United States

Environmental Protection

Agency

Air and Radiation EPA420-R-03-012

September 2003

M6.EXH.013

Update to the Accounting for

the Tier 2 and Heavy-Duty

2005/2007 Requirements in

MOBILE6

 Printed on Recycled Paper
EPA420-R-03-012

September 2003

Update to the Accounting for the Tier 2 and Heavy-Duty

2005/2007 Requirements in MOBILE6

M6.EXH.013

John Koupal

David Brzezinski

Assessment and Modeling Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency

NOTICE

This technical report does not necessarily represent final EPA decisions or positions.

It is intended to present technical analysis of issues using data that are currently available.

The purpose in the release of such reports is to facilitate the exchange of

technical information and to inform the public of technical developments which

may form the basis for a final EPA decision, position, or regulatory action.
1

Federal Register Volume 65, Number 28, February 10 2000, Page 6698 “Control of Air Pollution from

New Motor Vehicles: Tier 2 Motor Vehicle Emissions Standards and Gasoline Sulfur Control Requirements”

2

Federal Register Volume 65, Number 195, October 6, 2000, Page 59897 “Emissions Control, Air Pollution

from 2004 and Later Model Year Heavy-Duty Highway Engines and Vehicles”

3

Federal Register Volume 66, Number 12, January 18, 2001, Page 5002 “Control of Air Pollution from

New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control

Requirements”

-2- September 2003

Introduction

This document (M6.EXH.013) updates the CO emission factors originally described in

the document M6.EXH.004 (November 2001) for light duty Tier 2 vehicles. The update is

necessary to account for the changes made in MOBILE6 to account for the effects of Tier 2 HC

and NOx standards on CO emission rates. This document completely supercedes the previous

document (M6.EXH.004) and contains all of the descriptions contained in that document, but the

descriptions have been updated to reflect the subsequent changes in CO emission rates for

MOBILE6.

The purpose of this report is to describe how MOBILE6 accounts for the effects of the

Tier 2 vehicle and fuel program for light-duty vehicles,1 and new standards for heavy-duty

vehicles beginning as required under two recently finalized regulations known as the “HeavyDuty 2005 rule” and the “Heavy-Duty 2007 rule”.2,3 The focus of this report is to present the

methodology for implementing these requirements in MOBILE6, and contains only a brief

overview of each requirement. The requirements themselves should be consulted for an in-depth

treatment of the rule provisions, and for background on the terminology applied in the rules.

Tier 2

Vehicle exhaust standards

The Tier 2 vehicle program, finalized in December 1999, represents significantly more

stringent tailpipe standards for HC and NOx across all light-duty vehicles and trucks. 

Ultimately, all light-duty vehicles and trucks will be held to the same fleet average emission

standard. However, the Tier 2 program allows significant flexibility in meeting these fleet

average emission requirements, including the use of interim standards and the use of multiple

certification “bins” which manufacturers can use to comply with the overall Tier 2 requirement

(see Appendix B). This flexibility allows innumerable approaches which manufacturers can take

to comply with Tier 2, which in turn introduces considerable complexity in addressing Tier 2 in

MOBILE6. The approach for Tier 2 compliance contained in MOBILE6 (Appendix A) reflects

one set of assumptions about how manufacturers will comply with the requirement, but it is not

the sole approach available.
-3- September 2003

The overall Tier 2 requirement is implemented from model years 2004 through 2009. 

Ultimately, all light-duty vehicles (LDVs) and trucks (LDTs) are required to meet, on average, a

full-useful life NOx standard of 0.07 grams/mile by 2009. Prior to this, LDVs and trucks under

6,000 pounds (LDT1s and LDT2s) are subject to one set of fleet average NOx requirements, and

trucks over 6,000 pounds (LDT3s and LDT4s) another. The fleet average NOx emission

standards and phase-in schedules proposed for the vehicle component of the Tier 2/Sulfur

program are shown in Table 1. In 2004, LDT2s would meet the same emission standards

required under the National Low-Emitting Vehicle (NLEV) program for LDVs and LDT1s (i.e.

“LDV LEV” standards). LDVs, LDT1s and LDT2s as a group would then phase in to a 0.07 full

useful life (120,000 mile) gram/mile NOx standard from 2004 to 2007. LDT3s and LDT4s are

treated as a separate group; in 2004, these vehicles would meet standards for MDV2s under

California’s Low-Emitting Vehicle (LEV I) program; as a group, LDT3s and LDT4s would then

phase in to a 0.20 gram/mile NOx standard (and 0.156 gram/mile NMOG standard) from 2004 to

2007. Finally, LDT3s and LDT4s would phase in to the 0.07 gram/mile NOx and 0.09

gram/mile NMOG standards over 2008 and 2009.

