Nonroad Spark-Ignition Engine Emission 

Deterioration Factors 
Nonroad Spark-Ignition Engine Emission 
 

Deterioration Factors
 

NR-011d
 

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. 

EPA-420-R-10-020 

NR-011d 

July 2010 
Nonroad Spark-Ignition Engine Emission Deterioration Factors 

Report No. NR-011d 

July 2010
 

Assessment and Standards Division 

EPA, Office Transportation and Air Quality 

Purpose 

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

the final NONROAD2008a 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, recreational equipment, 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 

compression-ignition (diesel) engines are addressed in the report, Exhaust Emission Factors for 

Nonroad Engine Modeling - Compression Ignition (NR-009d). Relative to the December 2005 

version of this report, this version has been updated to incorporate the deterioration rates 

corresponding to the Phase 3 exhaust standards in the 2008 final rulemaking affecting small 

nonroad nonhandheld SI engines and equipment, as well as the 2010 exhaust standards for 

marine SI engines and vessels. [1] It describes updates to the deterioration rates for nonhandheld 

Phase 2 engines. It also reflects new technology type names assigned to offroad motorcycles, 

all-terrain vehicles, and snowmobiles. 

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. 

1
 
 

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 

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 all applications and power levels covered 

by NONROAD. The Office of Transportation and Air Quality has conducted emissions testing 

on small spark ignition lawn & garden engines and 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. 

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 

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-005d) and the technical report about scrappage (NR-007c). 

2
 
 

 

 

 

 

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

deterioration due to intentional disablement of engine components. 

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 = DF Coefficient for a given technology type 

b = Age Exponent 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. 

The NONROAD model also contains values for a third constant, labeled “Emission Cap” 

or “Cap.” When the Cap is equal to 1, deterioration is capped at the end of an engine’s median 

life. When the Cap is equal to 2, deterioration is not capped. In NONROAD2005, deterioration 

was capped for all engines, but in NONROAD2008a, the cap was removed for all nonhandheld 

engines. 

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 “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, b, and Cap 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 15 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. 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 rulemakings to date. [1,2,3,4,5,6] In other words, NONROAD models 

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

by using the same deterioration pattern for that technology type. 

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

This category includes all engines ≤ 25 hp except those used for recreational applications 

(such as motorcycles or snowmobiles), for marine propulsion, or for toy boats and airplanes. 

The engines in this category are used primarily in lawn and garden equipment. 

For this category, engines are segregated by the class of the engine (I - V). Each class is 

determined by the use of the engine, i.e., handheld or nonhandheld, and engine displacement. 

Classes I and II refer to nonhandheld small SI engines; classes III, IV, and V refer to handheld 

small SI engines. The classes have the following displacements: Class I (< 225cc); Class II (≥

225cc); Class III (< 20cc); Class IV (≥ 20cc and < 50cc); Class V (≥ 50cc). 

Engines in handheld applications (such as leafblowers and chainsaws) are subject to two 

phases of regulation (Phase 1 and Phase 2). Under the Phase 1 regulations, new engines have 

had to meet emission standards for HC, CO, and NOx since 1997. More stringent Phase 2 

standards phase in between 2002 and 2007. 

4
 
For nonhandheld applications (such as lawn and garden tractors and lawnmowers), 

similar Phase 1 regulations have been in place since 1997. More stringent Phase 2 standards 

phase in between 2001 and 2007. Phase 3 standards are phased in beginning in 2012 for Class I 

engines and 2011 for Class II engines. The test procedure used for the small SI regulations is the 

Small SI Engine Federal Steady-State Test Procedure. 

Tables 1-5 contain the inputs for the deterioration function for these five classes of 

engines. There are no LPG or CNG engines less than 25 hp in final NONROAD2008a; 

therefore, the emission factors in these tables are used for gasoline engines in the 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. The emission cap is set at 1 

for handheld and 2 for nonhandheld engines. 

