1

Exhaust Emission Factors

 for Nonroad Engine Modeling--

Compression-Ignition

Report No. NR-009A

February 13, 1998

revised June 15, 1998

Megan Beardsley and Chris Lindhjem

U.S. EPA Office of Mobile Sources, Assessment and Modeling Division

Purpose

This report describes and documents exhaust emission factors used for compression

ignition (CI) engines in the U.S. Environmental Protection Agency’s (EPA) NONROAD

emission inventory model. It covers factors for all diesel-fueled engines. Emission factors for

spark ignition engines (including gasoline and natural gas/propane) are covered in a separate

report, NR-010. Other EPA reports will describe additional issues relating to emission factors

including adjustments to emission rates due to variations in fuel and temperature (NR-001) and

adjustments to emission rates as equipment deteriorates with time and use (NR-011).

Introduction

The NONROAD model estimates air pollution from more than 80 types of compression

ignition (CI) and spark ignition (SI) nonroad sources including such items as lawnmowers,

motorboats, portable generators and construction equipment. By bringing together information

on equipment populations, equipment use, and emission factors, the NONROAD model

estimates mass emissions of hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx),

sulfur dioxide (SO2), particulate matter (PM) and carbon dioxide (CO2) for specific states and

counties for past and future years, providing a flexible tool that can be applied to a wide variety

of air quality modeling and planning functions. 

The NONROAD calculations rely on emission factors--estimates of the amount of

pollution emitted by a particular type of equipment during a unit of use. Typically emission

factors for nonroad sources are reported in grams per horsepower-hour, but they also may be

reported in grams per mile, grams per hour, and grams per gallon. The emission factors in the

NONROAD model are based on emissions test data, adjusted when necessary to account for the

effects of fuel sulfur and in-use operation that differ from the typical test conditions. Emission
2

factors are stored in NONROAD’s data input files. Emission changes with the age of the engine,

often called ‘deterioration,’are described in Report No. NR-011.

Currently EPA is preparing a version of the NONROAD model. A final version of

NONROAD is planned for release late in 1998. EPA expects to use the CI emission factors

described here in both the and the final version of the model. If comments on this document or

other information gathered during stakeholder and peer review cause us to rethink this approach,

we will document the changes in a subsequent report.

Background

There is little test data available on nonroad engines. In developing the emission factors

for NONROAD we have considered data from various sources. 

Previous Inventories

Prior to the NONROAD model, there have been three major efforts to estimate nonroad

emission inventories from CI engines. These are:

 EPA’s Nonroad Engine and Vehicle Emission Study (“NEVES”).[1] Published in

November, 1991, this study was mandated by Congress to determine whether nonroad

sources made a significant contribution to urban air pollution. It covers HC, CO, NOx,

PM, SOx and other pollutants. It provides inventories for 19 ozone and 16 CO

nonattainment areas.

 California Air Resources Board’s (ARB) nonroad model (“OFF-ROAD”) [2], designed to

estimate nonroad emissions for the state of California only. A version of this model was

released in late summer 1997. It covers HC, CO, NOx, PM, SO2, and CO2.

 EPA’s “Nonroad Engine Model”-- Designed as an internal tool for analyzing various

control scenarios, EPA has used this model primarily to estimate the effect of recently

proposed regulations on emissions from compression-ignition (CI) engines over 37 kW

(50 hp).[3] The model computes national-level inventories of nonroad diesel HC, NOx,

CO and PM.

All of these models/studies estimate emissions from uncontrolled engines. The

California model also includes California emission standards, and the EPA’s Nonroad Engine

Model includes proposed Federal emission standards. The sources of the emission factors used

in these inventories are described in Appendix A. Many of the emission factors are based on

data from the 1970s and early 1980s.

New Data
3

In addition to the data considered in developing previous emission factors, there is a

limited amount of new emission test data on newer (post-1988) uncontrolled engines. The post1988 engines were not designed to meet any new emission regulations, but the test data indicates

that emissions from these post-1988 engines (especially hydrocarbons and particulate matter) are

lower than the emission factors used in earlier inventories. EPA’s review of this data is

described in Appendix B.

Emission Standards

In addition to estimating emissions from uncontrolled engines, the NONROAD model is

designed to account for the effect of federal emissions standards. NONROAD will not cover

California emission standards or proposed federal standards that are not yet final. However,

because EPA expects to finalize a set of recently proposed standards for nonroad diesel engines

before the release of the final NONROAD model, these proposed standards have been included

in the version of the model. Thus, this document describes emission factors under two

regulations that establish three tiers of emission standards:

 “Determination of Significance for Nonroad Sources and Emission Standards for New

Nonroad Compression Ignition Engines at or above 37 Kilowatts.” This rule establishes

“Tier 1” standards for CI engines at or above 50 hp (37 kW). [4]

 “Control of Emissions from Nonroad Diesel Engines.” This proposed rule lists “Tier 1”

and “Tier 2” standards for CI engines below 50 hp, and “Tier 2” and “Tier 3 ” standards

for engines of 50 hp and greater. [5] “ ”

Of course, if changes are made to the proposed rule, the final version of the model will

reflect those changes. The standards are phased in over a number of years, and NONROAD’s

emission factors will follow the final schedule implementing the new standards.

The NONROAD emission factors for engines subject to the existing and proposed rules

are based on the factors used in the regulatory support documents for the proposed rule, “Draft

Regulatory Impact Analysis: Control of Emissions from Nonroad Diesel Engines.” However, as

explained below, the NONROAD model’s emission factors for pre-control engines differ from

the RIA in their use of EPA’s new data on cleaner post-88 engines. 

Steady State Emission Factors--HC, CO, NOx and PM

Nonroad engines are primarily tested with steady-state tests. However, the steady-state

operation typically used for emission testing is not always representative of the operation of

engines in many nonroad applications. Some of the differences can be due to load or engine

speed, and other differences can be due to transient demands. We will apply “in-use adjustment

factors” to the emission factors derived from steady state tests. The derivation and application of
4

these factors are described in Appendix C. EPA will create input files for NONROAD by

applying in-use adjustment factors to the steady-state emission factors described in this section.

 The remainder of this section describes steady-state fuel consumption and emission

factors for HC, CO, NOX and PM. These factors are listed in Table 1. We have used engine

model year and horsepower as categories to group NONROAD emission factors. These

groupings are consistent with emission standards for CI engines and with emissions test data.

