EPA-420-P-98-025
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
engine meets a required emission standard as defined by a regulation. Median life, as used in this
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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 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 after-
treatment 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.
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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 = EF0 * DF (1)
where: EF (aged) is the emission factor for an aged engine
EF0 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
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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 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 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
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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 ARE 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 atin.useload
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 atin.useload = 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 - EF0)/EF0] * [1 - exp(-3 * (Age Factor})] (3)
-------
where EFf = emission factor for a fully aged engine
EF0 = 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-EF0)/EF0] (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)a5 (6)
where C = A constant derived from a best-fit regression based on
manufacturer test data
Hourstotal = Engine Age * Annual hours of use
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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 ARE 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.
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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 four-
stroke 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, Ml0, Mil, Ml2, and Ml6 depending on the
specific control technology and application (outboard, personal water craft or inboard).
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Table 1
Class 1 (Displacement < 225 cc) Nonhandheld Deterioration Factor A
Engine Tech Type
G2N1 (gas 2-stroke nonhandheld Class 1, baseline)
G4N1S (gas, side-valve, 4-stroke nonhandheld Class 1,
baseline)
G4N1O (gas, overhead valve, 4-stroke nonhandheld Class 1,
baseline)
G2N1 (2-stroke, Phase 1)
G4N1S1 (Phase 1 side-valve, 4-stroke)
G4N1O1 (Phase 1 overhead valve, 4-stroke)
G4N1SC1 (Phase 1 side-valve, 4-stroke with catalyst)
G4N1S2 (Phase 2 side-valve, 4-stroke)
G4N1O2 (Phase 2 overhead valve, 4-stroke)
HC
0.201
1.1
1.1
0.266
5.103
1.753
5.103
5.103
1.753
CO
0.199
0.9
0.9
0.231
1.109
1.051
1.109
1.109
1.051
NOx
0
-0.6
-0.6
0
-0.33
-0.30
-0.33
-0.33
-0.30
PM
0
1.1
1.1
0
5.103
1.753
5.103
5.103
1.753
BSFC
0
0
0
0
0
0
0
0
0
Table 2
Class 2 (Displacement >225 cc; Power Rating < 25 hp) Nonhandheld Deterioration Factor A
Engine Tech Type
G2N2 (gas 2-stroke nonhandheld Class 2, baseline)
G4N2S (gas, side-valve, 4-stroke nonhandheld Class 2,
baseline)
G4N2O (gas, overhead valve, 4-stroke nonhandheld Class 2,
baseline)
G4N2S1 (Phase 1 side-valve, 4-stroke with catalyst)
G4N2O1 (Phase 1 overhead valve 4-stroke)
