United States

Environmental Protection

Agency

Air and Radiation EPA420-P-02-019

April 2002

NR-011a

Spark-Ignition Engine

Emission Deterioration

Factors for the

Draft NONROAD2002

Emissions Model

 Printed on Recycled Paper
EPA420-P-02-019

April 2002

Spark-Ignition Engine Emission Deterioration

Factors for the Draft NONROAD2002 Emissions Model

NR-011a

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 NONROAD2002 Emissions Model

Report No. NR-011a

revised April 24, 2002

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 NONROAD2002 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 light-duty

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,

the NEEMT has 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 NONROAD2002 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 NONROAD2002 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
6

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.

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)

Spark-ignition engines greater than 25 horsepower are primarily found in

recreational, commercial, recreational marine, and industrial equipment. The

deterioration rates discussed in this section can be found in Table 6.

A. Recreational Equipment

Due to a lack of deterioration data for large two-stroke spark-ignition engines

found in snowmobiles, all-terrain vehicles, and off-road motorcycles, EPA has chosen to

use deterioration rates associated with Class 1 and 2 Nonhandheld 2-stroke lawn and

garden equipment (Tables 1 and 2) in the draft NONROAD2002 model. The ‘b’ value

for these engines is 1.0, resulting in a linear deterioration rate. The deterioration rates are

the same for uncontrolled and controlled engines.

For 4-stroke ATVs and off-road motorcycles, EPA uses deterioration factors

based on pre-1978 uncontrolled 4-stroke on-highway motorcycles from the MOBILE

model. The ‘b’ value for these engines is 0.5, resulting in a curvilinear deterioration rate. 

The deterioration rates are the same for uncontrolled and controlled engines.

It should be noted that PM has not been addressed in the rulemaking process for

large 4-stroke spark-ignition engines used in recreational equipment and little or no data

exist for PM deterioration associated with this type of equipment. Based on EPA’s best

judgement at this time, PM deterioration has been equated with HC deterioration rates. 

EPA welcomes any comments or information that stakeholders may have concerning PM

deterioration.

B. Other Large Spark-Ignition Engines

The deterioration rates for large four-stroke spark-ignition engines used in

sterndrive and inboard recreational marine, industrial, commercial, agricultural, and

aircraft support equipment can be found in Table 6. 

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

engines. However, EPA now 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.5

 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”
10

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 NONROAD2002 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

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.6

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.7

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
11

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

information stakeholder may have concerning PM deterioration.

Table 6

NONROAD Deterioration Rates for Spark-Ignition Engines Greater Than 25hp (19 kW)

Equipment Engine

Type

Tech Type HC CO NOx PM BSFC

Off-road Motorcycle, ATVs,

Snowmobiles

2-stroke R12S 0.2 0.2 0 0.2 0

Off-road Motorcycle, ATVs 4-stroke R142 0.15 0.17 0 0.15 0

Recreational Marine and

Other Large SI

Base

Phase 1

Phase 2

4-stroke

G4GT25

G4GT251

G4GT252

0.26

0.64

0.64

0.35

0.36

0.36

0.03

0.15

0.15

0.26

0.64

0.64

0

0

0

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.

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.
12

5. “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.

6. 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.

7. See endnote 6.
13

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

Appendix 1

Deterioration Ratio Data for 1969 MY LDGTs
14

Appendix 2

Emission Deterioration Factors For the NONROAD Emissions Model

Report No. NR-011

September 4, 1998

Chris Lindhjem

Greg Janssen

Mike Sklar

Rich Wilcox

Nonroad Engine Emission Modeling Team

Assessment and Modeling Division

EPA, Office of Mobile Sources

I. Purpose

This report addresses the emission deterioration rates currently being used in the draft

version of NONROAD and discusses other sources of emission deterioration estimates. The

Nonroad Engine and Emissions Modeling Team (NEEMT) welcomes comments and suggestions

concerning our approach to modeling nonroad engine emissions deterioration.

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.

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
15

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, the NEEMT 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 Mobile Sources has conducted emissions testing

on several dozen small spark ignition lawn & garden engines and a few large compressionignition 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 light-duty

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 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 NEEMT requests that state and

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

maintenance they may have with EPA. The NEEMT 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 with EPA.
16

This report explicitly addresses the compatibility of NONROAD’s estimates of

deterioration with the estimates of deterioration produced by other nonroad emission models. 

These models include the nonroad compression ignition regulatory Nonroad Emissions Model

(NEM), the Phase 1 Nonroad Small Engine Emission Model (NSEEM1), the Phase 2 Nonroad

Small Engine Emission Model (NSEEM2), and the California Air Resources Board (ARB)

OFFROAD model. EPA used the NEM to support the proposed compression ignition (diesel)

engine rule, the NSEEM1 to support the Phase 1 Small Spark Ignition Engine Rule, and the

NSEEM2 to support the proposed Phase 2 Small Spark Ignition Engine Rule. During the

development of NONROAD, the NEEMT has used many of the same data sources and modeling

assumptions used in these earlier models. Once the final version of NONROAD is released, the

EPA expects to rely on NONROAD as its primary emission inventory model for future

rulemaking and inventory modeling activities.

A discussion of the calculation methods used in each of the earlier models can be found

in Section IV, Methods of Applying Deterioration. The specific deterioration inputs used in

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

horsepower; over 25 horsepower; liquid petroleum gas (LPG) and compressed natural gas

engines (CNG), and compression ignition (diesel) engines in subsequent sections.