Data on pre-controlled engines (see Appendix B) indicates that engines of more than 100 hp have

significantly different emission characteristics than engines under 100 hp. Perhaps for future

versions of NONROAD, emission factors may be distinguished by technologies such as turbocharging, fuel metering pumps, and cylinder size; however, there is not enough emissions data at

present to support such distinctions in NONROAD emission factors.

Fuel sulfur levels affect PM emissions. NONROAD users can adjust for local fuel sulfur

levels, but the model has a default diesel fuel sulfur level of 0.33 mass percent, the national

average for nonroad diesel [6], and the emission factors in NONROAD’s input files are intended

to be consistent with the default fuel sulfur level. Where emission tests were known to have been

performed with fuels with other sulfur contents the test results have been adjusted as described in

Appendix B.

Due to lack of data, the brake-specific fuel consumption (BSFC) for the 1988-and-later

uncontrolled engines is used for all engines, both earlier uncontrolled engines and later engines

subject to emissions standards. While it is likely that fuel consumption varies between these

categories, there is not sufficient data available at this time for EPA to specify alternate values.

Pre-1988, Engines < =50 hp: 

There are no known tests of pre-1988 CI engines of less than 50 hp. Thus NONROAD

will use the same emission factors as for the 1988 through Tier 1 years for engines of this size

described below.

 

Pre-1988, Engines > 50 hp:

 For pre-1988 CI engines of 50 hp or greater, NONROAD’s steady-state emission factors

are based on the emission factors used in NEVES. These vary by application. However, NEVES

includes an adjustment for in-use operation. Since NONROAD uses a different in-use

adjustment factor than NEVES (see Appendix C), the NEVES adjustment is removed to

determine pre-1988 average steady-state emissions.

Because the testing fuel is generally unknown, we assume that the NEVES PM factors are

appropriate for the default fuel sulfur content of 0.33 wt.% sulfur used in NONROAD.

A conversion from gram per gallon to gram per horsepower-hr was made to NEVES

emission rates for the greater than 50 horsepower engines for the diesel recreational marine

categories; inboard, outboard, and sailboat auxiliary. Outboard and sailboat auxiliary engines
5

above 50 hp were converted from the NEVES gram per gallon to gram per horsepower using the

higher fuel consumption of 0.408 lbs/hp-hr and 7.1 lbs/gallon fuel density because these engines

are primarily less than 100 hp. The NEVES emission rate for inboard engines was converted

using the lower fuel consumption rate of 0.367 lbs/hp-hr because these engines are primarily

above 100 horsepower.

1988 to Tier 1, Engines <= 50 hp:

For 1988-and-later pre-control engines less than or equal to 50 hp, we will use the

emission factors described in the documentation for ARB’s OFF-ROAD model. [2] We have

combined the direct injection and indirect injection factors using the technology fractions listed

in the EPA’s Regulatory Impact Analysis (RIA) for the proposed new emission standards. [5]

Again, because the sulfur content of fuels used in generating these emission factors is unknown,

we have assumed that the PM emission factors are appropriate for default fuel sulfur of 0.33%

sulfur.

1988 to Tier 1, Engines > 50 hp:

Recent studies have indicated that, in general, emission rates from 1988-and-later precontrol engines of greater than 50 hp are lower than the rates used in NEVES, necessitating a

revision to the NEVES emission factors.

For these engines we will use emission factors calculated from recent studies. These

studies are described in detail in Appendix B. As explained in Appendix B, a correction for fuel

sulfur content is applied.

Tier 1, Engines < =25 hp

The NONROAD model’s emission factors for Tier 1 <25 hp are based on data from

ARB, which already regulates engines <25 hp. EPA expects engines meeting federal Tier 1

standards to employ similar technology and emit at similar levels. As described in the RIA, EPA

weighted the California data using the national fractions of direct and indirect injection engines

for this size category. [5]

HC and NOx -- California certification data was used to split the combined HC+NOx

standard into single pollutant emission factors.

CO -- California certification data was used.

PM -- Emission factors for PM are estimated to be the Tier 1 standard for PM. We

assume that engines will meet the standard on default sulfur fuel.

Tier 1, Engines 25-50 hp

Data is not available on engines meeting this proposed standard. As in the RIA, emission

factors were estimated based on California data on smaller engines, but weighted to reflect the

estimated national fractions of direct and indirect injection engines for this size category . [5]
6

HC and NOx -- California certification data for engines 11-25 hp was used to split the

combined HC-NOx standard into single pollutant emission factors.

CO -- California certification data for engines 11-25 hp was used.

PM -- Emission factors for PM are estimated to be the Tier 1 standard for PM. We

assume that engines will meet the standard on default sulfur fuel.

Tier 1, Engines 50-175 hp

EPA has limited Tier 1 certification data on Tier 1 engines 50-175 hp.

NOx--EPA estimates that Tier 1 NOx emissions are at the Tier 1 standard. 

HC and CO--Emission factors are estimated using EPA’s Tier 1 certification data. 

PM--Because no emission standard was promulgated for Tier 1, PM emissions for precontrol, 1988-and-later engines were used. 

Tier 1, Engines >175 hp

EPA has limited Tier 1 certification data on Tier 1 engines > 175 hp.

NOx--EPA estimates that Tier 1 NOx emissions are at the Tier 1 standard. 

HC and CO--Emission factors are estimated using EPA’s Tier 1 certification data. 

PM--Because pre-Tier 1 PM emissions were below the Tier 1 standard (when the

standard was adjusted for fuel sulfur), we have assumed that Tier 1 PM emissions are at

the same PM levels as pre-control, 1988-and-later engines. 

Tier 2, Engines < =50 hp

Data is not available on engines meeting this proposed standard. Emission factors were

estimated as in the RIA based on ARB data.

HC and NOx--As in the RIA, EPA assumes minimum HC emissions of 0.6 g/hp-hr (0.8 

g/kW-hr) based on ARB data on indirect injection (IDI) engines under 25 hp (19 kW). 

EPA used this value to split the combined HC+NOx standard into single pollutant

emission factors.

CO--The same as under Tier 1.

PM–Because of uncertainties in PM emissions, NONROAD does not estimate a reduced

PM emission rate from the Tier 1 level at this time. EPA will continue to evaluate this

emission rate based on available data.

