United States Air and Radiation EPA420-F-03-011
Environmental Protection April 2003
Agency
Office of Transportation and Air Quality
&EPA Program
Update
Reducing Air Pollution from
Nonroad Engines
In response to environmental and public health concerns, the U. S.
Environmental Protection Agency (EPA) has established emission
standards for most categories of nonroad engines. These engines
operate in a wide variety of applications, including construction
equipment, marine vessels, lawn and garden equipment, and
locomotives. As a whole, these emission-control programs significantly
reduce the impact of nonroad engines and equipment on the nation's
air quality.
Background
Since the early 1970s, EPA has set increasingly stringent emission stan-
dards for highway cars and trucks. After making much progress in
controlling highway emissions, the Agency turned to the wide variety of
nonroad engines, which also contribute significantly to air pollution.
These emission standards reduce harmful air pollution and help states
meet the National Ambient Air Quality Standards, as required by the
Clean Air Act.
"Nonroad" is a term that covers a diverse collection of engines, equip-
ment, vehicles, and vessels. Sometimes referred to as "off-road" or "off-
highway," the nonroad category includes outdoor power equipment,
recreational vehicles, farm and construction machinery, lawn and garden
equipment, marine vessels, locomotives, and many other applications.1
Until the mid-1990s, emissions from these engines were largely uncon-
trolled.
i Printed on Recycled Paper
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The 1990 amendments to the Clean Air Act directed EPA to study the
contribution of nonroad engines to urban air pollution, and regulate them
if they contributed to air quality problems. In 1991, EPA published a
report showing that nonroad equipment emitted large amounts of nitro-
gen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO) and
particulate matter (PM). In general, the report showed that nonroad
engines had total emissions almost as high as highway motor vehicles. In
the case of diesel particulate matter, nonroad emissions were significantly
higher than highway emissions.2
In response, EPA has adopted emission standards for most categories of
new nonroad engines. The following sections summarize the status of
these programs for the various nonroad equipment categories.
Land-Based Diesel Engines
Diesel engines dominate the market for nonroad engines. They currently
contribute about 44 percent of diesel PM emissions and 12 percent of
total NOx emissions from mobile sources nationwide.3 Examples of land-
based nonroad applications using diesel engines include the following:
construction equipment such as backhoes, agricultural equipment such as
tractors, material handling equipment such as heavy forklifts, industrial
equipment such as airport service vehicles, and utility equipment such as
generators and pumps.
In 1994, EPA adopted the first set of emission standards (" Tier 1") for all
new nonroad diesel engines greater than 37 kilowatts (50 horsepower),
except those used in locomotives and marine vessels.4 The Tier 1 stan-
dards were phased in for different engine sizes between 1996 and 2000,
reducing NOx emissions from these engines by 30 percent.
EPA has since adopted more stringent emission standards for NOx, HC,
and PM from new nonroad diesel engines. This program includes the first
set of standards for nonroad diesel engines less than 37 kW (phasing in
between 1999 and 2000), including marine engines in this size range. It
also phases in more stringent "Tier 2" emission standards from 2001 to
2006 for all engine sizes and adds yet more stringent "Tier 3" standards
for engines between 37 and 560 kW (50 and 750 hp) from 2006 to 2008.
These standards will further reduce nonroad diesel engine emissions by 60
percent for NOx and 40 percent for PM from Tier 1 emission levels.
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Recent developments of advanced emission-control technologies have
made it possible to consider an new round of standards, with the potential
to reduce PM and NOx emissions by an additional 90 percent. These
technologies can be damaged by sulfur in diesel fuel, so EPA has pro-
posed a comprehensive program for low-sulfur fuels in combination with
the more stringent emission standards, with a plan to finalize these re-
quirements in 2004.
Land-Based Spark-Ignition Engines
EPA divided land-based spark-ignition engines into three broad catego-
ries—(1) small engines typically used for lawn and garden applications,
(2) large engines used in industrial applications, and (3) specialty engines
used in recreational applications
Small SI Nonroad spark-ignition engines below 19 kW (25 horsepower), which
Engines usually run on gasoline, are used primarily in lawn and garden equipment.
Lawnmowers, string trimmers, leaf blowers, chain saws, commercial turf
equipment, and lawn and garden tractors fall within this category, but
engines used for marine propulsion, recreational vehicles, or hobby
applications (such as remote-control airplanes) are treated separately.
These engines currently contribute about 16 percent of HC emissions and
21 percent of CO emissions from mobile sources nationwide.
