Air and Radiation EPA420-P-04-011

April 2004

NR-011b

Spark-Ignition Engine

Emission Deterioration

Factors for the

Draft NONROAD2004

Emissions Model
EPA420-P-04-011

Revised April 2004

Spark-Ignition Engine Emission Deterioration

Factors for the Draft NONROAD2004 Emissions Model

NR-011b

Assessment and Standards 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

Spark-Ignition Engine Emission Deterioration Factors 

For the draft NONROAD2004 Emissions Model

Report No. NR-011b

revised April 2004

Assessment and Standards Division

EPA, Office Transportation and Air Quality

I. Purpose

This report addresses the emission deterioration rates for spark-ignition engines currently

being used in the draft NONROAD2004 model. The specific deterioration inputs used in

NONROAD and their basis will be addressed for spark-ignition engines at or below 25

horsepower and over 25 horsepower, as well as liquid petroleum gas (LPG) and compressed

natural gas engines (CNG). Deterioration inputs for compression-ignition (diesel) engines are

addressed in the report, Exhaust Emission Factors for Nonroad Engine Modeling - Compression

Ignition (NR-009b). The EPA welcomes comments and suggestions concerning our approach to

modeling nonroad engine emissions deterioration. 

The previous version of this report contains discussions of the deterioration inputs used

in the original 1998 draft of the NONROAD model and sources of deterioration rates which have

been considered by EPA. It has been included as an appendix in this report for ease of reference. 

II. Background

As used here, the term “deterioration” refers to the degradation of an engine’s exhaust

emissions performance over its lifetime due to normal use or misuse (i.e., tampering or neglect). 

Engine deterioration increases exhaust emissions, usually leads to a loss of combustion

efficiency, and can in some cases increase nonexhaust emissions. The amount of emissions

increase depends on an engine’s design, production quality, and technology type (e.g., spark

ignition two-stroke and four-stroke, compression ignition). Other factors, such as the various

equipment applications in which an engine is used, usage patterns, and how it is stored and

maintained, may also affect deterioration.

The term “deterioration rate” refers to the degree to which an engine’s emissions increase

per unit of activity. Nonroad engine activity is expressed in terms of hours of use or fraction of

median life. The term “deterioration factor” refers to the ratio of an engine’s emissions at its

median life divided by its emissions when new.
2

The terms useful life and median life are used in the following manner in this report in

order to avoid confusion. Useful life is a regulatory term used to indicate the amount of time

during the life of a nonroad engine that a manufacturer must certify to the U.S. EPA that the

engine meets a required emission standard as defined by a regulation. Median life, as used in this

report, refers to the age at which 50 percent of the engines sold in a given year have ceased to

function and have been scrapped.1

III. Core Challenge

The core challenge associated with estimating nonroad engine deterioration is the

development of reasonably accurate deterioration rates for the enormous range of nonroad

engine types and applications from the limited amount of nonroad emission deterioration data

that exist at this time. To estimate deterioration, the emission performance of engines at various

ages is required. Such information can be obtained from a longitudinal study that examines the

same set of engines periodically as they age, or from a sampling study that tests engines of

various ages but the same basic design. In either case, the engines studied should be selected

randomly from the population of engines actually being used in the field.

Given the limited available test data, EPA is currently unable to develop unique

deterioration rates based on actual engine test data for the myriad of applications and power

levels covered by NONROAD. The Office of Transportation and Air Quality has conducted

emissions testing on several dozen small spark ignition lawn & garden engines and a few large

compression-ignition engines. The nonroad engine industry and a few States have also

conducted some nonroad engine emissions testing. However, the nonroad engine emissions data

currently available are still limited when compared to the large number of nonroad engine types

and applications for which these engines are used, particularly for the purposes of evaluating

emission deterioration as engines age. The EPA has obtained extensive data on the emissions

deterioration of light-duty highway engines, but these engines are unlikely to deteriorate in a

fashion typical of nonroad engines due to fundamental differences in engine and emission

control technology design, maintenance, and operation. Deterioration in emissions from lightduty vehicles (LDVs) is thought to be due in large part to gross failures of emission control aftertreatment systems, which nonroad engines do not have at this time. 