Tier 2, Engines > 50 hp

Data is not available on engines meeting this proposed standard.

NOx and HC--As in the RIA, NONROAD uses the proposed European NOx standard to

split the Tier 2 combined HC+NOx standard into single pollutant emission factors.

CO-- The same as under Tier 1. 

PM–Because of uncertainties in PM emissions, NONROAD does not estimate a reduced
7

PM emission rate from the Tier 1 level at this time. EPA will continue to evaluate this

emission rate estimate based on available data. 

Tier 3

The proposed Tier 3 standard applies only to engines greater than 50 hp and less than or

equal to 750 hp. Data is not available on engines meeting this proposed standard.

NOx and HC--For Tier 3 HC and NOx, NONROAD follows the RIA in using

engineering judgement to assume minimum HC emissions of 0.2 g/hp-hr. This rate is

then subtracted from the combined HC+NOx standard to split the standard into singlepollutant emission factors.

CO–We estimate at this time that CO will be the same as Tier 1.

PM–EPA has not yet established the Tier 3 PM standards. Therefore, we are estimating

the same credit as Tier 2.
8

Table 1--Steady-State Emission Factors* for CI Engines in the NONROAD Model 

Engine

Power (hp)

Model

Year

Regulation BSFC 

(lb/hp-hr)

Emission Factors (g/hp-hr)

HC CO NOx PM

>0 to 11 pre-88 -- 0.408** 1.5 5.0 10.0 1.0

88-99 -- 1.5 5.0 10.0 1.0

00-04 Tier 1 1.6 5.6 5.9 0.75

05- Tier 2 0.6 5.6 5.0 0.75

>11 to 16 pre-88 -- 0.408** 1.5 5.0 10.0 1.0

88-99 -- 1.5 5.0 10.0 1.0

00-04 Tier 1 0.7 2.0 5.2 0.6

05- Tier 2 0.6 2.0 5.0 0.6

>16 to 25 pre-88 -- 0.408** 1.8 5.0 6.9 0.8

88-99 -- 1.8 5.0 6.9 0.8

00-04 Tier 1 0.7 2.0 5.2 0.6

05- Tier 2 0.6 2.0 5.0 0.6

>25 to 50 pre-88 -- 0.408** 1.8 5.0 6.9 0.8

88-98 -- 1.8 5.0 6.9 0.8

99-03 Tier 1 0.8 2.5 5.5 0.6

04- Tier 2 0.6 2.5 5.0 0.6

>50 to 100 pre-88 -- 0.408 Vary by application, see NEVES

88-97 -- 0.99 3.49 8.30 0.72

98-03 Tier 1 0.7 1.0 6.9 0.72

04-07 Tier 2 0.4 1.0 5.2 0.72

08- Tier 3 0.2 1.0 3.3 Same as Tier 2

>100 to 175 pre-88 -- 0.367 Vary by application, see NEVES

88-96 -- 0.68 2.70 8.38 0.40

97-02 Tier 1 0.4 1.0 6.9 0.40

03-06 Tier 2 0.4 1.0 4.5 0.40

07- Tier 3 0.2 1.0 2.8 Same as Tier 2
9

Table 1, continued.

Engine

Power (hp)

Model

Year

Regulation BSFC 

(lb/hp-hr)

Emission Factors (g/hp-hr)

HC CO NOx PM

>175 to 300 pre-88 Vary by application, see NEVES

88-95 0.68 2.70 8.38 0.40

96-02 Tier 1 0.4 1.0 6.9 0.40

03-05 Tier 2 0.4 1.0 4.5 0.40

06- Tier 3 0.2 1.0 2.8 Same as Tier 2

>300 to 600 pre-88 -- 0.367 Vary by application, see NEVES

88-95 -- 0.68 2.70 8.38 0.40

96-00 Tier 1 0.3 1.0 6.9 0.40

01-05 Tier 2 0.3 1.0 4.5 0.40

06- Tier 3 0.2 1.0 2.8 Same as Tier 2

>600 to 750 pre-88 -- 0.367 Vary by application, see NEVES

88-95 -- 0.68 2.70 8.38 0.40

96-01 Tier 1 0.3 1.0 6.9 0.40

02-05 Tier 2 0.3 1.0 4.5 0.40

06- Tier 3 0.2 1.0 2.8 Same as Tier 2

>750 pre-88 -- 0.367 Vary by application, see NEVES

88-99 -- 0.68 2.70 8.38 0.40 

00-05 Tier 1 0.3 1.0 6.9 0.40 

06- Tier 2 0.3 1.0 4.5 0.40

*Prior to listing in NONROAD input files, these ISO-C1 emission factors are adjusted for in-use 

operation as explained in Appendix C.

**BSFC for engines <50 hp is assumed to be the same as 50-100 hp engines

Emission Factors--CO2 and SO2

Emission factors for CO2 and SO2 are rarely measured, instead they typically are
10

calculated based on brake-specific fuel consumption (BSFC).

The NONROAD model uses in-use adjusted BSFC to compute CO2 emissions directly.

BSFC and engine activity provides the means to estimate the tons of fuel consumed. We

assumed that all of the carbon in the fuel is converted to CO2. The average carbon fraction of

the fuel is estimated to be 87%. This does not require a CO2 emission factors input file. 

The model does not require an SO2 emission factors input file either. EPA will calculate

SO2 emission factor as shown in the equation below.

 SO2 = (BSFC * 453.6* (1 - 0.022) - HC) * 0.0033 * 2

where

SO2 is in g/hp-hr

BSFC is the in-use adjusted fuel consumption in lb/hp-hr

453.6 is the conversion factor from pounds to grams

1-0.022 is an adjustment for sulfur converted to direct PM

HC is the in-use adjusted hydrocarbon emissions in g/hp-hr

0.0033 is the default wt. fraction of sulfur in nonroad diesel fuel

2 is the grams of SO2 formed from a gram of sulfur

This equation includes corrections for the fraction of sulfur that is converted to direct PM

and for the fraction of sulfur remaining in unburned fuel. The direct PM correction factor

(0.022) was calculated by assuming that the direct sulfur PM is H2SO4:7H20 (sulfuric acid

hydrated seven times) and converting the direct sulfur PM (described in Appendix B) to a molar

fraction of sulfur which is subtracted from the fuel consumption. We also assume that the

unburned fuel, as indicated by HC emissions, has the same sulfur level as the base fuel. 