Under Phase 1 regulations, new Small SI engines have been meeting
standards for HC, CO, and NOx emissions since 1997. The Phase 1
standards have resulted in a 32 percent reduction in HC levels from these
engines.
EPA adopted Phase 2 standards for Small SI engines in two separate
rulemakings:
• For nonhandheld applications (such as lawn and garden tractors and
lawnmowers), the second set of emission standards phases in be-
tween 2001 and 2007 and will result in an additional 60 percent
reduction in HC and NOx emissions.
• For handheld applications (such as leaf blowers and chainsaws), the
second set of emission standards phases in between 2002 and 2007
and will result in an additional 70 percent reduction in HC and NOx
emissions.
Standards requiring control of evaporative emissions do not yet apply to
Small SI engines.
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Large SI
Engines
Recreational
Vehicles
Nonroad SI engines above 19 kW (25 hp), which are usually car and
truck engines installed in industrial equipment, are used in many different
applications, including forklifts, airport service equipment, generators,
compressors, welders, aerial lifts, and ice-grooming machines. These
engines— which may operate on liquefied petroleum gas, gasoline, or
natural gas—currently contribute about 2 percent of NOx emissions, and
3 percent of HC and CO emissions from mobile sources nationwide.
Many of them operate indoors, where high exhaust concentrations can
expose workers to elevated levels of CO emissions.
EPA has adopted emission standards for Large SI engines that take effect
for new engines starting in 2004. Manufacturers will rely on well-estab-
lished emission-control technologies from automotive engines, including
three-way catalysts and electronic fueling systems, to meet these emis-
sion standards. Starting in 2007, manufacturers will need to use opti-
mized engines, including new diagnostic systems, to meet more stringent
standards calling for a 90-percent reduction in NOx, HC, and CO emis-
sions. Additional control technologies will reduce evaporative HC
emissions from gasoline fuel tanks.
This category includes off-highway motorcycles, all-terrain vehicles, and
snowmobiles that operate on gasoline. This category may also include
some motorized scooters, mini-bikes, and mopeds. Recreational vehicles
currently contribute about 5 percent of HC emissions and 2 percent of
CO emissions from mobile sources nationwide. These estimated HC
emissions include combined exhaust and evaporative emissions. In
November 2002, EPA adopted emission standards for new recreational
vehicles that will be phased in starting in 2006. These new standards will
reduce HC emissions from these vehicles by 67 percent and will reduce
CO emissions by 28 percent. Manufacturers are likely to meet the new
standards primarily by increasing their use of 4-stroke engine technology.
Manufacturers are also likely to use advanced two-stroke engine system
designs in some applications. In addition, improved materials and barrier
treatments will reduce the permeation of gasoline through fuel tanks and
hoses.
Marine Engines and Vessels
A wide variety of engines are used in marine applications, including
gasoline engines for personal watercraft and outboard applications and
diesel engines used on recreational and commercial vessels ranging from
tugboats to very large ocean-going vessels. Because it is not possible to
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apply the same set of standards to all of these applications, EPA has
divided programs for reducing marine engine emissions into two broad
categories: (1) marine spark-ignition engines, including outboard engines
and personal watercraft, as well as gasoline-fueled sterndrive and inboard
engines and (2) marine diesel engines, including auxiliary engines and
both recreational and commercial propulsion engines.
Marine These engines, many of which have typically used simple two-stroke
Spark- technology, contribute about 10 percent of HC and 3 percent of CO
ignition emissions from mobile sources nationwide. However, their contribution
Engines to total emissions in and around marinas and harbors is significantly
higher. Also, CO in the exhaust from these engines poses an ongoing
safety threat to boaters.
Emission standards for outboard and personal watercraft engines call for
manufacturers to meet increasingly stringent HC levels over a nine-year
phase-in period starting in 1998. By 2006, manufacturers will produce all
their engines with 75 percent lower HC emissions on average. The
gradually decreasing emission standard lets manufacturers determine the
best approach to achieving the targeted reductions over time by allowing
them to phase in the types of control technologies in the most sensible
way, while minimizing the cost impact to the consumer.
Sterndrive and inboard gasoline engines typically use four-stroke auto-
motive engines that have been modified for sport boats. Uncontrolled
emission levels from these engines are usually considerably lower than
from outboard engines, but there is still an opportunity to significantly
reduce NOx, HC, and CO emissions. EPA is in the process of developing
emission standards that would require manufacturers to use catalysts and
other available emission-control technology on their new engines.