A related challenge is that the EPA has essentially no data on the incidence of tampering

and/or neglect of proper maintenance and only limited data that distinguish the effect of such

malmaintenance from the effects of normal usage. These data are based on emission tests of two

lawnmower engines that had various components, including the sparkplug, air filter, and oil,

manipulated to simulate bad maintenance practices (i.e., not changing the sparkplug, air filter

and oil on a regular basis, as recommended by the manufacturer). The results of this effort were

inconclusive, suggesting that intentional disablement of engine components does not adequately

simulate emissions deterioration from normal usage. The EPA requests that state and industry

stakeholders share any data regarding the incidence of tampering and neglect of proper

maintenance they may have. The EPA also requests that stakeholders share any data they have
3

regarding the relationship between emissions deterioration due to normal usage and emissions

deterioration due to intentional disablement of engine components.

IV. Method of Applying Deterioration In NONROAD

Generally, the NONROAD model addresses the effects of deterioration in the inventory

calculation by multiplying a zero hour emission factor for each category of engine by a

deterioration rate as the engine ages. The following formula describes the basic form of the

calculation:

EFaged = EFo * DF (1)

where: EF (aged) is the emission factor for an aged engine 

EFo is the emission factor for a new engine

DF is the deterioration factor.

In order for the NONROAD model to be compatible with the EPA’s small nonroad spark

ignition engine rulemaking process and also be able to calculate deterioration for other engines,

we have derived the following multi-purpose deterioration function:

DF = 1 + A * (Age Factor)b for Age Factor # 1 (2)

DF = 1 + A for Age Factor > 1

where Age Factor= [Cumulative Hours * Load Factor] 

Median Life at Full Load, in Hours

A, b = constants for a given technology type; b # 1.

The constants A and b can be varied to approximate a wide range of deterioration

patterns. “A” can be varied to reflect differences in maximum deterioration. For example,

setting A equal to 2.0 would result in emissions at the engine’s median life being three times the

emissions when new. The shape of the deterioration function is determined by the second

constant, “b.” This constant can be set at any level between zero and 1.0; currently, the

NONROAD model sets “b” equal to either 0.5 or 1.0. The first case results in a curvilinear

deterioration rate in which most of the deterioration occurs in the early part of an engine's life. 

The second case results in a linear deterioration pattern in which the rate of deterioration is

constant throughout the median life of an engine. In both cases, the EPA decided to cap

deterioration at the end of an engine's median life, under the assumption that an engine can only

deteriorate to a certain point beyond which it becomes inoperable. For spark ignition engines at

or below 25 horsepower, NONROAD uses the regulatory useful life values in Appendix F of the

Phase 1 regulatory support document for median life values. For other engines, NONROAD

uses the median life values from the Power Systems Research (PSR) database.2

 These functions

can be used to provide a close approximation to the shape of the deterioration curves used in
4

NSEEM1 and NSEEM2 (regulatory models for the Phase 1 and 2 Small Spark-Ignition Rules)

for spark ignition engines less than 25 horsepower.

SI engines have a wide range of designs that affect their emissions deterioration. To

model these different deterioration patterns, NONROAD categorizes SI engines into “technology

types” by their design and emission control equipment. A given technology type can apply to

one or more horsepower-application categories, and a given horsepower-application category

can be divided into more than one technology type. NONROAD applies a given deterioration

function (that is, a given A and b value) to all engines of a given technology type, regardless of

their application or power range. As a result, a single technology type may be applied to engines

with very different median lives, but this difference is handled by expressing engine age in terms

of the “Age Factor” defined above. The EPA believes this approach is reasonable, since

deterioration patterns should be more closely related to the design of the engine and its emission

control technology than to the kind of application in which it is used. Furthermore, the available

data on emissions deterioration of nonroad SI engines is insufficient to develop separate

deterioration functions for the many combinations of application, horsepower range, and

technology type.

NONROAD’s technology type feature allows each horsepower-application category to be

divided into as many as ten technology types, each with its own deterioration pattern. The

technology type feature gives the model flexibility to handle the full range of engine designs

used in nonroad equipment. For example, the technology type feature can handle the 33 distinct

engine types that are defined by EPA’s Phase 1 and 2 Small Engine Rules, as shown in Tables 1

through 5. However, deterioration data for each technology type across different applications

are not available at the present time. Thus, the NONROAD model does not apply different

deterioration patterns to engines of the same technology type used in different applications. 