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

deterioration rate reached at one median life. For the variable ‘A,’ EPA derived the deterioration 

values based on analyses done during the development of the various rules. The values were 

initially taken from the original Phase I Regulatory Support Document for maximum life 

emission factors and new engine emission factors. Based on later analysis done for the Phase 2 

nonhandheld final rule, all small (and large) spark ignition engine NOx deterioration factors 

were changed to zero. Also as a result of that analysis, the HC deterioration values for handheld 

2-stroke catalyst technology types (G2HxC2) were updated. 

Since the release of NONROAD2005, Phase 3 standards have been finalized for small SI 

nonhandheld engines. Based on analyses done during rule development, updates were made to 

the Phase 2 deterioration rates for these engines, based on in-use testing data for 16 walk behind 

mowers. [7] In addition, Phase 3 deterioration rates were developed. [8] 

It should be noted that particulate matter (PM) standards were not considered or included 

in rulemakings to date, and little data exists for PM deterioration rates. Based on EPA’s best 

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

in the final NONROAD2008 model whenever data were lacking. 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 approximate the levels of 

deterioration found in testing, including the testing summarized in NEVES and the testing done 

to support the 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 Rules, 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. The EPA believes that the 

deterioration rates used in NONROAD are more reflective of the deterioration rates that one 

5
 
would expect to find out in the field when equipment powered by small spark ignition engines is 

used by the average person. 