References

[1] EPA, “Nonroad Engine and Vehicle Emission Study” (NEVES), U.S. EPA, Office of Air

and Radiation, 21A-2001. November, 1991.

[2] EEA, “Documentation of Input Factors for the New Off-Road Mobile Source Emissions

Inventory Model,” (“Inputs...”) Energy and Environmental Analysis, Inc. for California Air

Resources Board. February, 1997.

[3] Caffrey, P., “Memorandum: Operation of the Nonroad Emissions Model” from Peter

Caffrey, U.S. EPA Office of Mobile Sources, Engine Programs and Compliance Division, to the

Docket A96-40, Draft 6/13/97.

[4] 59 FR 31306, June 17 1994.
11

[5] EPA, “Draft Regulatory Impact Analysis: Control of Emissions from Nonroad Diesel

Engines.” U.S. EPA Office of Mobile Sources, Engine Programs and Compliance Division. 

August 1997.

[6] Korotney, David. “Estimates for In-Use Nonroad Diesel Fuel Levels,” Memorandum to

Docket A-96-40. July 1, 1997.
A1

Appendix A

Sources of Previous Emission Factors for

Nonroad Compression Ignition Engines

There is little test data available on nonroad engines. Table A1 lists the data sources used

for EPA’s Nonroad Engine and Vehicle Study’s (NEVES) diesel emission factors. These factors

were also used for EPA’s internal Nonroad Emission Model. Table A2 lists the data sources

used for California’s Air Resources Board (ARB) OFF-ROAD diesel emission factors. The

studies listed in the tables are described below. 

Table A1--Data sources for NEVES Diesel Emission Factors

Application Emissions Test 

Data Source

Notes

Lawn and Garden and

Light Commercial

None NEVES emission factors

were based on factors for

“continuous service diesel <

50 hp” SwRI, 1991, which

are based on Radian, 1988

factors for truck/container

refrigeration units.

Agriculture Cal/ERT, 1982

Construction EMA 

SwRI, 1973

Cal/ERT, 1982

NEVES emission factors

were based on EMA when

possible. For PM and for

applications not available

from EMA, factors were

taken from AP-42, which

relies on Cal/ERT for most

emission factors and on

SwRI, 1973 for PM and

SOx.

Logging (skidders) EMA 

Industrial and

Airport Service Equipment

SwRI, 1973

Recreational Marine

(Inboard)

NMMA
A2

Table A2--Data sources for ARB Diesel Emission Factors

Horsepower Class Emissions Test 

Data Source

Notes

0-15 hp Manufacturers’ data--

2 Yanmar engines

1 Deutz engine

15-25 hp Manufacturers (ARB OffRoad Equipment Study,

1990)

25-50 hp Manufacturers Submissions

(ARB Off-Road Equipment

Study, 1990 )

50-125 hp Manufacturers (CA HD

Construction Study, 1988)

125-250

250+

Manufacturers (CA HD

Construction Study, 1988)

ARB factors on all engines

from 125 hp and above are

based on the same data, but

the weighting between turbocharged and naturally

aspirated engines is different

in the two horsepower

categories listed here.

Description and Citations of Sources used for Previous Emission Factors

Radian, 1988. Radian’s estimates of HC, CO, NOx and PM for truck/container

refrigeration units are not based on testing, but on Radian’s estimates for “typical small

direct injection and indirect injection diesel engines.” (Weaver, C.S., “Feasibility and

Cost Effectiveness of Controlling Emissions from Diesel Engines in Rail, Marine,

Construction, Farm and Other Mobile Off-Highway Equipment.” Final Report by Radian

Corporation for U.S. EPA, Office of Policy Analysis, under contract 68-01-7288,

February, 1988.) 

SwRI, 1973. Southwest Research Institute tested 8 diesel engines for HC, CO, NOx and

PM. Emissions of SOx were calculated for no. 2 diesel fuel assuming sulfur content of

0.22%. BSFC is not stated. The emissions tests were given different weightings to

estimate industrial, construction and farm equipment emission factors. (Hare, C.T and

K.J. Springer. Exhaust Emission from Uncontrolled Vehicles and Related Equipment

Using Internal Combustion Engines, Final Report, Part 5, Heavy Duty Farm,
A3

Construction and Agricultural Engines. San Antonio TX: Southwest Research Institute,

October 1973.)

EMA. Emission factors for 17 applications based on unknown number of tests, unknown

horsepower engines. Engine vintage unknown, but data was submitted by the Engine

Manufacturers Association to EPA prior to NEVES (1991). (Listed in NEVES table I06.)

Cal/ERT, 1982. Data from 13 engine manufacturers representing 391 models of

construction equipment. Raw data was aggregated by an accounting firm prior to analysis

and reporting. (Environmental Research and Technology, Inc. “Feasibility, Cost and Air

Quality Impact of Potential Emission Control Requirements on Farm, Construction and

Industrial Equipment in California”, Document PA841, sponsored by the Farm and

Industrial Equipment Institute, Engine Manufacturers Association, and Construction

Industry Manufacturers Association, May 1982.)

NMMA. The National Marine Manufacturers Association submitted data to EPA on HC,

CO, NOx and BSFC for 3 diesel inboard motors. Engine vintage unknown, but data was

submitted to EPA prior to NEVES (1991). (NEVES, Table I-11(e).)

ARB Off-Road Study, 1990. A study of lawn and garden and utility emissions. 

(Manufacturer Submissions to ARB on Exhaust Emission Standards for Utility and Lawn

and Garden Equipment Engines. California ARB, October 1990. EPA requests

assistance in locating this study)

ARB Heavy Duty Construction Study, 1988.1

 Reports HC, NOx and PM emission factors

based on emission information from four manufacturers. Does not include information

on test programs. It is not clear how data collected in the study was used to create the

inputs for the ARB model. (Energy and Environment Analysis, Inc. “ Feasibility of

Controlling Emissions from Off-Road, Heavy-Duty Construction Equipment.” Final

Report to the California Air Resources Board. Arlington, VA, December 1988.)
B1

Appendix B

1988-1995 Steady-State Emission Factors and Fuel Sulfur Adjustment

for Nonroad Compression Ignition Engines

Introduction

EPA’s 1991 Nonroad Engine and Vehicle Emission Study (NEVES) (1) used emission

factors for diesel engines based primarily on tests of older engines. All the NEVES particulate

matter (PM) emission factors are from tests conducted in 1972 and many of the other emissions

factors in NEVES are based on data from tests prior to 1982.