IV. Methods of Applying Deterioration

A. NONROAD Method

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, the NEEMT has 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
17

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 deterioration

curve 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 NEEMT 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 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 horsepowerapplication 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 NEEMT 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 proposed Phase 2 Small
18

Engine Rules, as shown in Tables 1-5. 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, four-stroke spark ignition, compression

ignition) based on the more detailed engine classes defined in the Phase 1 and proposed

Phase 2 Small Engine Rules 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.

B. Methods of Applying Deterioration in Other Models

1. California ARB OFFROAD Model

The California ARB OFFROAD model applies deterioration based on a linear

relationship. Emissions are modeled to increase by a fixed amount for every hour that

the engine is used, up to a fixed limit. The function used by OFFROAD is as follows:

EFaged = EFnew + DR * CumHours at in-use load

where EFaged = deteriorated emission factor

EFnew = zero hour emission factor

DR= fraction of the maximum deterioration added to the zero

 hour emission factor (EFnew) for each hour of age the engine

accumulates

CumHours at in-use load = Engine Age * Hours of use per year

Without the emission rate cap, the linear function presented above could show an

engine deteriorating indefinitely beyond one median life. This projection may not be

a realistic or accurate one, since an engine can only deteriorate to a certain point

beyond which it ceases to function and is scrapped. Like the NONROAD model, the 

OFFROAD model reflects the limit on how much an engine’s emissions can

deteriorate before the engine ceases to function by capping deterioration once an

engine has reached one median life.

2. Phase 1 Nonroad Small Engine Emission Model (NSEEM1) for Small Gasoline Four

and Two-Stroke (<25 hp) Engines

The Phase 1 Small Engine Rule calculates deterioration using the following

exponential function for both two and four-stroke spark ignition engines:

DF = 1 + [(EFf

 - EFo)/EFo] * [1 - exp(-3 * {Age Factor})] (3)
19

where EFf = emission factor for a fully aged engine

 EFo = zero hour emission factor

 Age = Age in years/Median life in years.

The deterioration function (3) in the NSEEM1 model results in 95% of the

deterioration occurring at an age of one median life. As stated above, the equation (2)

used in NONROAD closely approximates the Phase I deterioration curve, but caps

deterioration after one median life. The relationship between the deterioration in

NONROAD and NSEEM1 at one median life is given below.

A = [(EFf - EFo)/EFo] (4)

for Age Factor = 1

3. Proposed Phase 2 Nonroad Small Engine Emission Model (NSEEM2) for Small

Gasoline Four and Two-Stroke (< 25 hp) Engines

The proposed Phase 2 Small Engine Rule and its supporting model

(NSEEM2) use the following equations to calculate deterioration for small two and

four-stroke engine HC, CO, and NOx emissions. It should be noted that the following

deterioration functions were used to recalculate the original Phase 1 deterioration

rates as well as calculate the Phase 2 deterioration rates. Also, particulate matter (PM)

emissions and deterioration were not considered in either the first or second phase of

the Small Engine Rule. 

The deterioration function for spark ignition two stroke engines is linear and is

given by equation (5):

DF = 1 + C * (Hourstotal) (4)

where C = A constant derived from a best-fit regression based on EPA

and manufacturer test data3

Hourstotal = Engine age * Annual hours of use

For four-stroke engines, the deterioration function is a square root function

and is given by equation (6):

DF = 1 + C * (Hourstotal)

0.5 (6)

where C = A constant derived from a best-fit regression based on

manufacturer test data

Hourstotal = Engine Age * Annual hours of use
20

This function produces a curvilinear plot similar in shape to the NSEEM1/Phase 1

curve, where most of the deterioration occurs toward the early part of an engine’s

median life. This function is based on manufacturer’s emissions testing data from

engines undergoing accelerated aging in the laboratory and in the field.4

4. Compression-Ignition Nonroad Engine Model (NEM)

The NEM does not contain a deterioration function, since EPA assumes that

compression ignition engines do not significantly deteriorate. This assumption is

discussed in more detail later in this report, under the section addressing compression

ignition engines.

C. Using the NONROAD Deterioration Function to Represent Other Deterioration

Patterns

The NONROAD deterioration function can be modified to give results consistent

with the Phase 1 and proposed Phase 2 Small Engine Rules. The NONROAD

deterioration function also has the ability to describe other curvilinear or linear

deterioration patterns, such as the California ARB deterioration rates, by changing the

inputs for the function in equation (2).

V. Deterioration Inputs For Engines At or Below 25 Horsepower

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

Horsepower

The NONROAD deterioration function is given by equation (2):

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

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.

In NONROAD, 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.
21

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 proposed

Phase 2 Small Engine Rules. These values were derived from the values provided in the

Phase I Regulatory Support Document for maximum life emission factors and new engine

emission factors. 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

proposed Phase 2 Small Engine Rules. For the present time, PM deterioration in fourstroke engines will be equated to that of HC in NONROAD, and PM deterioration for

two-stroke engines will assumed to be zero. The NEEMT believes this assumption is

reasonable, since two-stroke engines are unlikely to experience the high PM deterioration

rates seen in four-stroke engines given the high PM emission rates of new two-stroke

engines. The NEEMT requests stakeholders with information about the PM emissions

deterioration of two-stroke engines to submit such data to EPA.

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

proposed Phase 2 Small Engine Rules. These include marine engines (SCC

2282xxxxxx) and certain recreational equipment such as snowmobiles (226x001020),

off-road motorcycles and 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 are

simply included in the G4N2O tech type since there are no different emission factors. 