Table 1 

Class I (Displacement < 225 cc) Nonhandheld Deterioration Factors*
 

Engine Tech Type 

A 

b Cap HC CO NOx PM BSFC 

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

G4N1S (side-valve, 4-stroke, baseline) 1.1 0.9 0 1.1 0 0.5 2 

G4N1O (overhead valve, 4-stroke, baseline) 1.1 0.9 0 1.1 0 0.5 2 

G4N1S1 (Phase 1 side-valve, 4-stroke) 5.103 1.109 0 5.103 0 0.5 2 

G4N1O1 (Phase 1 overhead valve, 4-stroke) 1.753 1.051 0 1.753 0 0.5 2 

G4N1S2 (Phase 2 side-valve, 4-stroke) 1.753 0.07 0.18 1.753 0 0.5 2 

G4N1O2 (Phase 2 overhead valve, 4-stroke) 1.753 0.07 0.18 1.753 0 0.5 2 

G4N1S3 (Phase 3 side-valve, 4-stroke) 0.797 0.07 0.302 1.753 0 0.5 2 

G4N1O3 (Phase 3 overhead valve, 4-stroke) 0.797 0.07 0.302 1.753 0 0.5 2 

* Assigned NONROAD hp range: 3-6 hp 

Table 2 

Class II (Displacement ≥225 cc) Nonhandheld Deterioration Factors* 

Engine Tech Type 

A 

b Cap 

HC CO NOx PM BSFC 

G2N2 (gas 2-stroke nonhandheld Class II, baseline) 0.201 0.199 0 0.201 0 1 2 

G4N2S (side-valve, 4, baseline) 1.1 0.9 0 1.1 0 0.5 2 

G4N2O (overhead valve, 4-stroke, baseline) 1.1 0.9 0 1.1 0 0.5 2 

G4N2S1 (Phase 1 side-valve, 4-stroke) 1.935 0.887 0 1.935 0 0.5 2 

G4N2O1 (Phase 1 overhead valve, 4-stroke) 1.095 1.307 0 1.095 0 0.5 2 

G4N2O2 (Phase 2 overhead valve, 4-stroke) 1.095 0.08 0 1.095 0 0.5 2 

G4N23a (Phase 3 overhead valve, 4-stroke) 0.797 0.08 0.302 1.095 0 0.5 2 

* Assigned NONROAD hp range: 6-25 hp 

6
 
Table 3 

Class III (Displacement < 20cc) Handheld Deterioration Factors*
 

Engine Tech Type 

A 

b Cap 

HC CO NOx PM BSFC 

G2H3 (gas 2-stroke handheld Class III, baseline) 0.2 0.2 0 0.2 0 1 1 

G2H31 (Phase 1) 0.24 0.24 0 0.24 0 1 1 

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

G2H3C2 (Phase 2 with catalysts) 0.72 0.24 0 0.24 0 1 1 

* Assigned NONROAD hp range: 0-1 hp 

Table 4 

Class IV (20cc < Displacement < 50 cc) Handheld Deterioration Factors* 

Engine Tech Type 

A 

b Cap 

HC CO NOx PM BSFC 

G2H4 (gas 2-stroke handheld Class IV, baseline) 0.2 0.2 0 0.2 0 1 1 

G2H41 (Phase 1) 0.29 0.24 0 0.29 0 1 1 

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

G4H41 (Phase 1 4-stroke) 1.1 0.9 0 1.1 0 0.5 1 

G2H4C2 (Phase 2 with catalyst) 0.77 0.24 0 0.29 0 1 1 

G4H42 (Phase 2 4-stroke) 1.1 0.9 0 1.1 0 0.5 1 

* Assigned NONROAD hp range: 1-3 hp 

Table 5 

Class V (Displacement ≥ 50cc) Handheld Deterioration Factors* 

Engine Tech Type 

A 

b Cap 

HC CO NOx PM BSFC 

G2H5 (gas 2-stroke handheld Class V, baseline) 0.2 0.2 0 0.2 0 1 1 

G2H51 (Phase 1) 0.266 0.231 0 0.266 0 1 1 

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

G2H52 (Phase 2) 0.266 0.231 0 0.266 0 1 1 

* Assigned NONROAD hp range: 3-6 hp 

7
 
Deterioration Inputs for Land-based Spark Ignition Engines Greater than 25 Horsepower 

(19 kilowatts) 

The deterioration factors currently used in NONROAD for 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. [9] These are based on on-highway deterioration data. The 

deterioration factors for recreational equipment are presented in the next section. 

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. [10] 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 ‘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 lightduty 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 final 

NONROAD2008a 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. 

Class IIb engines are the smallest heavy-duty engines and are comparable in size to many Large 

8
 
 

 

SI engines. They also employ catalyst/fuel system technology similar to the technologies we 

expect to be used on Large SI engines. [11] 

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. [11] 

Table 6 shows the deterioration factors used for large spark-ignition equipment. 

Table 6 

Deterioration Factors for Spark-Ignition Engines > 25 HP 

Engine Tech Type 

A 

b Cap 

HC CO NOx PM 

Uncontrolled 

G2GT25 (gas, 2-stroke, baseline) 0.201 0.199 0 0.201 1 1 

G4GT25 (gas, 4-stroke, baseline) 0.26 0.35 0.03 0.26 1 1 

LGT25 (LPG, baseline) 0.26 0.35 0.03 0.26 1 1 

NGT25 (CNG, baseline) 0.26 0.35 0.03 0.26 1 1 

Phase 1 

G4GT251 (gas, 4-stroke) 0.64 0.36 0.15 0.26 1 1 

LGT251 (LPG) 0.64 0.36 0.15 0.26 1 1 

NGT251 (CNG) 0.64 0.36 0.15 0.26 1 1 

Phase 2 

G4GT252 (gas, 4-stroke) 0.64 0.36 0.15 0.26 1 1 

LGT252 (LPG) 0.64 0.36 0.15 0.26 1 1 

NGT252 (CNG) 0.64 0.36 0.15 0.26 1 1 

Deterioration Inputs for Recreational Equipment 

The deterioration factors currently used in NONROAD for recreational equipment (i.e., 

snowmobiles, all-terrain vehicles, and offroad motorcycles) are based on those used in the final 

rulemaking for recreational equipment and large spark-ignition engines. [9] 

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 different tech type names 

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

9
 
 

 

these recreational equipment engines use deterioration rates based on pre-1978 uncontrolled 

four-stroke on-highway motorcycles from the MOBILE model. [12] 

Table 7 shows the deterioration factors used for recreational equipment. 