Table 1 - Fleet Average Tier 2 NOx Standards and Required Phase-In Schedules

Model Year

LDV/T1/T2 LDT3/4

Full Useful Life NOx

Fleet Average Standard

(g/mi)

Required

Phase-In

Full Useful Life NOx

Fleet Average Standard

(g/mi)

Required

Phase-In

2004 (Interim) 0.30 100% 0.60 100%

2004 0.07 25% 0.20 25%

2005 0.07 50% 0.20 50%

2006 0.07 75% 0.20 75%

2007 0.07 100% 0.20 100%

2008 0.07 100% 0.07 50%

2009 and later Fleet Average Across All Classes = 0.07 gram/mile

Under the Tier 2 program, manufacturers may certify their vehicles in any combination

of 10 certification emission standard “bins” (Appendix B) which result in the NOx fleet average

and phase-in requirements contained in Table 1 (for a complete description of the Tier 2 bin

structure and individual bin emission standards, consult the Tier 2 final rule). Many of these

certification bins overlap with the emission certification categories in California’s LEV II
4

California Air Resources Board, “LEV II and CAP 2000 Amendments to the California Exhaust and

Evaporative Emission Standards and Test Procedures for Passenger Cars, Light-Duty Trucks and Medium-Duty

Vehicles, and to the Evaporative Emission Requirements for Heavy-Duty Vehicles: Final Statement of Reasons”,

September 1999

-4- September 2003

program: LEV, ULEV, SULEV, and ZEV.4

We have developed one possible phase-in schedule for inclusion in MOBILE6, based on

several assumptions about how manufacturers will comply with the requirement. This phase-in

schedule is shown in Appendix A. This phase-in schedule is based on the premise that

manufacturers will take full advantage of the opportunity to trade off higher emissions on

heavier trucks with lower emissions on LDVs and lighter trucks. Specifically, we are assuming

that the bin structure will provide incentives for manufacturers to build LDV/LDT1 SULEVs

under the Tier 2 program because of this ability to trade off with the heavier trucks. It is also

likely that manufacturers who produce partial ZEVs (PZEVs) to comply with the ZEV

requirement in California will certify these vehicles as SULEVs federally. 

The default Tier 2 phase-in schedule included in MOBILE6 was developed using four

basic principles: 

1) Only LDV/LDT1s will certify in Bin 2 (SULEV) and Bin 3. 

2) During phase-in years, manufacturers will comply with the lightest classes first (i.e.,

100 percent of LDV/T1 will meet the 0.07 g/mi NOx requirement before any LDT2s are

brought in, and the 50 percent LDT3/4 0.07 g/mi NOx requirement in 2008 will be met

with LDT3s only). 

3) Manufacturers will trade off LDT2 vs. LDV/T1 in 2007, resulting in a 120,000 mile

NMOG average of 0.077 g/mi for LDV/LDT1/LDT in 2007 and 2008.

4) Manufacturers will trade off LDT3/4 vs. LDV/T1/T2 in 2009, so that all LDT3/4

(except the LDT3s required to be at 0.07 to meet the LDT3/4 requirement ) are in Bin 8;

this results in a 120,000 mile NMOG average of 0.07 g/mi across all vehicles for 2009

and later.

The Tier 2 program does not contain a specific NMOG fleet average requirement, but

NMOG emissions will be reduced under Tier 2 through the implementation of the certification

“bin” structure. The fleet-average NMOG emission values under Tier 2 are driven solely by the

distribution of vehicles across the certification bins. Table 2 shows the NOx and NMOG fleet

averages which result when the default MOBILE6 phase-in assumptions are employed in
5

MOBILE6 assumes that the share of truck sales relative to vehicles would grow to 60 percent in 2008, then

level off. Within the truck classes, the splits were held constant: LDT1 = 18%, LDT2 = 57%, LDT3 = 17%, LDT4 =

8%, as derived from projected sales data for the 1999 model year.

-5- September 2003

conjunction with the projected sales splits assumed implicitly within MOBILE6.5

Table 2: 120K Light-Duty NOx/NMOG Fleet Averages (g/mi)

Model 

Year NOx NMOG

2004 0.277 0.108

2005 0.214 0.106

2006 0.152 0.104

2007 0.088 0.088

2008 0.079 0.081

2009 0.070 0.070

2010 0.070 0.070

For MOBILE6, basic emission rates for each Tier 2 certification bin were estimated

based on the basic emission rates for Tier 1vehicles adjusted by the ratio of the Tier 2 standards

to the Tier 1 standards. The method is similar to the methodology presented in MOBILE6 report

M6.EXH.007, “Determination of NOx and HC Basic Emission Rates, OBD and I/M Effects for

Tier 1 and later LDVs and LDTs” and report M6.EXH.12, “Update to the Determination of CO

Basic Emission Rates, OBD and I/M Effects for Tier 1 and Later LDVs and LDTs”. This is

done by weighting the Tier 2 emission standard rates (in Appendix B) by the phase in fractions

(in Appendix A) to give a composite emission standard rate. This rate is divided by the

corresponding Tier 1 emission standard and the ratio is multiplied by the emission rate

determined for Tier 1 vehicles by MOBILE6 to give the Tier 2 emission rate.

The exception to this method is the determination of CO emission rates. As described in

M6.EXH.12, the LEV CO emission rates are adjusted by the ratio of LEV certification test

results to Tier 1 certification test results to reflect the effect of enhanced emission control

systems on LEVs necessary to meet the more stringent HC and NOx LEV emission standards. 

This allows the CO emissions for LEVs to be reduced even though the CO emission standard for

LEVs is identical to the CO emission standard for Tier 1 vehicles. The same adjustment (0.505)

used for LEVs is used when determining the composite emission standard rates for Tier 2 bins 5

through 10. The Tier 2 CO emission standard rate for these bins (as shown in Appendix B) is

not used. The adjustment is applied to the corresponding Tier 1 CO emission standard rate and
-6- September 2003

that adjusted rate is used instead. This reduces the effective composite CO emission standard

rate used to determine the CO emission rates for Tier 2 vehicles. The effective Tier 2 CO

standards are shown in Appendix C.

