effects of RVP and 

temperature are preferred representations for emission changes, even if their coefficient 

values are influenced by T50 changes. 
-63- 

Table 5-13 

Alternative Model for CO FTP Composite 

(N=180, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) -0.01857 0.00 -0.01889 0.00 

 T · OxPct 0.00006 0.98 0.00006 0.93 

 RVPL (RVP-9) 0.00013 -0.00659 0.88 

 RVPH (RVP-9) 0.07946 0.00 0.05543 0.01 

 RVPH · T 0.00370 0.00 0.00378 0.00 

 RVP · OxPct -0.00360 0.92 n/a n/a 

 OxPct -0.09466 0.00 -0.07007 0.00 

 OxPct · OxPct 0.00640 0.08 n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00348 0.35 

Reduced Model 

 T (T-75) -0.01879 0.00 -0.01909 0.00 

 RVPL (RVP-9) 0.00001 1.00 -0.00752 0.85 

 RVPH (RVP-9) 0.07271 0.00 0.05565 0.01 

 RVPH · T 0.00373 0.00 0.00380 0.00 

 OxPct -0.10337 0.00 -0.06965 0.00 

 OxPct · OxPct 0.00746 0.02 n/a n/a 

 dT50 (T50–190F) -0.01879 0.00 -0.00352 0.33 

Technology Model 

T Groups 1+2 -0.01315 0.00 -0.01344 0.00 

 Groups 3+4 -0.02519 0.00 -0.02550 0.00 

RVPL (RVP-9) All -0.00025 0.99 -0.00749 0.84 

RVPH Groups 1+2 0.10843 0.00 0.09161 0.00 

Groups 3+4 0.03396 0.12 0.01725 0.48 

RVP · T Groups 1+2 0.00474 0.00 0.00480 0.00 

Groups 3+4 0.00276 0.03 0.00284 0.03 

OxPct -0.10312 0.00 -0.06918 0.00 

dT50 (T50–190F) 0.00743 0.01 -0.00343 0.32 
-64- 

Table 5-14 

Alternative Model for CO FTP Bag 1 

(N=180, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) -0.02751 0.00 -0.02795 0.00 

 T · OxPct 0.00035 0.57 0.00036 0.58 

 RVPL (RVP-9) -0.03644 0.31 -0.04108 0.29 

 RVPH (RVP-9) 0.05231 0.01 0.01944 0.31 

 RVPH · T 0.00315 0.00 0.00325 0.00 

 RVP · OxPct -0.00717 0.25 n/a n/a 

 OxPct -0.09410 0.00 -0.06403 0.00 

 OxPct · OxPct 0.00754 0.03 n/a n/a 

 dT50 (T50–190F) -- -- -0.00348 0.30 

Reduced Model 

 T (T-75) -0.02623 0.00 -0.02665 0.00 

 RVPL (RVP-9) -0.02974 0.39 -0.03508 0.34 

 RVPH (RVP-9) 0.03591 0.02 0.01803 0.34 

 RVPH · T 0.00299 0.00 0.00309 0.00 

 OxPct -0.11536 0.00 -0.06670 0.00 

 OxPct · OxPct 0.00950 0.00 n/a n/a 

 dT50 (T50–190F) -0.02623 0.00 -0.00324 0.33 

Technology Model 

T Groups 1+2 -0.02377 0.00 -0.02665 0.00 

 Groups 3+4 -0.02896 0.00 Same 

RVPL (RVP-9) All -0.02967 0.38 -0.03508 0.34 

RVPH Groups 1+2 0.03599 0.02 0.01803 0.34 

 Groups 3+4 Same Same 

RVPH · T Groups 1+2 0.00300 0.00 0.00309 0.00 

 Groups 3+4 Same Same 

OxPct -0.11523 0.00 -0.06670 0.00 

dT50 (T50–190F) n/a n/a -0.00324 0.33 
-65- 

Table 5-15 

Alternative Model for CO FTP Bag 2 

(N=180, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) 0.01718 0.20 0.01736 0.19 

 T · OxPct -0.00473 0.07 -0.00474 0.07 

 RVPL (RVP-9) 0.33022 0.03 0.33987 0.03 

 RVPH (RVP-9) 0.13600 0.11 0.15060 0.06 

 RVPH · T -0.00486 0.20 0.00482 0.21 

 RVP · OxPct 0.00041 0.99 n/a n/a 

 OxPct -0.10208 0.35 -0.11998 0.10 

 OxPct · OxPct -0.00514 0.72 n/a n/a 

 dT50 (T50–190F) -- -- 0.00366 0.79 

Reduced Model 

 T (T-75) -- -- -- -- 

 RVPL (RVP-9) 0.03584 0.74 0.03779 0.75 

 dVeh07 · RVPL 3.32832 0.00 3.32832 0.00 

 RVPH (RVP-9) 0.16848 0.00 0.17009 0.00 

 RVPH · T 0.00705 0.00 0.00705 0.00 

 OxPct -0.08735 0.00 -0.08487 0.14 

 OxPct · OxPct -- -- n/a n/a 

 dT50 (T50–190F) -- -- 0.00054 0.96 

Technology Model 

T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

RVPL (RVP-9) All 0.03584 0.74 0.03779 0.75 

dVeh07 · RVPL 3.32832 0.00 3.32832 0.00 

RVPH Groups 1+2 0.16848 0.00 0.17009 0.04 

 Groups 3+4 Same same 

RVPH · T Groups 1+2 0.00705 0.00 0.00705 0.00 

 Groups 3+4 Same same 

OxPct -0.08735 0.00 -0.08487 0.14 

dT50 (T50–190F) n/a n/a 0.00054 0.96 
-66- 

Table 5-16 

Alternative Model for CO FTP Bag 3 

(N = 156, excluding Tests with COBag3 = 0.000)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) 0.00307 0.66 0.00252 0.72 

 T · OxPct 0.00022 0.87 0.00024 0.86 

 RVPL (RVP-9) 0.02292 0.76 0.02144 0.79 

 RVPH (RVP-9) 0.10408 0.02 0.06034 0.14 

 RVPH · T 0.00138 0.49 0.00156 0.44 

 RVP · OxPct -0.01126 0.40 n/a n/a 

 OxPct -0.10838 0.05 -0.07098 0.06 

 OxPct · OxPct 0.00905 0.22 n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00358 0.61 

Reduced Model 

 T (T-75) -- -- -- -- 

 RVPL (RVP-9) 0.00248 0.97 0.00328 0.96 

 RVPH (RVP-9) 0.06640 0.01 0.07101 0.05 

 RVPH · T -- -- 0.00230 0.12 

 OxPct -0.13783 0.00 -0.07256 0.04 

 OxPct · OxPct 0.01191 0.06 n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00319 0.65 

Technology Model 

T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

RVPL (RVP-9) 0.02253 0.71 0.00623 0.93 

RVPH Groups 1+2 0.14635 0.00 0.12626 0.00 

 Groups 3+4 None None 

RVPH · T Groups 1+2 0.00527 0.00 0.00526 0.00 

 Groups 3+4 None None 

OxPct -0.13279 0.00 -0.07535 0.01 

dT50 (T50–190F) n/a n/a -0.00383 0.52 
-67- 

Table 5-17 

Alternative Model for HC FTP Composite

(N = 168, excluding Vehicle 11)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) -0.01164 0.00 -0.01166 0.00 

 T · OxPct -0.00058 0.11 -0.00058 0.11 

 RVPL (RVP-9) 0.00022 0.99 0.00099 0.96 

 RVPH (RVP-9) 0.01679 0.15 0.01548 0.15 

 RVPH · T 0.00059 0.26 0.00059 0.26 

 RVP · OxPct -0.00075 0.83 n/a n/a 

 OxPct -0.02045 0.18 -0.01994 0.05 

 OxPct · OxPct 0.00006 0.98 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00013 0.95 

Reduced Model 

 T (T-75) -0.01026 0.00 -0.01034 0.00 

 T · OxPct -0.00071 0.04 -0.00069 0.05 

 RVPL (RVP-9) 0.01840 0.29 0.01069 0.60 

 RVPH (RVP-9) -- -- -- -- 

 RVPH · T -- -- -- -- 

 OxPct -0.02281 0.00 -0.02672 0.00 

 OxPct · OxPct -- -- n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00101 0.48 

Technology Model 

T Groups 1+2 -0.00812 0.00 -0.00820 0.00 

 Groups 3+4 -0.01301 0.00 -0.01308 0.00 

T · OxPct -0.00072 0.03 -0.00069 0.04 

RVPL (RVP-9) All 0.01850 0.27 0.01100 0.58 

RVPH Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct -0.02279 0.00 -0.02660 0.00 

dT50 (T50–190F) n/a n/a -0.00098 0.48 
-68- 

Table 5-18 

Alternative Model for HC FTP Bag 1

(N = 140, excluding Vehicle 11)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) -0.01760 0.00 -0.01765 0.00 

 T · OxPct -0.00074 0.08 -0.00073 0.08 

 RVPL (RVP-9) -0.00613 0.80 -0.00631 0.80 

 RVPH (RVP-9) 0.01549 0.25 0.01214 0.33 

 RVPH · T 0.00080 0.19 0.00081 0.18 

 RVP · OxPct -0.00087 0.83 n/a n/a 

 OxPct -0.02842 0.11 -0.02559 0.03 

 OxPct · OxPct 0.00069 0.76 n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00027 0.90 

Reduced Model 

 T (T-75) -0.01579 0.00 -0.01583 0.00 

 T · OxPct -0.00092 0.02 -0.00090 0.02 

 RVPL (RVP-9) 0.00909 0.65 0.00486 0.84 

 RVPH (RVP-9) -- -- -- -- 

 RVPH · T -- -- -- -- 

 OxPct -0.02634 0.00 -0.02848 0.00 

 OxPct · OxPct -- -- n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00055 0.74 

Technology Model 

T Groups 1+2 -0.01379 0.00 -0.01383 0.00 

 Groups 3+4 -0.01835 0.00 -0.01838 0.00 

T · OxPct -0.00092 0.02 -0.00091 0.02 

RVPL (RVP-9) All 0.00919 0.64 0.00515 0.83 

RVPH Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct -0.02633 0.00 -0.02837 0.00 

dT50 (T50–190F) n/a n/a -0.00053 0.75 
-69- 

Table 5-19 

Alternative Model for HC FTP Bag 2

(N = 180, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) 0.00410 0.23 0.00433 0.20 

 T · OxPct -0.00079 0.24 -0.00079 0.24 

 RVPL (RVP-9) 0.02665 0.49 0.03335 0.41 

 RVPH (RVP-9) 0.00926 0.97 0.01659 0.41 

 RVPH · T -0.00086 0.38 -0.00091 0.35 

 RVP · OxPct 0.00177 0.79 n/a n/a 

 OxPct 0.02271 0.42 0.00368 0.84 

 OxPct · OxPct -0.00510 0.16 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00304 0.39 

Reduced Model 

 T (T-75) -- -- -- -- 

 T · OxPct -- -- -- -- 

 RVPL (RVP-9) 0.02654 0.37 0.01669 0.6386 

 RVPH (RVP-9) -- -- -- -- 

 RVPH · T -- -- -- -- 

 OxPct -0.01021 0.44 

 OxPct · OxPct n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00115 0.67 

Technology Model 

T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

T · OxPct -- -- -- -- 

RVPL (RVP-9) All -0.00258 0.93 0.01063 0.76 

RVPH Groups 1+2 0.06932 0.00 0.04831 0.01 

Groups 3+4 0.00230 0.02 0.00237 0.90 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct -- -- 0.00957 0.58 

dT50 (T50–190F) n/a n/a 0.00262 0.44 
-70- 

Table 5-20 

Alternative Model for HC FTP Bag 3

(N = 180, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) 0.00613 0.02 0.00608 0.02 

 T · OxPct -0.00072 0.17 -0.00072 0.17 

 RVPL (RVP-9) 0.00241 0.93 0.00987 0.75 

 RVPH (RVP-9) 0.02259 0.18 0.01966 0.20 

 RVPH · T -0.00020 0.79 -0.00019 0.80 

 RVP · OxPct -0.00448 0.38 n/a n/a 

 OxPct -0.00362 0.87 -0.00665 0.61 

 OxPct · OxPct -0.00135 0.63 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00191 0.48 

Reduced Model 

 T (T-75) 0.00387 0.01 0.00370 0.01 

 T · OxPct -- -- -- -- 

 RVPL (RVP-9) -0.00662 0.81 0.00015 1.00 

 RVPH (RVP-9) 0.01942 0.03 0.02146 0.02 

 RVPH · T -- -- -- -- 

 OxPct -- -- -- -- 

 OxPct · OxPct -- -- n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00164 0.16 

Technology Model 

T Groups 1+2 0.00039 0.01 0.00370 0.01 

 Groups 3+4 same -- -- 

RVPL (RVP-9) All -0.00662 0.81 -0.00015 1.00 

RVPH Groups 1+2 0.01942 0.03 0.02146 0.02 

 Groups 3+4 same -- -- 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct -- -- -- -- 

dT50 (T50–190F) n/a n/a 0.00164 0.16 
-71- 

Table 5-21 

Alternative Model for NOx FTP Composite 

(N=180, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) -0.00397 0.16 -0.00410 0.16 

 T · OxPct -0.00069 0.22 -0.00068 0.23 

 RVPL (RVP-9) -0.01120 0.73 -0.00753 0.83 

 RVPH (RVP-9) 0.03777 0.04 0.02988 0.08 

 RVPH · T -0.00026 0.75 -0.00023 0.78 

 RVP · OxPct -0.00411 0.46 n/a n/a 

 OxPct 0.01520 0.52 0.01887 0.23 

 OxPct · OxPct 0.00056 0.85 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00052 0.86 