To better characterize emissions from more recent, pre-controlled engines, EPA analyzed

available emission test data on 1988-1995 nonroad diesel engines. This analysis provides the

basis for NONROAD emission factors for 1988-and-later engines greater than 50 hp, as

described in the main body of this report. The analysis indicated a significant difference in

emissions based on engine power. Engines between 50 and 100 horsepower in general had

higher emissions and fuel consumption than engines larger than 100 horsepower. Table B1

summarizes these results.

Table B1-- Average Emission Test Results for 1988 to 1995 Model Year Engines

Engine

(Reference)

HC 

(g/hp-hr)

CO

(g/hp-hr)

NOx

(g/hp-hr)

PM 

(g/hp-hr)

BSFC 

(lb/hp-hr)

Average (50

to 100 hp)

0.99 3.49 8.30 0.722 0.408

Average

(>=100 hp)

0.68 2.70 8.38 0.402 0.367

A summary of test results for individual engines is presented in Table B2. Note that

testing was conducted using the current certification test procedure, also known as ISO-C1. The

procedure uses eight steady-state modes weighted by time to produce one number in units such as

grams per horsepower-hour. EPA adjusted this test data to account for differences between the

test fuel and typical in-use fuel sulfur levels of 0.33 wt. percent as explained below.
B2

Table B2--Summary of ISO-C1 Emission Results for 1988 through 1995 Engines

Engine

(Reference)

Model

Year

Age

(Hrs)

Fuel

Sulfur

(wt. %)

Power

Level

(hp)

HC 

(g/hp-hr)

CO 

(g/hp-hr)

NOx

(g/hp-hr)

PM 

(g/hp-hr)

BSFC

(lb/hp-hr)

Ford New

Holland (2)

1991 0 0.26 127 1.02 7.70 7.48 1.10 0.358

John Deere

7068T (2)

1990 0 0.26 139 0.45 2.98 11.74 0.41 0.349

Volvo TD

71G (avg. of

2) (3)

1984 0 0.046 144 0.47 1.64 12.68 0.149 0.373

Volvo TD73

KBE (avg. of

2) (3)

1992 0 0.046 139 0.64 0.85 4.52 0.12 0.386

Weterbeke

32BEDA (4)

1995 0 0.033 95 1.95 7.43 7.99 1.50 0.484

Caterpillar

3176B (4)

1995 0 0.033 451 0.09 2.94 6.37 0.213 0.358

Cummins

KTA19-M3

(4)

1995 0 0.033 599 0.68 3.26 8.78 0.257 0.359

Caterpillar

3306

(Nonroad) (5)

1990 0 0.26 285 1.1 1.4 6.5 0.18 0.354

Cummins 4BT

(Nonroad) (5)

1990 0 0.26 100 0.8 2.1 11 0.39 0.365

John Deere

4039D (6)

1991 0 0.25 72 0.6 3.5 7.2 0.59 0.385

Caterpillar

3116 (7)

1991 2,511 0.28 201 0.07 2.51 9.38 0.406 0.352

0.035 0.350

Caterpillar

3054 (7)

1991 1,964 0.28 85 0.66 1.00 7.53 0.387 0.393

0.035 0.340

John Deere 

4039 (7)

1994 2,265 0.28 86 0.41 2.17 11.22 0.384 0.389

0.035 0.256

John Deere 

7076 (7)

1993 3,300 0.28 174 0.53 2.05 10.22 0.250 0.385

0.035 0.205
(table continued from previous page)

B3

Consolidated

Diesel

6TA-830 (7)

1990 4,370 0.28 226 0.86 1.50 6.53 0.397 0.365

0.035 0.338

John Deere

6619 (7)

1993 4,970 0.28 275 0.82 4.69 7.29 0.662 0.397

0.035 0.556

Consolidated

Diesel 4039

(7)

1988 3,570 

 

0.28 71 1.32 3.37 7.57 0.581 0.389

0.035 0.484

Caterpillar

3306 (7)

1990 6,700 0.28 278 1.27 1.46 6.52 0.248 0.373

0.035 0.245

Average 

(50 to 100 hp)

0.33 0.99 3.49 8.30 0.722* 0.408

Average

(>=100 hp)

0.33 0.68 2.70 8.38 0.402* 0.367

* Adjusted to the national average fuel sulfur level of 0.33 weight percent

Fuel Sulfur Adjustment

PM emissions from diesel engines are highly dependent on the sulfur content of the fuel

the engine is burning. PM emissions from diesel engines are generally comprised of unburned or

partially burned fuel, engine oil, and sulfur compounds. When the engine burns fuel, the fuel

sulfur is oxidized to both sulfur dioxide and sulfur trioxide. The sulfur trioxide rapidly absorbs

water to form hydrated sulfuric acid which condenses and is collected on filters as particulate

matter (PM) during emission testing. 

Because the sulfur content of diesel fuel can vary considerably, it is important to account

for fuel sulfur in establishing emission factors for PM. To adjust emission test data to the default

sulfur level used in NONROAD (0.33 wt. percent), EPA followed the approach described below.

 EPA measured particulate emissions from nine nonroad diesel engines using fuel with

two different sulfur levels, a typical highway diesel fuel at a sulfur level of 0.035 weight percent

and a typical nonroad diesel fuel doped to a sulfur level of 0.28 weight percent to simulate more

closely the average nonroad diesel fuel sulfur level of 0.33 weight percent. Most data from this

study is listed in Table B2, above. In addition, the study included a 1997 John Deere nonroad

engine. This engine is not shown in Table B2 because it certified for the Tier 1 emission

regulations and should not be used to determine an overall emission factor for pre-controlled

engines. Its PM emissions for high and low sulfur levels were 0.186 and 0.129 g/hp-hr,

respectively, with an average fuel consumption of 0.350 lb/hp-hr. (7) Test results from this study
B4

(including all 9 engines tested) were used to determine the emission adjustment associated with

fuel sulfur level. Other fuel parameter differences such as cetane and fuel distillation that might

also have affected particulate emissions were ignored for this analysis. 