Vehicle Evaporative Standards

The Tier 2 requirement includes more stringent standards for the 2 and 3-day evaporative

test procedure. California’s LEV II requirement also includes evaporative emission standards. 

The standards for both the Tier 2 and LEV II programs are shown in Table 

Table 3: Evaporative HC Standards Under Tier 2 and LEV II 

(grams/test over 3-day diurnal + hot soak)

Vehicle Class Current Tier 2 LEV II

LDV

2.0

0.95 0.5

LDT1 0.95 0.65

LDT2 0.95 0.65

LDT3/LD4 1.2 0.95

California’s program requires the phase-in to the LEV II standards at 40 percent in 2004,

80 percent in 2005, and 100 percent in 2006. The Tier 2 standards are phased-in according to the

same schedule required for the final NOx exhaust standards, presented in Table 1. 

For MOBILE6 we are assuming that the LEV II evaporative standards will drive benefits

under the Tier 2 program as well. This approach is based on our analysis of the relative

stringency of the California and EPA standards as well as input from auto manufacturers, who

have indicated to EPA their plans to build a single evaporative emission control system to

comply with both the Federal and California evaporative requirements. The primary driver of

this is that the Tier 2 evaporative program, while having slightly less stringent certification

standards, includes a provision which requires manufacturers to certify the durability of their

systems using the maximum allowable alcohol fuel levels; California does not require this

provision. To compensate for the increased vulnerability of system components to alcohol fuel,

manufacturers will need to build a more durable system than the standard would imply using the

same low permeability hoses and low loss connections planned for LEV II vehicles. 

Manufacturers have provided written assurances to EPA that the alcohol fuels provision

of the federal standards, and relative difficulty in “finessing” evaporative emissions between the

LEV II and Tier 2 standards, will necessitate the development of a single federal system

complying with the California standards. We will revisit this assumption when certification data

is available on evaporative Tier 2 vehicles to determine whether this approach is still warranted.
6

“Development of Light-Duty Emission Inventory Estimates in the Final Rulemaking for Tier 2 and Sulfur

Standards”, Memorandum from John Koupal to Docket A-97-10, December 15, 1999.

7

Under the API/NPRA proposal, Eastern U.S. consists of eastern Texas, Oklahoma, Mississippi, Tennessee,

Missouri, Illionois, Wisconsin, and all those states (including the District of Columbia) east of these states. A

detailed accounting of the API proposal is contained in the Tier 2 regulatory docket, A-97-10

-7- September 2003

MOBILE6 estimates evaporative emissions under the new standards by applying a

percent reduction to the basic emission rates for diurnals and hot soak according to the percent

reduction between the current standards and the LEV II standards. Thus, the percent reduction

for LDVs is 75 percent, for LDT1s and LDT2s 67.5 percent, and for LDT3s and LDT4s 52.5

percent.

Fuel standards

Under the Tier 2 rule, gasoline producers are required to reduce fuel sulfur levels to 120

ppm in 2004, 90 ppm in 2005 and 30 ppm in 2006, on average. However, there are provisions

which allow small refiners and gasoline producers in western states to achieve the 30 ppm

average on a longer timetable. In addition, Averaging, Banking and Trading (ABT) provisions

allow refiners who achieve early reductions in gasoline fuel sulfur levels to apply these

reductions against the requirement in later years. 

MOBILE6 accounts for the small refiner (termed “SBREFA”), geographic phase-in

(termed “GPI”) and ABT provisions contained in the Tier 2 fuel program through the

development of composite by-calendar year fuel sulfur levels which estimate the effects of these

provisions on a volume basis. The MOBILE6 modeling approach is based directly on the

modeling assumptions developed in support of the Tier 2 rule, which developed composite fuel

sulfur levels by calendar year for several fuel “categories” accounting all fuel sold in the U.S.6

Based on the definition of Eastern U.S and Western U.S. defined by API and NPRA in their

sulfur program proposed to EPA,7 the Tier 2 modeling methodology divided the fuel produced in

the 47-state region into five fuel categories, as shown in Table 4. The primary modification

between the approach used in the Tier 2 rule modeling and MOBILE6 is the definition of these

fuel categories; MOBILE6 developed three categories based on aggregating the five categories

defined for the Tier 2 modeling. As shown in Table 4, the three MOBILE6 categories are East

Conventional, RFG, and West.