Reduced Model 

 T (T-75) -0.00644 0.00 -0.00645 0.00 

 RVPL (RVP-9) -- -- -0.01809 0.56 

 RVPH (RVP-9) -0.01831 0.53 0.03153 0.02 

 RVPH · T 0.03134 0.00 -- -- 

 OxPct -- -- 0.002391 0.11 

 OxPct · OxPct 0.02362 0.00 n/a n/a 

 dedT50 (T50–190F) n/a n/a 0.000063 0.98 

Technology Model 

T Groups 1+2 -0.00691 0.00 -0.00691 0.00 

 Groups 3+4 -0.00594 0.01 -0.00594 0.01 

RVPL (RVP-9) All -0.01834 0.53 -0.01815 0.56 

RVPH Groups 1+2 0.03135 0.00 0.03152 0.02 

 Groups 3+4 same same 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct 0.02361 0.00 0.02388 0.11 

dT50 (T50–190F) n/a n/a 0.00006 0.98 
-72- 

Table 5-22 

Alternative Model for NOx FTP Bag 1 

(N=180, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) -0.00696 0.00 -0.00700 0.00 

 T · OxPct -0.00060 0.21 -0.00060 0.21 

 RVPL (RVP-9) -0.01051 0.70 -0.01704 0.55 

 RVPH (RVP-9) 0.00833 0.58 0.00479 0.73 

 RVPH · T -0.00061 0.37 -0.00060 0.38 

 RVP · OxPct 0.00216 0.64 n/a n/a 

 OxPct -0.00651 0.74 0.00106 0.93 

 OxPct · OxPct 0.00235 0.36 n/a n/a 

 dT50 (T50–190F) -- -- -0.00207 0.40 

Reduced Model 

 T (T-75) -0.00974 0.00 -0.00970 0.00 

 RVPL (RVP-9) -- -- -0.03050 0.25 

 RVPH (RVP-9) -0.02198 0.38 0.01127 0.32 

 RVPH · T 0.01855 0.03 -- -- 

 OxPct -- -- 0.00550 0.66 

 OxPct · OxPct 0.01670 0.00 n/a n/a 

 dT50 (T50–190F) n/a n/a -0.00243 0.32 

Technology Model 

T Groups 1+2 -0.01046 0.00 -0.01042 0.00 

 Groups 3+4 -0.00896 0.00 -0.00894 0.00 

RVPL (RVP-9) All -0.02204 0.38 -0.03058 0.25 

RVPH Groups 1+2 0.01857 0.03 0.01126 0.32 

 Groups 3+4 Same same 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct 0.01669 0.00 0.00544 0.66 

dT50 (T50–190F) n/a n/a -0.00244 0.32 
-73- 

Table 5-23 

Alternative Model for NOx FTP Bag 2 

(N=150, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) -0.00514 0.52 -0.00594 0.46 

 T · OxPct 0.00031 0.84 0.00032 0.84 

 RVPL (RVP-9) -0.12002 0.18 -0.08635 0.37 

 RVPH (RVP-9) 0.16090 0.00 0.10606 0.03 

 RVPH · T 0.00191 0.40 0.00211 0.36 

 RVP · OxPct -0.03218 0.04 n/a n/a 

 OxPct 0.04019 0.54 0.06005 0.17 

 OxPct · OxPct 0.00191 0.82 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00587 0.48 

Reduced Model 

 T (T-75) -- -- -- -- 

 RVPL (RVP-9) -- -- -0.04970 0.55 

 RVPH (RVP-9) -0.08755 0.26 -- -- 

 RVPH · T 0.14026 0.00 0.07927 0.04 

 OxPct -0.03448 0.01 0.05762 0.17 

 OxPct · OxPct 0.05243 0.01 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00575 0.48 

Technology Model 

T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

RVPL (RVP-9) All -0.07059 0.37 -0.04970 0.55 

RVPH Groups 1+2 0.06209 0.03 0.07927 0.04 

 Groups 3+4 Same same 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct 0.03110 0.01 0.05762 0.17 

dT50 (T50–190F) n/a n/a 0.00575 0.48 
-74- 

Table 5-24 

Alternative Model for NOx FTP Bag 3 

(N=150, 15 Vehicles)

Base Models Including T50 Effect 

 Coefficient Prob>|t| Coefficient Prob>|t| 

Full Model 

 Intercept -- -- -- -- 

 T (T-75) 0.00669 0.22 0.00675 0.21 

 T · OxPct -0.00202 0.06 -0.00202 0.06 

 RVPL (RVP-9) -0.01100 0.86 0.00761 0.91 

 RVPH (RVP-9) 0.05348 0.12 0.05987 0.06 

 RVPH · T -0.00011 0.94 -0.00012 0.94 

 RVP · OxPct -0.00726 0.50 n/a n/a 

 OxPct 0.05997 0.18 0.04104 0.16 

 OxPct · OxPct -0.00605 0.30 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00567 0.31 

Reduced Model 

 T (T-75) -- -- -- -- 

 RVPL (RVP-9) -- -- -0.02230 0.69 

 RVPH (RVP-9) -0.03790 0.47 -- -- 

 RVPH · T 0.04520 0.02 0.05803 0.02 

 OxPct -- -- 0.05600 0.05 

 OxPct · OxPct 0.03620 0.00 n/a n/a 

 dT50 (T50–190F) n/a n/a 0.00429 0.44 

Technology Model 

T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

RVPL (RVP-9) All -0.03790 0.47 -0.02230 0.69 

RVPH Groups 1+2 0.04520 0.02 0.05803 0.02 

 Groups 3+4 same same 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct 0.03620 0.00 0.05600 0.05 

dT50 (T50–190F) n/a n/a 0.00429 0.44 
-75- 

5.5 Summary of Correction Factors Based on Primary Analysis

This subsection summarizes the coefficient values for the correction factor equations 

developed from the primary analysis. In addition, the combined effects of temperature, 

RVP, and oxygenate effects are separated into their individual contributions. Tables 5-25 

and 5-26 summarize the correction factor results for CO emissions. 

Table 5-25 

Correction Factor Coefficients for FTP CO Emissions 

Composite Bag 1 Bag 2 Bag 3 

T Groups 1+2 -0.01315 -0.02327 -- -- 

 Groups 3+4 -0.02519 -0.02846 -- -- 

RVPH Groups 1+2 0.10843 0.03599 0.16848 0.14635 

 Groups 3+4 0.03396 none 

RVPH · T Groups 1+2 0.00474 0.00300 0.00705 0.00527 

 Groups 3+4 0.00276 none 

OxPct -0.10312 -0.11523 -0.08735 -0.13279 

OxPct · OxPct 0.00743 0.00949 -- 0.01105 

Table 5-26 

Estimated Effects of Design Variables on FTP CO Emissions 

(Compared to Design Variable Conditions Stated, Percent)

Design Variable 

Conditions Composite Bag 1 Bag 2 Bag 3 

T = 50°F 

Groups 1+2 T 75F->50F, 

RVP=9, E0 

39% 81% -- -- 

Groups 3+4 88% 106% -- -- 

RVP = 13 psi at 75°F 

Groups 1+2 RVP 9->13, 

T=75°F, E0 

54% 

 15% 96% 

80% 

Groups 3+4 15% none 

RVP = 13 psi at 50°F 

Groups 1+2 RVP 9->13, 

T=50°F, E0 

- 4% 

-14% -3% 

 6% 

Groups 3+4 -13% none 

Oxygenation at 75°F and 50°F 

E10 E0->E10-E20, 

RVP = Any, 

T = Any 

-24% -26% -28% -29% 

E15 -29% -30% -38% -33% 

E20 -30% -30% -48% -33% 
-76- 

For CO, the effect of non-FTP conditions is largely driven by low ambient temperature. 

At 50°F, CO has increased substantially due to temperature alone (at constant RVP). 

Increasing gasoline RVP to 13 psi offsets a small part of the cold-temperature emissions 

increase in Bag 1 and has a small benefit in Bag 2 and a small adverse effect in Bag 3. 

The Bag 1 RVP effect switches from adverse to beneficial at temperatures below 63°F. 

At 75°F and higher, increased RVP has a consistently adverse effect on CO. Fuel 

oxygenation at the E10 level decreases CO emissions by 24–29 percent in all Bags and 

independently of temperature and RVP, but during vehicle start (Bags 1 and 3) little 

additional benefit is seen from oxygen content in excess of E10. 

To illustrate these trends, Figures 5-1 through 5-6 show estimated CO emissions as a 

function of temperature and RVP. Emissions for RVP 7 psi fuels are the same as shown 

for 9 psi because no statistically significant emissions change could be detected for RVP 

between 7 and 9 psi. Only Group 1 (Tier 1) and Group 4 (Tier 2 Enhanced) vehicles are 

shown because the trends do not differ for the other groups. As the graphs make clear, 

the primary effect on Bag 1 CO emissions is cold ambient temperatures, with a relative 

minor beneficial effect for high RVP gasoline at temperatures below about 55°F. RVP 

has a much larger and consistently adverse effect in Bags 2 and 3. 

Figure 5-1 

Group 1, Bag 1 CO Trends 
-77- 

Figure 5-2 

Group 1, Bag 2 CO Trends 

 

Figure 5-3 

Group 1, Bag 3 CO Trends 
-78- 

Figure 5-4 

Group 4, Bag 1 CO Trends 

Figure 5-5 

Group 4, Bag 2 CO Trends 
-79- 

Figure 5-6 

Group 4, Bag 3 CO Trends 

Tables 5-27 and 5-28 summarize the correction factor results for THC emissions. As for 

CO, cold ambient temperatures significantly increase Bag 1 THC emissions. Unlike CO, 

however, no RVP effect can be detected for Bag 1 THC. For Bags 2 and 3, the RVP 

effect is found to be the same at both 50°F and 75°F. For Bag 2, gasoline RVP of 13 psi 

has a substantial effect on THC emissions for Group 1 and 2 vehicles, but only a 

negligibly small effect is seen for Groups 3 and 4 vehicles. A small but adverse Bag 3 

effect is seen for all vehicles. Fuel oxygenation has a small beneficial effect for 

Table 5-27 

Correction Factor Coefficients for FTP THC Emissions 

Composite Bag 1 Bag 2 Bag 3 

T Groups 1+2 -0.00812 -0.01379 -- 0.00039 Groups 3+4 -0.01301 -0.01835 -- 

T · OxPct -0.00072 -0.00092 -- -- 

RVPH Groups 1+2 -- -- 0.06932 0.01942 Groups 3+4 -- -- 0.00230 

RVPH · T Groups 1+2 -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct -0.02279 -0.02633 -- -- 

OxPct · OxPct -- -- -- -- 
-80- 

Table 5-28 

Estimated Effects of Design Variables on FTP THC Emissions 

(Compared to Design Variable Conditions Stated, Percent)

Design 

Variable 

Conditions 

Composite Bag 1 Bag 2 Bag 3 

T = 50°F 

Groups 1+2 T 75F->50F, 

RVP=9, E0 

23% 41% -- 

negligible Groups 3+4 38% 58% -- 

RVP = 13 psi at 75°F 

Groups 1+2 RVP 9->13, 

T=75°F, E0 -- -- 32% 

8% 

Groups 3+4 1% 

RVP = 13 psi at 50°F 

Groups 1+2 RVP 9->13, 

T=50°F, E0 -- -- 32% 

8% 

Groups 3+4 1% 

Oxygenation at 75°F 

E10 E0->E10-E20, 

RVP = Any, 

T = 75°F 

-8% - 9% -- -- 

E15 -12% -14% -- -- 

E20 -16% -18% -- -- 

Oxygenation at 50°F 

E0->E10-E20, 

RVP = Any, 

T = 50°F 

negligible negligible -- -- 

Composite Bag 1 THC emissions only and only at an ambient temperature of 75°F. The 

oxygenation benefit decreases with temperature and is negligible at an ambient 

temperature of 50°F. 

Tables 5-29 and 5-30 summarize the correction factor results for NOx emissions. 

Because the Bag 1 RVP effects were found to differ between PCs and LDTs, separate 

estimates are given in the tables; however, no such differences could be detected for the 

FTP Composite or Bags 2 and 3 phases. Cold ambient temperatures increase Bag 1 NOx 

emissions by 25 to 30 percent depending on the vehicle group. High RVP gasoline has 

no direct effect on Bag 1 NOx emissions of PCs, but is found to increase LDT emissions 

by 18 percent at an RVP of 13 psi at all temperatures. High RVP gasoline has adverse 

effects on Bag 2 and Bag 3 NOx emissions for all vehicles at all temperatures. Fuel 

oxygenation at the E10 level increases NOx emissions by approximately 10 percent in all 

FTP Bags and by larger amounts at higher oxygen contents. 
-81- 

Table 5-29 

Correction Factor Coefficients for FTP NOx Emissions 

Composite Bag 1 Bag 2 Bag 3 

All PCs LDTs All All 

T Groups 1+2 -0.00691 -0.01046 -0.01046 -- -- Groups 3+4 -0.00594 -0.00896 -0.00896 

RVP Groups 1+2 0.03135 -- 0.04152 0.06290 0.04520 Groups 3+4 -- 

RVP · T Groups 1+2 -- -- -- -- -- 

 Groups 3+4 -- -- -- -- 

OxPct 0.02361 0.01640 0.01640 0.03110 0.03620 

OxPct · OxPct -- -- -- -- -- 

Table 5-30 

Estimated Effects of Design Variables on FTP NOx Emissions 

(Compared to Design Variable Values as Stated, Percent) 

Design 

Variable 

Conditions 

Composite Bag 1 Bag 2 Bag 3 

All PC LDT All All 

T = 50°F 

Groups 1+2 T 75F->50F, 

RVP = 9, E0 

19% 30% -- -- 

Groups 3+4 16% 25% -- -- 

RVP = 13 psi at 75°F 

Groups 1+2 RVP 9->13, 

T=75°F, E0 

13% 

none 18% 28% 20% 

Groups 3+4 13% 

RVP = 13 psi at 50°F 

Groups 1+2 RVP 9->13, 

T=50°F, E0 

13% 

none 18% 28% 20% 

Groups 3+4 13% 

Oxygenation at 75°F and 50°F 

E10 E0->E10-

E20, 

RVP = Any, 

T = Any 

9% 6% 12% 14% 

E15 14% 10% 19% 22% 

E20 19% 13% 26% 31% 

5.6 Comparison of Adjustment Factors to Those in MOBILE6.2

Table 5-31 compares the CO adjustment factors estimated for this study to those 

currently incorporated in the MOBILE6.2 model. One major finding is the continued 

presence of an oxygenate effect in Tier 1 and later vehicles that reduces CO emissions on 
-82- 