Table 7 

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

Equipment/Tech Type 

A 

b Cap 

HC CO NOx PM 

Precontrol 2-stroke offroad motorcycles (RM2) 0.201 0.199 0 0.2 1 1 

Precontrol 4-stroke offroad motorcycles (RM4) 0.15 0.17 0 0.15 0.5 1 

Closed crankcase 4-stroke offroad motorcycles (RM40) 0.15 0.17 0 0.15 0.5 1 

Phase 1 4-stroke offroad motorcycles (RM41) 0.15 0.17 0 0.15 0.5 1 

Precontrol 2-stroke all terrain vehicles (RA2) 0.201 0.199 0 0.2 1 1 

Precontrol 4-stroke all terrain vehicles (RA4) 0.15 0.17 0 0.2 0.5 1 

Closed crankcase 4-stroke all terrain vehicles (RA40) 0.15 0.17 0 0.15 0.5 1 

Phase 1 4-stroke all terrain vehicles (RA41) 0.15 0.17 0 0.15 0.5 1 

Precontrol 2-stroke snowmobiles (RS2) 0.201 0.199 0 0.2 1 1 

Modified 2-stroke snowmobiles (RS21) 0.201 0.199 0 0.2 1 1 

Direct Injection 2-stroke snowmobiles (RS22) 0.201 0.199 0 0.2 1 1 

Closed crankcase 4-stroke snowmobiles (RS40) 0.15 0.17 0 0.15 0.5 1 

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. [13] Deterioration factors for outboard and personal watercraft have been 

updated starting with the NONROAD2005 model, using 1998-2005 model year emissions 

certification data for these engines. [14] 

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. 

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Table 8 

Marine Engine Technology Class and Designations 

Technology Class Differentiation Class Designation 

Type Cycle Fuel System Aftertreatment NONROAD 

2004 

NONROAD 

2005 

NONROAD 

2008a 

Outboard 

2-Stroke 

Carbureted none M1 MO2C MO2C 

Carburetor Modifications none M5 -- --

Carbureted 3- Way Catalyst M6 -- --

Indirect Injection none M8 MO2I MO2I 

Direct Injection none M9 MO2D MO2D 

4-Stroke 

Carbureted none M4 MO4C MO4C 

Indirect Injection none -- MO4I MO4I 

Direct Injection none -- MO4D MO4D 

Meets 2010+ standards -- -- MOC1 

PWC 

2-Stroke 

Carbureted none M2 MP2C MP2C 

Carburetor Modifications none M14 -- --

Carbureted 2- Way Catalyst -- MP2CA MP2CA 

Indirect Injection none -- MP2I MP2I 

Direct Injection none -- MP2D MP2D 

4-Stroke 

Carbureted none M13 MP4C MP4C 

Indirect Injection none -- MP4I MP4I 

Direct Injection none -- MP4D MP4D 

Meets 2010+ standards -- -- MPC1 

SD/I 

≤600 hp 4-stroke 

Carbureted none M3 MS4C MS4C 

Direct Injection none M10 MS4D MS4D 

Meets 2010+ standards -- -- MSC1 

SD/I 

>600 hp 4-stroke 

Carbureted none M3 MS4C MS4C 

Direct Injection none M10 MS4D MS4D 

Meets 2010+ standards -- -- MS4X 

11
 
 

 