G4N2S2 (Phase 2 side-valve)
G4N1O2 (Phase 2 overhead valve)
HC
0.201
1.1
1.1
1.935
1.095
1.935
1.095
CO
0.199
0.9
0.9
0.887
1.307
0.887
1.307
NOx
0
-0.6
-0.6
-0.274
-0.599
-0.274
-0.599
PM
0
1.1
1.1
1.935
1.095
1.935
1.095
BSFC
0
0
0
0
0
0
0
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Table 3
Class 3 (Displacement < 20cc) Handheld Deterioration Factor A
Engine Tech Type
G2H3 (gas 2-stroke handheld Class 3, baseline)
G2H31 (Phase 1)
G2H3C1 (Phase 1 with catalyst)
G2H32 (Phase 2)
G2H3C2 (Phase 2 with catalysts)
HC
0.2
0.24
0.24
0.24
0.24
CO
0.2
0.24
0.24
0.24
0.24
NOx
0
0
0
0
0
PM
0
0
0
0
0
BSFC
0
0
0
0
0
Table 4
Class 4 (20cc < Displacement < 50 cc) Handheld Deterioration Factor A
Engine Tech Type
G2H4 (gas 2-stroke handheld Class 4, baseline)
G2H41 (Phase 1)
G2H4C1 (Phase 1 with catalyst)
G4H41 (Phase 1 4-stroke)
G2H42 (Phase 2)
G2H4C2 (Phase 2 with catalyst)
G4H42 (Phase 2 4-stroke)
HC
0.2
0.29
0.29
1.1
0.29
0.29
1.1
CO
0.2
0.24
0.24
0.9
0.24
0.24
0.9
NOx
0
0
0
-0.6
0
0
-0.6
PM
0
0
0
1.1
0
0
1.1
BSFC
0
0
0
0
0
0
0
Table 5
Class 5 (Displacement > 50cc; Power Rating <25 HP) Handheld Deterioration Factor A
Engine Tech Type
G2H5 (gas 2-stroke handheld Class 5, baseline)
G2H51 (Phase 1)
G2H5C1 (Phase 1 with catalyst)
G2H52 (Phase 2)
G2H5C2 (Phase 2 with catalyst)
HC
0.2
0.266
0.266
0.266
0.266
CO
0.2
0.231
0.231
0.231
0.231
NOx
-0.031
0
0
0
0
PM
0
0
0
0
0
BSFC
0
0
0
0
0
B. Other Sources of Deterioration Rates for Spark Ignition Engines At or Below 25
Horsepower
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TheNEEMT 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 four-
stroke 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 four-
stroke 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
Uncontrolled
Tierl
Tier 2
Uncontrolled
Tierl
Uncontrolled
Tierl
Tier 2
Model Yr.
pre-95
1995-99
2000+
pre-95
1995-99
2000+
pre-95
1995-99
2000+
HP
0-2
2-15
15-25
HCDR
0
0
0.2513
0
0
0.2513
0
0
0.2513
CODR
0
0
0
0
0
0
0
0
0
NOxDR
0
0
0
0
0
0
0
0
0
PMDR
0
0
0.01117
0
0
0.00808
0
0
0.00808
11
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Table 6b
Small Engine (<25hp) Spark Ignition Four-Stroke OFFROAD Deterioration Rates
Standards
Uncontrolled
Tierl
Tier 2
Uncontrolled
Tierl
Tier 2
Uncontrolled
Tierl
Tier 2
Model Yr.
pre-95
1995-96
1997-99
2000-03
pre-95
1995-96
1997-99
2000-03
pre-95
1995-96
1997-99
2000-03
HP
0-5
5-15
15-25
HCDR
0.0948
0.0565
0.0565
0.0144
0.0178
0.0207
0.0207
0.0047
0.0141
0.0166
0.0166
0.0049
CODR
0.5196
-0.067
-0.067
-0.3849
0.0337
0.0895
0.0895
0
0.0276
0.0345
0.0345
0
NOxDR
0.0002
0.0031
0.0031
0.0065
0.0013
0
0
0.0035
0.0011
0
0
0.0032
PMDR
0.0026
0.0026
0.0026
0.0026
0.0002
0.0002
0.0002
0.0002
0.0002
0.0002
0.0002
0.0002
2. EPA Phase 1 Small Engine Model (NSEEMn
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
12
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deterioration rates for two-stroke spark ignition engines from the ones found in the
NEVES report.
3. EPA Phase 2 Small Engine Model (NSEEM2N)
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
Phase 1
Res.
HC
CO
NOx
Phase 1
Com.
HC
CO
NOx
Phase 2
Res.
HC
CO
NOx
Phase 2
Com.