Instead, the model applies different deterioration patterns to engines within each engine type

(i.e., two-stroke and four-stroke spark ignition) based on the more detailed engine classes

defined in the Phase 1 and 2 Small Engine Rules, the proposed Large Spark-Ignition Equipment,

Recreational Marine and Recreational Equipment Rule, instead of by application. In other

words, NONROAD models deterioration for a tiller and a lawn mower equipped with engines of

the same technology type using the same deterioration pattern.
5

V. Deterioration Inputs For Engines At or Below 25 Horsepower

A. Deterioration Inputs Used In NONROAD For Spark Ignition Engines Less than 25

Horsepower

In the draft NONROAD2004 model, the constant ‘b’ is set at 0.5 for four-stroke

engines, resulting in a square root relationship between age and deterioration. The

constant ‘b’ is set at 1.0 for two-stroke engines, which produces a linear relationship

between age and deterioration. This use of a curvilinear deterioration pattern for fourstroke engines and a linear deterioration pattern for two-stroke engines is similar to the

approach used in the NSEEM2 model used for the Phase 2 Small Engine Rule.

The inputs for the variable ‘A’ of the NONROAD deterioration function are

shown in Tables 1-5 for the small engine classes defined in the Phase 1 and 2 Small

Engine Rules. EPA derived the deterioration values for Phase 2 engines with catalysts

(G2HxC2) and set NOx deterioration values to zero based on analyses done during the

development of the Phase 2 rule.3

 For the other types of small engines included in the

Phase 1 and 2 rulemakings, the values came from the Phase I Regulatory Support

Document for maximum life emission factors and new engine emission factors. It should

be noted the HC deterioration ‘A’ value (0.201) for snowblowers (G2GT25) is the same

as that used for baseline Class 1 and 2 two-stroke nonhandheld engines (G1N1 and

G2N2).

For each pollutant and each engine type, variable ‘A’ represents the maximum

deterioration rate reached at one median life. It should be noted that particulate matter

(PM) standards were not considered or included in the Phase 1 and Phase 2 Small Engine

Rules, and little data exists for PM deterioration rates. Based on EPA’s best judgement

at this time, PM deterioration in two and four-stroke engines are equated to that of HC in

the draft NONROAD2004 model. The EPA requests stakeholders with information

about the PM emissions deterioration of two-stroke engines to submit such data.

The deterioration rates used in NONROAD for small engines covered under the

Phase 1 and 2 Small Engine Rules approximate the levels of deterioration found in

testing, including the testing summarized in NEVES and the testing done to support the

Phase 1 and 2 Small Engine Rules. Where these test results differ, the EPA has chosen to

give greater weight to data taken from engines which have experienced usage patterns

that reflect expected field conditions. The test data submitted to EPA for the Phase 2

Small Engine Rule, for example, reflects testing of engines that have undergone

accelerated aging which EPA does not believe to be representative of the aging

experienced by engines in use. After evaluating all available data, the EPA has

determined that the level of deterioration used in NSEEM1 and Phase 1 Small Engine

Rule provides a reasonable basis for the deterioration rates used in NONROAD. These

deterioration rates are generally higher than the deterioration rates used for regulatory

purposes in NSEEM2 and the Phase 2 Small Engine Rule, but are generally smaller than
6

those used in NEVES. The EPA believes that the deterioration rates used in NONROAD

are more reflective of the deterioration rates that one would expect to find out in the field

when equipment powered by small spark ignition engines is used by the average person

than are the deterioration rates found in NSEEM2 and the Phase 2 Small Engine Rule.

It should be noted that EPA increased HC deterioration rates for two-stroke

engines with catalysts that small engine manufacturers plan to use in handheld equipment

(Classes 3, 4, and 5) based on additional analyses for the final Phase 2 Rule. However,

the EPA did not update the PM deterioration rates for these engines to match the revised

HC deterioration rates. This was an oversight and will be in the next update of the

model. EPA welcomes any comments or information concerning PM deterioration rates

for these types of engines.

There are some small engine applications that are not covered by the Phase 1 or 2

Small Engine Rules. These include marine engines (SCC 2282xxxxxx) and certain

recreational equipment such as snowmobiles (226x001020), off-road motorcycles, allterrain vehicles (226x001030), and specialty vehicle carts (226x001060). In NONROAD

the two-stroke versions of the recreational equipment engines are assigned deterioration

values equal to the G2N2 tech type shown in Table 2, but they use a tech type name of

R12S since the emission factors differ from the other engine applications. Four-stroke

versions of these recreational equipment engines use deterioration rates based on pre1978 uncontrolled four-stroke on-highway motorcycles from the MOBILE model.4