Table 4 - MOBILE6 Fuel Categories
8 “Draft Regulatory Impact Analysis - Control of Air Pollution from New Motor Vehicles: Tier 2 Motor

Vehicle Emissions Standards and Gasoline Sulfur Control Requirements”, EPA Report EPA420-D-99-001, April

1999

-8- September 2003

Tier 2 Fuel Category Description MOBILE6

Category

East Convential Gasoline (CG) Conventional gasoline areas in the east

East CG

East SBREFA Fuel produced by SBREFA refiners in the east

Reformulated Gasoline (RFG) Reformulated Gasoline areas (all in the east) RFG

West SBREFA Fuel produced by SBREFA refiners in the west West

West GPI Fuel produced by western refiners under the

geographic phase-in 

The default sulfur levels contained in MOBILE6 were developed by first estimating

sulfur levels for each of the five Tier 2 categories shown in Table 4, then aggregating into the

three MOBILE6 categories according to weightings of fuel production across each of the

categories. The first step in this analysis was to define the sulfur levels (average and cap) for

each fuel category by calendar year for the baseline and control scenarios. Focusing on the

projection of the average sulfur levels first, the sulfur levels in 2000 were determined from an

assessment of refiner’s certification records from 1998. Outside of California, gasoline sulfur

levels averaged 268 ppm in 1998. EPA projects that RFG will average roughly 150 ppm

beginning in 2000 in order to meet the Phase 2 RFG NOx performance specification.8

Comments from a number of oil refiners and NPRA indicated that refiners would not reduce the

sulfur of their total gasoline pool in order to meet the Phase 2 RFG NOx performance

specification in 2000, but would shift sulfur from RFG to CG in the summer and vice versa in

the winter. The average sulfur level of RFG in 1998 was 207 ppm. Because this level is fairly

close to the 150 ppm RFG target, it is quite conceivable that refiners could perform the sulfur

shift outlined in the comments to the proposed rule. Assuming that the sulfur level of summer

RFG was reduced from 207 to 150 ppm, we determined that the sulfur level of CG and winter

RFG would increase from its 1998 level of 295 ppm to 300 ppm. For the baseline case, sulfur

levels are assumed to stay constant from calendar year 2000 onward; the baseline levels for years

2000 and later are shown in Table 5. Because the SBREFA and GPI provisions are not

applicable in the baseline case, the fuel categories developed for the Tier 2 modeling

methodology are directly applicable in MOBILE6.

Table 5 - Default MOBILE6 Sulfur Levels Without Tier 2 (ppm)
9

“Regulatory Impact Analysis - Control of Air Pollution from New Motor Vehicles: Tier 2 Motor Vehicle

Emissions Standards and Gasoline Sulfur Control Requirements”, EPA Report EPA420-R-99-023, December 1999

-9- September 2003

Calendar Year

East Conventional RFG West Conventional

Average Cap Average Cap Average Cap

2000 & later 300 1000 150 500 300 1000

For the “with Tier 2" case, sulfur levels in 2001-2003 were estimated from 2000 sulfur

levels using the sulfur reductions which would occur from desulfurization units projected to be

built and operating prior to 2004. These projections are described in Section IV.B.8. of the Final

Tier 2 Regulatory Impact Analysis (RIA).9 Based on the operation of these new units, we project

that pool sulfur levels will decrease by 1, 21 and 37 ppm in 2001, 2002, and 2003. These

reductions were applied uniformly to each fuel category with one exception. In 2003, a

reduction of 37 ppm would have reduced RFG sulfur levels to less than 120 ppm, the corporate

average standard in 2004. To avoid this, the RFG sulfur level was assumed to decrease to only

120 ppm in 2003 and the sulfur level of the remainder category of CG and RFG was decreased

by 41 ppm instead of only 37 ppm. This results in a 37 ppm reduction in the non-California pool

average sulfur level. 

In 2004 and 2005, fuel subject to the corporate average standards, RFG and the

remainder category of RFG and CG, was assumed to average at the corporate average standards,

120 and 90 ppm, respectively. The average sulfur levels of fuel certified to these standards may

be below these levels due to refiners desire to maintain a safety margin between their actual

sulfur levels and enforcement levels. However, the degree of this potential margin is not known

and is not guaranteed by the applicable standards. 

In 2004-2007, small refiners under the SBREFA program are governed by average

standards which are a function of their current sulfur level. We estimated these standards for the

16 small refiners based on their sulfur certification data in 1998. In the east, the volumeweighted average of these standards was 191 ppm and in the west was 208 ppm. We assumed

that these refiners would produce fuel at these sulfur levels until 2008, when the 30 ppm refinery

average standard applies. 

In 2004-2006, refineries covered by the geographic phase-in must meet a 150 ppm

refinery average standard. We assumed that these refineries would produce fuel at this level. 

For all categories of fuel, once the 30 ppm refinery average standard began to apply, we

assumed that commercial gasoline in these categories would average at the standard, 30 ppm.

With respect to the maximum sulfur level possible in any fuel category, we based these

levels on the maximum allowable sulfur level from any individual refinery in the category. The
-10- September 2003

Complex Model places a limit of 500 ppm sulfur on RFG and 1000 ppm for CG; therefore these

levels were applied to RFG and CG fuel categories, respectively, from 2000-2003. Beginning in

2004, the maximum sulfur level of each fuel category was assumed to be the cap applicable to

that category of fuel. Thus, these levels are simply a function of the final caps for these fuel

categories. Maximum sulfur levels are used only for the calculation of sulfur “irreversibility”

effects, discussed in detail in the MOBILE6 report M6.FUL.001, “Fuel Sulfur Effects on

Exhaust Emissions”. 

Table 6 shows the sulfur levels with Tier 2 as derived by the process described above, for

the disaggregated categories from Table 4. These disaggregate categories were then weighted by

the fuel production weightings in Table 7, resulting in the MOBILE6 sulfur levels with Tier 2

across the three MOBILE6 fuel categories. 