HC
CO
NOx
G2H3
0.002
0.002
0.000
0.0003
0.0003
0.0000
0.002
0.002
0.000
0.0003
0.0003
0.0000
G2H4
0.002
0.002
0.000
0.0003
0.0003
0.0000
0.002
0.002
0.000
0.0003
0.0003
0.0000
G2H5
0.002
0.002
0.000
0.0003
0.0003
0.0000
0.002
0.002
0.000
0.0003
0.0003
0.0000
G2N1
0.000
0.002
0.000
0.000
0.002
0.000
0.000
0.000
0.000
0.000
0.000
0.000
G2N2
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
G4N10
0.050
0.022
0.030
0.0245
0.0110
0.0147
0.050
0.022
0.030
0.0245
0.0110
0.0147
G4N1S
0.1300
0.0220
0.0200
0.0637
0.0110
0.0098
0.1300
0.0220
0.0200
0.0637
0.0110
0.0098
G4N20
0.0800
0.0110
0.0200
0.0566
0.0080
0.0141
0.0280
0.0110
0.0060
0.0198
0.0080
0.0042
G4N2S
0.0400
0.0110
0.0200
0.0283
0.0080
0.0141
0.0400
0.0110
0.0200
0.0283
0.0080
0.0141
G4H4
0.1840
0.0020
0.0230
0.0751
0.0008
0.0094
0.1840
0.0020
0.0230
0.0751
0.0008
0.0094
13
-------
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
14
-------
Table 8
Phase 2 Small Engine Rule Average Annual Use and Load Factor
Equipment
LN MOWERS
LN MOWERS
TRIM/EDGE CUTTER
TRIM/EDGE CUTTER
CHAINSAWS
CHAINSAWS
LEAF BLOW/VAC
LEAF BLOW/VAC
GENERATOR SETS
GENERATOR SETS
TILLERS
TILLERS
SNOWBLOWERS
SNOWBLOWERS
COMMTURF
COMMTURF
REAR ENG RIDER
REAR ENG RIDER
LN/GROUND
TRACTOR
LN/GROUND
TRACTOR
PUMPS
PUMPS
ALL OTHER
EQUIPMENT
ALL OTHER
EQUIPMENT
Use
res
prof
res
prof
res
prof
res
prof
res
prof
res
prof
res
prof
res
prof
res
prof
res
prof
res
prof
prof
res
Hr/Year*Load Factor
8.38
134.12
4.55
68.64
6.25
151.25
4.8
141.14
6.08
97.36
6.69
188.64
2.97
47.49
NA
340.85
13.5
216.07
19.84
317.37
9.34
149.44
7.3
116.84
Hr/Yea
r
25.4
406.42
9.1
137.29
12.5
302.5
9.59
282.29
8.95
143.18
16.73
471.6
8.48
135.68
NA
681.69
35.54
568.6
45.08
721.31
13.54
216.58
14.61
233.68
B50
5.8
2
4.3
2.3
4.3
0.9
4.3
2.3
5.8
2.3
5.8
4.4
4.4
4.4
NA
2.9
5.8
2.9
5.8
2.9
5.8
2.3
5.8
2.3
4. Nonroad Engine and Vehicle Emissions Study (NEVES)
15
-------
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 four-
stroke 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 two-
strokes. These consistent test results prompted NEVES' authors to use a deterioration
16
-------
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 four-
stroke 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
17
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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 pre-
controlled 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 on-
highway 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
18
-------
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 pre-
control 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
19
-------
Table 9
California ARE Deterioration Rates For Four-Stroke
Spark-Ignition Engine Over 25 Horsepower
(Percent increase per percent of median life)
HP
Category
25 to 50
50 to 120
120+
Equivalent
On-hwy.
None
LDGT
HDGV
On-hwy.
MYR
N/A
1969
NCAT
1970
NCAT
On-hwy.
Useful Life
N/A
120,000
120,000
Off-hwy.
HC d.f.
1.38%
1.38%
0.37%
Off-hwy.
CO d.f.
0.83%
0.83%
0.56%
Off-hwy.
NOx d.f.
0.064%
0.064%
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 two-
stroke 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.
20
-------
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 spark-
ignition 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
ofNONROAD.
21
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The EPA/EMA testing program mentioned above in Section VLB. 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 ARE
incorporates diesel engine deterioration rates in its OFFROAD model that were derived from on-
highway 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 ARE test
results.
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-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.I.I, 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
22
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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 F-
05 and F-06, December 1997.
11. Nonroad Engine and Vehicle Emissions Study. November 1991, Appendix I, Table 1-14, p. 1-61.
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, 21A-
2001, November 1991, Appendix I, p. 1-12, 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.