Recreational marine engines are handled differently from the recreational

equipment engines. Based on information gathered for the recreational marine engine

rulemaking (61 FR 52087, October 4, 1996), two-stroke marine engines are modeled as

having no deterioration. We request comment on whether this should be changed to

model two-stroke marine engine deterioration similarly to other two-stroke engines or

possibly use some other deterioration rate. 
7

Table 1

Class 1 (Displacement < 225 cc) Nonhandheld Deterioration Factor A

Engine Tech Type HC CO NOx PM BSFC

G2N1 (gas 2-stroke nonhandheld Class 1, baseline) 0.201 0.199 0 0.201 0

G4N1S (gas, side-valve, 4-stroke nonhandheld Class 1,

baseline)

1.1 0.9 0 1.1 0

G4N1O (gas, overhead valve, 4-stroke nonhandheld Class 1,

baseline)

1.1 0.9 0 1.1 0

G2N11 (2-stroke, Phase 1) 0.266 0.231 0 0.266 0

G4N1S1 (Phase 1 side-valve, 4-stroke) 5.103 1.109 0 5.103 0

G4N1O1 (Phase 1 overhead valve, 4-stroke) 1.753 1.051 0 1.753 0

G4N1SC1 (Phase 1 side-valve, 4-stroke with catalyst) 5.103 1.109 0 5.103 0

G4N1S2 (Phase 2 side-valve, 4-stroke) 5.103 1.109 0 5.103 0

G4N1O2 (Phase 2 overhead valve, 4-stroke) 1.753 1.051 0 1.753 0

Table 2 

Class 2 (Displacement $225 cc; Power Rating < 25 hp) Nonhandheld Deterioration Factor A

Engine Tech Type HC CO NOx PM BSFC

G2N2 (gas 2-stroke nonhandheld Class 2, baseline) 0.201 0.199 0 0.201 0

G4N2S (gas, side-valve, 4-stroke nonhandheld Class 2,

baseline)

1.1 0.9 0 1.1 0

G4N2O (gas, overhead valve, 4-stroke nonhandheld Class 2,

baseline)

1.1 0.9 0 1.1 0

G4N2S1 (Phase 1 side-valve, 4-stroke with catalyst) 1.935 0.887 0 1.935 0

G4N2O1 (Phase 1 overhead valve 4-stroke) 1.095 1.307 0 1.095 0

G4N2S2 (Phase 2 side-valve) 1.935 0.887 0 1.935 0

G4N2O2 (Phase 2 overhead valve) 1.095 1.307 0 1.095 0
8

Table 3 

Class 3 (Displacement < 20cc) Handheld Deterioration Factor A

Engine Tech Type HC CO NOx PM BSFC

G2H3 (gas 2-stroke handheld Class 3, baseline) 0.2 0.2 0 0.2 0

G2H31 (Phase 1) 0.24 0.24 0 0.24 0

G2H3C1 (Phase 1 with catalyst) 0.24 0.24 0 0.24 0

G2H32 (Phase 2) 0.24 0.24 0 0.24 0

G2H3C2 (Phase 2 with catalysts) 0.72 0.24 0 0.24 0

Table 4

Class 4 (20cc < Displacement < 50 cc) Handheld Deterioration Factor A

Engine Tech Type HC CO NOx PM BSFC

G2H4 (gas 2-stroke handheld Class 4, baseline) 0.2 0.2 0 0.2 0

G2H41 (Phase 1) 0.29 0.24 0 0.29 0

G2H4C1 (Phase 1 with catalyst) 0.29 0.24 0 0.29 0

G4H41 (Phase 1 4-stroke) 1.1 0.9 0 1.1 0

G2H42 (Phase 2) 0.29 0.24 0 0.29 0

G2H4C2 (Phase 2 with catalyst) 0.77 0.24 0 0.29 0

G4H42 (Phase 2 4-stroke) 1.1 0.9 0 1.1 0

Table 5

Class 5 (Displacement $ 50cc; Power Rating <25 HP) Handheld Deterioration Factor A

Engine Tech Type HC CO NOx PM BSFC

G2H5 (gas 2-stroke handheld Class 5, baseline) 0.2 0.2 0 0.2 0

G2H51 (Phase 1) 0.266 0.231 0 0.266 0

G2H5C1 (Phase 1 with catalyst) 0.266 0.231 0 0.266 0

G2H52 (Phase 2) 0.266 0.231 0 0.266 0

G2H5C2 (Phase 2 with catalyst) 0.626 0.231 0 0.266 0
9

VI. Deterioration Inputs for Spark Ignition Engines Greater than 25 Horsepower (19 

kilowatts)