Table 6 - Sulfur Levels With Tier 2: Disaggregate Categories (ppm)

Year

East

Conventional

East SBREFA RFG West SBREFA West GPI

Avg Cap Avg Cap Avg Cap Avg Cap Avg Cap

2000 300 1000 300 1000 150 500 300 1000 300 1000

2001 299 1000 299 1000 149 500 299 1000 299 1000

2002 279 1000 279 1000 129 500 279 1000 279 1000

2003 259 1000 263 1000 120 500 263 1000 263 1000

2004 120 300 191 450 120 300 208 450 150 300

2005 90 300 191 450 90 300 208 450 150 300

2006 30 80 191 450 30 80 208 450 150 300

2007 30 80 191 450 30 80 208 450 30 80

2008 & later 30 80 30 80 30 80 30 80 30 80

Table 7 - Non-RFG Category Weightings (by fuel consumption)
-11- September 2003

Tier 2 (Disaggregate) Fuel

Category

Weightings MOBILE6

Category

East CG 0.98

East CG

East SBREFA 0.02

West SBREFA 0.16 West

West GPI 0.84

Table 8 - Sulfur Levels With Tier 2: MOBILE6 Categories (ppm)

Year

East Conventional RFG West Conventional

Average Cap Average Cap Average Cap

2000 300 1000 150 500 300 1000

2001 299 1000 149 500 299 1000

2002 279 1000 129 500 279 1000

2003 259 1000 120 500 263 1000

2004 121 303 120 300 160 325

2005 92 303 90 300 160 325

2006 33 87 30 80 160 325

2007 33 87 30 80 60 142

2008 & later 30 80 30 80 30 80

New Standards for Heavy-Duty Gasoline Vehicles

Methodology for Developing Basic Exhaust Emission Rates

Heavy-Duty Gas Vehicles (HDGVs) will be subject to new standards under three

separate requirements. A first phase of exhaust and evaporative standards affecting all HDGVs

will begin implementation in 2005, and hence are referred to as the “2005 rule"; the Tier 2

“Medium Duty Passenger Vehicle” (MDPV) standards will reduce emissions further for a subset

of HDGV2bs beginning in 2008. The recently finalized Heavy-Duty 2007 rule (“2007 rule”) for

diesel engines also will require emission reductions for the remainder of HDGVs beginning in

2008. These standards are shown in Table 9. 
10“Regulatory Impact Analysis: Control of Emissions of Air Pollution from Highway Heavy-Duty

Engines”, EPA Report EPA420-R-00-010, July 2000

-12- September 2003

Table 9: HC/NOx 120,000 Mile Standards for HDGV (g/mi unless otherwise noted)

Class

2b 3

4-8 

MDPV Other (g/bhp-hr)

Complete

Incomplete

(g/bhp-hr) Complete Incomplete(g/bhp-hr)

Pre-2005 

(all g/bhp-hr) 0.9/4.00 1.7/4.0

2005 Rule 0.28/0.9 0.28/0.9 0.2/0.8 0.33/1.0 0.2/0.8 0.2/0.8

Tier 2 0.075/0.07 0.28/0.9 0.2/0.8 0.33/1.0 0.2/0.8 0.2/0.8

2007 Rule 0.075/0.07 0.195/0.2 0.14/0.2 0.23/0.4 0.14/0.2 0.14/0.2

2005 Standards

The methodology for deriving HC and NOx BERs for HDGVs under the 2005

requirements is contained in the Chapter 7 of the Regulatory Impact Analysis (RIA) for the

Heavy-Duty Gas rulemaking.10 As outlined in this document, BERs were derived by assuming a

similar margin of compliance with the certification standards as for the pre-control BERs. In

the RIA, separate BERs were derived for three sets of HDG classes: 2b Completes, 3 Completes,

and Incomplete for all classes. Because MOBILE6 will not differentiate between Complete and

Incomplete certification classes, an additional step was required for this analysis to generate a

combined BER for the 2b and 3 classes. The was performed by weighting together the

Complete/Incomplete emission rates according to sales figures for the 1996 model year provided

by manufacturers in the Heavy-Duty Gas 2005 rule, which indicated that Completes would

comprise 96 percent of HDGV2b (458,447 out of 485,046) and 15 percent of HDGV3 (38,733

out of 124,265). For the MOBILE6 analysis, the BERs for Completes/Incompletes presented in

the HDG rule where therefore weighted according to 96/4 and 15/85 splits for 2bs and 3s,

respectively. The resulting BERs are shown in Tables 2 and 3. Because the 2005 HDG

standards for HC are expressed as NMOG, the BERs also reflect NMOG and should be handled

accordingly in the model. CO standards are not reduced in 2005, so updated BERs are not

required to reflect the heavy-duty rule.

Tier 2 MDPV Standards

The Tier 2 Medium-Duty Passenger Vehicle provisions require that a subset of HDG2bs

used primarily as passenger vehicles (i.e. large sport utility vehicles such as the GM Suburban)

meet the final Tier 2 standards (NMOG, NOx and CO) for light-duty trucks over 6,000 pounds

by 2009. The specific requirement for these trucks is a full useful life standard of 0.09 g/mi
11“Regulatory Impact Analysis - Control of Air Pollution from New Motor Vehicles: Tier 2 Motor Vehicle

Emissions Standards and Gasoline Sulfur Control Requirements”, EPA Report EPA420-R-99-023, December 1999

-13- September 2003

NMOG and 0.07 g/mi NOx, phasing-in beginning in 2008 at 50 percent and 100 percent in 2009. 