Table 5-31 

Comparison of CO Adjustment Factors to MOBILE6.2 Factors 

MOBILE6.2 Factors CRC E74b Factors 

Oxygenate Effect 

(Tier 1 and Later Vehicles) 

Normal Emitters no effect Bag 1 -8.4% per %O2 a

Bag 2 -8.7% per %O2 a

Bag 3 -9.5% per %O2 

High Emitters -5.3% per %Oxygen not tested 

RVP Effect (RVP 9-13) at 75°F 

Group 1/2 Vehicles 

Bag 1 4.2% per psi Bag 1 3.7% per psi 

Bag 2 30% per psi Bag 2 18.4% per psi 

Bag 3 26% per psi Bag 3 15.8% per psi 

Group 3/4 Vehicles 

Bag 1 4.2% per psi Bag 1 3.7% per psi 

Bag 2 30% per psi Bag 2 18.4% per psi 

Bag 3 26% per psi Bag 3 not detected 

RVP Effect (RVP 9-13) at 50°F 

Group 1/2 Vehicles 

Bag 1 0.7% per psi Bag 1 -3.8% per psi 

Bag 2 5.0% per psi Bag 2 0.7% per psi 

Bag 3 4.4% per psi Bag 3 2.5% per psi 

Group 3/4 Vehicles 

Bag 1 0.7% per psi Bag 1 -3.8% per psi 

Bag 2 5.0% per psi Bag 2 0.7% per psi 

Bag 3 4.4% per psi Bag 3 not detected a

 Oxygenate effect depends on oxygen content. Value shown is for E10.

the order of 8% per percent oxygen content of the fuel. MOBILE6.2 assumes no benefit 

from oxygenated fuels in normal emitting Tier 1 and later vehicles. The approximately 

7-9% per percent effect found here is even larger than the ~5% per percent effect 

assumed for high emitters in MOBILE6.2. As previously noted, none of the vehicles 

tested in this program were high emitters and therefore no inferences can be drawn from 

the data, although for inventory purposes it would be reasonable to assume that high 

emitters experience at least the same effect as normal emitters. 

For Tier 1 and later vehicles (Groups 1 and 2), the CO emissions effects due to gasoline 

RVP in the range 9 to 13 psi are generally comparable to (Bag 1) or much smaller than 

(Bags 2 and 3) the responses assumed in MOBILE6.2. For Tier 2 vehicles (Groups 3 and 

4), this study estimates a comparable effect in Bag 1, a much smaller effect in Bag 2, and 

cannot detect an effect in Bag 3. The overall consequence of the revised CO RVP 
-83- 

adjustment factors for a fleet of in-use vehicles will depend on the mix of vehicles in the 

fleet and the relative contributions of cold-start, hot-start, and running emissions. 

As demonstrated in Section 4.6, this study confirms the assumption made in MOBILE6.2 

that gasoline RVP reductions below 9 psi have little or no effect on CO emissions. 

Correction factors developed in this study for exhaust NOx and THC emissions are 

compared in the following tables. As Table 5-32 shows, the correction factors for 

Table 5-32 

Comparison of THC Adjustment Factors to MOBILE6.2 Factors 

MOBILE6.2 Factors CRC E74b Factors 

Oxygenate Effect a

(Tier 1 and Later Vehicles) 

Normal Emitters Variable but negative a

Bag 1 -2.6% per 

%oxygen b

 

Bag 2 no effect

Bag 3 no effect 

High Emitters Variable but negative a not tested 

RVP Effect (RVP 9-13) at 75°F 

Group 1/2 Vehicles 

Bag 1 2.3% per psi Bag 1 no effect 

Bag 2 17% per psi Bag 2 7.2% per psi 

Bag 3 14% per psi Bag 3 2.0% per psi 

Group 3/4 Vehicles 

Bag 1 2.3% per psi Bag 1 no effect 

Bag 2 17% per psi Bag 2 0.2% per psi 

Bag 3 14% per psi Bag 3 2.0% per psi 

RVP Effect (RVP 9-13) at 50°F 

Group 1/2 Vehicles 

Bag 1 0.4% per psi Bag 1 no effect 

Bag 2 2.8% per psi Bag 2 7.2% per psi 

Bag 3 2.4% per psi Bag 3 2.0% per psi 

Group 3/4 Vehicles 

Bag 1 0.4% per psi Bag 1 no effect 

Bag 2 2.8% per psi Bag 2 0.2% per psi 

Bag 3 2.4% per psi Bag 3 2.0% per psi a

 Oxygenate effect in MOBILE6.2 depends on the absolute level of the basic emission rate at standard 

conditions computed using a methodology carried over from MOBILE4.1. 

b Oxygenate effects tabulated for this study are at 75°. Oxygenate is estimated to have negligible effect at 

50°.
-84- 

oxygenate effects on THC emissions cannot be effectively compared owing to the 

dependence of the MOBILE6.2 factors on the base THC emission rate of the vehicle 

technology group in question. For Bag 1, both MOBILE6.2 and the current study 

indicate declining THC emissions with increasing oxygen content, but this study does not 

detect an oxygenate effect on THC emissions in Bags 2 and 3. Adjustments for RVP 

effects on exhaust THC emissions based on the current study are again similar to those in 

MOBILE6.2, with increasing RVP leading to higher THC emissions, although the Bag 2 

effect seen here is larger. However, this study finds no difference in the magnitude of the 

effect (on a percentage basis) at 50°F compared to that at 75°F. 

Table 5-33 shows that, as expected, increasing oxygen content leads to increased NOx 

emissions, despite the fact that MOBILE6.2 ignores this effect. Directionally, the 

adjustment factors for RVP effects on NOx are consistent with those in MOBILE6.2, 

although somewhat larger in size, with NOx emissions increasing with increasing RVP. 

Table 5-33 

Comparison of NOx Adjustment Factors to MOBILE6.2 Factors 

MOBILE6.2 Factors CRC E74b Factors 

Oxygenate Effect 

(Tier 1 and Later Vehicles) 

Normal Emitters No effect 

Bag 1 1.6% per 

%oxygen

Bag 2 3.1% per 

%oxygen

Bag 3 3.6% per 

%oxygen

High Emitters No effect not tested 

RVP Effect (RVP 9-13) at 75°F 

All Vehicles 

Bag 1 1.4% per psi Bag 1 4.2% per psi 

Bag 2 2.8% per psi Bag 2 6.4% per psi 

Bag 3 No effect Bag 3 4.6% per psi 

RVP Effect (RVP 9-13) at 50°F 

All Vehicles 

Bag 1 0.2% per psi Bag 1 4.2% per psi 

Bag 2 0.5% per psi Bag 2 6.4% per psi 

Bag 3 No effect Bag 3 4.6% per psi 

However, this study finds no difference in the magnitude of the RVP effect (on a 

percentage basis) at 50°F compared to that at 75°F. The current study does, however, 

show Bag 3 impacts, whereas MOBILE6.2 assumes no effect. 
-85- 

5.7 Comparison of RVP and Oxygenate Effects to Those of Previous Sierra 

Study

As noted previously, in 2003 Sierra examined available CO exhaust test data at 

temperatures below 75°F and developed RVP and temperature adjustments using the 

same form used in this study.*

 That study compiled data from seven test programs and 

extracted data from 1988-and-newer model year, fuel-injected vehicles tested at 

temperatures between 35° and 75°F for use in adjustment factor analysis. It was 

observed in that analysis that the RVP and RVP · T coefficients were significantly more 

uncertain than the temperature coefficient. Because the overall goal was to develop a 

new RVP adjustment approach, the RVP-related coefficients were defined even if not 

statistically significant.†

Table 5-34 presents the RVP and temperature correction coefficients for CO exhaust 

from both studies for comparative purposes. The temperature coefficient from the E-74b 

test program is about half that of the previous Sierra analysis, which may be a reflection 

of the effects of cold temperature CO standards. The RVP coefficient of the E-74b test 

program is greater and the coefficient that defines how the RVP effect changes with 

temperature is also greater. 

Table 5-35 presents the percent change in emissions due to reducing RVP from 11.7 psi 

to 9.0 psi using the equation coefficients of the two studies. Additionally, the percent 

change in emissions as estimated by MOBILE6.2 is presented. The RVP of 11.7 was 

chosen as this is the MOBILE6.2 upper limit for RVP adjustment.‡

 Overall, the relative 

RVP effects observed in the E-74b data are distinctly different from those of the previous 

Sierra analysis. However, it should be recalled that the absolute (e.g., g/mi) CO 

emissions of the vehicles previously analyzed by Sierra were much higher than those of 

the E-74b program vehicles. In addition, at lower temperatures, the E-74b data show a 

reduction in CO emissions at higher RVP. Finally, both the E-74b data and previous 

Sierra analysis show a smaller relative impact of RVP on CO emissions than is predicted 

by MOBILE6.2.§ 

 

*

“Review of Current and Future CO Emissions From On-Road Vehicles in Selected Western Areas,” 

Report No. SR03-01-01, prepared for Western States Petroleum Association by Sierra Research, January 

2003. 

†

There is a greater degree of variability inherent in the previous Sierra analysis due to the wider variability 

of vehicles and test conditions reflected in the data. Only FTP-composite and matched vehicle test data 

were included in the analysis. 

‡

The modeling limit is discussed further in Section 6 of this report. 

§

As discussed in the 2003 Sierra report, the MOBILE6.2 RVP corrections are based on 75°F test data only, 

and the RVP effect is assumed to decline linearly to no effect at 45°F. 
-86- 

Table 5-34 

Comparison of RVP and Temperature Adjustment Equation Coefficients for FTP 

Composite Exhaust CO Emissions 

Modeling Coefficient CRC E-74b Previous Sierra (All Data)

T -0.01857 -0.0355 

RVP 0.07946 0.0116 

RVP · T 0.00370 0.000144 

Table 5-35 

Estimated Impact of Reducing RVP from 11.7 to 9.0 psi on FTP Composite CO 

Emissions 

Temperature (°F) CRC E-74b 

Previous Sierra 

(All Data) MOBILE6.2*

75 -19.3% -3.1% -46.1% 

65 -10.8% -2.7% -35.6% 

55 -1.5% -2.3% -20.4% 

45 8.9% -1.9% 0.0% 

### 

 

*

MOBILE6.2 was operated for calendar year 2007 using a national default fleet mix. Trip length, vehicle 

soak periods, start emissions, and driving cycle adjustments were defined to simulate those characteristics 

of the FTP composite test cycle. 
-87- 

6. COMPARISON OF MOBILE6.2 AND UPDATED CO 

ADJUSTMENT FACTORS 

This section first describes the methodology to incorporate the emission adjustment 

factors presented in the previous section into MOBILE6.2; it then compares the estimated 

wintertime CO emissions inventory for Clark County (Las Vegas), Nevada obtained 

using the updated adjustment factors to that derived with the original factors in 

MOBILE6.2. The Las Vegas area was selected for this comparison for several reasons. 

It—along with the Phoenix, Arizona area—represents one of the two major urban areas 

where regulations requiring winter gasoline to contain 3.5 percent oxygen by weight and 

limiting RVP to 9 psi were implemented in order to reduce CO emissions from on-road 

vehicles. Because limited project resources precluded comparisons in both areas, it was 

selected over Phoenix due to the availability of the emission inventory data required to 

perform the comparison. 

6.1 Methodology

MOBILE6.2 – For the Las Vegas CO inventory analysis, selected winter gasoline RVP 

and oxygenate scenarios were analyzed under typical winter conditions for the CO SIP 

evaluation years of 2006, 2010, and 2015. Emission factors were estimated by the U.S. 

EPA’s MOBILE6.2 model* and combined with data on vehicle miles traveled (VMT) to 

yield on-road CO inventories for the study area. 

The MOBILE6.2 emission factor modeling relied on input data specific to Clark County, 

which reflect local winter temperatures, fuel parameters, registration distributions, VMT 

distributions by vehicle class, VMT distributions by hour of day, distribution of vehicle 

starts by hour of day, and inspection and maintenance (I/M) parameters. These modeling 

data, specific to the evaluation calendar years, were those from the recent 2005 SIP 

revision.†

 Hourly winter temperatures, a key assumption for the analysis, fell within the 

range of 42oF (minimum) and 66oF (maximum). The diurnal profiles for temperature and 

VMT are shown in Figure 6-1. Combining the hourly temperature profile with the hourly 

VMT profile showed that 70% of the VMT on the average winter day fell within the 50oF 

to 75oF range, making the Clark County area ideally suited for an evaluation of fuel 

adjustment factors at these temperatures. 

 

*

Version 6.2.03 dated September 2003. 

†

“Carbon Monoxide State Implementation Plan Revision Las Vegas Valley Nonattainment Area 

Clark County, Nevada,” Clark County Department of Air Quality and Environmental Management and 

Clark County Board of Commissioners, October 2005. 
-88- 

Figure 6-1 

Las Vegas Typical Winter Day Diurnal Profiles 

40

45

50

55

60

65

70

12:00 AM

1:00 AM2:00 AM3:00 AM4:00 AM5:00 AM6:00 AM7:00 AM8:00 AM9:00 AM

10:00 AM11:00 AM12:00 PM

1:00 PM2:00 PM3:00 PM4:00 PM5:00 PM6:00 PM7:00 PM8:00 PM9:00 PM

10:00 PM11:00 PM

Begin Hour

Temperature (Degrees F)

0.0%

1.0%

2.0%

3.0%

4.0%

5.0%

6.0%

7.0%

8.0%

Hourly VMT (Percent of Daily Total)

Temperature

Hourly VMT

Las Vegas VMT data were taken from a 2007 analysis of summer gasoline volatility 

control options as these represented more recent travel demand modeling since the 2005 

SIP revision.*

 Interpolation between calendar years was completed, as needed, to match 

the inventory years of this analysis. The VMT data used represent the urban portion of 

Clark County, which is also the region subject to the local I/M program requirements. 

Average daily VMT estimates used in this evaluation were 40,050,285 for 2006; 

50,608,417 for 2010; and 59,804,322 miles for 2015. 

