Air and Radiation EPA420-R-05-023 

December 2005 

NR-011c 

Nonroad Spark-Ignition

Engine Emission

Deterioration Factors 
EPA420-R-05-023 

December 2005 

Nonroad Spark-Ignition Engine

Emission Deterioration Factors

NR-011c

Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

NOTICE

This technical report does not necessarily represent fi nal 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 fi nal EPA decision, position, or regulatory action.
I. Purpose 

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

the final NONROAD2005 model. The specific deterioration inputs used in NONROAD and 

their basis will be addressed for land-based spark-ignition engines at or below 25 horsepower, 

land-based spark-ignition engines over 25 horsepower, and recreational marine spark-ignition 

engines using gasoline. Deterioration is also addressed for land-based liquid petroleum gas 

(LPG) and compressed natural gas engines (CNG). Deterioration inputs for compressionignition (diesel) engines are addressed in the report, Exhaust Emission Factors for Nonroad 

Engine Modeling - Compression Ignition (NR-009c). The EPA welcomes comments and 

suggestions concerning our approach to modeling nonroad engine emissions deterioration. 

II. Background 

As used here, the term Adeterioration@ 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 Adeterioration 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 Adeterioration factor@ refers to the ratio of an engine=s emissions at its 

median life divided by its emissions when new. 

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 

1 
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 

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

deterioration due to intentional disablement of engine components. 

2 
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. AA@ 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, Ab.@ This constant can be set at any level between zero and 1.0; currently, the 

NONROAD model sets Ab@ 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 

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

for spark ignition engines less than 25 horsepower. 

3 
SI engines have a wide range of designs that affect their emissions deterioration. To 

model these different deterioration patterns, NONROAD categorizes SI engines into Atechnology 

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 AAge 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, and a analysis of 1998-2005 model year 

emission certification data for recreational marine.3 In other words, NONROAD models 

deterioration for tiller and a lawn mower applications that are equipped with the same engine 

type by using the same deterioration pattern for that technology type. 

V. Deterioration Inputs For Land-based Engines At or Below 25 Horsepower 

In the final NONROAD2005 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 four-stroke 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 

4 
deterioration values to zero based on analyses done during the development of the Phase 2 rule.4

 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 final 

NONROAD2005 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 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. 

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, all-terrain 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 pre-1978 uncontrolled four-stroke onhighway motorcycles from the MOBILE model.5 

5 
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 

6 
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 

7 
VI. Deterioration Inputs for Land-based 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 spark-ignition 

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.6 These are based on on-highway deterioration data. 

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 

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 AA@ 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 Ab@ value of 1.0 in Equation 2. 

As a check on these deterioration rates, we reviewed emission data from ten 1969 lightduty gasoline trucks in an EPA report titled AProcurement 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 final 

NONROAD2005 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 non-catalyzed 

engines with fuel injection because catalysts were introduced before fuel-injection into the onhighway market. Anecdotal information suggests that deterioration is low from these engines 

compared to deterioration in a catalyst. For instance, accepted 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. 

8 
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 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 6 shows the deterioration factors used for recreational equipment and Table 7 

shows the deterioration factors used for other large spark-ignition equipment. 

Table 6 

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 

9 
Table 7 

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 

VII. Deterioration Inputs for Recreational Marine Spark-Ignition Engines 

Deterioration factors for sterndrive/inboard engines are those used in the draft 

NONROAD2004 model. They are based on information gathered for the recreational marine 

engine rulemaking (61 FR 52087, October 4, 1996).10 Deterioration factors for outboard and 

personal watercraft have been updated for the final NONROAD2005 model, using 1998-2005 

model year emissions certification data for these engines.3 

The technology class descriptions and associated designations, which are used in the 

NONROAD model, are shown in Table 8. The deterioration values for each technology class by 

designation are shown in Table 9. 

VIII. 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. 

10 
Table 8 

Marine Engine Technology Class and Designations 

Technology Class Differentiation Class Designation 

Type Cycle Fuel System Aftertreatment 

NONROAD 

2004* 

NONROAD 

2005 

Outboard 

2-Stroke 

Carbureted none M1 MO2C 

Carburetor Modifications none M5 -- 

Carbureted 3- Way Catalyst M6 -- 

Indirect Injection none M8 MO2I 

Direct Injection none M9 MO2D 

4-Stroke 

Carbureted none M4 MO4C 

Indirect Injection none -- MO4I 

Direct Injection none -- MO4D 

PWC 

2-Stroke 

Carbureted none M2 MP2C 

Carburetor Modifications none M14 -- 

Carbureted 2- Way Catalyst -- MP2CA 

Indirect Injection none -- MP2I 

Direct Injection none -- MP2D 

4-Stroke 

Carbureted none M13 MP4C 

Indirect Injection none -- MP4I 

Direct Injection none -- MP4D 

SD/I 4-stroke 

Carbureted none M3 MS4C 

Direct Injection none M10 MS4D 

* NONROAD2004, the previous version, has additional marine designations that have 

placeholders but are not used. 

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Table 9 

Deterioration Factors for Recreational SI Marine Engines 

Technology Class HC CO NOx PM 

MO2C, MP2C 0.00 0.00 0.00 0.00 

MO2I, MP2I 0.03 0.03 0.08 0.00 

MO2D, MP2D 0.03 0.03 0.05 0.00 

MP2CA 0.26 0.26 0.06 0.00 

MO4C, MP4C 0.05 0.05 0.05 0.00 

MO4I, MP4I 0.03 0.03 0.03 0.00 

MO4D, MP4D 0.03 0.03 0.03 0.00 

MS4C, MS4D 0.26 0.35 0.03 0.26 

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-005c) and the technical 

report about scrappage (NR-007c). 

2. See endnote 1. 

3. “Updates to Technology Mix, Emissions Factors, Deterioration Rates, Power Distribution, 

and Fuel Consumption Estimates for SI Marine Engines in the NONROAD Emissions 

Inventory Model,” EPA Memorandum From Mike Samulski to Docket EPA-HQ-OAR-2004-

0008, November 30, 2005. 

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

March 24, 1999. 

5. AEmission Modeling for Recreational Equipment,@ EPA Memorandum From Linc Wehrly to 

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

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

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

7. ARevisions 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 

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

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

9. See endnote 8. 

12 
10. ADeterioration 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. 

13 
Appendix 1 

Deterioration Ratio Data for 1969 MY LDGTs 

H C 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 

C O 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 

N Ox 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 m inus HC/NOx outlier = 1.39 

average = 1.10 

average m inus outlier = 1.05 

14