The study found that emissions of all pollutants were reduced by using highway fuel as

compared to the nonroad fuel; however, only the average PM reduction was statistically

significant at the 90% confidence level.

The particulate sulfur emission rate should be proportional to the fuel consumption and

the fuel sulfur level. By dividing the difference in particulate emissions by the fuel consumption,

EPA calculated the average effect of fuel sulfur levels for the nine engines. This analysis

provided the constant “A” in the equation below, which describes the relationship between

particulate emissions and fuel sulfur content, with the national average sulfur level of 0.33

weight percent (8) as the default sulfur level.

PMBase = PM + BSFC * A * (0.0033 - Fuel Sulfur)

where

PMBase = PM emissions with default fuel, in g/hp-hr

PM = PM emissions with test fuel, in g/hp-hr

BSFC = Brake Specific Fuel Consumption in g/hp-hr

A = 0.157 g PM/hp-hr/Weight Fraction sulfur/BSFC

0.0033= the default weight fraction of fuel sulfur for nonroad diesel

Fuel Sulfur = Weight Fraction of sulfur in test fuel

EPA then used this equation for all tests listed in Table B2 to correct PM emissions from

the test-fuel sulfur level to a fuel sulfur level of 0.33 wt.% before computing the averages listed

in Table B1 and at the bottom of Table B2. 

References

(1)“Nonroad Engine and Vehicle Emission Study” (NEVES), U.S. EPA, Office of Air and

Radiation, 21A-2001. November, 1991.

(2) Doorlag, M. and M. Samulski. “Heavy-Duty Engine Testing Report: Non-Road Engine

Configurations, Test Results 1991" EPA Technical Report, 1991.

(3) Hedbom, A. “Emission tests of two Volvo//VME Heavy Duty Off Road Engines.”

Motortestcenter, Hanige, Sweden. MTC 9307A. March. 1994.

(4) Carroll, J.N. and C. M. Urban. “Emission Testing of Nonroad Compression Ignition

Engines.” Draft Final Report. Southwest Research Institute, 6886-802. September 1995.
B5

(5) Fritz, S. G., “Dynamometer Testing of Heavy-Duty Diesel Engines to Support 

Non-Road Regulations,” SwRI Report No. 08-3426-010, Work Assignment 0-10 of 

EPA Contract No. 68-C0-0014 (September 1991).

(6) Smith, Michael. “Dynamometer Testing of Nonroad Diesel Engines to Support Nonroad

Regulations.” Southwest Research Institute, 08-4855-150, EPA Docket A-91-24, June 1992.

(7) Fritz, S. G., “Emission Factors for Compression Ignition Nonroad Engines Operated on

Number 2 Highway and Nonroad Diesel Fuel,” Southwest Research Institute. EPA contract #

68-C5-0077, SwRI 08-7601-822. Report expected 1998.

(8) Korotney, David. “Estimates for In-Use Nonroad Diesel Fuel Levels,” Memorandum to

Docket A-96-40. July 1, 1997.
C1

Appendix C

Adjustment for In-Use Operation of

Nonroad Compression Ignition Engines

Nonroad engines often operate under conditions unlike that of the steady-state ISO-C1

testing procedure typically used in emissions testing. This alternate operation can cause a change

in the emission characteristics of nonroad compression ignition (CI) engines. As in NEVES, the

NONROAD model accounts for in-use operation in CI engines by applying an adjustment to

emission factors generated using the ISO-C1 tests. Unlike NEVES, the NONROAD model uses

in-use adjustment factors derived from emission testing designed to represent operational

behavior of nonroad equipment. Note that the in-use adjustments are not applied by the

NONROAD model, but are applied by EPA during the creation of the NONROAD emission

factor input files.

Development of In-Use Adjustment Factors

In NEVES, EPA adjusted the ISO-C1-derived emission factor data available at the time

to account for in-use operation by applying a set of multipliers. These factors were derived from

a comparison of only a few engines tested with both the ISO-C1 test procedure and the highway

Federal Test Procedure (FTP). (1) These factors shown in Table C1 were applied in NEVES

only to engines used in applications judged to be sufficiently transient in nature.

Table C1 NEVES Test Cycle Adjustment from ISO-C1 Emission Factors

NEVES

Adjustment

HC CO NOx PM

1.4 2.0 1 1.6

The NEVES adjustment was derived from tests of engines operating on steady-state

cycles and the Federal Test Procedure for highway heavy-duty engines. However, the highway

test procedure may not simulate engine behavior when used in nonroad applications. Therefore,

a joint EMA\EPA project was initiated to develop more realistic test cycles for nonroad engine

emissions characterization. The project developed cycles to represent typical operation of an

agricultural tractor, a crawler dozer, and a backhoe\loader. (2) The cycles were developed from

data acquired from instrumenting one piece of each type of equipment. This data was used to

construct appropriate test cycles from statistical criteria developed by EMA and EPA. Southwest

Research Institute (SwRI) then tested nine late-model nonroad engines using the steady-state

ISO-C1 certification procedure and the three nonroad test cycles. (3) These test results average

to the adjustment factors shown in Table C2.
C2

Table C2 In-use Adjustment Factor (Ratio of Application Test Cycle to Steady-State ISO-C1

Emissions)

Test Cycle HC CO NOx PM BSFC

Agricultural Tractor 0.89 0.42 0.99 0.64 0.98

Backhoe\Loader 2.19 2.31 1.03 2.04 1.18

Crawler Dozer 0.93 1.27 0.99 1.21 0.98

Table C3 lists summarizes the cycle specific results for individual engines. Individual

engine steady-state results are listed in Table B2 of Appendix B with the exception of the John

Deere 6101. The ISO-C1 results for the John Deere 6101 were 0.47 g/hp-hr for HC, 0.86 for CO,

5.55 for NOx, 0.186 for PM, and 0.350 lb/hp-hr for BSFC. The John Deere 6101 engine was not

included in Appendix B because it was designed for and meets the Tier 1 emission standard. 