Table 9 

Deterioration Factors for Recreational SI Marine Engines 

Technology Class A b Cap HC CO NOx PM 

MO2C, MP2C 0.00 0.00 0.00 0.00 1 1 

MO2I, MP2I 0.03 0.03 0.08 0.00 1 1 

MO2D, MP2D 0.03 0.03 0.05 0.00 1 1 

MP2CA 0.26 0.26 0.06 0.00 1 1 

MO4C, MP4C 0.05 0.05 0.05 0.00 1 1 

MO4I, MP4I 0.03 0.03 0.03 0.00 1 1 

MO4D, MP4D 0.03 0.03 0.03 0.00 1 1 

MS4C, MS4D 0.26 0.35 0.03 0.26 1 1 

MOC1, MPC1 0.05 0.05 0.05 0.00 1 1 

MSC1 0.64 0.36 0.15 0.26 1 1 

MS4X 0.26 0.35 0.03 0.26 1 1 

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. 

Example Calculation 

The following example illustrates how deterioration factors (DFs) are calculated in 

NONROAD. 

Example: Calculate the NOX deterioration factor for a ten year old 300-600 hp 4-stroke 

inboard/sterndrive recreational marine engine in 2020. (In NONROAD, ten year old equipment 

in 2020 translates to equipment made in model year 2011, since the calendar year of interest is 

assigned age =1 year). 

The deterioration factor, DF, is calculated as: 

DF = 1 + A*(cumulative hours * load factor) [Equation 4] 

 median life at full load, in hours 

where: MSC1 NOX Deterioration “A” = 0.15 (from Table 9) 

Activity = 47.6 hours/year (from activity.dat input file) 

12
 
Load factor = 0.21 (from activity.dat input file) 

Median life = 197 hours (from pop input file) 

Cumulative hours = age * activity = 10*47.6 = 470.6 hours 

Substituting the above values into the equation yields: 

DF = 1 + 0.15*(470.6 * 0.21) = 1 + 0.15 * 0.507 = 1.076 

197 

References 

1. “Control of Emissions From Nonroad Spark-Ignition Engines and Equipment; Final Rule,” 

73 FR 59034, October 8, 2008. 

2. “Emissions for New Nonroad Spark-Ignition Engines At or Below 19 Kilowatts; Final Rule,” 

60 FR 34581, July 3, 1995. 

3. “Phase 2: Emission Standards for New Nonroad Nonhandheld Spark Ignition Engines At or 

Below 19 Kilowatts,” 64 FR 15207, March 30, 1999. 

4. “Phase 2: Emission Standards for New Nonroad Spark-Ignition Handheld Engines At or 

Below 19 Kilowatts and Minor Amendments to Emission Requirements Applicable to Small 

Spark-Ignition Engines and Marine Spark-Ignition Engines; Final Rule,” 65 FR 24268, April 

25, 2000. 

5. “Final Rule for New Gasoline Spark-Ignition Marine Engines; Exemptions for New Nonroad 

Compression-Ignition Engines at or Above 37 Kilowatts and New Nonroad Spark-Ignition 

Engines at or Below 19 Kilowatts,” 61 FR 52088, October 4, 1996. 

6. “Control of Emissions From Nonroad Large Spark-Ignition Engines and Recreational 

Engines (Marine and Land-Based); Final Rule,” 67 FR 68241, November 8, 2002. 

7. “Updates to Phase 2 Technology Mix, Emission Factors, and Deterioration Rates for SparkIgnition Nonroad Nonhandheld Engines at or below 19 Kilowatts for the NONROAD 

Emissions Inventory Model,” EPA Memorandum from Phil Carlson to Docket EPA-HQOAR-2004-0008, March 6, 2007. 

8. “Phase 3 Technology Mix, Emission Factors, and Deterioration Rates for Spark-Ignition 

Nonroad Nonhandheld Engines at or below 19 Kilowatts for the NONROAD Emissions 

Inventory Model for the Final Rule,” EPA Memorandum from Phil Carlson to Docket EPAHQ-OAR-2004-0008, May 21, 2008. 

13
 
9. Final Regulatory Support Document: Control of Emissions from Unregulated Nonroad 

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

10. “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. 

11. 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. 

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

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

13. “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. 

14. “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. 

14
 
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 

15