UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY 

2565 PLYMOUTH ROAD 

ANN ARBOR, MICHIGAN 48105-2498 

OFFICEOF 

AIR AND RADIATION 

May 26,2005 CCD-05-10 (JDV/LDT/MDPV/HDV/ICI/LD-AFC) 

Dear Manufacturer: 

Subject: Assigned Deterioration Factors 

This letter provides revised EPA assigned deterioration factors (ADFs) for determining 

compliance with chassis-based exhaust and evaporative mission standards. These assigned 

deterioration factors may be used for small volume manufacturers under the provisions of 40 

CFR 86.1826-01, and are applicable for chassis tested vehicles using petroleum based fuels 

(gasoline and diesel), alcohol fuels (ethanol and methanol) and gaseous fuels (natural gas and 

liquified petroleum gas). ADFs are provided for current vehicle standards and, because 

aftermarket alternative fuels converters and Independent Commercial Importers (ICIs) may 

convert or modify older model year vehicles, ADFs are also listed for previous model year 

standards. These ADFs must be used by qualifying small volume manufacturers and ICIs who 

certify new test groups after October 15,2005. Small volume manufacturers and ICIs may 

optionally use these ADFs immediately. 

Applicability 

EPA's regulations at 40 CFR 86.1826-01(a) define the applicability of ADFs. 

These revised deterioration factors (DFs) supercede previous assigned deterioration 

factors presented in EPA Advisory Circular 51C', guidance letters CCD-00-12 dated August 24, 

2000 and CD-95-14 dated September 27, 1995, and the ADFs presented in the most recent 

version of a template letter sent to prospective new small volume manufacturers and Independent 

Commercial Importers (ICIS).~ 

Guidance letter CCD-00-12 continues to be the appropriate source for determining EPA 

ADFs for aftermarket conversions of heavy-duty engines for operation on alternative fuels. 

The new ADFs do not necessarily apply to vehicles certified to comply with California 

emission standards. Manufacturers who desire to certify vehicles in California by using ADFs 

will need to satisfy the current requirements from the California Air Resources Board (CARB). 

The CARB contact is Duc Nguyen (e-mail: dnguyen@arb.ca.gov). 

'The assigned deterioration factors contained in Advisory Circular 51C are still applicable for IC1Tier 0 vehicles. 

The assigned exhaust and evaporative emission deterioration factors used by new small volume manufacturers and ICIs are based 

on California Air Resources Board Manufacturer Advisory Correspondence documents No. 91-04 and 97-01, respectively. 

1 
Background 

The EPA authority to develop and provide vehicle and engine manufacturers with ADFs 

is based on Section 206(a)( 1) of the Clean Air Act. EPA subsequently enacted regulations which 

allowed manufacturers to use ADFs. These provisions were described in $86.084-14 and 

§86.085-24(e)(2), and ADFs were published in Office of Mobile Sources (OMS) Advisory 

Circular (NC) letter No. 51C, dated December 4, 1986.3 

Effective with the Tier 1 emission standards, EPA accepted the use of the deterioration 

factors contained in the California Air Resources Board (CARB) Manufacturers Advisory 

Correspondence (MAC) letter No. 91-04. EPA also accepted use of the evaporative emission 

assigned deterioration factors in CARB MAC letter No. 97-01. These CARB developed ADFs 

were used in lieu of EPA supplied industry-wide ADFs for Tier 1exhaust emissions and 

enhanced (Tier 1) evaporative emission standards. These same ADFs were also used by 

manufacturers for determining compliance with the NLEV emission standards, and were also 

used as EPA ADFs to meet interim non-Tier 2 standards and final Tier 2 emission standards. 