As noted above, winter gasoline sold in Clark County is currently subject to RVP limits 

as well as specifications for oxygenate content. In addition, sulfur and aromatic content 

restrictions apply. The current wintertime gasoline fuel requirements in Clark County are 

summarized in Table 6-1; the 2006 winter Clark County gasoline properties are 

summarized in Table 6-2. These data were taken from the Winter 2006 Alliance of 

Automobile Manufacturers (AAM) Fuel Survey Data.†

 

 

*

“Demonstration of the Necessity of Regulations Requiring 7.0 PSI RVP Gasoline in Clark County, 

Nevada as an Ozone Control Strategy,” Sierra Research, November 2007. 

†

“Alliance of Automobile Manufacturers North American Fuel Survey Motor Gasoline Winter 2006,” 

Alliance of Automobile Manufacturers, 2006. 
-89- 

Table 6-1 

Wintertime Gasoline Fuel Requirements for Clark County 

Fuel Property Standard 

Reid Vapor Pressure (RVP) Max 9.0 psi (10.0 psi for fuel with 9+ vol % EtOH) 

Sulfur Content Max 80 ppmw; Flat limit of 40 ppmw 

Aromatic Content Max 30 vol %; Flat limit of 25 vol % 

Oxygen Content Min 3.5 wt % 

Table 6-2 

Winter 2006 Gasoline Parameters 

Fuel Property Clark County Gasoline 

Methyl Tertiary Butyl Ether (MTBE) (wt% oxygen) 0 

Ethyl Tertiary Butyl Ether (ETBE) (wt% oxygen) 0 

Ethanol (wt% oxygen) 3.47 

Tertiary Amyl Methyl Ether (TAME) (wt% oxygen) 0 

Sulfur (ppm) 31 

RVP (psi) 8.8 

E200 (%) 46.4 

E300 (%) 78.7 

Aromatics (vol%) 20.2 

Olefins (vol%) 6.7 

Benzene (vol%) 0.60 

For the fuel scenarios, both RVP and oxygenate levels were varied. A total of nine fuel 

scenarios were modeled (the unique combinations of three RVP and three oxygenate 

levels) by including the following parameters: 

 RVP of 9, 11.7, and 13.3 psi; and 

 Oxygen content of 0, 2.7, and 3.5 weight percent. 

The RVP levels selected reflect the current 9 psi limit, the maximum RVP adjustment 

currently allowed in MOBILE6.2 (11.7 psi), and the maximum RVP of the fuels in this 

test program (13.3 psi).*

 The oxygenate levels were chosen on the basis of the minimum 

content required for serious CO nonattainment areas (2.7 weight percent), the maximum 

 

*

11.7 psi is the upper bound for gasoline volatility effects in the U.S. EPA MOBILE6.2 model. This level 

represents the highest RVP of the test fuels from which the model’s gasoline volatility algorithms are 

based. As such, the standard version of the model treats any gasoline with volatility over 11.7 psi as 11.7 

psi fuel. 
-90- 

level currently allowed (3.5 weight percent), and the elimination of an oxygenate 

requirement (0 weight percent).*

Code Modifications to Incorporate Adjustment Factors and Provide for Comparisons – 

Two versions of MOBILE6.2 were used in the inventory analysis of the nine fuel 

scenarios. One was the standard U.S. EPA model with the 11.7 psi RVP upper limit 

raised to 13.3 psi, and the second was developed by modifying the source code to update 

the treatment of temperature, volatility, and oxygenate effects as measured in the CRC E74b test data. A summary of these models is outlined below. 

 U.S. EPA MOBILE6.2 – This is the standard regulatory model currently available 

from the U.S. EPA. The maximum volatility effect of 11.7 psi was modified for 

this project by raising it to 13.3 psi. This means that the model’s existing RVP 

correction algorithms were extrapolated to 13.3 psi, and the correction equation 

coefficients were unchanged. 

 Updated Adjustment Factor Version of MOBILE6.2 – The U.S. EPA model was 

modified with updated Tier 1 and later vehicle adjustment factors for varying 

temperature, gasoline volatility, and oxygenate levels based on the CRC E-74b 

test program. The maximum volatility effect of 11.7 psi was raised to the test 

program maximum of 13.3 psi. Note that although none of the vehicles in the test 

program were “high emitters,” the oxygenate adjustment factors developed here 

were also applied to vehicles in that emissions regime.†

 

For modeling volatility effects below 75oF, the U.S. EPA version of MOBILE6.2 applies 

a multiplicative adjustment factor to correct for gasoline volatility in excess of 9.0 psi 

(where the adjustment factor equals unity at 9.0 psi). The exponential equation used to 

define the multiplicative adjustment factor below 75oF is as follows: 

    



 



    30

45T RVPADJ RVPEXP COEFF 9RVP

Where 

RVPADJ = RVP adjustment (unitless multiplier), 

RVPCOEFF = RVP equation coefficient (psi-1), 

RVP = RVP (psi), and 

T = Temperature (oF). 

 

*

Because Clark County is still designated as a “serious” nonattainment area with respect to attainment of 

the eight-hour CO NAAQS, winter gasoline is still required by the Clean Air Act to contain at least 2.7% 

oxygen by weight. 

†

The revised Tier 1 and later vehicle oxygenate corrections (for normal emitters) were found to be greater 

than the existing model assumption for high emitters (a value carried over from Tier 0 vehicles). 

Engineering judgment was applied in which the oxygenate effect for high emitters of a given vehicle 

technology would not be less than those estimated for normal emitters. Therefore, the Tier 1 and later 

vehicle high emitter oxygenate corrections were modified to equal those estimated for normal emitters. 
-91- 

However, an alternate form of the RVP adjustment equation (that used by the model for 

temperatures over 75oF) was used as the basis for the updated adjustment factor version 

of MOBILE6.2. This equation, which combines both temperature and RVP adjustments, 

is shown below. The equation also includes a combined temperature and RVP term 

allowing for a varying RVP effect as temperature changes.* 

RVP&T RVPEXP     RT75TT9RVP   75T9RVP  ADJ  COEFF COEFF  COEFF 

Where 

T & RVPADJ = Combined temperature and RVP adjustment (unitless multiplier), 

RVPCOEFF = RVP term coefficient (psi-1), 

TCOEFF = Temperature term coefficient (o

F -1), 

RTCOEFF = Combined RVP and temperature term coefficient (oF -1psi-1), 

RVP = RVP (psi), and 

T = Temperature (o

F). 

The updated equation coefficients (RVPCOEFF, TCOEFF, and RTCOEFF) were programmed 

directly into the source code, including conditional statements needed to make proper 

vehicle technology distinctions (i.e., keep the Tier 0 code unchanged and continuing to 

use the existing U.S. EPA modeling approach). Additional minor code modifications 

were made so that additional vehicle characteristics were available (for model year and 

vehicle class) such that vehicle technologies could be correctly identified. Lastly, the 

model’s existing temperature corrections for Tier 1 and later vehicles were deactivated to 

avoid double counting the temperature correction, given that the new equation and 

coefficients in the updated model encompass both temperature and volatility corrections. 

For modeling oxygenate effects, MOBILE6.2 applies a multiplicative adjustment factor 

to correct for oxygen levels between zero and 3.5 weight percent (where the adjustment 

factor equals unity at zero oxygen content). The equation used to define the 

multiplicative adjustment is as follows: 





 



  

100

OXY OXY 1OXY COEFF

ADJ

Where 

OXYADJ = OXY adjustment (unitless multiplier), 

OXYCOEFF = OXY equation coefficient (% exhaust impact/wt. % oxygen), and 

OXY = Weight percent oxygen (in gasoline-oxygenate blend). 

 

*

This equation is improved over the default MOBILE6.2 equation because it allows for the evaluation of all 

coefficients (temperature and RVP) based on the actual test data and because it does not simply assume a 

linear decay in the 75oF RVP effect between 75o and 45o as computed by the U.S. EPA model. 
-92- 

The updated oxygenate effect coefficients (OXYCOEFF) were programmed directly into 

the source code, including conditional statements needed to make proper vehicle 

technology distinctions. Additional code modifications were made so that FTP phasespecific coefficients could be applied. This differs from the regulatory version of the 

model in which the coefficients are uniform for all FTP phases (i.e., based on FTP 

composite test results). Combining the FTP phase-specific corrections into start and 

running exhaust corrections was modeled on the similar approach developed for 

temperature and volatility by the U.S. EPA.*† 

It should be noted that because the fuel scenarios include the case of 9.0 psi and zero 

oxygen content (instances where the adjustment factors for these two effects become 

unity), the only difference in predicted emission rates between model versions for this 

specific case becomes the temperature correction adjustments. This allows for a 

quantification of the temperature adjustment differences alone, independent of the other 

fuel adjustments. 

6.2 Results 

The winter on-road CO emission inventories for Las Vegas obtained using MOBILE6.2 

and the updated adjustment factors are presented in Table 6-3 for each of the nine 

combinations of RVP and oxygen content, for each of the three analysis years. The 

results are also presented graphically in Figures 6-2 through 6-4. 

As can be seen from the data in Table 6-3 and more easily in Figure 6-2, use of the 

updated adjustment factors for oxygenate content has a profound impact on the Las 

Vegas CO inventory. Figure 6-2 shows only the oxygenate effect at the three oxygenate 

levels analyzed for gasoline at 9.0 psi RVP for the three analysis years. The first point is 

that the predicted reduction in CO emissions associated with moving from zero to 3.5% 

oxygen by weight is more than 3 times greater using the updated adjustments than is 

 

*

In MOBILE6.2, exhaust emissions are estimated for two components: the running LA4 plus the 

incremental start offset; however, correction factors within MOBILE6.2 continue to be applied on an FTP 

phase-specific basis, as they were originally derived in MOBILE5 and earlier versions. The MOBILE6.2 

model applies both Phase 1 and Phase 3 corrections to the incremental start exhaust (depending on the 

length of the vehicle soak period); the model applies a weighted Bag 2 and Bag 3 correction to the running 

LA4 exhaust. See the MOBILE6.2 technical documentation “Exhaust Emission Temperature Correction 

Factors for MOBILE6: Adjustments for Engine Start and Running LA4 Emissions for Gasoline Vehicles 

(M6.STE.004)” for an elaboration and justification of this approach as well as a discussion of its shortfalls. 

†

Consideration was given to whether phase-specific corrections should be retained or alternatively whether 

corrections should be converted into “start increments” and “running exhaust” using the regression analysis 

of the U.S. EPA for the development of exhaust basic emission rates. The concerns with the alternative 

approach were (1) that the U.S. EPA analysis was based on predominately high-emitting Tier 0 vehicles 

and was not representative of the CRC test fleet, and (2) that the regression coefficients should not remain 

constant across conditions that include varying temperature and fuel parameters. For these reasons, and for 

maintaining consistency with MOBILE6.2, the phase-specific correction method was retained. 
-93- 

Table 6-3 

Comparison of Las Vegas Winter On-Road CO Inventory Based on MOBILE6.2 

and Updated Adjustment Factors (tons per day) 

RVP 

MOBILE6.2 Updated Adjustment Factors 

0 % 

Oxygen 

2.7% 

Oxygen 

3.5% 

Oxygen 

0 % 

Oxygen 

2.7% 

Oxygen 

3.5% 

Oxygen 

2006

9 473 443 434 392 319 301 

11.7 559 523 513 440 359 339 

13.3 643 602 590 449 366 345 

2010 

9 480 459 453 368 294 277 

11.7 566 540 532 402 322 303 

13.3 650 620 611 411 329 310 

2015 

9 475 459 455 341 268 252 

11.7 556 537 531 360 284 267 

13.3 635 613 607 367 290 272 

Figure 6-2 

Winter On-Road CO Emission Inventory for Clark County, Nevada 

9 RVP Gasoline 

200

250

300

350

400

450

500

200

250

300

350

400

450

500

2006 2010 2015 2006 2010 2015

CO TPDCO TPD

YEAR                                                       YEAR

MOBILE 6.2                           Updated Adjustments

0% Oxygen

2.7% Oxygen

3.5% Oxygen
-94- 

Figure 6-3 

2010 Winter On-Road CO Emission Inventory for Clark County, Nevada 

as a Function of RVP 

200

250

300

350

400

450

500

550

600

650

700

200

250

300

350

400

450

500

550

600

650

700

9 11.7 13.3 9 11.7 13.3

CO TPD

CO TPD

RVP                                                        RVP

2010 MOBILE 6.2                  2010 Updated Adjustments

0% Oxygen

2.7% Oxygen

3.5% Oxygen

Figure 6-4 

2010 Winter On-Road CO Emission Inventory for Clark County, Nevada 

as a Function of Oxygenate Level 

200

250

300

350

400

450

500

550

600

650

700

200

250

300

350

400

450

500

550

600

650

700

0 2.7 3.5 0 2.7 3.5

CO TPDCO TPD

% OXYGEN                                            % OXYGEN

2010 MOBILE 6.2                  2010Updated Adjustments

9 RVP

11.7 RVP

13.3 RVP
-95- 

predicted by MOBILE6.2. The second point is that because the updated adjustments 

show oxygen impacts in advanced technology vehicles, the trend in CO emissions over 

time at a given oxygen content decreases, rather than increases as predicted by 

MOBILE6.2. 

Figures 6-2 and 6-3 compare the 2010 inventories generated using MOBILE6.2 and the 

updated adjustment factors as a function of RVP for constant oxygenate levels and as a 

function of oxygenate content for constant RVP, respectively. As shown in Figure 6-2, 

the updated adjustment factors show significantly smaller RVP impacts, as evidenced by 

the smaller slopes of the lines. Indeed, the updated adjustment model results in a 45 

percent reduction in the RVP effect in 2010 for this modeling scenario. Figure 6-3 again 

highlights the large differences between the MOBILE6.2 and updated oxygenate 

adjustments. 

Moreover, the two model results for 0% oxygen at 9.0 psi can be compared to illustrate 

the differences in temperature corrections (as reported in Table 6-3). In 2010, the 

updated adjustment model inventory of 368 tons per day is 23 percent less than the 480 

tons per day inventory using the standard MOBILE6.2. Both MOBILE6.2 models 

estimate an increase in CO for temperatures below 75oF; however, the increase in CO at 

lower temperatures is significantly less in the updated adjustments model. 