23
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Appendix 1
SwRI In-Use Small Utility Engine Test Results
Engine
4-Stroke
2 yr. WBM
4 yr. WBM
8 yr. WBM
New Engine EFs
In-use adjustment (avg. test/EF)
2-Stroke
llyr. WBM
New Engine EFs
4 yr. String Trimmer
New Engine EFs
Test
1A
1A
2A
1A
2A
3A
1
2
1
2
HC
g/hp-hr
67.9
83.9
112.6
VOID
77.3
74.9
37.7
187
177
208
1369
1205
224
HC
test/EF
1.80
2.23
2.99
VOID
2.05
1.99
2.10
0.90
0.85
6.11
5.38
CO
g/hp-hr
650
928
1033
VOID
835
829
430
415
418
486
2244
1936
722
CO
test/EF
1.51
2.16
2.40
VOID
1.94
1.93
1.90
0.85
0.86
3.11
2.68
NOx
g/hp-hr
0.94
0.37
0.47
VOID
0.90
0.71
2.02
0.51
0.52
0.29
0.77
0.69
0.90
NOx
test/EF
0.47
0.18
0.23
VOID
0.45
0.35
0.40
1.76
1.79
0.86
0.77
PM
g/hp-hr
1.35
1.11
2.05
VOID
6.27
4.08
0.75
5.75
6.61
7.7
61.3
54.3
3.99
PM
test/El
1.80
1.48
2.73
VOID
8.36
5.44
3.60
0.75
0.86
15.36
13.61
24
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Appendix 2
Baseline and In-Use Emissions Numbers from EPA's 1991 Nonroad Study
Equipment Category
HC
Baseline
(g/kw-hr)
CO
NOx
HC
In-Use
(g/kw-hr)
CO
NOx HC
I n -
Use
Factor
CO NOx
Adjusted In-Use
Factors
HC
2.1 1.9 0.4 2.1
50.5
32.41
NA
26.01
12.73
50.54
50.54
12.6
12.47
12.6
12.47
576.4
527.27
NA
509.79
473.19
576.41
576.41
474.53
473.19
474.53
473.19
2.71
2.71
NA
2.72
2.72
2.71
2.71
2.83
2.72
2.83
2.72
106.13
68.07
NA
54.61
26.74
106.13
106.13
26.46
26.18
26.46
26.18
1095.17
1001.81
NA
968.59
899.06
1095.17
1095.17
901.61
899.06
901.61
899.06
1.09
1.09
NA
1.09
1.09
1.09
1.09
1.13
1.09
1.13
1.09
2.1 1.9 1.0 1.2 1.9 1.0
4-Stroke Engines
Lawnmowers
Trimmers/Edge rs/Brush
Cutters
Chainsaws
Leaf Blower/Vacuum
Generator Sets
Tillers
Snowblowers
Commercial Turf
Rear Engine Riders
Lawn and Garden Tractors
Pumps
All Other Equipment
2-Stroke Engines
Lawnmowers
Trimmers/Edge rs/Brush
Cutters
Chainsaws
Leaf Blower/Vacuum
Generator Sets
Tillers
Snowblowers
Commercial Turf
Rear Engine Riders
Lawn and Garden Tractors
Pumps
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.
C NOx
O
1.9 0.4
278.82
301.1
399.46
288.59
278.82
278.82
278.82
278.82
NA
NA
5.74
486
728.22
699
716.81
486
486
486
486
NA
NA
113
0.39
1.22
1.29
1.29
0.39
0.39
0.39
0.39
NA
NA
9.44
585.52
632.14
842.9
606.05
585.52
585.52
585.52
585.52
NA
NA
12.05
1237.8
1854.72
1780.29
1825.66
1237.8
1237.8
1237.8
1237.8
NA
NA
287.8
0.39
1.22
1.29
129
0.39
0.39
0.39
0.39
NA
NA
3.78
25
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