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 for the same reasons mentioned above regarding particulate

matter (PM) emissions. 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. NONROAD assigns four-stroke marine

engines deterioration values equal to the G4N2O tech type shown in Table 2, but they use

different tech type names such as M3, M10, M11, M12, and M16 depending on the

specific control technology and application (outboard, personal water craft or inboard). 
22

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 0

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

baseline)

1.1 0.9 -0.6 1.1 0

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

baseline)

1.1 0.9 -0.6 1.1 0

G2N1 (2-stroke, Phase 1) 0.266 0.231 0 0 0

G4N1S1 (Phase 1 side-valve, 4-stroke) 5.103 1.109 -0.33 5.103 0

G4N1O1 (Phase 1 overhead valve, 4-stroke) 1.753 1.051 -0.30 1.753 0

G4N1SC1 (Phase 1 side-valve, 4-stroke with catalyst) 5.103 1.109 -0.33 5.103 0

G4N1S2 (Phase 2 side-valve, 4-stroke) 5.103 1.109 -0.33 5.103 0

G4N1O2 (Phase 2 overhead valve, 4-stroke) 1.753 1.051 -0.30 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 0

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

baseline)

1.1 0.9 -0.6 1.1 0

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

baseline)

1.1 0.9 -0.6 1.1 0

G4N2S1 (Phase 1 side-valve, 4-stroke with catalyst) 1.935 0.887 -0.274 1.935 0

G4N2O1 (Phase 1 overhead valve 4-stroke) 1.095 1.307 -0.599 1.095 0

G4N2S2 (Phase 2 side-valve) 1.935 0.887 -0.274 1.935 0

G4N1O2 (Phase 2 overhead valve) 1.095 1.307 -0.599 1.095 0
23

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 0

G2H31 (Phase 1) 0.24 0.24 0 0 0

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

G2H32 (Phase 2) 0.24 0.24 0 0 0

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

G2H41 (Phase 1) 0.29 0.24 0 0 0

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

G4H41 (Phase 1 4-stroke) 1.1 0.9 -0.6 1.1 0

G2H42 (Phase 2) 0.29 0.24 0 0 0

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

G4H42 (Phase 2 4-stroke) 1.1 0.9 -0.6 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 -0.031 0 0

G2H51 (Phase 1) 0.266 0.231 0 0 0

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

G2H52 (Phase 2) 0.266 0.231 0 0 0

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

B. Other Sources of Deterioration Rates for Spark Ignition Engines At or Below 25

Horsepower
24

The NEEMT considered several sources of information regarding deterioration

factors. These sources included the Nonroad Engine and Vehicle Emissions Study5

(NEVES), the technical documentation for the California ARB OFFROAD model, and

the small engine regulatory impact analysis and support documents for the Phase 1 and

proposed Phase 2 Small Spark Ignited Engine Rules.

1. California ARB

To estimate deterioration rates for pre-control, Tier 1, and Tier 2 two and fourstroke engines, the California ARB uses deterioration factors for HC, CO, and NOx

derived from analysis of manufacturer emissions data submitted to EPA for

consideration during the regulatory negotiation process for small engine standards, as

well as additional manufacturer data submitted to the California ARB during its small

engine rulemaking process.6,7 These data include the testing of engines that have

undergone accelerated aging under both field and laboratory conditions. The

deterioration rates for two-stroke engines appear in Table 6a and the rates for fourstroke engines appear in Table 6b. It should be noted that the four-stroke

deterioration rates are weighted averages of the deterioration rates for side and

overhead valve engines. At this time, the NEEMT has not received sufficient

information from the California ARB to show the separate deterioration rates for side

and overhead valve engines. However, all other things being equal, side-valve

engines usually deteriorate significantly more than overhead valve engines, based on

tests conducted by both EPA and the Equipment Manufacturers Association (EMA).

Table 6a

Small Engine (<25hp) Spark Ignition Two-Stroke OFFROAD Deterioration Rates

Standards Model Yr. HP HC DR CO DR NOx DR PM DR

Uncontrolled

Tier 1

Tier 2

pre-95

1995-99

2000+

0-2 0

0

0.2513

0

0

0

0

0

0

0

0

0.01117

Uncontrolled

Tier 1

pre-95

1995-99

2000+

2-15 0

0

0.2513

0

0

0

0

0

0

0

0

0.00808

Uncontrolled

Tier 1

Tier 2

pre-95

1995-99

2000+

15-25 0

0

0.2513

0

0

0

0

0

0

0

0

0.00808
25

Table 6b

Small Engine (<25hp) Spark Ignition Four-Stroke OFFROAD Deterioration Rates

Standards Model Yr. HP HC DR CO DR NOx DR PM DR

Uncontrolled

Tier 1

Tier 2

pre-95

1995-96

1997-99

2000-03

0-5 0.0948

0.0565

0.0565

0.0144

0.5196

-0.067

-0.067

-0.3849

0.0002

0.0031

0.0031

0.0065

0.0026

0.0026

0.0026

0.0026

Uncontrolled

Tier 1

Tier 2

pre-95

1995-96

1997-99

2000-03

5-15 0.0178

0.0207

0.0207

0.0047

0.0337

0.0895

0.0895

0

0.0013

0

0

0.0035

0.0002

0.0002

0.0002

0.0002

Uncontrolled

Tier 1

Tier 2

pre-95

1995-96

1997-99

2000-03

15-25 0.0141

0.0166

0.0166

0.0049

0.0276

0.0345

0.0345

0

0.0011

0

0

0.0032

0.0002

0.0002

0.0002

0.0002

2. EPA Phase 1 Small Engine Model (NSEEM1)

For both uncontrolled and controlled four-stroke spark ignition engines, the

maximum deterioration derived from the NSEEM1 model occurs at the end of one

median life for HC, CO, and NOx. The deterioration rates in the two models,

expressed in terms of the absolute increase in g/bhp-hr emission rates over the course

of the engine’s life, are the same and can be found in the regulatory impact analysis

and support document for EPA’s Phase 1 Small Engine Rule for engines at or below

25 horsepower (19 kw).8

 The NSEEM1 model uses the same deterioration rates

found in the NEVES report for small four-stroke engines less than 20 horsepower

(discussed in section 4 below).9

 These deterioration rates were originally based on

tests done by Southwest Research Institute (SwRI) on three different four-stroke

engines.