Finally, one additional comparison of the E-74b data to MOBILE6.2 was performed. In 

this comparison, FTP composite CO emission rates at standard conditions from the E-74b 

program were compared against the MOBILE6.2 output emission rates at similar 

conditions. In order to perform this comparison, MOBILE6.2 was run at 75°F, 9.0 psi, 

and 0 wt% oxygen for calendar year 2006.*

 The individual test vehicles were matched to 

MOBILE6.2 emission factor predictions based on vehicle weight class and model year, 

and the results were averaged over the four technology groups examined for this study. 

The four results are shown in Table 6-4. Notably, the Tier 1 technology group and the 

model prediction are the most similar (a 16 percent difference). However, the 

improvement in CO exhaust with successive technology groups is much greater in the 

test fleet (relative to that predicted by the model). This sample population suggests that 

CO emission rates are declining more quickly than what is assumed in MOBILE6.2. 

 

*

Trip length, vehicle soak periods, start emissions and driving cycle adjustments were defined to simulate 

those characteristics of the FTP composite test cycle. Moreover, the high emitter fraction of the fleet was 

forced to zero (i.e., 100 percent of the fleet was normal emitters). 
-96- 

Table 6-4 

Comparison of E-74b and MOBILE6.2 Emission Rates FTP Composite CO Exhaust 

Emissions at Standard Conditions (grams per mile) 

Technology Group MOBILE6.2 CRC E-74b 

Percent 

Difference 

Tier 1 5.8 4.9 -16% 

NLEV 2.2 1.3 -41% 

Tier 2, Enhanced Evaporative 1.3 0.7 -50% 

Tier 2, Near Zero Evaporative 1.2 0.2 -81% 

 

### 
 

APPENDIX A 

Sulfur Removal Protocol Used in Testing 
A-1

Sulfur Removal Protocol Used in Testing

This procedure is designed to cause the vehicle to transiently run rich at high catalyst 

temperature, so as to remove accumulated sulfur from the catalyst via hydrogen sulfide 

formation. The drive trace is shown below the descriptive protocol. The catalyst inlet 

temperature and the exhaust air/fuel (A/F) ratio must be monitored during this procedure. 

It is required to demonstrate that the catalyst inlet temperature exceeds 700°C during the 

wide-open throttle (WOT) accelerations and that rich air/fuel mixtures are achieved 

during WOT. If these parameters are not achieved, increased loading on the 

dynamometer should be added for this protocol (but not during the emissions test). 

1. Drive the vehicle from idle to 55 mph and hold speed for 5 minutes (to bring 

catalyst to full working temperature). 

2. Reduce vehicle speed to 30 mph and hold speed for one minute. 

3. Accelerate at WOT for a minimum of 5 seconds, to achieve a speed in excess of 

70 mph. Continue WOT above 70 mph, if necessary to achieve 5-second 

acceleration duration. Hold the peak speed for 15 seconds and then decelerate to 

30 mph. 

4. Maintain 30 mph for one minute. 

5. Repeat steps 3 and 4 to achieve 5 WOT excursions. 

6. One sulfur removal cycle has been completed. 

7. Repeat steps 1 to 5 for the second sulfur removal cycle. 

8. The protocol is complete if the necessary parameters have been achieved. 

WOT Acceleration must exceed 5 seconds duration, 

Extended by peak speed greater than 70 mph 

0

20

40

60

80

0 5 10 15 20 25

Vehicle Speed, mph

Test Time, minutes

Monitor Catalyst inlet Temperature and 

Exhaust A/F Ratio. 

Demonstrate that Cat. In. Temp > 

700C and A/F Ratio goes rich.
APPENDIX B 

Additional Vehicle and Test Information and Emissions Data 
 B-1

Test Vehicle VIN and Engine/Evap Family 

Veh 

No 

Model 

Year Make VIN Engine Family Evaporative Family 

001 1994 Chevrolet 2G1WL54T0R1115291 R1G3.1V7GAEA R1G1058AYM0A 

002 1996 Ford 1FALP52U6TG137967 TFM3.0V8GKEK TFM1115AYMEB 

003 1995 Jeep 1J4FJ67S6SL657625 SCR4.078GAEA SCR1058AYP0N 

 

004 1999 Honda AHGCG5651XA016867 XHNXV02.3PA3 XHNXR0130AAA 

005 2001 Toyota 1NXBR12E81Z533653 1TYXV01.8FFA 1TYXR0115AK1 

006 2002 Nissan 1N4AL11D42C224558 2NSXV02.5D5A 2NSXR0120RCB 

007 2001 Dodge 2B4GP44361R210600 1CRXT03.32DP 1CRXR0165XAA 

008 2002 Chevrolet 1GNDS13S422364628 2GMXT04.2185 2GMXR0175922 

 

009 2004 Dodge 1B3EL36X54N278471 4CRXV02.4VE0 4CRXR0130GBA 

010 2004 Chevrolet 2G1WF52E049104510 4GMXV03.8042 4GMXR0124919 

011 2004 Toyota 4T1BF30K94U575699 4TYXV03.0WMA 4TYXR0130A11 

012 2006 Ford 1FAFP53U16A148832 6FMXV03.0VEY 6FMXR0185GAK 

013 2004 Dodge 1D7HA16N94J136979 4CRXT04.75J0 4CRXR0218GDH 

014 2004 Ford 1FMYU02174KA86202 4FMXT03.01FE 4FMXR0110BBE 

015 2004 Toyota JTEDPZ1AZ40035821 4TYXT03.3PEM 4TYXR0165P21 
 B-2

Test Results - Vehicle 001 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO N

4831 AsRcvd 75 0.786 0.841 10.35 1.523 423.9 20.1 0.073 0.117 3.53 0.5060 1 50 0.935 1.050 10.67 1.993 469.2 17.4 0.073 0.110 2.22 0.5034 2 50 0.857 0.965 11.01 1.817 452.0 18.0 0.058 0.103 2.49 0.5082 3 50 0.945 1.078 14.74 1.830 474.4 17.3 0.063 0.117 2.37 0.5165 4 50 1.132 1.274 16.92 2.552 476.7 16.2 0.055 0.095 1.64 0.5072 5 50 0.925 1.057 14.35 1.871 459.9 17.7 0.096 0.146 4.05 0.5138 1 75 0.742 0.838 7.41 1.784 443.9 18.6 0.058 0.098 2.42 0.5010 2 75 0.801 0.911 10.34 1.487 463.4 17.6 0.102 0.175 6.39 0.5154 3 75 0.829 0.944 10.90 1.648 435.1 19.0 0.115 0.173 5.48 0.5131 4 75 0.716 0.807 8.19 1.892 448.7 17.7 0.051 0.097 2.73 0.5148 5 75 0.866 0.986 14.07 1.728 438.4 18.6 0.128 0.197 7.46 0.5089 6 75 0.900 1.027 12.63 1.713 441.6 18.9 0.058 0.109 2.29 0.5097 6 75 0.903 1.023 10.74 1.755 452.1 18.6 0.061 0.108 2.25 0.5112 7 75 0.873 0.987 10.07 1.701 452.6 18.2 0.071 0.118 2.37 0.5119 7 75 0.814 0.924 9.37 1.742 453.9 18.2 0.059 0.106 2.66 0.

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO N

4831 AsRcvd 75 0.158 0.193 3.82 1.042 350.9 24.9 0.244 0.288 5.03 0.5060 1 50 0.160 0.208 3.29 1.042 386.7 21.7 0.276 0.332 4.27 1.5034 2 50 0.124 0.163 3.31 0.970 379.3 22.1 0.242 0.298 4.48 1.5082 3 50 0.186 0.239 3.90 1.102 387.6 22.0 0.280 0.350 5.36 1.5165 4 50 0.186 0.236 4.73 1.345 378.1 21.2 0.314 0.378 5.66 1.5072 5 50 0.205 0.274 6.25 1.200 389.4 21.5 0.298 0.371 6.79 1.5138 1 75 0.125 0.165 5.22 1.076 386.6 21.6 0.218 0.270 4.23 1.5010 2 75 0.237 0.308 11.65 0.716 378.2 21.4 0.285 0.365 8.66 0.5154 3 75 0.147 0.195 4.40 0.955 377.3 22.5 0.272 0.339 6.31 0.5131 4 75 0.179 0.236 5.35 1.237 384.3 20.8 0.224 0.282 4.58 1.5148 5 75 0.329 0.414 14.43 0.870 365.6 22.1 0.336 0.420 10.75 1.5089 6 75 0.167 0.215 3.58 1.034 387.2 22.4 0.263 0.329 4.79 1.5097 6 75 0.153 0.209 6.05 1.200 391.8 21.9 0.261 0.326 5.05 1.5112 7 75 0.178 0.230 5.68 1.121 379.1 22.0 0.267 0.329 4.87 1.5119 7 75 0.177 0.234 5.61 0.959 388.1 21.5 0.248 0.311 4.86 0.
 B-3

Test Results - Vehicle 002 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4784 AsRcvd 75 0.418 0.469 4.96 0.768 398.0 21.9 0.025 0.057 1.22 0.34903 1 50 0.555 0.664 10.37 0.862 431.2 19.0 0.030 0.068 1.14 0.34816 2 50 0.544 0.650 11.47 0.845 426.1 19.1 0.013 0.056 1.16 0.34827 3 50 0.562 0.680 14.55 0.732 409.8 19.9 0.002 0.039 1.05 0.34836 4 50 0.673 0.803 18.73 1.116 411.5 18.5 0.029 0.057 0.51 0.34926 5 50 0.532 0.645 12.38 0.824 413.9 19.8 0.008 0.036 1.26 0.34938 1 75 0.431 0.515 3.96 0.751 394.9 21.2 0.029 0.066 0.83 0.34880 2 75 0.410 0.486 5.23 0.698 390.3 21.3 0.031 0.055 0.84 0.34957 3 75 0.428 0.520 6.15 0.743 400.2 21.1 0.010 0.050 1.07 0.34949 4 75 0.359 0.439 4.32 0.780 396.5 20.3 0.012 0.048 0.63 0.44890 5 75 0.434 0.518 7.26 0.733 392.3 21.3 0.021 0.053 1.07 0.34982 6 75 0.430 0.516 5.42 0.798 398.9 21.5 0.020 0.055 0.65 0.34990 6 75 0.497 0.596 6.84 0.818 402.3 21.2 0.017 0.053 1.09 0.34964 7 75 0.406 0.496 5.10 0.782 398.3 21.0 0.030 0.070 0.81 0.34972 7 75 0.400 0.487 5.31 0.768 400.8 20.8 0.030 0.069 0.90 0.3

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4784 AsRcvd 75 0.123 0.162 1.71 0.469 331.2 26.6 0.133 0.171 2.13 0.44903 1 50 0.080 0.129 1.58 0.521 337.5 25.1 0.153 0.208 3.17 0.54816 2 50 0.075 0.121 1.40 0.522 332.4 25.4 0.140 0.197 3.36 0.44827 3 50 0.097 0.148 1.71 0.468 329.1 26.1 0.144 0.202 4.03 0.44836 4 50 0.078 0.123 1.39 0.506 328.0 24.8 0.176 0.230 4.53 0.54926 5 50 0.090 0.134 1.56 0.570 338.6 25.2 0.139 0.189 3.65 0.54938 1 75 0.074 0.120 1.50 0.502 335.0 25.3 0.125 0.174 1.67 0.44880 2 75 0.066 0.112 1.48 0.484 324.0 26.1 0.119 0.160 1.92 0.44957 3 75 0.079 0.125 1.49 0.446 335.8 25.6 0.116 0.168 2.24 0.44949 4 75 0.069 0.116 1.41 0.501 334.0 24.3 0.100 0.148 1.61 0.54890 5 75 0.101 0.133 1.76 0.424 320.4 26.6 0.128 0.172 2.54 0.44982 6 75 0.159 0.208 1.59 0.571 330.1 26.4 0.143 0.192 1.90 0.44990 6 75 0.094 0.143 1.58 0.504 346.3 25.2 0.138 0.190 2.42 0.44964 7 75 0.086 0.135 1.50 0.483 337.1 25.2 0.124 0.176 1.89 0.44972 7 75 0.081 0.127 1.52 0.527 335.5 25.3 0.121 0.172 1.98 0.4
 B-4

Test Results – Vehicle 003 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4975 AsRcvd 75 1.149 1.267 12.29 2.988 462.1 18.3 0.423 0.533 7.69 1.85001 1 50 1.134 1.344 14.11 2.274 489.7 16.5 0.167 0.278 2.10 0.75118 2 50 1.140 1.310 10.33 3.260 476.5 17.1 0.272 0.396 4.77 1.35035 3 50 1.176 1.381 15.14 2.629 490.9 16.7 0.224 0.345 3.87 0.95128 4 50 1.279 1.484 12.96 3.661 485.1 16.1 0.214 0.332 3.99 1.45055 5 50 1.343 1.570 18.34 2.674 486.0 16.6 0.304 0.432 5.58 0.95005 1 75 0.932 1.079 7.93 2.146 463.6 17.8 0.209 0.328 2.67 0.65075 2 75 1.091 1.251 9.92 2.917 470.1 17.4 0.326 0.446 4.94 1.05046 3 75 1.039 1.199 10.33 2.290 467.1 17.8 0.282 0.407 4.55 0.75021 4 75 0.779 0.901 6.43 2.106 459.6 17.3 0.165 0.260 1.54 0.65013 5 75 1.034 1.194 11.22 2.036 455.2 18.1 0.401 0.545 6.32 0.65065 6 75 1.148 1.330 11.92 2.325 477.6 17.6 0.249 0.383 4.41 0.75068 6 75 1.036 1.215 10.43 2.338 461.0 18.3 0.259 0.388 4.75 0.95096 7 75 1.075 1.247 9.53 2.973 474.1 17.4 0.266 0.396 4.19 1.25103 7 75 1.027 1.214 9.41 3.059 472.0 17.5 0.269 0.380 4.49 1.2