In the September 21, 1994 Federal Register, EPA published emission standards and test 

procedures for gaseous fueled vehicles and engines. In a separate rulemaking action on 

September 30, 1994, EPA published emission standards for Clean-Fuel Vehicles (CFVs) and 

Engines. These regulations prompted EPA to publish ADFs for the Clean-Fuel Vehicle program 

in EPA guidance letter CD-95-14 in 1995, and to re-issue this as guidance letter CCD-00-12, in 

2000. The ADFs in these guidance letters are identical. The ADFs for gaseous vehicles were not 

based on data, but instead they were based on an analysis of emission standards values. 

The current EPA policy regarding ADFs is found in 40 CFR 586.1826-Ol(b)(l)(i). This 

CFR section discusses using a 70” percentile analysis of industry-wide data to determine ADFs 

for manufacturers with sales volumes less than 300 vehicles, while 586.1826-01(b)(2)(i)(A) 

discusses using either a 70” percentile or arithmetic average of a manufacturer’s deterioration 

factor data, whichever is less, to determine ADFs for a manufacturer with sales volumes of 301- 

14,999 vehicles. In §86.1826-01(b)(l)(ii) and in §86.1826-01(b)(2)(i)(C) the CFR authorizes the 

use of “alternative methods’’ to calculate ADFs. It is this flexibility in 586-1826-01 which was 

exercised in developing the revised EPA ADFs in Tables 1 and 2. 

Summary 

Small volume manufacturers of light-duty vehicles, light-duty trucks, medium-duty 

passenger vehicles, and heavy-duty chassis tested vehicles should use the ADFs presented in this 

letter. Aftermarket alternative fuels converters for these same vehicle classes should use the 

same ADFs, or alternatively, fuels converters may use OEM DFs as optionally permitted in EPA 

guidance document CCD-04-20. Aftermarket alternative fuels converters of heavy-duty engines 

should continue to use EPA guidance document CCD-00-12. 

’A/C51Csuperceded A/CNos. 51B and 51-1and was effective beginning with the 1988model year 

2 
Revised ADFs 

Tables 1 and 2 present the new ADFs. Attachment 3 describes the analysis methodology 

used to develop Tables 1 and 2. Questions concerning the derivation or usage of these factors 

may be directed to Martin Reineman, 734-2 14-4430, or reineman.martin @epa.gov 

Sincerely, 

-G.$/s-=bQMerrylin Zaw-Mon, Director 

Certification and Compliance Division 

Office of Transportation and Air Quality 

Attachments: Tables 1 and 2 

Attachment 3 

3 

\ 
Table 1 to CCD-05-10 

Standards NMOGI co NOx HCHO 

NMHC 

50K 120K 50K 120K 50K 120K 50K 120K 

Tier 2 1.14 1.37 1.22 1.62 1.27 1.73 1.63 2.34 

NLEVI 1.14 1.36 1.32 1.78 1.30 1.90 1.54 2.3 1 

Interim non-Tier 2 

Tier 1 1.09 1.23 1.11 1.27 1.13 1.32 NIA NIA 

HDV NIA 1.37 N/A 1.62 NIA 1.73 NIA 2.344 

lOOK ADF = 1 + (120K ADF - 1)*(96W116K) 

Where: lOOK ADF = The converted 120,000mile multiplicative ADF 

120K ADF = The 120,000 mile multiplicative ADF 

96K, 116K = 96,000 and 116,000miles, respectively 

3) Tier 2 standards have an optional useful life of 150K. Use the following equation to convert 

120K ADFs to 150K ADFs: 

150K ADF = 1 + (120K ADF - 1)*(146W116K) 

Where: 150K ADF = The converted 120,000mile multiplicative ADF 

120K ADF = The 120,000mile multiplicative ADF 

146K, 116K = 146,000 and 116,000 miles, respectively 

4) HCHO standards apply to HDVs effective with the 2008 MY. 

4 
Table 2 to CCD-05-10 

Evaworative Emission ADFslJY3 - 120,000 Mile A ditive ADFs4$ -

24D + HS), g 

2 Day (High 

24D+ HS),g6 

Running 

Loss, gtmi' 

ORVR, 

Tier 29 0.05 0.004 0.022 

LDT2 

Tier 1 LDV, LDT1, 0.29 0.33 0.006 0.041 

LDT2 ~~ 

LDT31°, 0.47 0.56 0.005 0.026 

LDT41°,HDV, 

Heavy-asLight'' 

Notes: 

1) This table does not apply to diesel vehicles. 