The deterioration factors currently used in NONROAD for recreational equipment

(i.e., snowmobiles, all-terrain vehicles, and offroad motorcycles) and other large sparkignition engines over 25 horsepower found in industrial and commercial equipment (e.g.,

forklifts, generators, compressors) are based on those used in the final rulemaking for

recreational equipment and large spark-ignition engines.5 Both these and the

deterioration factors used for four-stroke recreational marine spark-ignition engines over

25 horsepower are based on on-highway deterioration data. For two-stroke recreational

marine engines, no deterioration is assumed at this time based on data from the National

Marine Manufacturers Association.6

At this time, EPA does not have deterioration data on large spark-ignition

engines. However, EPA currently believes that larger uncontrolled carbureted gasoline

nonroad engines would likely deteriorate more similarly to on-highway light-duty

gasoline truck engines from the 1960's and 1970's.7 These older on-highway engine

models used similar technology as today’s carbureted SD/I marine engines and large

nonroad gasoline engines.

MOBILE5 includes emission factors and deterioration and tampering rates for onhighway heavy-duty gasoline engines. From this information, we can calculate the “A”

value in Equation 2 by dividing the deteriorated emission factor at 100,000 miles by the

new engine emission factor (and subtracting 1). To capture carbureted engines, we

looked at the 20-year average for the 1960 through 1979 model years. Also, MOBILE5

uses linear deterioration for heavy-duty gasoline engines which translates to a “b” value

of 1.0 in Equation 2. 

As a check on these deterioration rates, we reviewed emission data from ten 1969

light-duty gasoline trucks in an EPA report titled “Procurement and Emissions Testing of

1969 and 1972/1973 Model Year Gasoline Powered Light Duty Trucks” (EPA-460/3-80-

11). These trucks were emission tested in 1980 before and after engine maintenance. 

The ratio of the emissions before and after maintenance gives some insight into the

emission deterioration of the engines. These data showed equivalent A values of 0.11 to

0.58 for HC, 0.31 to 0.39 for CO, and 0.05 to 0.10 for NOx. These data are consistent

with the deterioration rates used in the draft NONROAD2004 model (see Appendix 1). 

The ranges of A values from the test data are due to reporting the averages with and

without one truck that appeared to be an outlier.

At this time, we do not have any information on the deterioration of fuel-injected

gasoline engines (without catalysts). MOBILE does not include emission rates for noncatalyzed engines with fuel injection because catalysts were introduced before fuelinjection into the on-highway market. Anecdotal information suggests that deterioration

is low from these engines compared to deterioration in a catalyst. For instance, accepted
10

emission deterioration test methods for current on-highway engines are performed by

aging the catalyst to full life but using a relatively new engine. Because we do not have

better information, EPA used the same deterioration coefficients for fuel-injected engines

(without catalysts) as for carbureted engines.

To estimate the Phase 1 deterioration factors, we relied upon deterioration

information for current Class IIb heavy-duty gasoline engines developed for the

MOBILE6 emission model. Class IIb engines are the smallest heavy-duty engines and are

comparable in size to many Large SI engines. They also employ catalyst/fuel system

technology similar to the technologies we expect to be used on Large SI engines.8

To estimate the Phase 2 deterioration factors, we relied upon the same

information noted above for Phase 1 engines. The technologies used to comply with the

proposed Phase 2 standards are expected to be further refinements of the technologies we

expect to be used on Phase 1 Large SI engines. For that reason, we are applying the

Phase 1 deterioration factors to the Phase 2 engines.9

It should be noted that PM is not addressed in the rulemaking process for large SI

engines used in recreational marine, commercial, industrial, and other types of equipment

and little or no data exist for PM deterioration associated with these types of equipment. 

Based on EPA’s best judgement at this time, PM deterioration has been equated with HC

deterioration rates for these types of engines. EPA welcomes any comments or

information stakeholder may have concerning PM deterioration.