In developing MOBILE6 BERs it was assumed that the subset of HDGV2bs required to meet

these standards will follow this phase-in schedule. 

The effect of these standards was estimated through the 2009 and later BERs for

HDG2bs. BERs for MDPVs were calculated by reducing the 2005 BERs (ZML and DR) by the

ratio of the MDPV standards to the 2005 standards. The fraction of HDGV2b sales attributed to

MDPVs was derived by dividing an estimate of annual sales for MDPVs of 75,000 from the Tier

2 RIA (Chapter 6)11 by the number of HDGV2bs estimated in the heavy-duty rule (485,046),

resulting in a fraction of 0.155. The overall 2009 HDGV2b BERs was then calculated by

weighting together the 2005 (pre-Tier 2 BER) and the MDPV BER by a weighting split of

0.845/0.155. To model the 50 percent phase-in in 2008, the 2009 and 2005 BERs were

averaged. 

2007 Rule Standards

Basic emission rates corresponding to the standards under the 2007 rule were developed

using the same methodology applied for the 2005 rule. Specifically, the same level of

compliance was assumed in relation to the certification standard between the baseline (pre2005), 2005 rule standards and 2007 rule standards. The emission rates were thus derived by

applying the ratio of the 2005 and 2007 standards to the model year 2005 emission rates for all

of the vehicles affected by the 2007 standards (including Class 2b vehicles not falling under the

Tier 2 MDPV requirement). 

The resulting emission rates reflecting the 2005, Tier 2 MPDV and 2007 rules are shown

in Tables 10 through 13, by HDGV class 2b through 8b, and buses.

Table 10: Low Altitude NMOG Basic Emission Rates for MOBILE6 (g/mi)

NMOG ZML

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.118 0.104 0.096 0.113 0.111 0.123 0.131 0.131 0.153

2008 0.098 0.088 0.082 0.096 0.095 0.105 0.112 0.112 0.130

2009+ 0.078 0.073 0.067 0.079 0.078 0.086 0.092 0.092 0.107
-14- September 2003

NMOG DR (per 10K miles)

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.008 0.006 0.006 0.007 0.007 0.007 0.008 0.008 0.009

2008 0.007 0.005 0.005 0.006 0.006 0.006 0.007 0.007 0.008

2009+ 0.005 0.004 0.004 0.005 0.005 0.005 0.006 0.006 0.006

Table 11: Low Altitude NOx Basic Emission Rates for MOBILE6 (g/mi)

NOx ZML

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.573 0.594 0.578 0.675 0.669 0.737 0.785 0.785 0.916

2008 0.347 0.379 0.361 0.422 0.418 0.461 0.491 0.491 0.573

2009+ 0.121 0.163 0.145 0.169 0.167 0.184 0.196 0.196 0.229

NOx DR (per 10K miles)

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.008 0.008 0.008 0.009 0.009 0.010 0.011 0.011 0.013

2008 0.005 0.005 0.005 0.006 0.006 0.006 0.007 0.007 0.008

2009+ 0.002 0.002 0.002 0.002 0.002 0.003 0.003 0.003 0.003

Table 12: High Altitude NMOG Basic Emission Rates for MOBILE6 (g/mi)

NMOG ZML

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.219 0.193 0.179 0.209 0.207 0.228 0.243 0.243 0.283

2008 0.182 0.163 0.152 0.178 0.176 0.194 0.207 0.207 0.241

2009+ 0.145 0.136 0.125 0.146 0.145 0.160 0.170 0.170 0.198
-15- September 2003

NMOG DR

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.015 0.012 0.011 0.012 0.012 0.013 0.014 0.014 0.017

2008 0.013 0.009 0.009 0.010 0.010 0.011 0.012 0.012 0.014

2009+ 0.009 0.007 0.008 0.008 0.008 0.009 0.010 0.010 0.012

Table 13: High Altitude NOx Basic Emission Rates for MOBILE6 (g/mi)

NOx ZML

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.469 0.486 0.473 0.552 0.547 0.603 0.642 0.642 0.749

2008 0.284 0.310 0.296 0.345 0.342 0.377 0.401 0.401 0.468

2009+ 0.098 0.134 0.118 0.138 0.137 0.151 0.161 0.161 0.187

NOX DR

Class: 2b 3 4 5 6 7 8a 8b Bus

2005-07 0.007 0.007 0.006 0.008 0.008 0.008 0.009 0.009 0.010

2008 0.004 0.004 0.004 0.005 0.005 0.005 0.006 0.006 0.006

2009+ 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.003

Evaporative Emission Rates for HDGV 2005/2007 Requirements

The 2005 and 2007 rules contain evaporative emission standards as well as exhaust

standards. The methodology and emission rates for these requirements are contained in

MOBILE6 report M6.EVP.001, “Evaluating Resting Loss and Diurnal Evaporative Emissions

Using RTD Tests”, April 2001.