2) This table does not apply to alcohol fueled vehicles. ADFs for alcohol fueled vehicles will be 

assigned on a case-by-case basis based on latest industry wide-information. 

3) Evaporative emission test waivers may apply to aftermarket fuels conversions to CNG or LPG 

if approved in advance by EPA. See EPA guidance letter CCD-04-20 dated October 1,2004. 

4) Some Tier 1 and Interim non-Tier 2 evaporative emission standards have a useful life of 100K 

miles. Use the following equation to convert 120K additive ADFs to lOOK additive ADFs: 

lOOK ADF = (120K ADF)*(96K/116K) 

Where: lOOK ADF = The converted 120,000mile additive ADF 

120K ADF = The 120,000mile additive ADF 

96K, 116K = 96,000 and 116,000 miles, respectively 

5) Tier 2 evaporative emission standards have an optional useful life of 150K miles. Use the 

following equation to convert 120K addltive ADFs to 150K additive ADFs: 

150K ADF = (120K ADF)*(146W116K) 

Where: 150K ADF = The converted 120,000 mile additive ADF 

120K ADF = The 120,000mile additive ADF 

146K, 116K = 146,000 and 116,000 miles, respectively 

6) No 2-day standards for dedicated CNG or dedicated LGP vehicles. 

7) No running loss standards for dedicated CNG or dedicated LPG vehicles. 

8) No ORVR standards for dedicated CNG vehicles. 

9) ADFs for Tier 2 LDT3, LDT4, MDPV, and HDV evaporative standards will be provided after 

phase-in starts in the 2008 MY. 

10) ADFs apply to Tier 1 LDT3 and LDT4 vehicles regardless of fuel tank capacity. 

1 1) Heavy duty vehicles optionally certified under light-duty provisions. 

5 
Attachment 3 to CCD-05-10 

Development of Revised EPA Assigned Deterioration Factors 

Data Base 

This analysis was based on 2001 - 2005 model year vehicle data contained in EPA’s Certification 

and Fuel Economy Information data base, CFEIS. The certification data include information 

from passenger cars, light-duty vehicle trucks (LDT1 through LDT4), medium-duty passenger 

vehicles, and optionally chassis certified heavy-duty vehicles. 

Analysis Approach - General 

In addition to needing revised ADFs for the Tier 2 and HDV standards, because ICIs and 

aftermarket alternative fuels converters may certify older model year vehicles, revised exhaust 

emission ADFs were also developed for manufacturers certifying to Tier 1 and NLEV 

standard^.^ 

The development of revised ADFs for exhaust emissions were based on a number of 

compromises which met an objective based on simplicity, applicability and good judgment. To 

satisfy those objectives the following criteria were developed and employed: 

Simplicity - Provide sets of multiplicative ADFs which can be applied across multiple 

levels of program specific emission standards. 

Applicability - Develop ADFs for all applicable EPA emission control “program types,” 

i.e. vehicles certified to Tier 1 standards, NLEV standards (includes Clean 

Fuel Vehicle (CFV) standards), Tier 2 standards, and HDV standard^.^ 

Provide multiplicative ADFs for petroleum fuels (gasoline and diesel), 

alcohol fuels (ethanol and methanol), and gaseous fuels (compressed 

natural gas and liquified petroleum gas) for intermediate and full useful 

life standards. Provide multiplicative ADFs at a common full useful life, 

and provide a means to scale them to a longer or shorter full useful life as 

necessary.6 

Good Judgment - Exercise other options than using a 70” percentile value, such as 

Tier 1 standards were in effect starting with 1994 model year passenger cars and light trucks under 6000 lbs GVW, and were 

phased-in for 100% of 1999 model year light trucks with GVW over 6OOO lbs. NLEV standards became effective with 1999 model year 

passenger cars and LDTls,and were phased-in for 100% of 2001 model year LD’I2.s. 