In addition, EPA has proposed requirements that would address evapora-
tive emissions from all types of vessels using gasoline engines. These
requirements would reduce venting of evaporated gasoline from fuel
tanks and reduce the permeation of fuel through the walls of fuel tanks
and hoses.
Marine Marine diesel engines are used for propulsion and auxiliary power in a
Diesel variety of marine applications, including recreational yachts, fishing
Engines boats, tug and towboats, dredgers, and coastal and ocean-going vessels.
These engines currently contribute about 8 percent of NOx emissions and
9 percent of diesel PM emissions from mobile sources, though the contri-
bution is greater in areas with commercial ports.
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Internationally, emissions from marine diesel engines are controlled by
Annex VI of the International Convention for the Prevention of Pollution
from Ships (known as the MARPOL convention). The NOx limits,
contained in Regulation 13 of Annex VI apply to marine diesel engines
rated above 130 kW and are similar in stringency to the first tier of
emission standards adopted for land-based nonroad diesel engines (de-
scribed above). These standards apply to any engine rated above 130 kW
installed on a vessel constructed on or after January 1, 2000. The stan-
dards are also triggered if an engine is substantially modified (it is ad-
justed in such a way that its emissions may be increased) on or after
January 1, 2000, regardless of when the engine was made or installed on a
vessel. As of the date of this publication, the international standards have
not yet gone into effect. However, EPA adopted requirements earlier this
year to make these standards enforceable beginning January 2004 for
engines above 2.5 liters per cylinder installed on vessels flagged in the
United States. The MARPOL standards are expected to be enforceable
back to January 1, 2000 for all vessels, once enough nations have ratified
the Annex for it to go into effect.
In addition to the international standards, EPA has adopted more strin-
gent national standards for certain categories of marine diesel engines
installed on vessels flagged in the United States. The levels of the stan-
dards and their application dates vary depending on engine size:
• Engines below 37 kW: the standards are the same as for land-based
nonroad diesel engines of that size, and begin in 1999 or 2000 for
Tier 1 and 2004 or 2005 for Tier 2, depending on engine size.
• Engines above 37 kW with per-cylinder displacement below 5 liters:
these are Category 1 marine diesel engines. The national standards
begin in 2004 or 2005, depending on engine size; the MARPOL
standards apply voluntarily until then for engines above 130 kW.
• Engines with per-cylinder displacement between 5 and 30 liters:
these are Category 2 marine diesel engines. The national standards
begin in 2007; the MARPOL standards apply voluntarily until 2004,
and are mandatory from 2004 until 2007.
• Engines with per-cylinder displacement above 30 liters: these are
Category 3 marine diesel engines and are subject only to the MAR-
POL standards. These standards are voluntary until 2004 and man-
datory after 2004.
• Recreational marine diesel engines: these are marine diesel engines
with per-cylinder displacement up to 5 liters per cylinder used in
recreational vessels. They are subject to the same numerical stan-
dards as Category 1 marine diesel engines, beginning in 2006.
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In the February 2003 rulemaking related to marine diesel engines, EPA
made a commitment to consider additional standards for Category 3
marine diesel engines and to finalize standards by April 27, 2007. That
rulemaking may also include more stringent standards for Category 1 and
Category 2 marine diesel engines.
Locomotives
Locomotives contribute about 7 percent of NOx emissions and 5 percent
of diesel PM emissions from mobile sources nationwide. These engines
are generally larger than any land-based nonroad diesel engines in dis-
placement volume and total power and may last for 40 years or longer.
New emission standards will reduce NOx emissions by two-thirds, while
HC and PM emissions from these engines will decrease by 50 percent.
EPA has adopted three separate sets of emission standards, with the
standards taking effect depending on the date a locomotive is first manu-
factured.
• The first set of standards (Tier 0) apply to locomotives and locomo-
tive engines originally manufactured from 1973 through 2001 any
time they are manufactured or remanufactured. This unique feature
of the locomotive program is critical, because locomotives are
generally remanufactured five to ten times during their total service
lives of 40 years or more.
• The second set of standards (Tier 1) apply to locomotives and
locomotive engines originally manufactured from 2002 through
2004. These locomotives and locomotive engines must meet the
Tier 1 standards at the time of original manufacture and at each
subsequent remanufacture.
• The final set of standards (Tier 2) apply to locomotives and locomo-
tive engines originally manufactured in 2005 and later. Tier 2 loco-
motives and locomotive engines must meet the applicable standards
at the time of original manufacture and at each subsequent remanu-
facture.