 The two-stroke spark-ignition deterioration factors for HC, CO, and NOx

used by the Phase 1 Small Engine Rule Team used can be found in the regulatory

impact analysis and support document for EPA’s Phase 1 Small Engine Rule for

engines at or below 25 horsepower (19 kw). The two-stroke engine deterioration

factors represent the ratio between the emission rates at one median life (when

emissions reach their maximum level) and the emission rates at zero hours of age. 

The two-stroke maximum deterioration rates are 1.2, 1.9, and 1.0 for HC, CO, and

NOx, respectively. This translates into a 20 percent HC increase, a 90 percent CO

increase, and no change in NOx emissions over the engine’s life. The deterioration

rates used in the Phase 1 Small Engine Rule were based on information from SAE

technical papers and industry-supplied data. The OMS analysis of this information

during the development of the Phase 1 Small Engine Rule supported changing the
26

deterioration rates for two-stroke spark ignition engines from the ones found in the

NEVES report.

3. EPA Phase 2 Small Engine Model (NSEEM2)

As discussed above, the Phase 2 Small Engine Model uses a linear function

for two-stroke engines and a curvilinear square root function for four-stroke engines

to define deterioration as the engine ages. The Small Engine Rule Team used these

functions to derive deterioration rates for Phase 2 small engines, and they also revised

the Phase 1 deterioration rates originally calculated for the Phase 1 Small Engine

Rule. However, the uncontrolled deterioration rates remain unchanged from the

original ones used in the Phase 1 Small Engine Rule.

As shown above in the “Methods of Applying Deterioration” section (Section

IV.A), the two and four-stroke Phase 2 deterioration functions employ a unique

constant for HC, CO, and NOx for each class of small engines, as shown in Table 7. 

Table 7

Constants Used in the Phase 2 Small Engine Rule Deterioration Function

G2H3 G2H4 G2H5 G2N1 G2N2 G4N10 G4N1S G4N20 G4N2S G4H4

Phase 1

Res.

HC

CO

NOx

0.002

0.002

0.000

0.002

0.002

0.000

0.002

0.002

0.000

0.000

0.002

0.000

0.000

0.000

0.000

0.050

0.022

0.030

0.1300

0.0220

0.0200

0.0800

0.0110

0.0200

0.0400

0.0110

0.0200

0.1840

0.0020

0.0230

Phase 1

Com.

HC

CO

NOx

0.0003

0.0003

0.0000

0.0003

0.0003

0.0000

0.0003

0.0003

0.0000

0.000

0.002

0.000

0.000

0.000

0.000

0.0245

0.0110

0.0147

0.0637

0.0110

0.0098

0.0566

0.0080

0.0141

0.0283

0.0080

0.0141

0.0751

0.0008

0.0094

Phase 2

Res.

HC

CO

NOx

0.002

0.002

0.000

0.002

0.002

0.000

0.002

0.002

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.050

0.022

0.030

0.1300

0.0220

0.0200

0.0280

0.0110

0.0060

0.0400

0.0110

0.0200

0.1840

0.0020

0.0230

Phase 2

Com.

HC

CO

NOx

0.0003

0.0003

0.0000

0.0003

0.0003

0.0000

0.0003

0.0003

0.0000

0.000

0.000

0.000

0.000

0.000

0.000

0.0245

0.0110

0.0147

0.0637

0.0110

0.0098

0.0198

0.0080

0.0042

0.0283

0.0080

0.0141

0.0751

0.0008

0.0094
27

The other input used in the deterioration functions is the median life in hours

for each equipment type. This value is derived by multiplying the annual hours of

activity by the half-life (B50 value) in years of each equipment type. The half-life in

years is the point on the NSEEM2 scrappage curve when 50 percent of the equipment