In this analysis, the CFV program is assumed to be an extension of the NLEV program. The standards are similar for passenger 

cars, LDTl and LDT2. The LDT3 and LDT 4 standards in the CFV program were used for determining compliance with Federal standards 

under the NLEV program, as there are no specific LDT3 and LDT4 standards under the EPA NLEV program. 

For EPA emission purposes, Useful Life is defined as l00K miles for passenger cars and light light-duty trucks but 120K miles for 

the heavy light-duty vehicles under the Tier 1, NLEV, and Clean Fuel Vehicle programs. Useful life is 1 20K, with an optional useful life of 

150K for all classes of vehicles under the Tier 2 program. 

6 
calculating an average value, to develop ADFs when sample sizes are very 

small. The resulting ADFs should not be unrepresentatively high or low 

relative to the CFEIS deterioration factor (DF) data from all 

manufacturers. 

Multiplicative ADFs were developed because they can be applied across a range of standards for 

a particular program type with many exhaust emission categories (for example, the 11bins of-the 

Tier 2 program). Providing additive ADFs has the disadvantage that they should be unique 

across different emission standards. Providing additive ADFs would yield an undesirable 

number of ADFs per program type (for example, four sets per pollutant type for Tier 1 vehicles, 

six sets per pollutant type for NLEV vehicles, 14 sets per pollutant type for Clean Fuel Vehicles, 

11 sets per pollutant for Tier 2 vehicles, and two sets per pollutant for Heavy-Duty Vehicles, for 

a total of 37 ADFs for a particular exhaust pollutant). Such a large set of ADFs was judged to be 

too complex, and stratifying the DF data into so many unique groups would result in sample sizes 

too small to provide either representative 70”’percentiles or averages. 

Providing a reduced number of multiplicative ADFs does not imply that the technology across a 

particular set of emission standards is the same. For example, the technology to achieve Bin 2 

standards vs. Bin 10 standards under the Tier 2 program may be considerably different, but using 

multiplicative ADFs assumes the g& of deterioration across the Tier 2 program type is the same. 

The same reasoning holds for the other EPA program types: Tier 1,NLEV, and HDV where 

there are multiple sets of standards. By using multiplicative ADFs, a much reduced number of 

exhaust emission ADFs may be applied across different levels of standards. This is the approach 

taken in Table 1, where ADFs are presented on a program specific basis. 

The methodology used to analyze and develop evaporative emission ADFs is similar to that 

described above with the exception that because the vast majority of manufacturer submitted 

evaporative emission DFs are additive, only additive DFs were analyzed. Instead of the four 

program types described above for exhaust emissions, there are two evaporative emission 

program types - the Enhanced Evaporative Emission Standards (Tier l), which has four unique 

sets of standards, and the Tier 2 Evaporative Emission Standards, also containing four unique 

sets of standards when heavy duty vehicles are included. Because an additive ADF cannot be 

applied across different standards, Table 2 provides unique additive ADFs across the different 

evaporative emission standard levels. . Exhaust Emission Analysis Approach 

A query was constructed to extract the DF data from of the Oracle based EPA CFEIS data 

system. The CFR requires an analysis using unique DFs.’ Data fields in the CFEIS relationa1 

data base which were used to conduct this analysis included the following: 

Model Year - Identifies the model year of interest, or 2001 - 2005 model year data for this 

’Unique DFs are associated with a “durability group,” a basic classification used for grouping vehicles. 

7 
analysis 

Manufacturer - Identifies specific LDV,LDT, MDPV, or HDV vehicle manufacturers 

through unique manufacturer codes 

Sales Area - Represents different standards (program types), such as Federal vs. 

California 

Vehicle Class Code - Distinguishes passenger cars from four categories of light trucks. 