Heavy-Duty Diesel 2007 Rule

The heavy-duty 2007 rule requires significant reductions in PM, HC and NOx for all

heavy-duty diesel engines beginning in 2007. Standards of 0.20 g/bhp-hr for NOx and 0.14

g/bhp-hr for NMHC are required on 50 percent of engines in 2007, and 100 percent in 2010. 

However, a 0.01 g/bhp-hr PM standard applies to 100 percent of engines in 2007, and the

exhaust aftertreatment required to comply with this standard is expected to drive 100 percent

compliance with the HC standard in 2007, and provide residual benefits in CO as well. These
12“Regulatory Impact Analysis - Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine

and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements”, EPA Report EPA420-R-00-026,

December 2000

13“Updated Heavy-Duty Engine Emission Conversion Factors for MOBILE6: Analysis of BSFCs and

Calculation of Heavy-Duty Engine Emission Conversion Factors”, EPA Report EPA420-P-98-015, May 1998

-16- September 2003

effects are modeled through the basic emission rates developed in MOBILE6. 

The basic emission rates for MOBILE6 have been developed directly from those used in

the emission inventory work in support of the final rule, detailed in the Regulatory Impact

Analysis of the final rule.12 The primary modifications required for inclusion in MOBILE6 were

a) the conversion of g/bhp-hour emission rates to grams/mile, using conversion factors

developed for late-model heavy-duty engines and discussed in separate MOBILE6

documentation; 13 and b) the disaggregation of weight classes from those used in the regulatory

support work to the MOBILE6 weight class definitions. The weight classes used in the

regulatory work were simply an aggregation of the MOBILE6 classes, and the disaggregation

process consisted of applying the aggregate emission rates (e.g. for the regulatory modeling class

“light-heavy duty diesels”) across each of the sub-classes (e.g. the MOBILE6 weight classes 2b

and 3). This was therefore a trivial step but resulted in duplicate emission rates across multiple

MOBILE6 classes. The basic emission rates, in g/bhp-hr and gram/mile, are shown in Tables

14-16. 