from a given model year are no longer functioning. These values are included in

Tables F-05 by F-06 in the Phase 2 Small Engine Rule Regulatory Support Document

and are reprinted here in Table 8.10
28

Table 8

Phase 2 Small Engine Rule Average Annual Use and Load Factor

Equipment Use Hr/Year*Load Factor Hr/Yea

r

B50

LN MOWERS res 8.38 25.4 5.8

LN MOWERS prof 134.12 406.42 2

TRIM/EDGE CUTTER res 4.55 9.1 4.3

TRIM/EDGE CUTTER prof 68.64 137.29 2.3

CHAINSAWS res 6.25 12.5 4.3

CHAINSAWS prof 151.25 302.5 0.9

LEAF BLOW/VAC res 4.8 9.59 4.3

LEAF BLOW/VAC prof 141.14 282.29 2.3

GENERATOR SETS res 6.08 8.95 5.8

GENERATOR SETS prof 97.36 143.18 2.3

TILLERS res 6.69 16.73 5.8

TILLERS prof 188.64 471.6 4.4

SNOWBLOWERS res 2.97 8.48 4.4

SNOWBLOWERS prof 47.49 135.68 4.4

COMM TURF res NA NA NA

COMM TURF prof 340.85 681.69 2.9

REAR ENG RIDER res 13.5 35.54 5.8

REAR ENG RIDER prof 216.07 568.6 2.9

LN/GROUND

TRACTOR

res 19.84 45.08 5.8

LN/GROUND

TRACTOR

prof 317.37 721.31 2.9

PUMPS res 9.34 13.54 5.8

PUMPS prof 149.44 216.58 2.3

ALL OTHER

EQUIPMENT

prof 7.3 14.61 5.8

ALL OTHER

EQUIPMENT

res 116.84 233.68 2.3

4. Nonroad Engine and Vehicle Emissions Study (NEVES)
29

Four-Stroke SI Engines

The deterioration rates used in the NEVES for four-stroke engines at or below

20 horsepower were applied to zero-hour emission factors to generate an in-use

emission factor. These deterioration rates were derived from tests done by Southwest

Research Institute (SwRI) on three four-stroke engines.11 A table of the SwRI testing

results can be found in Appendix 1 of this report. For four-stroke engines, the

maximum deterioration factor at the engine’s average useful life based on the SwRI

tests are multiplicative factors of 2.1, 1.9, and 0.4 for exhaust hydrocarbons (HC),

carbon monoxide (CO), and oxides of nitrogen (NOx), respectively (i.e., 110 percent

increase for HC, 90 percent increase for CO, and 60 percent decrease for NOx at the

median life of this type of engine). The particulate matter (PM) deterioration factor

taken from the NEVES report is 3.6, which translates into a 260 percent increase in

emissions at the median life for this engine category.12 The decrease in NOx

emissions was not seen as being unreasonable, given that wear and tear on small

engines tends to cause the fuel to air ratio to become more fuel-rich, thereby

increasing products of incomplete combustion such as hydrocarbons, particulate

matter, and carbon monoxide emissions while suppressing NOx formation.13 The

authors of NEVES assumed that four-stroke LPG and CNG engines deteriorated the

same amount as their gasoline counterparts, since design differences between the

gasoline and LPG/CNG engines were negligible.

Two-Stroke SI Engines

With the exception of recreational marine engines, the NEVES report equated

all two-stroke SI engine deterioration rates for HC and CO to the four-stroke SI

engine deterioration rates in NEVES for below-25 horsepower (19 kw) engines. The

authors of NEVES used this approach because the available two-stroke SI emissions

testing data from Southwest Research Institute (SwRI) provided inconclusive results. 

As discussed in the NEVES report, SwRI tested two small (at or below 20 hp), aged

two-stroke SI engines , but these results differed widely for HC and CO. The SwRI

deterioration data for small four-stroke SI engines fell between the results for the two

two-stroke engines, and the authors of the NEVES report decided to use this fourstroke deterioration rate for all small SI engines (both two- and four-stroke). This

approach was considered to be preferable to basing the small two-stroke engine

deterioration estimates on two data points that differed so greatly. For two-stroke

recreational marine engines the NEVES report used a multiplicative deterioration

factor of 1.2 (20 percent) that was based on data submitted by the National Marine

Manufacturers Association (NMMA). 

For NOx, both of the two-stroke SI engines tested by SwRI showed almost

equal or slightly higher emissions compared to new engine emission factors for twostrokes. These consistent test results prompted NEVES’ authors to use a deterioration
30

factor of 1.0 (zero percent deterioration) for NOx emissions from all small two-stroke

SI engines (including recreational marine engines), instead of using the four-stroke SI

engine NOx deterioration factor.

For PM, the NEVES report set the PM deterioration factors for all two-stroke

spark-ignition engines to a multiplicative factor of 1.0 (zero percent) due to the

perceived inappropriateness of applying the four-stroke spark-ignition deterioration

rate (3.6 or 260 percent over the median life of the engine) to two-stroke engines. PM

emission rates from new two-stroke SI engines are already so high that the NEVES

authors believed that they could not experience such a large increase in emissions and

remain operational. In the absence of other information, they chose to assume no

deterioration in PM emissions. A copy of the table containing these deterioration

rates can be found in Appendix 2.

C. Discussion of Deterioration Factor Data for Spark-Ignition Engines At or Below 25

Horsepower

The deterioration rates used in NONROAD approximate the levels of

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

done to support EPA’s Phase 1 and proposed Phase 2 Small Engine Rules. Where these

test results differ, the NEEMT 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 proposed Phase 2 Small Engine Rule, for example,

reflects testing of engines that have undergone accelerated aging which the NEEMT does

not believe to be representative of the aging experienced by engines in use. After

evaluating all available data, the NEEMT 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 proposed

Phase 2 Small Engine Rule, but are generally smaller than those used in NEVES. The

NEEMT 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 proposed Phase 2 Small Engine Rule.

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

A. Deterioration Factors Used in NONROAD for Spark-Ignition Engines Greater Than

25 Horsepower (19 kilowatts)

Currently, there are few emission testing data concerning dedicated nonroad fourstroke spark ignition engines over 25 horsepower. Both the NEVES and the California

ARB used deterioration rates for these types of engines that originated from on-highway
31

spark-ignition engine emissions data. These approaches will be discussed later in this

document. 