Differences in class vehicle codes also identify different emission standards. 

DF Twe Code - Distinguishes type of aging process used in a manufacturer’s durability 

demonstration 

Fuel Twe - Identifies the fuels which were analyzed, which include gasoline, diesel, 

ethanol, and CNG 

Individual test groups within a durability group were analyzed to extract the following data 

fields: 

Emission Name - Identifies the exhaust or evaporative emission pollutants of interest 

Useful Life - 50K or 120K miles (or lOOK or 150K), specific to the standard and 

pollutant of interest 

Result - The low mileage (4K) test result 

Additive DF - The quantity in g/mi (exhaust) or g (evap) added to the low mileage test 

result to show the effect of deterioration, if any, at 50Kor 120K miles’ 

Multiplicative DF - Dimensionless multiplier applied to the low mileage test result to 

show the effect of deterioration, if any, at 50K or 120K miles’ 

Certification Level - The emission result after either (but not both) the additive DF or the 

multiplicative DF is applied to the low mileage test result and compared to the 

appropriate standards. 

Emission Standard - Standards in g/mi (exhaust) or g (evap) at 50K or 120K miles 

-Tier - The specific emission program (or standard) of interest, for example, TI (Tier l), 

LEV (NLEV), B5 (Tier 2, Bin 5), or HDV 

The query results were sorted using the relational and filtering capabilities of Microsoft Access 

and reduced using the statistical analysis capabilities of Microsoft Excel. The exhaust emission 

query results were filtered for: 

Usable DFs - Unusable entries included DFs representing durability demonstrations using 

aged components, which by definition, cannot be used for developing quantitative 

By definition, an additive emission DF equals the useful life emission value minus the 4K emission result. 

By definition, a multiplicative DF is the ratio of emissions at 50K or 120K miles divided by the emissions at low mileage, nominally 

4K miles. 

8 
ADFs.lo 

DF Tvpe Code/DF Twe - The records filtered out in this step included DF Types 

described as: Aged Components, EPA ADFs, and MFR ADFs. 

Vehicle Class Code - This code was used for obtaining DFs from the vehicles of interest, 

which included passenger cars, light trucks of the categories LDT1 - LDT4, medium-duty 

passenger vehicles, and optionally chassis certified heavy-duty vehicles. 

Vehicle Manufacturer - The DF data from 23 large volume vehicle manufacturers were 

selected for analysis. 

Emission Name - This step filtered for the pollutants of interest. They included: HC-NM 

(non-methane hydrocarbon), OMHCE (alcohol fuel organic material hydrocarbon 

equivalent), OMNMHCE (alcohol fuel organic material non-methane hydrocarbon 

equivalent), NMOG (non-methane organic gas), HCHO (formaldehyde), CO (carbon 

monoxide), NOx (nitrogen oxides), and PM (particulate matter). OMHCE and 

OMNMHCE DFs are associated with emission tests on ethanol flex-fueled vehicles and 

their sample sizes after all screening criteria were applied were extremely small. 

OMHCE, OMNMHCE, and HC-NM data were combined to calculate “NMOG’ DFs. 

Sales Area - The data were filtered to exclude vehicles sold in California due to their 

unique program requirements and standards. 

Duplicate Records - $86.1826-01(a)(2)(ii)(A) requires unique records be used for 

developing ADFs. This filtering step removed duplicate DF values which occur because, 

by definition, multiple test groups may use the DFs developed for a unique durability 

group. 

EPA emission standards for Tier 1 and NLEV programs have useful life standards for some 

vehicle classes of lOOK miles, while the Tier 2 program have optional useful life standards of 

150K miles. To avoid presenting multiple tables of ADFs based on various useful lifes, the 

analysis converted lOOK and 150K multiplicative DFs (MultDFs) to 120K MultDFs. The 

objective was to create a larger sample size for developing 120K ADFs while avoiding inaccurate 

results from analyzing small samples of DFs at lOOK or 150K miles. The resulting 120K ADFs 

developed from 70* percentiles were then scaled by applying adjustment factors that yielded 

1OOK and 150K ADFs. 