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4975 AsRcvd 75 0.712 0.796 8.85 3.183 407.9 21.0 0.653 0.757 8.96 2.45001 1 50 0.547 0.664 4.51 2.294 420.9 19.8 0.473 0.606 5.26 1.45118 2 50 0.614 0.726 5.80 2.992 412.7 20.1 0.547 0.677 6.21 2.15035 3 50 0.624 0.744 5.97 2.699 427.1 19.7 0.532 0.670 6.79 1.75128 4 50 0.538 0.652 5.40 3.120 411.2 19.4 0.524 0.659 6.24 2.35055 5 50 0.626 0.748 6.73 2.513 418.8 20.0 0.608 0.755 8.55 1.75005 1 75 0.535 0.654 4.88 1.998 410.7 20.3 0.449 0.574 4.37 1.35075 2 75 0.673 0.794 7.56 2.542 410.3 20.1 0.580 0.709 6.70 1.85046 3 75 0.593 0.702 5.73 2.158 412.2 20.5 0.524 0.653 6.08 1.45021 4 75 0.472 0.582 3.84 2.016 407.5 19.7 0.377 0.482 3.19 1.35013 5 75 0.736 0.871 8.50 2.157 404.4 20.5 0.625 0.770 7.94 1.35065 6 75 0.588 0.720 6.23 2.219 411.8 20.8 0.529 0.672 6.47 1.45068 6 75 0.602 0.719 6.44 2.330 414.7 20.6 0.515 0.651 6.39 1.65096 7 75 0.624 0.752 6.07 2.791 413.2 20.1 0.532 0.671 5.82 2.05103 7 75 0.575 0.684 5.80 2.854 413.1 20.2 0.510 0.636 5.87 2.0
 B-5

Test Results - Vehicle 004 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4896 AsRcvd 75 0.257 0.260 3.11 0.409 343.5 25.5 0.000 0.008 0.94 0.05347 1 50 0.325 0.391 4.05 0.816 389.8 21.5 0.014 0.025 1.13 0.05392 2 50 0.343 0.404 3.56 0.767 382.3 21.9 0.016 0.028 1.09 0.05416 3 50 0.333 0.399 6.75 0.558 387.4 21.7 0.005 0.020 1.26 0.05371 4 50 0.308 0.371 3.28 0.812 385.8 20.9 0.006 0.020 0.67 0.05378 5 50 0.329 0.390 6.21 0.537 381.7 22.0 0.010 0.024 1.25 0.05408 1 75 0.202 0.245 2.72 0.456 357.7 23.5 0.014 0.024 1.08 0.05398 2 75 0.250 0.301 3.11 0.430 360.7 23.2 0.012 0.028 1.50 0.05357 3 75 0.204 0.247 3.60 0.391 356.4 23.9 0.005 0.026 1.35 0.05344 4 75 0.189 0.228 2.25 0.451 363.7 22.3 0.011 0.019 0.54 0.05363 5 75 0.310 0.370 5.13 0.352 359.2 23.4 0.018 0.033 1.36 0.05350 6 75 0.198 0.239 4.28 0.325 358.3 24.1 0.006 0.031 1.96 0.05353 6 75 0.266 0.321 4.93 0.389 361.9 23.8 0.014 0.032 1.26 0.05333 7 75 0.243 0.292 2.82 0.431 363.6 23.2 0.010 0.025 1.20 0.05335 7 75 0.203 0.247 2.58 0.442 363.3 23.3 0.008 0.024 0.88 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4896 AsRcvd 75 0.001 0.014 0.76 0.041 285.9 31.0 0.054 0.062 1.34 0.15347 1 50 0.007 0.022 0.70 0.066 328.2 25.9 0.077 0.100 1.62 0.15392 2 50 0.014 0.027 0.71 0.035 315.7 26.9 0.083 0.105 1.50 0.15416 3 50 0.003 0.017 0.84 0.033 321.3 26.9 0.073 0.098 2.28 0.15371 4 50 0.005 0.019 0.65 0.060 317.2 25.7 0.068 0.093 1.21 0.15378 5 50 0.012 0.027 0.87 0.066 313.6 27.4 0.077 0.101 2.17 0.15408 1 75 0.009 0.022 0.71 0.039 311.5 27.3 0.051 0.069 1.32 0.15398 2 75 0.012 0.026 0.95 0.041 316.9 26.7 0.061 0.084 1.68 0.15357 3 75 0.012 0.027 1.10 0.054 311.2 27.7 0.048 0.072 1.75 0.15344 4 75 0.011 0.024 0.68 0.043 320.0 25.5 0.048 0.064 0.93 0.15363 5 75 0.015 0.028 1.25 0.034 316.8 27.0 0.078 0.102 2.11 0.05350 6 75 0.018 0.034 1.41 0.059 319.1 27.4 0.049 0.075 2.29 0.05353 6 75 0.025 0.038 1.32 0.062 316.3 27.6 0.069 0.093 2.04 0.15333 7 75 0.010 0.023 0.67 0.034 319.6 26.7 0.058 0.080 1.39 0.15335 7 75 0.014 0.025 0.76 0.054 318.5 26.8 0.050 0.071 1.20 0.1
 B-6

Test Results - Vehicle 005 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4729 AsRcvd 75 0.261 0.282 2.69 0.341 304.9 28.7 0.039 0.058 1.14 0.04755 1 50 0.360 0.423 5.08 0.349 326.8 25.4 0.002 0.008 0.48 0.04759 2 50 0.376 0.448 4.85 0.326 325.4 25.5 0.022 0.042 0.73 0.04802 3 50 0.338 0.410 5.55 0.309 320.5 26.2 0.020 0.035 0.27 0.14747 4 50 0.416 0.484 4.09 0.362 325.6 24.6 0.026 0.047 0.75 0.04821 5 50 0.335 0.404 5.53 0.365 329.0 25.4 0.014 0.030 0.62 0.04776 1 75 0.218 0.266 2.58 0.326 301.9 27.8 0.028 0.037 0.45 0.14782 2 75 0.238 0.285 3.20 0.295 309.9 27.0 0.027 0.062 1.65 0.04733 3 75 0.230 0.280 3.51 0.272 302.2 28.1 0.021 0.036 0.69 0.04767 4 75 0.220 0.257 2.62 0.310 313.7 25.7 0.016 0.026 0.42 0.04808 5 75 0.212 0.272 3.48 0.255 301.3 28.0 0.025 0.036 0.69 0.04845 6 75 0.209 0.256 3.17 0.295 307.3 28.1 0.006 0.017 0.39 0.14855 6 75 0.223 0.273 3.60 0.260 300.6 28.7 0.019 0.036 0.66 0.04870 7 75 0.217 0.264 3.08 0.282 301.4 27.9 0.011 0.026 0.32 0.04875 7 75 0.210 0.256 2.90 0.314 303.6 27.7 0.007 0.014 0.22 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4729 AsRcvd 75 0.090 0.105 1.09 0.189 241.5 36.6 0.099 0.117 1.45 0.14755 1 50 0.034 0.053 1.22 0.181 264.4 32.0 0.085 0.106 1.63 0.14759 2 50 0.045 0.064 1.06 0.149 265.9 31.8 0.102 0.133 1.68 0.14802 3 50 0.048 0.073 1.14 0.150 257.5 33.4 0.094 0.123 1.60 0.14747 4 50 0.042 0.059 0.89 0.151 271.5 30.0 0.111 0.141 1.48 0.14821 5 50 0.039 0.058 1.26 0.170 260.3 32.8 0.087 0.115 1.82 0.14776 1 75 0.041 0.057 0.80 0.176 256.0 33.1 0.071 0.090 0.99 0.14782 2 75 0.054 0.073 1.56 0.238 253.5 33.2 0.078 0.111 1.95 0.14733 3 75 0.045 0.062 0.93 0.142 251.6 34.2 0.071 0.094 1.34 0.14767 4 75 0.038 0.055 1.01 0.176 256.3 31.7 0.064 0.082 1.04 0.14808 5 75 0.051 0.067 1.53 0.159 256.8 33.2 0.071 0.094 1.50 0.14845 6 75 0.037 0.061 1.42 0.145 250.8 34.8 0.057 0.079 1.25 0.14855 6 75 0.025 0.051 0.68 0.146 249.1 35.2 0.063 0.089 1.28 0.14870 7 75 0.035 0.057 1.19 0.172 253.9 33.4 0.060 0.084 1.13 0.14875 7 75 0.024 0.040 0.67 0.156 252.9 33.7 0.054 0.071 0.90 0.1
 B-7

Test Results - Vehicle 006 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4726 AsRcvd 75 0.152 0.180 3.657 0.306 401.7 21.8 0.016 0.027 0.623 0.04778 1 50 0.327 0.381 5.19 0.745 435.3 19.2 0.019 0.036 0.82 0.04770 2 50 0.315 0.368 4.42 0.605 436.7 19.1 0.012 0.026 0.73 0.04791 3 50 0.352 0.412 5.95 0.770 432.8 19.5 0.018 0.041 1.13 0.04765 4 50 0.301 0.356 4.81 0.782 423.8 18.9 0.016 0.038 0.85 0.04815 5 50 0.291 0.362 5.69 0.824 433.2 19.4 0.013 0.029 0.94 0.04781 1 75 0.144 0.180 3.72 0.380 413.8 20.3 0.020 0.042 1.20 0.04804 2 75 0.159 0.201 4.54 0.444 415.2 20.1 0.015 0.049 2.57 0.14753 3 75 0.135 0.173 4.06 0.380 414.8 20.5 0.008 0.029 1.00 0.04760 4 75 0.156 0.195 3.79 0.387 420.9 19.2 0.019 0.044 0.64 0.04823 5 75 0.108 0.156 3.77 0.391 403.0 21.1 0.010 0.037 1.68 0.04877 6 75 0.153 0.197 4.74 0.472 405.3 21.3 0.014 0.036 1.18 0.04881 6 75 0.142 0.186 4.20 0.372 413.2 20.9 0.013 0.035 0.81 0.04841 7 75 0.164 0.210 4.51 0.402 412.2 20.4 0.006 0.031 0.72 0.04849 7 75 0.144 0.182 3.62 0.349 410.9 20.5 0.013 0.032 0.64 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4726 AsRcvd 75 0.023 0.037 1.17 0.158 345.2 25.6 0.046 0.062 1.40 0.14778 1 50 0.025 0.049 1.75 0.323 364.4 23.2 0.085 0.111 1.98 0.24770 2 50 0.032 0.049 1.88 0.291 364.9 23.1 0.080 0.104 1.81 0.24791 3 50 0.035 0.051 1.89 0.287 356.1 24.1 0.092 0.120 2.34 0.24765 4 50 0.028 0.045 1.30 0.342 353.4 23.0 0.078 0.106 1.79 0.24815 5 50 0.018 0.047 1.97 0.316 359.1 23.8 0.072 0.103 2.21 0.24781 1 75 0.032 0.052 1.98 0.286 353.0 23.9 0.049 0.073 1.94 0.14804 2 75 0.029 0.055 2.80 0.307 348.7 24.1 0.049 0.082 3.04 0.24753 3 75 0.030 0.050 1.69 0.223 357.3 24.1 0.040 0.065 1.82 0.14760 4 75 0.030 0.054 1.53 0.244 361.4 22.5 0.051 0.078 1.54 0.14823 5 75 0.034 0.052 1.88 0.277 356.2 24.0 0.037 0.066 2.17 0.14877 6 75 0.021 0.046 1.95 0.281 346.5 25.2 0.045 0.072 2.13 0.24881 6 75 0.016 0.042 1.51 0.240 346.8 25.2 0.041 0.068 1.71 0.14841 7 75 0.019 0.048 1.26 0.249 349.3 24.4 0.042 0.073 1.66 0.14849 7 75 0.022 0.045 1.30 0.275 350.0 24.3 0.043 0.067 1.44 0.1
 B-8

Test Results - Vehicle 007 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4794 AsRcvd 75 0.234 0.263 1.85 0.645 436.9 20.2 0.015 0.023 0.47 0.14920 1 50 0.329 0.390 2.45 0.971 486.1 17.4 0.010 0.020 0.04 0.24953 2 50 0.454 0.547 3.13 1.378 504.1 16.7 0.000 0.026 0.03 0.34835 3 50 0.300 0.369 2.88 0.795 485.8 17.6 0.015 0.023 0.13 0.04828 4 50 0.311 0.368 2.51 0.916 479.7 16.9 0.003 0.011 0.06 0.14927 5 50 0.329 0.391 2.83 1.434 497.7 17.1 0.012 0.026 0.59 0.34895 1 75 0.253 0.281 1.95 0.788 452.3 18.7 0.012 0.021 0.08 0.14885 2 75 0.232 0.271 1.91 0.805 438.4 19.3 0.011 0.024 1.99 0.14848 3 75 0.225 0.271 1.82 0.704 446.7 19.2 0.004 0.023 0.82 0.04944 4 75 0.223 0.266 1.53 1.152 456.1 17.8 0.007 0.018 0.00 0.34956 5 75 0.233 0.283 2.22 1.151 452.7 18.9 0.013 0.032 1.06 0.44966 6 75 0.241 0.296 1.73 1.197 455.5 19.2 0.013 0.025 0.00 0.34971 6 75 0.222 0.270 1.48 1.015 453.4 19.3 0.011 0.025 0.00 0.24983 7 75 0.244 0.293 1.62 0.912 453.3 18.7 0.011 0.020 0.00 0.24989 7 75 0.239 0.288 1.69 0.828 447.6 19.0 0.014 0.026 0.00 0.1