Therefore the average ISO-C1 results shown in Table C1 are lower than the average given in

Appendix B, Table B2.
C3

Table C3 Summary of the Emission Results of Various Nonroad Test Cycles

Engine Test Cycle HC 

(g/hp-hr)

CO 

(g/hp-hr)

NOx

(g/hp-hr)

PM 

(g/hp-hr)

BSFC 

(lb/hp-hr)

Caterpillar 3116 (3) Ag. Tract. 0.04 0.75 9.40 0.280 0.357

Backhoe 0.36 7.47 9.46 0.652 0.411

Dozer 0.09 7.30 8.70 0.713 0.362

Caterpillar 3054 (3) Ag. Tract. 0.46 0.47 9.46 0.263 0.377

Backhoe 1.22 3.34 5.45 0.759 0.446

Dozer 0.51 1.06 8.28 0.384 0.372

John Deere 4039 (3) Ag. Tract. 0.20 0.56 11.70 0.173 0.361

Backhoe 1.00 2.62 9.57 0.447 0.471

Dozer 0.33 1.42 11.70 0.254 0.372

John Deere 7076 (3) Ag. Tract. 0.54 0.57 9.45 0.168 0.366

Backhoe 1.13 4.82 14.35 0.522 0.493

Dozer 0.52 2.22 10.14 0.303 0.370

Consolidated Diesel

6TA-830 (3)

Ag. Tract. 0.90 1.07 5.62 0.304 0.377

Backhoe 2.08 9.86 6.69 1.698 0.438

Dozer 0.83 3.76 6.06 0.805 0.370

John Deere 6619 (3) Ag. Tract. 0.87 1.16 6.77 0.283 0.400

Backhoe 1.99 6.89 8.29 1.102 0.466

Dozer 0.80 3.31 7.01 0.698 0.398

Consolidated Diesel

4039 (3)

Ag. Tract. 0.86 2.50 7.28 0.430 0.367

Backhoe 2.89 3.31 6.52 0.725 0.436

Dozer 1.22 2.10 7.40 0.413 0.364

Caterpillar 3306 (3) Ag. Tract. 1.33 0.82 6.46 0.201 0.372

Backhoe 2.30 5.14 7.22 0.813 0.415

Dozer 1.16 2.70 6.54 0.436 0.370

John Deere 6101 (3) Ag. Tract. 0.50 0.32 4.93 0.125 0.362

Backhoe 1.07 1.92 6.36 0.430 0.434

Dozer 0.51 1.17 5.25 0.246 0.362

Average Ag. Tractor 0.63 0.91 7.90 0.247 0.371

Backhoe 1.56 5.04 8.21 0.794 0.446

Dozer 0.66 2.77 7.88 0.473 0.371

ISO-C1 0.71 2.18 7.98 0.389 0.377
C4

Because the in-use adjustment factors used in NEVES were based on limited testing and

unrepresentative test procedures, EPA plans to replace in them NONROAD with the more

representative factors shown in Table C2. These factors will be continually evaluated and

improved, but, because of the need to produce a working version of NONROAD, EPA is

including the above SwRI-derived factors in the version as the best available estimation. EPA is

aware that some of these factors are quite different than those used in NEVES and will have a

large impact on the corresponding emission inventories. Users of this version of NONROAD

should note that these factors, and the list of applications to which the factors are applied, may

change in later releases. EPA may reconsider the in-use adjustment factors due to comments

received during testing and peer review or due to the following issues and activities planned by

EPA:

q Generation of additional in-use test cycles and engine testing on these cycles

q Evaluation of technology effects on adjustment factors

q Contribution of load factor differences to the SwRI-derived adjustment factors

q Representativeness of engine\equipment model and work activity used to generate

the data upon which the nonroad cycles were generated

q Appropriateness of statistical criteria (such as time in mode weighting factors)

used to generate the backhoe\loader, crawler dozer, and agricultural tractor cycles

EPA also plans to continue investigating the effects of in-use behavior which may change

the understanding of the correction from the ISO-C1 steady-state test results. This continuing

evaluation may prompt EPA to revise the emission factors used in NONROAD as part of a new

release of the model. EPA is interested in comments about the approach outlined here.

Applying In-use Adjustment Factors

To apply the in-use adjustment factors listed in Table C2 to the entire CI equipment

population, EPA matched nonroad applications with the test cycle that most closely represents

the nonroad activity for the application. Table C4 lists the nonroad application used in the

NONROAD model and the in-use adjustment most representative of that application. If steadystate operation is typical of an application no adjustment was made, and the cycle adjustment is

listed as ‘none’. Some applications have no diesel engines, and therefore an adjustment is not

applicable and is indicated by ‘N\A’.

The steady-state emission factors listed in the main body of this report were then

multiplied by the appropriate in-use adjustment factor to create NONROAD’s emission factor

inputs for CI engines.

Table C4 Diesel Engines, In-Use Emission Factor Adjustment by Application Category