The conversion of lOOK MultDFs to 120K MultDFs assumes a linear deterioration rate from 4K 

to 120K miles, and uses the known emission results at 4K and 1OOK miles. Knowing the slope 

of the line relating emission level vs. mileage, one can calculate an assumed value for emissions 

at 120K miles. Using the definition of a MultDF as 120K emission value divided by 4K 

emission value, the equation for converting a lOOK MultDF to a 120K MultDF becomes: 

Io In the CFEIS data system, manufacturers that used aged components in lieu of submitting additive or multiplicative DFs, often 

coded the entries differently. For example, manufacturers selecting this durability option sometimes submitted multiplicative DFs of 1 and an 

additive DF of 0.0, others simply left the multiplicative and additive DF fields blank, others have combinations of multiplicative DFs of 1, 

additive DFs or 0.0, and blank entries. 

9 
Eq 1: 120K MultDF = 1 + (100KMultDF - 1)*(116K/96K)" 

Where: 120K MultDF = The converted 100,000mile multiplicative DF 

1OOK'MultDF= The 100,000mile multiplicative DF from the CFEIS data base 

116K, 96K = 116,000and 96,000miles, respectively 

Similar to equation 1, the equation for converting 150K MultDFs to 120K MultDFs is: 

Eq 2: 120K MultDF = 1 + (150KMultDF - l)*(l16K/146K) 

Given the substantial number of additive DFs in the data base, the initial analysis approach 

created "equivalent" multiplicative DFs from the additive DFs using the low mileage test result 

(Result) and the 50K or 120K result (Certification Level). The objective was to able use the 

additive DFs in order to develop a larger sample size to find the 70* percentile values. An 

equivalent multiplicative DF was calculated by dividing individual CFEIS Certification Level 

values by the correspondlng CFEIS Result values. The resulting equivalent multiplicative DFs 

were then combined with manufacturer reported multiplicative DFs in the CFEIS data base (the 

actual multiplicative DFs) and the combined values ranked from lowest to highest DF, with the 

70* percentile value selected as a new ADF. 

Unfortunately, the viability of using additive DFs converted to equivalent multiplicative DFs 

breaks down when the 4K test result is very low. The resulting multiplicative DF becomes very 

large, which is why manufactures were given the option of using additive DFs in lieu of 

multiplicative DFs. Various options were considered in order to include "reasonable" converted 

additive DFs in the analysis. These options included: 1) using converted DFs capped at selected 

subjective levels (for example those below 3.0); 2) capping the converted DFs at the maximum 

value of the actual multiplicative DFs; and 3) calculating an average DF based on using the 

actual multiplicative DFs together with the converted additive DFs. None of these options were 

determined to be satisfactory due to their arbitrary nature in the case of the first two options, or 

the unrepresentatively high ADFs resulting from using the third option. 

By process of elimination, the approach selected was to analyze only the actual multiplicative 

DFs and ignore the additive DFs. This solution was deemed acceptable as long as there were 

sufficient data for a particular combination of emission control program, pollutant, and fuel type. 

This is the analysis approach used for developing the gasoline fueled vehicle ADFs in Table 1. 

Because the ADFs in Table 1 are based on 120K multiplicative DFs, manufacturers who wish to 

use the multiplicative ADFs in Table 1 for vehicle classes with full useful life of lOOK miles may 

use the following equation: 

I' This equation assumes the low mileage test is conducted at 4K miles. In actuality, the 4K test is conducted at a mileage not exactly 

equal to 4K miles. 