Table 9 shows the deterioration factors used for recreational equipment, Table 10

shows the deterioration factors used for other large spark-ignition equipment, and Table

11 shows the deterioration factors used for recreational marine engine. 
11

Table 9

Deterioration Factors for Offroad Motorcycles, All-Terrain Vehicles, and Snowmobiles

Equipment/Tech Type HC CO NOx PM

Precontrol 2-stroke offroad motorcycles (R12S) 0.2 0.2 0 0.2

Precontrol 4-stroke offroad motorcycles (R14S) 0.15 0.17 0 0.15

Phase 1 4-stroke offroad motorcycles (R14S1) 0.15 0.17 0 0.15

Precontrol 2-stroke all terrain vehicles (R12S) 0.2 0.2 0 0.2

Precontrol 4-stroke all terrain vehicles (R14S) 0.15 0.17 0 0.2

Phase 1 4-stroke all terrain vehicles (R14S1) 0.15 0.17 0 0.15

Precontrol 2-stroke snowmobiles (R12S) 0.2 0.2 0 0.2

Modified 2-stroke snowmobiles (R12S1) 0.2 0.2 0 0.2

Direct Injection 2-stroke snowmobiles (R12S2) 0.2 0.2 0 0.2

4-stroke snowmobiles (R14S) 0.15 0.17 0 0.15

Table 10

Deterioration Factors for Spark-Ignition Engines > 25 HP

Engine Tech Type HC CO NOx PM

Uncontrolled

G4GT25 (gas, 4-stroke, baseline) 0.26 0.35 0.03 0.26

LGT25 (LPG, baseline) 0.26 0.35 0.03 0.26

NGT25 (CNG, baseline) 0.26 0.35 0.03 0.26

Phase 1

G4GT251 (gas, 4-stroke) 0.64 0.36 0.15 0.26

LGT251 (LPG) 0.64 0.36 0.15 0.26

NGT251 (CNG) 0.64 0.36 0.15 0.26

Phase 2

G4GT252 (gas, 4-stroke) 0.64 0.36 0.15 0.26

LGT252 (LPG) 0.64 0.36 0.15 0.26

NGT252 (CNG) 0.64 0.36 0.15 0.26
12

Table 11

Deterioration Factors for Four-Stroke Recreational Marine Engines > 25 HP

HC CO NOx PM

0.26 0.35 0.03 0.26

Note: No deterioration assumed for 2-stroke recreational marine engines.

VII. Liquid Petroleum and Compressed Natural Gas Spark-Ignition Engines

Because liquid petroleum gas (LPG) and compressed natural gas (CNG) engines

are primarily four-stroke engines, the EPA decided to assume that they would deteriorate

at the same rate as the corresponding gasoline-powered four-stroke SI engines for all

pollutants. The EPA is not aware of any deterioration data available for LPG and CNG

engines and requests that commenters submit any such data they may have to EPA. If

such data become available, EPA will revise the deterioration rates for these engines in

NONROAD accordingly.

Endnotes

1. Median life is defined as the midpoint of the scrappage curve at which half of the engines in

a given population cease to function and are scrapped. For more information, please refer to

the technical report on activity, load factors and median life ( NR-005a) and the technical

report about scrappage (NR-007a).

2. See endnote 1.

3. U.S. EPA NONROAD Model Technical Report Addenda for Tier 2 Rulemaking Version,

March 24, 1999.

4. “Emission Modeling for Recreational Equipment,” EPA Memorandum From Linc Wehrly to

Docket A-98-01, November 13, 2000.

5. Final Regulatory Support Document: Control of Emissions from Unregulated Nonroad

Engines, Chapter 6, Office of Air and Radiation, EPA420-R-02-022, September 2002.

6. “Deterioration Factors for Existing Technology, Gasoline, Outboard Marine Engines,” EPA

memorandum from Mike Samulski to Chester J. France, Director, Engine Programs and

Compliance Division, March 4, 1996.

7. “Revisions to the June 2000 Release of NONROAD to Reflect New Information and

Analysis on Marine and Industrial Engines,” EPA memorandum from Mike Samulski to

Docket A-98-01, November 2, 2000, Docket A-2000-01, Document II-B-08.

8. Proposed Control of Emissions from Nonroad Large Spark Ignition Engines, Recreational
13

Engines (Marine and Land-based), and Highway Motorcycles, Regulatory Support

Document, EPA420-D-01-004, September 2001, Chapter 6.

9. See endnote 8.
14

HC deterioration ratio

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 20,000 40,000 60,000 80,000 100,000

m ile s

CO deterioration ratio

0.00

1.00

2.00

3.00

4.00

0 20,000 40,000 60,000 80,000 100,000

m ile s

NOx deterioration ratio

0.00

0.50

1.00

1.50

2.00

2.50

0 20,000 40,000 60,000 80,000 100,000

m ile s

average = 1.58

average w/o outlier = 1.11

average = 1.31

average minus HC/NOx outlier = 1.39

average = 1.10

average minus outlier = 1.05

Appendix 1

Deterioration Ratio Data for 1969 MY LDGTs