SCC SCC Description Cycle Adjustment

2270000000 All Diesel Off-Highway Vehicle: Total

2270001000 Recreational Vehicles Total
(table continued from previous page)

C5

2270001010 Recreational Vehicles Motorcycles: Off-Road N\A

2270001020 Recreational Vehicles Snowmobiles N\A

2270001030 Recreational Vehicles All Terrain Vehicles N\A

2270001040 Recreational Vehicles Minibikes N\A

2270001050 Recreational Vehicles Golf Carts N\A

2270001060 Recreational Vehicles Speciality Vehicle Carts Backhoe

2270002000 Construction Equipment Total

2270002003 Construction Equipment Pavers Dozer

2270002006 Construction Equipment Tampers/Rammers N\A

2270002009 Construction Equipment Plate Compactors Backhoe

2270002012 Construction Equipment Concrete Pavers Unused SCC

2270002015 Construction Equipment Rollers Dozer

2270002018 Construction Equipment Scrapers Dozer

2270002021 Construction Equipment Paving Equipment Dozer

2270002024 Construction Equipment Surfacing Equipment Dozer

2270002027 Construction Equipment Signal Boards None

2270002030 Construction Equipment Trenchers Backhoe

2270002033 Construction Equipment Bore/Drill Rigs Dozer

2270002036 Construction Equipment Excavators Backhoe

2270002039 Construction Equipment Concrete/Industrial Saws Dozer

2270002042 Construction Equipment Cement & Mortar Mixers None

2270002045 Construction Equipment Cranes Dozer

2270002048 Construction Equipment Graders Dozer

2270002051 Construction Equipment Off-highway Trucks Backhoe

2270002054 Construction Equipment Crushing/Proc. Equipment Dozer

2270002057 Construction Equipment Rough Terrain Forklifts Backhoe

2270002060 Construction Equipment Rubber Tire Loaders Backhoe

2270002063 Construction Equipment Rubber Tire Dozers Dozer

2270002066 Construction Equipment Tractors/Loaders/Backhoes Backhoe

2270002069 Construction Equipment Crawler Dozer Dozer

2270002072 Construction Equipment Skid Steer Loaders Backhoe

2270002075 Construction Equipment Off-Highway Tractors Backhoe

2270002078 Construction Equipment Dumpers/Tenders Backhoe

2270002081 Construction Equipment Other Construction Equipment Dozer

2270003000 Industrial Equipment Total

2270003010 Industrial Equipment Aerial Lifts Dozer

2270003020 Industrial Equipment Forklifts Backhoe

2270003030 Industrial Equipment Sweepers/Scrubbers Ag. Tractor

2270003040 Industrial Equipment Other General Industrial Equipment None

2270003050 Industrial Equipment Other Material Handling Equipment Backhoe

2270003060 Industrial Equipment AC\Refrigeration None

2270004000 Lawn & Garden Equipment Total

2270004010 Lawn & Garden Equipment Lawn mowers (Residential) N\A

2270004011 Lawn & Garden Equipment Lawn mowers (Commercial) N\A

2270004015 Lawn & Garden Equipment Rotary Tillers < 6 HP N\A

2270004016 Lawn & Garden Equipment Rotary Tillers < 6 HP (Commercial) N\A

2270004020 Lawn & Garden Equipment Chain Saws < 6 HP N\A

2270004021 Lawn & Garden Equipment Chain Saws < 6 HP (Commercial) N\A

2270004025 Lawn & Garden Equipment Trimmers/Edgers/Brush Cutters N\A

2270004026 Lawn & Garden Equipment Trimmers/Edgers/Brush Cutters (Commercial) N\A
(table continued from previous page)

C6

2270004030 Lawn & Garden Equipment Leafblowers/Vacuums None

2270004031 Lawn & Garden Equipment Leafblowers/Vacuums (Commercial) None

2270004035 Lawn & Garden Equipment Snowblowers None

2270004036 Lawn & Garden Equipment Snowblowers (Commercial) None

2270004040 Lawn & Garden Equipment Rear Engine Riding Mowers None

2270004041 Lawn & Garden Equipment Rear Engine Riding Mowers (Commercial) None

2270004045 Lawn & Garden Equipment Front Mowers None

2270004046 Lawn & Garden Equipment Front Mowers (Commercial) None

2270004050 Lawn & Garden Equipment Shredders < 6 HP None

2270004051 Lawn & Garden Equipment Shredders < 6 HP (Commercial) None

2270004055 Lawn & Garden Equipment Lawn & Garden Tractors None

2270004056 Lawn & Garden Equipment Lawn & Garden Tractors (Commercial) None

2270004060 Lawn & Garden Equipment Wood Splitters N\A

2270004061 Lawn & Garden Equipment Wood Splitters (Commercial) N\A

2270004065 Lawn & Garden Equipment Chippers/Stump Grinders N\A

2270004066 Lawn & Garden Equipment Chippers/Stump Grinders (Commercial) N\A

2270004070 Lawn & Garden Equipment Commercial Turf Equipment Unused SCC

2270004071 Lawn & Garden Equipment Commercial Turf Equipment (Commercial) None

2270004075 Lawn & Garden Equipment Other Lawn & Garden Equipment None

2270004076 Lawn & Garden Equipment Other Lawn & Garden Equipment (Commercial) None

2270005000 Farm Equipment Total

2270005010 Farm Equipment 2-Wheel Tractors Ag. Tractor

2270005015 Farm Equipment Agricultural Tractors Ag. Tractor

2270005020 Farm Equipment Combines Ag. Tractor

2270005025 Farm Equipment Balers Ag. Tractor

2270005030 Farm Equipment Agricultural Mowers Ag. Tractor

2270005035 Farm Equipment Sprayers Ag. Tractor

2270005040 Farm Equipment Tillers > 6 HP Ag. Tractor

2270005045 Farm Equipment Swathers Ag. Tractor

2270005050 Farm Equipment Hydro Power Units None

2270005055 Farm Equipment Other Agricultural Equipment Ag. Tractor

2270005060 Farm Equipment Irrigation Sets None

2270006000 Light Commercial Total

2270006005 Light Commercial Generator Sets None

2270006010 Light Commercial Pumps None

2270006015 Light Commercial Air Compressors None

2270006020 Light Commercial Gas Compressors None

2270006025 Light Commercial Welders None

2270006030 Light Commercial Pressure Washers None

2270007000 Logging Equipment Total

2270007005 Logging Equipment Chain Saws > 6 HP N\A

2270007010 Logging Equipment Shredders > 6 HP None

2270007015 Logging Equipment Skidders Dozer

2270007020 Logging Equipment Fellers/Bunchers Backhoe

2270008000 Airport Service Equipment Total

2270008005 Airport Service Equipment Airport Support Equipment Backhoe

2270008010 Airport Service Equipment Terminal Tractors Backhoe

2270009000 Underground Mining Equipment Total

2270009010 Other Underground Mining Equipment Backhoe

2270010000 Oil Field Equipment Total
(table continued from previous page)

C7

2270010010 Other Oil Field Equipment None

2282005025 Recreational Pleasure Craft, Sailboat Aux. Outboard None

2285003015 Railway Maintenance Backhoe

2282005000 Recreational Pleasure Craft, Total

2282005005 Recreational Pleasure Craft, Inboards None

2282005010 Recreational Pleasure Craft, Outboards None

2282005015 Recreational Pleasure Craft, Personal Water Craft N\A

References

(1) EPA, “Nonroad Engine and Vehicle Emission Study” (NEVES), U.S. EPA, Office of Air

and Radiation, 21A-2001. November, 1991

(2) Jackson, C., “Nonroad Composite Cycle Development and Data Analysis.” EPA Office of

Mobile Sources. Report expected 1998.

(3) Fritz S.G., “Emission Factors for Compression Ignition Nonroad Engines Operated on

Number 2 Highway and Nonroad Diesel Fuel,” Southwest Research Institute. EPA contract

#68-C5-0077, SwRI 08-7601-822. Report expected 1998.