10 
Eq 3: lOOK ADF = 1 + (120K ADF - 1)*(96W116K) 

Similarly, the following equation allows a manufacturer to use Table 1 to calculate an exhaust 

ADF appropriate for a useful life of 150K miles: 

Eq 4: 150K ADF = 1 + (120K ADF - 1)*(146W116K) 

Evaporative Emission Analysis Approach 

The analysis of evaporative emission data required an analysis of additive DFs, but the general 

approach to developing the evaporative emissions ADFs was similar to the methodology used in 

the development of the exhaust emission ADFs. Specifically, the same 2001 - 2005 MY CFEIS 

data source was used, the same 23 largest manufactures, the same vehicle classes (LDV, LDT1-4, 

MDPVs, HDVs), the same sales area (no California data), and duplicate DFs were excluded. For 

sample sizes of 10 or less the additive ADF was calculated using the average of the DFs. This 

occurred only once during the analysis of the Tier 2 running loss data. 

Similar to exhaust emission DFs, evaporative emission DFs are based on full useful life mileage. 

To account for differences in mileage, an assumption of linear deterioration was used to convert 

lOOK DFs to 120K DFs. Due to the difference in definition of additive DF (AddDF) vs. 

multiplicative DF, the equation used to convert lOOK additive DFs to 120K additive DFs 

becomes the following: 

Eq 5: 120K AddDF = (100K AddDF)*(116W96K) 

Where: 120K AddDF = The converted 100,000 mile additive DF 

lOOK AddDF = The 100,000 mile additive DF from the CFEIS data base 

116K, 96K = 116,000 and 96,000 miles, respectively 

Similarly, any 150K additive DFs were converted to 120K additive DFs using the equation: 

Eq 6: 120K AddDF = (150K AddDF)*(116W146K) 

Because the ADFs in Table 2 are based on additive DFs, manufacturers may use the following 

equation to convert 120K evaporative emission ADFs to lOOK ADFs: 

Eq. 7: lOOK ADF = (120K ADF)*(96W116K) 

Similarly, manufacturers may use the following equation to convert 120K evaporative emission 

ADFs to 150K ADFs: 

Eq. 8: 150K ADF = (120K ADF)*(146W116K) 

Discussion of Tables 1 and 2 

11 
Table 1 - Table 1 presents multiplicative ADFs at 50K and 120K miles for four exhaust emission 

types (NMOG/NMHC, COYNOx, HCHO) as a function of program type, or standards. 

The results presented in Table 1 are based on a ranlung of multiplicative DFs from lowest to 

highest and then selecting the 70" percentile value. The sample sizes used in developing the 

values in Table 1 varied from 30 unique DF values for Tier 1 vehicles, to 110 values for NLEV 

vehicles, to 85 values for Tier 2 vehicles. Owing to the very small sample sizes for fuel types 

other than gasoline, the ethanol, methanol, CNG, and LPG fuel types will use the DFs derived 

from analysis of gasoline DFs. This is based on the conservative assumption that multiplicative 

ADFs for vehicles fueled on other fuel types should be no worse than the DFs for vehicles 

operating on gasoline. 

An exception is diesel vehicles where it may be unreasonable to use gasoline ADFs as a 

surrogate for diesel ADFs. EPA will address manufacturers' needs for diesel ADFs on a case-bycase basis using knowledge of the vehicle control system and current industry wide data to assign 

representative ADFs. 

Inadequate sample sizes prevent use of a statistical approach to determine representative DFs 

from heavy-duty vehicles. Until more data are available and a revised set of ADFs are published, 

EPA will permit manufacturers to use the Tier 2 ADFs in Table 1 in absence of HDV ADFs 

based on actual data. 

Table 2 - Table 2 presents evaporative emission ADFs for three types of evaporative emission 

tests (3 Day, 2 Day, Running Loss), and the onboard refueling vapor recovery test (ORVR). The 

ADFs are presented as a function of vehicle class. The Tier 1 sample sizes from which the 70* 

percentile values were selected varied from a high of 165 3 Day DFs to a low of 85 running loss 

DFs.. Tier 2 sample sizes ranged from a high of 46 ORVR DFs to a low of 2 running loss DFs. 

12