Table 14: 2007+ HDDV CO Basic Emission Rates for MOBILE6

Class Start MY

g/bhp-hr Correction

Factor 

g/mile

ZML DR ZML DR

2b 2007 0.120 0.000 1.09 0.131 0.000

3 2007 0.120 0.000 1.25 0.150 0.000

4 2007 0.120 0.000 1.458 0.175 0.000

5 2007 0.120 0.000 1.573 0.189 0.000

6 2007 0.100 0.000 1.942 0.194 0.000

7 2007 0.100 0.000 2.409 0.241 0.000

8a 2007 0.120 0.000 2.763 0.332 0.000

8b 2007 0.120 0.000 3.031 0.364 0.000

School Bus 2007 0.100 0.000 2.989 0.299 0.000

Transit Bus 2007 0.110 0.000 4.679 0.515 0.000
-17- September 2003

Table 15: 2007+ HDDV NMHC Basic Emission Rates for MOBILE6

Class Start MY

g/bhp-hr Correction

Factor 

g/mile

ZML DR ZML DR

2b 2007 0.129 0.000 1.09 0.141 0.000

3 2007 0.129 0.000 1.25 0.161 0.000

4 2007 0.129 0.000 1.458 0.188 0.000

5 2007 0.129 0.000 1.573 0.203 0.000

6 2007 0.129 0.000 1.942 0.251 0.000

7 2007 0.129 0.000 2.409 0.311 0.000

8a 2007 0.129 0.000 2.763 0.356 0.000

8b 2007 0.129 0.000 3.031 0.391 0.000

School Bus 2007 0.129 0.000 2.989 0.386 0.000

Transit Bus 2007 0.080 0.000 4.679 0.374 0.000

Table 16: 2007+ HDDV NOx Basic Emission Rates for MOBILE6

Class Start MY

g/bhp-hr Correction

Factor 

g/mile

ZML DR ZML DR

2b 2007 1.139 0.001 1.09 1.242 0.001

2b 2010 0.180 0.000 1.09 0.196 0.000

3 2007 1.139 0.001 1.25 1.424 0.001

3 2010 0.180 0.000 1.25 0.225 0.000

4 2007 1.139 0.001 1.458 1.661 0.001

4 2010 0.180 0.000 1.458 0.262 0.000

5 2007 1.139 0.001 1.573 1.792 0.002

5 2010 0.180 0.000 1.573 0.283 0.000

6 2007 1.131 0.001 1.942 2.196 0.002

6 2010 0.180 0.000 1.942 0.350 0.000

7 2007 1.131 0.001 2.409 2.725 0.002

7 2010 0.180 0.000 2.409 0.434 0.000

8a 2007 1.063 0.002 2.763 2.937 0.006

8a 2010 0.180 0.000 2.763 0.497 0.000

8b 2007 1.063 0.002 3.031 3.222 0.006

8b 2010 0.180 0.000 3.031 0.546 0.000

School Bus 2007 1.131 0.001 2.989 3.381 0.003

School Bus 2010 0.180 0.000 2.989 0.538 0.000

Transit Bus 2007 1.200 0.002 4.679 5.615 0.009

Transit Bus 2010 0.180 0.000 4.679 0.842 0.000
-18- September 2003

Appendix A

Tier 2 Phase-In Schedule

Model Year Emission Certification Bin

LDV/LDT1 1 2 3 4 5 6 7 8 9 10 11

2004 0.000 0.000 0.000 0.000 0.386 0.000 0.000 0.000 0.614 0.000 0.000

2005 0.000 0.000 0.000 0.000 0.787 0.000 0.000 0.000 0.213 0.000 0.000

2006 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000

2007 0.000 0.100 0.300 0.200 0.400 0.000 0.000 0.000 0.000 0.000 0.000

2008 0.000 0.100 0.300 0.200 0.400 0.000 0.000 0.000 0.000 0.000 0.000

2009 0.000 0.250 0.550 0.100 0.100 0.000 0.000 0.000 0.000 0.000 0.000

2010 0.000 0.250 0.550 0.100 0.100 0.000 0.000 0.000 0.000 0.000 0.000

LDT2 1 2 3 4 5 6 7 8 9 10 11

2004 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000

2005 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000

2006 0.000 0.000 0.000 0.000 0.337 0.000 0.000 0.000 0.663 0.000 0.000

2007 0.000 0.000 0.000 0.000 0.400 0.300 0.300 0.000 0.000 0.000 0.000

2008 0.000 0.000 0.000 0.000 0.400 0.300 0.300 0.000 0.000 0.000 0.000

2009 0.000 0.000 0.000 0.200 0.200 0.300 0.300 0.000 0.000 0.000 0.000

2010 0.000 0.000 0.000 0.200 0.200 0.300 0.300 0.000 0.000 0.000 0.000

LDT3 1 2 3 4 5 6 7 8 9 10 11

2004 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.370 0.000 0.630 0.000

2005 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.740 0.000 0.260 0.000

2006 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000

2007 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000

2008 0.000 0.000 0.000 0.000 0.740 0.000 0.000 0.260 0.000 0.000 0.000

2009 0.000 0.000 0.000 0.000 0.740 0.000 0.000 0.000 0.000 0.000 0.260

2010 0.000 0.000 0.000 0.000 0.740 0.000 0.000 0.000 0.000 0.000 0.260

LDT4 1 2 3 4 5 6 7 8 9 10 11

2004 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000

2005 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000

2006 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.220 0.000 0.780 0.000

2007 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000

2008 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000

2009 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000

2010 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000
-19- September 2003

Appendix B

Tier 2 Standards at 50,000 Miles

As Used in MOBILE6

Non-Methane Organic Gases (grams per mile)

Bin LDV LDT1 LDT2 LDT3 LDT4

1 0.000 0.000 0.000 0.000 0.000

2 0.007 0.007 0.007 0.007 0.007

3 0.040 0.040 0.040 0.040 0.040

4 0.051 0.051 0.051 0.051 0.051

5 0.075 0.075 0.075 0.075 0.075

6 0.075 0.075 0.075 0.075 0.075

7 0.075 0.075 0.075 0.075 0.075

8 0.100 0.100 0.100 0.125 0.125

9 0.075 0.075 0.100 0.140 0.140

10 0.125 0.125 0.125 0.160 0.195

11 0.000 0.000 0.000 0.100 0.100

Carbon Monoxide (grams per mile)

Bin LDV LDT1 LDT2 LDT3 LDT4

1 0.0 0.0 0.0 0.0 0.0

2 1.7 1.7 1.7 1.7 1.7

3 1.7 1.7 1.7 1.7 1.7

4 1.7 1.7 1.7 1.7 1.7

5 3.4 3.4 3.4 3.4 3.4

6 3.4 3.4 3.4 3.4 3.4

7 3.4 3.4 3.4 3.4 3.4

8 3.4 3.4 3.4 3.4 3.4

9 3.4 3.4 3.4 3.4 3.4

10 3.4 3.4 3.4 4.4 4.4

11 0.0 0.0 0.0 0.0 0.0

Oxides of Nitrogen (grams per mile)

Bin LDV LDT1 LDT2 LDT3 LDT4

1 0.000 0.000 0.000 0.000 0.000

2 0.014 0.014 0.014 0.014 0.014

3 0.021 0.021 0.021 0.021 0.021

4 0.029 0.029 0.029 0.029 0.029

5 0.050 0.050 0.050 0.050 0.050

6 0.080 0.080 0.080 0.080 0.080

7 0.110 0.110 0.110 0.110 0.110

8 0.140 0.140 0.140 0.140 0.140

9 0.200 0.200 0.200 0.200 0.200

10 0.400 0.400 0.400 0.400 0.400

11 0.000 0.000 0.000 0.000 0.000
-20- September 2003

Appendix C

Effective Tier 2 Standards at 50,000 Miles

As Used in MOBILE6 For CO Emissions

Carbon Monoxide (grams per mile)

Bin LDV LDT1 LDT2 LDT3 LDT4

1 0.0 0.0 0.0 0.0 0.0

2 1.7 1.7 1.7 1.7 1.7

3 1.7 1.7 1.7 1.7 1.7

4 1.7 1.7 1.7 1.7 1.7

5 1.717 1.717 2.222 2.222 2.525

6 1.717 1.717 2.222 2.222 2.525

7 1.717 1.717 2.222 2.222 2.525

8 1.717 1.717 2.222 2.222 2.525

9 1.717 1.717 2.222 2.222 2.525

10 1.717 1.717 2.222 2.222 2.525

11 0.0 0.0 0.0 0.0 0.0

Tier 1 3.4 3.4 4.4 4.4 5.0