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4794 AsRcvd 75 0.029 0.044 0.74 0.246 385.3 23.0 0.064 0.078 0.83 0.24920 1 50 0.017 0.034 0.22 0.249 407.1 20.9 0.078 0.101 0.59 0.44953 2 50 0.002 0.036 0.46 0.672 400.5 21.2 0.094 0.137 0.79 0.64835 3 50 0.020 0.033 0.30 0.227 394.3 21.9 0.075 0.097 0.75 0.24828 4 50 0.006 0.023 0.15 0.318 393.8 20.8 0.067 0.088 0.60 0.34927 5 50 0.015 0.035 0.48 0.620 402.8 21.4 0.079 0.104 1.02 0.64895 1 75 0.029 0.032 0.45 0.228 388.1 21.9 0.066 0.078 0.57 0.24885 2 75 0.030 0.047 2.35 0.265 381.8 22.1 0.062 0.082 2.07 0.34848 3 75 0.017 0.032 0.85 0.246 390.6 22.1 0.053 0.077 1.04 0.24944 4 75 0.006 0.027 0.13 0.359 403.9 20.3 0.051 0.072 0.35 0.54956 5 75 0.028 0.056 2.41 0.463 399.2 21.4 0.063 0.090 1.67 0.54966 6 75 0.020 0.037 0.25 0.403 403.4 21.8 0.062 0.084 0.43 0.54971 6 75 0.019 0.041 0.29 0.487 401.0 21.9 0.057 0.080 0.39 0.44983 7 75 0.017 0.035 0.18 0.289 411.7 20.8 0.061 0.081 0.39 0.34989 7 75 0.019 0.040 0.26 0.432 401.1 21.3 0.062 0.084 0.42 0.3
 B-9

Test Results - Vehicle 008 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5136 AsRcvd 75 0.240 0.265 1.80 0.605 584.4 15.1 0.009 0.017 0.12 0.05169 1 50 0.380 0.436 2.32 0.519 613.4 13.8 0.014 0.019 0.08 0.05203 2 50 0.491 0.552 1.80 0.697 636.6 13.3 0.009 0.020 0.17 0.05212 3 50 0.712 0.789 7.10 0.471 644.9 13.2 0.007 0.017 0.17 0.05163 4 50 0.349 0.396 2.15 0.572 630.9 12.9 0.007 0.018 0.10 0.05235 5 50 0.431 0.482 2.53 0.618 630.8 13.5 0.005 0.013 0.34 0.05223 1 75 0.349 0.394 1.88 0.466 615.0 13.8 0.018 0.020 0.21 0.05252 2 75 0.271 0.310 1.33 0.496 598.9 14.1 0.013 0.017 0.33 0.05228 3 75 0.345 0.390 1.88 0.588 615.4 14.0 0.006 0.011 0.28 0.05207 4 75 0.250 0.289 1.55 0.520 593.3 13.7 0.007 0.013 0.16 0.05149 5 75 0.301 0.346 2.61 0.593 586.6 14.6 0.004 0.016 0.25 0.05271 6 75 0.284 0.322 1.60 0.552 581.4 15.1 0.008 0.013 0.25 0.05276 6 75 0.271 0.308 1.59 0.588 606.5 14.4 0.009 0.014 0.21 0.05184 7 75 0.252 0.291 1.78 0.528 580.5 14.7 0.013 0.022 0.11 0.05187 7 75 0.254 0.297 1.68 0.505 590.3 14.4 0.017 0.023 0.19 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5136 AsRcvd 75 0.018 0.030 0.20 0.215 493.7 18.0 0.059 0.072 0.49 0.25169 1 50 0.011 0.026 0.10 0.244 495.8 17.2 0.089 0.107 0.55 0.15203 2 50 0.014 0.022 0.20 0.283 506.8 16.8 0.110 0.131 0.52 0.25212 3 50 0.014 0.028 0.29 0.177 514.0 16.8 0.155 0.180 1.64 0.15163 4 50 0.008 0.024 0.10 0.243 515.6 15.9 0.078 0.098 0.52 0.15235 5 50 0.006 0.015 0.18 0.289 517.9 16.6 0.094 0.111 0.75 0.25223 1 75 0.009 0.018 0.10 0.210 498.2 17.1 0.084 0.097 0.52 0.15252 2 75 0.009 0.020 0.25 0.289 494.3 17.2 0.065 0.078 0.51 0.25228 3 75 0.012 0.024 0.24 0.239 505.8 17.1 0.078 0.093 0.60 0.25207 4 75 0.011 0.022 0.13 0.237 503.7 16.3 0.058 0.073 0.44 0.15149 5 75 0.015 0.026 0.22 0.298 485.8 17.7 0.069 0.087 0.73 0.25271 6 75 0.008 0.020 0.19 0.209 490.5 17.9 0.065 0.079 0.51 0.15276 6 75 0.008 0.019 0.16 0.185 491.2 17.9 0.063 0.077 0.48 0.15184 7 75 0.014 0.026 0.17 0.237 494.6 17.3 0.063 0.079 0.47 0.15187 7 75 0.008 0.022 0.23 0.253 496.3 17.2 0.064 0.080 0.51 0.1
 B-10

Test Results - Vehicle 009 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5351 AsRcvd 75 0.119 0.128 1.25 0.167 352.1 25.1 0.010 0.009 0.07 0.05430 1 50 0.241 0.268 1.71 0.253 433.8 19.5 0.010 0.014 0.06 0.05366 2 50 0.238 0.263 1.78 0.197 436.9 19.3 0.014 0.019 0.07 0.05413 3 50 0.232 0.264 2.41 0.227 435.5 19.7 0.006 0.006 0.13 0.05379 4 50 0.205 0.232 1.50 0.282 436.3 18.6 0.004 0.012 0.04 0.05393 5 50 0.247 0.278 2.68 0.206 434.7 19.6 0.001 0.010 0.14 0.05439 1 75 0.136 0.158 1.36 0.188 410.7 20.6 0.012 0.016 0.11 0.05372 2 75 0.119 0.138 1.15 0.192 414.5 20.4 0.002 0.010 0.23 0.05361 3 75 0.114 0.131 1.63 0.149 404.6 21.3 0.002 0.007 0.16 0.05385 4 75 0.106 0.126 1.25 0.189 408.3 20.0 0.000 0.005 0.02 0.05449 5 75 0.127 0.146 1.37 0.196 414.7 20.7 0.005 0.007 0.20 0.05421 6 75 0.138 0.161 1.55 0.189 409.2 21.4 0.008 0.010 0.03 0.05427 6 75 0.163 0.187 1.72 0.191 415.9 21.0 0.005 0.009 0.11 0.05403 7 75 0.136 0.157 1.03 0.180 413.3 20.6 0.010 0.012 0.08 0.05407 7 75 0.135 0.155 1.47 0.192 407.4 20.9 0.005 0.007 0.05 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5351 AsRcvd 75 0.003 0.005 0.05 0.014 302.4 29.4 0.031 0.033 0.31 0.05430 1 50 0.005 0.005 0.02 0.007 378.9 22.5 0.057 0.064 0.39 0.05366 2 50 0.009 0.015 0.05 0.017 375.4 22.7 0.059 0.068 0.42 0.05413 3 50 0.000 0.002 0.13 0.016 374.5 23.1 0.051 0.058 0.61 0.05379 4 50 0.000 0.007 0.02 0.023 377.8 21.7 0.045 0.056 0.34 0.05393 5 50 0.004 0.008 0.18 0.015 378.3 22.8 0.053 0.065 0.68 0.05439 1 75 0.006 0.010 0.08 0.016 372.4 22.9 0.036 0.044 0.36 0.05372 2 75 0.005 0.008 0.02 0.016 378.0 22.5 0.027 0.036 0.36 0.05361 3 75 0.009 0.011 0.07 0.010 365.7 23.7 0.027 0.034 0.44 0.05385 4 75 0.005 0.008 0.04 0.028 369.4 22.2 0.023 0.031 0.28 0.05449 5 75 0.002 0.009 0.20 0.013 371.5 23.2 0.030 0.036 0.44 0.05421 6 75 0.003 0.010 0.07 0.015 373.3 23.6 0.034 0.041 0.36 0.05427 6 75 0.004 0.011 0.15 0.016 371.9 23.7 0.037 0.046 0.45 0.05403 7 75 0.006 0.012 0.01 0.020 375.7 22.8 0.035 0.042 0.26 0.05407 7 75 0.004 0.007 0.04 0.017 372.9 23.0 0.032 0.037 0.34 0.0
 B-11

Test Results - Vehicle 010 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

25649 AsRcvd 75 0.197 0.232 2.40 0.125 469.4 18.8 0.015 0.037 0.20 0.0

4737 1 50 0.331 0.396 7.14 0.127 442.6 18.8 0.011 0.030 0.07 0.04746 2 50 0.318 0.382 5.22 0.127 443.4 18.8 0.023 0.042 0.16 0.04766 3 50 0.325 0.388 7.17 0.124 440.0 19.1 0.017 0.035 0.10 0.04771 4 50 0.314 0.377 6.03 0.127 441.9 18.1 0.014 0.032 0.15 0.04820 5 50 0.253 0.318 5.48 0.139 427.7 19.7 0.012 0.036 0.09 0.04787 1 75 0.177 0.218 1.98 0.122 428.8 19.7 0.022 0.041 0.09 0.04752 2 75 0.163 0.202 2.54 0.092 425.4 19.8 0.000 0.021 0.12 0.04761 3 75 0.192 0.241 2.74 0.094 422.6 20.3 0.027 0.045 0.22 0.04793 4 75 0.149 0.189 2.12 0.079 400.4 20.3 0.016 0.036 0.10 0.04807 5 75 0.176 0.226 2.67 0.083 406.8 20.9 0.018 0.036 0.07 0.04862 6 75 0.142 0.193 2.63 0.092 408.5 21.3 0.012 0.040 0.15 0.04871 6 75 0.175 0.223 2.72 0.111 413.4 21.0 0.017 0.043 0.24 0.04840 7 75 0.139 0.190 2.37 0.092 404.2 21.0 0.000 0.032 0.13 0.04844 7 75 0.173 0.216 2.62 0.092 402.0 21.0 0.010 0.034 0.15 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

25649 AsRcvd 75 0.028 0.053 0.29 0.023 377.7 23.5 0.056 0.082 0.68 0.0

4737 1 50 0.012 0.030 0.06 0.014 351.7 24.2 0.078 0.106 1.53 0.04746 2 50 0.015 0.038 0.17 0.012 356.3 23.9 0.082 0.111 1.21 0.04766 3 50 0.017 0.036 0.12 0.014 346.2 25.0 0.081 0.109 1.57 0.04771 4 50 0.013 0.033 0.14 0.015 358.5 22.8 0.076 0.104 1.37 0.04820 5 50 0.011 0.034 0.17 0.016 343.6 25.1 0.062 0.094 1.23 0.04787 1 75 0.021 0.040 0.15 0.047 349.2 24.4 0.054 0.078 0.50 0.04752 2 75 0.010 0.029 0.17 0.022 350.0 24.3 0.037 0.061 0.63 0.04761 3 75 0.025 0.044 0.14 0.011 352.8 24.5 0.061 0.086 0.72 0.04793 4 75 0.017 0.035 0.10 0.018 344.5 23.8 0.044 0.068 0.52 0.04807 5 75 0.015 0.038 0.10 0.019 343.4 25.1 0.050 0.076 0.62 0.04862 6 75 0.015 0.041 0.17 0.017 344.3 25.5 0.040 0.072 0.67 0.04871 6 75 0.013 0.035 0.23 0.020 339.8 25.9 0.049 0.078 0.75 0.04840 7 75 0.009 0.038 0.13 0.019 343.4 24.9 0.031 0.066 0.60 0.04844 7 75 0.014 0.036 0.21 0.022 338.7 25.2 0.045 0.072 0.68 0.0
 B-12

Test Results - Vehicle 011 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5354 AsRcvd 75 0.165 0.181 1.12 0.072 420.6 21.1 0.015 0.014 0.00 0.05431 1 50 0.259 0.295 0.99 0.126 458.2 18.5 0.011 0.017 0.00 0.05412 2 50 0.344 0.387 1.69 0.173 453.6 18.6 0.013 0.018 0.00 0.05397 3 50 0.248 0.284 1.71 0.111 451.6 19.0 0.011 0.014 0.00 0.05370 4 50 0.246 0.284 1.26 0.147 463.4 17.6 0.019 0.021 0.00 0.05426 5 50 0.208 0.242 1.48 0.101 452.7 18.9 0.014 0.014 0.00 0.05404 1 75 0.091 0.107 0.75 0.106 424.4 20.0 0.006 0.017 0.00 0.05448 2 75 0.089 0.105 0.77 0.142 421.3 20.1 0.006 0.012 0.00 0.05443 3 75 0.085 0.102 0.68 0.135 420.1 20.6 0.006 0.011 0.00 0.05435 4 75 0.077 0.094 0.86 0.109 423.8 19.3 0.011 0.012 0.00 0.05374 5 75 0.099 0.116 0.93 0.101 422.8 20.3 0.008 0.013 0.00 0.05380 6 75 0.091 0.107 0.68 0.098 424.1 20.7 0.010 0.010 0.00 0.05382 6 75 0.087 0.105 1.01 0.098 421.2 20.8 0.004 0.011 0.00 0.05386 7 75 0.074 0.089 0.72 0.099 420.9 20.3 0.005 0.009 0.00 0.05388 7 75 0.082 0.098 0.99 0.104 414.4 20.6 0.012 0.016 0.00 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5354 AsRcvd 75 0.010 0.010 0.00 0.019 347.9 25.6 0.045 0.047 0.23 0.05431 1 50 0.001 0.006 0.00 0.053 360.6 23.7 0.060 0.072 0.20 0.05412 2 50 0.004 0.008 0.00 0.104 351.1 24.2 0.079 0.092 0.35 0.05397 3 50 0.004 0.009 0.00 0.066 357.2 24.3 0.058 0.069 0.35 0.05370 4 50 0.007 0.012 0.00 0.034 358.9 22.8 0.063 0.073 0.26 0.05426 5 50 0.003 0.007 0.00 0.004 354.7 24.3 0.051 0.059 0.31 0.05404 1 75 0.008 0.010 0.00 0.079 358.3 23.8 0.024 0.034 0.15 0.05448 2 75 0.001 0.008 0.00 0.036 359.6 23.7 0.022 0.030 0.16 0.05443 3 75 0.002 0.009 0.00 0.054 354.4 24.4 0.022 0.029 0.14 0.05435 4 75 0.008 0.009 0.00 0.041 352.2 23.3 0.024 0.028 0.18 0.05374 5 75 0.002 0.009 0.00 0.037 356.7 24.2 0.025 0.033 0.20 0.05380 6 75 0.003 0.006 0.00 0.047 353.8 24.9 0.025 0.029 0.14 0.05382 6 75 0.006 0.008 0.00 0.009 354.6 24.8 0.021 0.030 0.21 0.05386 7 75 0.007 0.007 0.00 0.027 349.4 24.5 0.020 0.025 0.15 0.05388 7 75 0.006 0.008 0.00 0.032 355.5 24.1 0.025 0.031 0.20 0.0
 B-13