For the purpose of the draft release of NONROAD, the NEEMT has decided to

equate deterioration of four-stroke SI engines over 25 horsepower to that of the Class 2,

non-handheld four-stroke engines, which are the largest class of engines found in the

Phase 1 and proposed Phase 2 rules. Since four-stroke engines over 25 horsepower are

not currently regulated, have overhead valve technology, and have no catalytic technology

applied to them, the NEEMT will use the baseline deterioration factors found in Table 2

listed next to the label “G4N2O” (i.e., gasoline, four-stroke, non-handheld, Class 2,

overhead valve engines). The deterioration rate for the large ones will be curvilinear,

using 0.5 for the ‘b’ constant, as is the case for small four-stroke engines.

Two-stroke SI engines over 25 horsepower are also unregulated at this time. For

these engines, the NEEMT has decided to use the pre-control deterioration inputs being

used in NONROAD for the largest class of small engines in the Phase 1 and proposed

Phase 2 Small Engine Rules. These can be found in table 2 next to the label “G2N2"

(i.e., gasoline, two-stroke, non-handheld, Class 2 engines). The deterioration rate for the

large ones will be linear, using 1.0 for the ‘b’ constant in the NONROAD deterioration

function, as is the case for small two-stroke engines.

B. Other Sources of Deterioration Factors for SI Engines Greater than 25 Horsepower

1. NEVES Deterioration Factors for Gasoline Spark Ignition Engines Greater than 20

Horsepower

The data for the large four-stroke SI deterioration rates in the NEVES report

were developed by a 1983 joint testing program by EPA and the Equipment

Manufacturers Association (EMA) to test heavy-duty on-highway engines, including

both spark-ignition and compression-ignition engines. For heavy-duty, four-stroke,

spark-ignition engines, the program used an unknown number of 1979 to 1982 precontrolled highway engines. EMA’s calculation of the deterioration rates used

regression equations based upon a number of assumptions, most notably that the

engines had logged 55,000 miles. Based on this assumption, the engines had reached

the halfway point of their median life in relation to the existing heavy-duty onhighway gasoline engine regulations, which defined the median life of such engines to

be 110,000 miles. Deterioration rates for HC and CO were calculated by dividing

in-use engine emissions by those of new heavy duty gas engines. The deterioration

factor for HC was calculated to be 1.5 (a 50 percent increase), while the deterioration

factor for CO was calculated to be 1.3 (a 30 percent increase). NOx emissions did not

show a significant increase in emissions, so a deterioration factor of 1.0 (zero percent

increase) was used. No testing was done to measure PM deterioration. The NEVES

report assumed that large nonroad four-stroke SI engines experienced similar
32

deterioration patterns, in part because of the similarities in engine design between

such nonroad engines and the uncontrolled highway engines tested by EMA and EPA.

The NEVES report equated the large two-stroke spark ignition deterioration

rates to the deterioration rates for the greater than 20 horsepower (19 kW) four-stroke

spark-ignition engines in NEVES for HC, CO, and NOx. As stated in section V.B.4,

the NEVES report assumed no deterioration in PM emissions for all two-stroke spark

ignition engines.

2. California ARB's Deterioration Factors for Spark Ignition Nonroad Engines Greater

than 25 Horsepower

The California ARB nonroad model, OFFROAD, uses deterioration rates for

gasoline four-stroke spark-ignition engines over 25 horsepower that are based on precontrol on-highway engine deterioration rates found in EMFAC7E, the California

ARB on-highway emissions model. These deterioration rates, in the form of percent

deterioration per percent of median life, are shown in Table 9.14 The California ARB

matched nonroad and on-highway engines as closely as possible by horsepower and

used a ratio to convert the on-highway deterioration rates based on gram/10,000 miles

traveled to rates based on number of hours an engine has been used. This ratio is

shown below, with the median life for off-road engines expressed in terms of hours

and the median life for on-highway engines expressed in terms of miles traveled. The

deterioration factors are expressed as the percent increase in emissions per percent of

median life. Since there were no equivalent on-highway engines for the 25 to 50

horsepower category of nonroad engines, the California ARB set the deterioration rate

for these engines equal to that used for the 50 to 120 horsepower engines. No data

were available for PM. 

Off-Road d.f. * Median Life = On-Highway d.f. * Median Life

Off-Road Zero Hour Factor On-Highway Zero Mile Factor
33

Table 9

California ARB Deterioration Rates For Four-Stroke 

Spark-Ignition Engine Over 25 Horsepower

(Percent increase per percent of median life)

HP

Category

Equivalent

On-hwy.

On-hwy.

MYR

On-hwy.

Useful Life

Off-hwy.

HC d.f.

Off-hwy.

CO d.f.

Off-hwy.

NOx d.f.

25 to 50 None N/A N/A 1.38% 0.83% 0.064%

50 to 120 LDGT 1969

NCAT

120,000 1.38% 0.83% 0.064%

120+ HDGV 1970

NCAT

120,000 0.37% 0.56% 0.140%

The technical support document for the California ARB’s OFFROAD model

stated that baseline deterioration rates for two-stroke SI engines had been set equal to the

two-stroke deterioration rates contained in the NEVES report, with the exception of twostroke nonroad motorcycles, all terrain vehicles (ATVs) and snowmobiles. For nonroad

motorcycles and ATVs, the California ARB calculated deterioration rates based on data

from pre-control on-highway motorcycle engines. Snowmobile deterioration rates in

OFFROAD were set to zero percent because the California ARB believed that it did not

have sufficient data concerning their emissions.

C. Discussion of Deterioration Factors for Spark Ignition Engines Greater Than 25

Horsepower

The NEEMT has several misgivings about using the on-highway engine deterioration

rates derived from the EPA/EMA testing program and used in NEVES. Nonroad and

highway engines are used in different applications and on different operating cycles,

experience different maintenance patterns, and are operated at different power levels. 