Test Results - Vehicle 012 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4993 AsRcvd 75 0.245 0.263 1.63 0.092 445.2 19.8 0.032 0.032 0.00 0.05133 1 50 0.170 0.201 2.08 0.069 485.8 17.4 0.011 0.017 0.01 0.05142 2 50 0.065 0.081 0.39 0.115 464.7 18.3 0.004 0.012 0.05 0.05079 3 50 0.206 0.243 3.67 0.129 496.5 17.2 0.010 0.017 0.02 0.05073 4 50 0.156 0.186 1.39 0.202 485.3 16.8 0.015 0.021 0.00 0.15018 5 50 0.224 0.263 3.37 0.083 490.7 17.4 0.011 0.015 0.00 0.05111 1 75 0.100 0.120 0.95 0.105 453.6 18.7 0.010 0.019 0.01 0.05037 2 75 0.094 0.116 1.26 0.115 440.1 19.2 0.007 0.012 0.00 0.05006 3 75 0.086 0.106 0.76 0.078 453.7 19.0 0.011 0.017 0.00 0.05124 4 75 0.069 0.080 0.27 0.137 450.1 18.2 0.012 0.015 0.00 0.15155 5 75 0.081 0.110 1.18 0.100 440.8 19.5 0.001 0.009 0.20 0.05053 6 75 0.087 0.108 0.85 0.064 452.0 19.4 0.011 0.015 0.00 0.05056 6 75 0.093 0.114 0.87 0.056 454.0 19.3 0.007 0.013 0.01 0.05091 7 75 0.070 0.089 0.59 0.076 459.4 18.6 0.014 0.020 0.00 0.05102 7 75 0.074 0.095 0.57 0.073 453.8 18.8 0.008 0.012 0.01 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4993 AsRcvd 75 0.017 0.025 0.11 0.024 382.7 23.2 0.072 0.078 0.37 0.05133 1 50 0.017 0.025 0.10 0.028 397.0 21.5 0.046 0.057 0.47 0.05142 2 50 0.012 0.021 0.08 0.038 393.0 21.7 0.019 0.029 0.13 0.05079 3 50 0.007 0.015 0.06 0.010 395.7 21.9 0.050 0.063 0.79 0.05073 4 50 0.015 0.019 0.00 0.069 392.6 20.9 0.044 0.055 0.29 0.15018 5 50 0.010 0.015 0.00 0.023 387.0 22.3 0.055 0.066 0.70 0.05111 1 75 0.013 0.022 0.10 0.040 405.5 21.0 0.030 0.041 0.23 0.05037 2 75 0.012 0.020 0.04 0.122 377.7 22.5 0.026 0.036 0.27 0.05006 3 75 0.011 0.020 0.11 0.015 390.3 22.2 0.027 0.036 0.19 0.05124 4 75 0.010 0.019 0.03 0.024 389.0 21.1 0.023 0.030 0.06 0.05155 5 75 0.016 0.026 0.19 0.144 393.3 21.9 0.022 0.035 0.40 0.15053 6 75 0.007 0.017 0.08 0.031 397.5 22.1 0.026 0.035 0.20 0.05056 6 75 0.012 0.022 0.13 0.035 399.6 22.0 0.026 0.036 0.22 0.05091 7 75 0.011 0.023 0.09 0.018 394.0 21.7 0.025 0.035 0.15 0.05102 7 75 0.011 0.020 0.14 0.058 386.3 22.1 0.023 0.032 0.16 0.0
 B-14

Test Results - Vehicle 013 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5150 AsRcvd 75 0.195 0.252 1.81 0.299 690.6 12.8 0.028 0.082 0.39 0.05211 1 50 0.353 0.436 3.28 0.546 727.5 11.6 0.024 0.079 0.46 0.05173 2 50 0.297 0.375 2.02 0.547 729.4 11.6 0.033 0.093 0.53 0.05170 3 50 0.360 0.449 4.43 0.562 767.0 11.2 0.031 0.091 0.50 0.05247 4 50 0.359 0.436 3.03 0.392 727.3 11.2 0.025 0.070 0.46 0.05196 5 50 0.340 0.412 4.83 0.508 724.6 11.8 0.031 0.082 0.42 0.05240 1 75 0.202 0.267 1.78 0.341 700.3 12.1 0.014 0.067 0.44 0.05222 2 75 0.229 0.295 1.99 0.345 683.4 12.4 0.034 0.082 0.46 0.05261 3 75 0.220 0.285 2.74 0.282 691.4 12.4 0.014 0.061 0.40 0.05208 4 75 0.183 0.244 1.80 0.391 697.7 11.7 0.025 0.074 0.38 0.05201 5 75 0.211 0.273 3.00 0.430 699.5 12.2 0.010 0.050 0.43 0.05227 6 75 0.192 0.259 2.51 0.356 689.8 12.7 0.026 0.076 0.51 0.05231 6 75 0.212 0.281 2.73 0.388 694.8 12.6 0.028 0.082 0.53 0.05158 7 75 0.194 0.258 2.06 0.333 681.0 12.5 0.000 0.088 0.49 0.05160 7 75 0.174 0.241 1.71 0.324 682.0 12.5 0.032 0.093 0.48 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5150 AsRcvd 75 0.028 0.066 0.34 0.078 580.8 15.3 0.063 0.113 0.67 0.05211 1 50 0.018 0.056 0.27 0.067 613.8 13.9 0.091 0.147 0.99 0.15173 2 50 0.019 0.058 0.27 0.061 600.2 14.2 0.084 0.142 0.77 0.15170 3 50 0.026 0.065 0.33 0.068 630.8 13.7 0.098 0.158 1.27 0.15247 4 50 0.015 0.051 0.30 0.079 610.4 13.4 0.091 0.140 0.95 0.15196 5 50 0.019 0.052 0.33 0.059 595.0 14.5 0.092 0.142 1.31 0.15240 1 75 0.018 0.058 0.31 0.069 604.7 14.1 0.054 0.106 0.68 0.05222 2 75 0.021 0.056 0.28 0.056 602.4 14.1 0.071 0.119 0.73 0.05261 3 75 0.016 0.048 0.36 0.043 598.6 14.5 0.057 0.104 0.87 0.05208 4 75 0.019 0.055 0.34 0.076 612.3 13.4 0.056 0.104 0.66 0.15201 5 75 0.040 0.079 0.36 0.078 614.3 14.0 0.060 0.104 0.94 0.15227 6 75 0.017 0.055 0.37 0.055 615.2 14.3 0.058 0.108 0.88 0.05231 6 75 0.016 0.054 0.38 0.049 613.0 14.3 0.063 0.116 0.94 0.15158 7 75 0.003 0.065 0.38 0.079 590.3 14.5 0.041 0.117 0.79 0.15160 7 75 0.017 0.063 0.40 0.078 591.6 14.4 0.057 0.115 0.71 0.0
 B-15

Test Results - Vehicle 014 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4891 AsRcvd 75 0.158 0.159 1.11 0.150 471.0 18.8 0.007 0.013 0.03 0.04996 1 50 0.246 0.286 1.91 0.284 499.0 17.0 0.015 0.021 0.00 0.05017 2 50 0.263 0.302 1.47 0.277 491.4 17.2 0.015 0.020 0.00 0.04952 3 50 0.231 0.274 2.58 0.228 493.6 17.4 0.006 0.013 0.00 0.05002 4 50 0.293 0.341 3.22 0.201 496.6 16.3 0.007 0.013 0.00 0.05078 5 50 0.226 0.271 2.97 0.229 487.1 17.5 0.019 0.025 0.00 0.05009 1 75 0.134 0.159 0.96 0.168 483.8 17.6 0.012 0.018 0.00 0.04959 2 75 0.134 0.160 1.17 0.180 481.8 17.6 0.015 0.022 0.00 0.04931 3 75 0.192 0.219 1.38 0.207 479.7 18.0 0.021 0.026 0.03 0.05029 4 75 0.099 0.121 0.83 0.133 454.1 18.0 0.019 0.023 0.00 0.05106 5 75 0.323 0.359 1.55 0.177 485.4 17.6 0.016 0.021 0.02 0.04943 6 75 0.121 0.149 1.47 0.201 477.0 18.4 0.010 0.016 0.00 0.04948 6 75 0.180 0.208 1.26 0.143 472.7 18.5 0.016 0.021 0.00 0.05061 7 75 0.121 0.151 1.05 0.162 484.8 17.6 0.009 0.016 0.00 0.05064 7 75 0.115 0.135 1.27 0.152 480.5 17.7 0.008 0.015 0.00 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

4891 AsRcvd 75 0.009 0.013 0.08 0.015 387.3 23.0 0.039 0.043 0.27 0.04996 1 50 0.008 0.020 0.00 0.057 420.1 20.3 0.061 0.075 0.40 0.05017 2 50 0.015 0.021 0.03 0.106 417.8 20.4 0.066 0.078 0.31 0.04952 3 50 0.006 0.014 0.00 0.008 415.6 20.8 0.053 0.068 0.53 0.05002 4 50 0.008 0.014 0.00 0.238 430.3 19.0 0.067 0.082 0.67 0.15078 5 50 0.003 0.025 0.20 0.052 416.4 20.7 0.058 0.076 0.67 0.05009 1 75 0.010 0.021 0.00 0.041 422.1 20.2 0.037 0.048 0.20 0.04959 2 75 0.005 0.014 0.00 0.093 407.7 20.9 0.037 0.048 0.24 0.04931 3 75 0.014 0.023 0.11 0.043 413.5 20.9 0.054 0.065 0.33 0.05029 4 75 0.014 0.019 0.00 0.019 397.2 20.6 0.034 0.042 0.17 0.05106 5 75 0.017 0.025 0.12 0.024 428.6 20.1 0.080 0.092 0.36 0.04943 6 75 0.007 0.018 0.01 0.019 408.5 21.6 0.032 0.044 0.31 0.04948 6 75 0.013 0.020 0.01 0.015 407.8 21.6 0.049 0.060 0.26 0.05061 7 75 0.012 0.024 0.11 0.004 428.2 20.0 0.033 0.046 0.25 0.05064 7 75 0.013 0.020 0.05 0.045 423.1 20.2 0.032 0.041 0.28 0.0
 B-16

Test Results - Vehicle 015 

Bag 1 Bag 2 

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5269 AsRcvd 75 0.167 0.188 1.38 0.157 431.8 20.5 0.008 0.018 0.00 0.05327 1 50 0.109 0.131 1.13 0.051 456.9 18.6 0.015 0.020 0.00 0.05315 2 50 0.213 0.241 1.35 0.170 471.4 18.0 0.008 0.014 0.00 0.05291 3 50 0.172 0.200 1.64 0.100 402.3 21.4 0.006 0.010 0.00 0.05303 4 50 0.172 0.201 1.31 0.160 470.9 17.3 0.005 0.007 0.00 0.05325 5 50 0.238 0.269 1.80 0.142 480.4 17.8 0.006 0.012 0.00 0.05290 1 75 0.097 0.114 0.67 0.118 449.5 18.9 0.004 0.010 0.00 0.05320 2 75 0.121 0.139 0.75 0.133 438.7 19.3 0.002 0.010 0.02 0.05311 3 75 0.118 0.141 1.29 0.100 430.3 20.0 0.010 0.015 0.00 0.05338 4 75 0.097 0.117 1.07 0.128 443.9 18.4 0.008 0.015 0.00 0.05341 5 75 0.137 0.161 1.59 0.109 439.4 19.5 0.007 0.010 0.00 0.05329 6 75 0.158 0.185 1.28 0.121 441.3 19.8 0.005 0.012 0.00 0.05332 6 75 0.118 0.141 1.24 0.116 442.4 19.8 0.003 0.011 0.00 0.05294 7 75 0.091 0.105 0.75 0.119 440.7 19.4 0.000 0.009 0.00 0.05301 7 75 0.106 0.127 0.94 0.128 445.0 19.2 0.002 0.012 0.00 0.0

 Bag 3 FTP Composit

Test Fuel Temp NMHC HC CO NOX CO2 MPG NMHC HC CO NO

5269 AsRcvd 75 0.004 0.013 0.00 0.067 360.4 24.7 0.040 0.052 0.29 0.15327 1 50 0.009 0.015 0.01 0.028 367.6 23.2 0.033 0.042 0.24 0.05315 2 50 0.004 0.010 0.00 0.020 365.2 23.3 0.050 0.060 0.28 0.05291 3 50 0.010 0.015 0.04 0.016 374.9 23.1 0.042 0.050 0.35 0.05303 4 50 0.001 0.009 0.02 0.018 360.6 22.7 0.039 0.048 0.28 0.05325 5 50 0.004 0.010 0.00 0.025 362.9 23.8 0.054 0.065 0.37 0.05290 1 75 0.007 0.015 0.00 0.026 363.8 23.5 0.024 0.033 0.14 0.05320 2 75 0.009 0.012 0.01 0.026 365.0 23.3 0.029 0.038 0.17 0.05311 3 75 0.010 0.014 0.00 0.031 357.4 24.2 0.033 0.041 0.27 0.05338 4 75 0.008 0.014 0.04 0.023 371.5 22.0 0.026 0.036 0.23 0.05341 5 75 0.004 0.011 0.00 0.041 368.6 23.4 0.033 0.042 0.33 0.05329 6 75 0.006 0.015 0.02 0.033 370.5 23.8 0.037 0.049 0.27 0.05332 6 75 0.006 0.013 0.01 0.020 368.0 23.9 0.028 0.039 0.26 0.05294 7 75 0.004 0.011 0.01 0.020 363.9 23.5 0.020 0.029 0.16 0.05301 7 75 0.003 0.013 0.02 0.030 368.8 23.2 0.024 0.036 0.20 0.0