Highway SI engines also may be tuned to run differently or be configured differently than

those used in nonroad applications. These differences are likely to result in significantly

different rates of deterioration for nonroad engines when compared to highway engines of

similar rated power levels. The cycles used in the EPA/EMA test program were not

documented in the NEVES report and supporting documentation, but it is likely that the

program used highway testing cycles since it used highway engines and since EPA had not

yet developed representative test cycles for nonroad applications at that time. The NEEMT

also has reservations about using the California ARB deterioration factors, and its general

approach for deriving nonroad deterioration rates from highway engine test data, for similar

reasons. Furthermore, neither the EPA/EMA test program nor the California program 

measureed PM emissions, although PM deterioration could be assumed to be equal to HC

deterioration, as the California ARB did for small four-stroke SI engines.
34

Given the paucity of actual nonroad testing data for spark-ignition engines greater

than 25 horsepower and the concerns with the deterioration factors used in NEVES report

and the OFFROAD model, the NEEMT has chosen to equate spark-ignition engine

deterioration for large (>25 hp) engines to the deterioration of Class 2 SI engines in its draft

version of NONROAD. Class 2 engines are the largest class of under-25 horsepower sparkignition engines, and there is sufficient test data on such engines to permit estimation of their

deterioration rates without having to use data taken from tests of highway engines. The

NEEMT requests comments regarding the appropriateness of this approach and welcomes

suggestions regarding more appropriate alternatives. The NEEMT also requests that

commenters submit any additional data that could be used to assess deterioration for large

spark-ignition engines (both two and four-stroke).

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 NEEMT decided to assume that they would deteriorate at

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

The NEEMT 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 the NEEMT. If such data

become available, the NEEMT will revise the deterioration rates for these engines in

NONROAD accordingly.

IX.Diesel Engines

In the draft version of NONROAD, the NEEMT has chosen to assume that no

deterioration takes place in compression ignition nonroad engines. This approach is consistent

with the approach used by EPA in modeling emissions from highway compression ignition

engines. However, recent preliminary test results suggest that nonroad diesel engines may

experience significant rates of deterioration. In a 1997 test program conducted by Southwest

Research Institute for OMS 15, nine late-model, in-use nonroad diesel engines were tested. Four

of the engines had significant problems necessitating repairs. Manifold or turbocharger leaks

were found in all four of the malmaintained engines; two of the engines also required other

repairs to the fueling system in addition to the leaks. Leaks in the manifold or turbocharger

would affect the functionality of the turbocharger and would likely increase emissions. The

manifold leaks made it impracticable to perform emission measurements on these engines, so

repairs were required before emissions testing. Therefore, it is likely that the measured emissions

and fuel consumption of these engines underestimated their in-use emissions. EPA expects to

have a testing program commencing soon that will investigate deterioration rates in nonroad

compression ignition engines. The NEEMT hopes to incorporate the data from this testing

program in future versions of NONROAD and, if time and resources allow, in the final version

of NONROAD.
35

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

2. See endnote 1.

3. Regulatory Impact Analysis and Regulatory Support Document, Control of Air Pollution; Emission

Standards for New Nonroad Spark-Ignition Engines At or Below 19 Kilowatts, Office of Air and Radiation,

Office of Mobile Sources, A-93-25, May 1995, section C.1.1, p. C-4.

4. Regulatory Impact Analysis and Regulatory Support Document, Control of Air Pollution; Emission

Standards for New Nonroad Spark-Ignition Engines At or Below 19 Kilowatts, Office of Air and Radiation,

Office of Mobile Sources, A-93-25, May 1995, Section 5.4.2.

5. Nonroad Engine and Vehicle Emission Study - Report and Appendices, USEPA, Office of Air and Radiation, Office of

Mobile Sources, 21A-2001, November 1991.

6. Documentation of Input Factors For The New Off-Road Mobile Source Emissions Inventory Model,

Prepared for the California Air Resources Board by Energy and Environmental Analysis, Inc., August 1995,

p. 6-21.

7. Fax sent to NEEMT on 4/3/98 from Archana Agrawal of the California Air Resources Board. The fax

contains tables of the official adopted deterioration rates in the California OFFROAD model as of 3/26/98.

8. Regulatory Impact Analysis and Regulatory Support Document, Control of Air Pollution; Emission

Standards for New Nonroad Spark-Ignition Engines At or Below 19 Kilowatts, Office of Air and Radiation,

Office of Mobile Sources, A-93-25, May 1995, Appendix C.

9. A slight discrepancy exists between NEVES and the small engine nonroad regulation concerning the

classification of small versus large spark ignition engines. The NEVES report divided smaller and larger

The EPA/EMA testing program mentioned above in Section VI.B.1 tested on-highway

heavy-duty diesel engines as well as heavy duty gasoline engines. The results of this testing

showed no increase in HC or NOx and only a slight increase in PM as engines aged. These

results are reflected in EPA’s MOBILE emissions models and the Nonroad Emissions Model

(developed to support EPA’s 1997 proposed nonroad diesel engine standards), both of which

assume that diesel engines experience no emissions deterioration. The California ARB

incorporates diesel engine deterioration rates in its OFFROAD model that were derived from onhighway data in the California ARB’s EMFAC model. The same concerns regarding the

relevance of highway engine emissions testing data to nonroad engine deterioration rates

discussed in Section VI.C also apply to nonroad diesel engines. The NEEMT is not aware of any

nonroad diesel emissions testing programs that were designed to isolate the effects of

deterioration and that could be used to confirm or refute the EPA/EMA and California ARB test

results.

Endnotes
36

four-stroke and two-stroke engines at 20 horsepower. The regulations that have been promulgated since the

publishing of NEVES set the dividing point at 25 horsepower (19 kilowatts). 

10. EPA Regulatory Support Document, Phase 2: Emission Standards for New Nonroad Spark-Ignition

Engines At or Below 19 Kilowatts, Appendix F: Nonroad Small Engine Emission Model Tables, Tables F05 and F-06, December 1997.

11. Nonroad Engine and Vehicle Emissions Study, November 1991, Appendix I, Table I-14, p. I-61.

12. The first and second phases of the small engine rule did not address PM emissions.

13. Nonroad Engine and Vehicle Emission Study, USEPA, Office of Air and Radiation, Office of Mobile Sources, 21A2001, November 1991, Appendix I, p. I-12, Section 2.2.1.

14. Recreated from Table 6-9, p. 6-22, in Documentation of Input Factors For The New Off-Road Mobile

Source Emissions Inventory Model, Prepared for the California Air Resources Board by Energy and

Environmental Analysis, Inc., August 1995

15. Fritz, S. G., Emission Factors for Compression Ignition Nonroad Engines Operated on Number 2 Highway

and Nonroad Diesel Fuel, Southwest Research Institute. EPA EPA 420-R-98-001, March 1998.
37

Appendix 1

SwRI In-Use Small Utility Engine Test Results

Engine Test HC

g/hp-hr

HC

test/EF

CO

g/hp-hr

CO

test/EF

NOx

g/hp-hr

NOx

test/EF

PM

g/hp-hr

PM

test/EF

4-Stroke

2 yr. WBM 1A 67.9 1.80 650 1.51 0.94 0.47 1.35 1.80

4 yr. WBM 1A 83.9 2.23 928 2.16 0.37 0.18 1.11 1.48

2A 112.6 2.99 1033 2.40 0.47 0.23 2.05 2.73

8 yr. WBM 1A VOID VOID VOID VOID VOID VOID VOID VOID

2A 77.3 2.05 835 1.94 0.90 0.45 6.27 8.36

3A 74.9 1.99 829 1.93 0.71 0.35 4.08 5.44

New Engine EFs 37.7 430 2.02 0.75

In-use adjustment (avg. test/EF) 2.10 1.90 0.40 3.60

2-Stroke

11 yr. WBM 1 187 0.90 415 0.85 0.51 1.76 5.75 0.75

2 177 0.85 418 0.86 0.52 1.79 6.61 0.86

New Engine EFs 208 486 0.29 7.7

4 yr. String Trimmer 1 1369 6.11 2244 3.11 0.77 0.86 61.3 15.36

2 1205 5.38 1936 2.68 0.69 0.77 54.3 13.61

New Engine EFs 224 722 0.90 3.99
38

Appendix 2

Baseline and In-Use Emissions Numbers from EPA’s 1991 Nonroad Study 

Equipment Category Baseline

(g/kw-hr)

In-Use

(g/kw-hr)

In-Use

Factor

Adjusted In-Use

Factors

HC CO NOx HC CO NOx HC CO NOx HC CO NOx

4-Stroke Engines 2.1 1.9 0.4 2.1 1.9 0.4

Lawnmowers 50.5 576.4 2.71 106.13 1095.17 1.09

Trimmers/Edgers/Brush

Cutters

32.41 527.27 2.71 68.07 1001.81 1.09

Chainsaws NA NA NA NA NA NA

Leaf Blower/Vacuum 26.01 509.79 2.72 54.61 968.59 1.09

Generator Sets 12.73 473.19 2.72 26.74 899.06 1.09

Tillers 50.54 576.41 2.71 106.13 1095.17 1.09

Snowblowers 50.54 576.41 2.71 106.13 1095.17 1.09

Commercial Turf 12.6 474.53 2.83 26.46 901.61 1.13

Rear Engine Riders 12.47 473.19 2.72 26.18 899.06 1.09

Lawn and Garden Tractors 12.6 474.53 2.83 26.46 901.61 1.13

Pumps 12.47 473.19 2.72 26.18 899.06 1.09

All Other Equipment 2.1 1.9 1.0 1.2 1.9 1.0

2-Stroke Engines

Lawnmowers 278.82 486 0.39 585.52 1237.8 0.39

Trimmers/Edgers/Brush

Cutters

301.1 728.22 1.22 632.14 1854.72 1.22

Chainsaws 399.46 699 1.29 842.9 1780.29 1.29

Leaf Blower/Vacuum 288.59 716.81 1.29 606.05 1825.66 129

Generator Sets 278.82 486 0.39 585.52 1237.8 0.39

Tillers 278.82 486 0.39 585.52 1237.8 0.39

Snowblowers 278.82 486 0.39 585.52 1237.8 0.39

Commercial Turf 278.82 486 0.39 585.52 1237.8 0.39

Rear Engine Riders NA NA NA NA NA NA

Lawn and Garden Tractors NA NA NA NA NA NA

Pumps 5.74 113 9.44 12.05 287.8 3.78

All Other Equipment

N/A=Not Applicable

Note: All Other Equipment includes the following: Distributed Loose Engines, Commercial Turf Equipment, Other Lawn and Garden, Wood

Splitters, Pressure Washers, Front Mowers, Welders, Specialty Vehicles and Carts, Shredders, Cement/Mtr Mixers, Golf Carts, Paving

Equipment, Air Compressors, and Sprayers.