Aircraft
Aircraft emissions contribute about 1 percent of NOx emissions and 2
percent of HC emissions from mobile sources nationwide. Some cities
with high airport traffic see a more pronounced impact from these en-
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gines. In addition, commercial aircraft emissions are a fast-growing
segment in the transportation sector. Aircraft emissions also include
greenhouse gases and may contribute significantly to depletion of the
stratospheric ozone layer.
Emission standards for gas turbine engines that power civil aircraft have
been in place for about 20 years. These engines are used in virtually all
commercial aircraft, including both scheduled and freight airlines. The
standards do not apply to general aviation or military aircraft. Controls on
engine smoke and prohibitions on fuel venting were established in 1974
and have been revised several times since then. Gas turbine engines have
been subject to limits on hydrocarbon emissions for each landing and
takeoff cycle since 1984.
The International Civil Aviation Organization (ICAO) plays an important
role in defining uniform emission standards that can be adopted by indi-
vidual nations. In May 1997, EPA adopted ICAO's NOx and CO emission
standards for gas turbine engines. In addition, EPA plans in the near
future to adopt a second round of more stringent ICAO NOx standards
for gas turbine engines for implementation in 2004.
EPA is also exploring other ways to reduce air pollution from air trans-
portation. Since 1998, EPA and the Federal Aviation Administration have
jointly chaired a national stakeholder initiative to reduce aviation emis-
sions through a voluntary program. Stakeholders include airlines, aircraft
engine manufacturers, airports, state and local air pollution control offi-
cials, and environmental organizations. The stakeholder initiative has
narrowed its focus to a two-step program—near-term emission reduc-
tions from ground-service equipment and longer-term reductions from
aircraft. If stakeholders are able to reach an agreement for voluntary
reductions, this would represent a big step toward establishing a compre-
hensive national program to reduce aviation-related emissions.
For More Information
You can access additional documents on nonroad engine programs on the
Office of Transportation and Air Quality (OTAQ) Web site at:
www. epa. gov/otaq/nonroad. htm
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You can also contact the OTAQ library for document information at:
U. S. Environmental Protection Agency
OTAQ Library
2000 Traverwood Drive
Ann Arbor, Michigan 48105
(734)214-4311
The following additional fact sheets go into more detail on these nonroad
engine control programs:
General:
How to Maintain or Rebuild Engines Certified to EPA Standards
(EPA420-F-02-035), September 2002.
Blue Sky Series Engines (EPA420-F-02-036), September 2002.
Emission Regulations for Stationary and Mobile Engines
(EPA420-F-02-034), September 2002.
Land-Based Diesel Engines:
Summary of EPA's Proposed Program for Low-Emission Nonroad
Engines and Fuel (EPA420-F-03-008), April 2003.
Public Health and Environmental Benefits of EPA's Proposed
Program for Low-Emission Nonroad Diesel Engines and Fuel (EPA420-
F-03-010), April 2003.
New Emission Standards for Nonroad Diesel Engines (EPA420-F-
98-034), August 1998.
Small Spark-Ignition Engines:
Final Phase 2 Standards for Small Spark-Ignition Handheld
Engines (EPA420-F-00-007), March 2000.
New Phase 2 Standards for Small Spark-Ignition Nonhandheld
Engines (EPA420-F-99-008), March 1999.
Small Engine Emission Standards—Answers to Commonly Asked
Questions from Dealers and Distributors (EPA420-F-98-025), September
1998.
Be a Grower, Not a Mower (EPA420-F-96-018), April 1997.
Recreational Vehicles and Large Spark-ignition Engines:
Emission Standards for New Nonroad Engines (EPA420-F-02-
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037), September 2002. This fact sheet describes new emission standards
for recreational vehicles, Large SI engines, and recreational marine diesel
engines.
Environmental Impacts of Newly Regulated Nonroad Engines
(EPA420-F-02-033), September 2002.
Frequently Asked Questions from AW Riders (EPA420-F-02-
038), September 2002.
Frequently Asked Questions from Off-highway Motorcycle Riders
(EPA420-F-02-039), September 2002.
Frequently Asked Questions from Snowmobile Riders (EPA420-F-
02-040), September 2002.
Frequently Asked Questions from Facility Managers and Other
Owners of Industrial Spark-ignition Engines (EPA420-F-02-041), Sep-
tember 2002.
Emission Exemption for Racing Motorcycles and Other Competi-
tion Vehicles (EPA420-F-02-045), September 2002.
Marine Spark-Ignition Engines:
Organization of Gasoline and Diesel Marine Engine Emission
Standards (EPA420-F-99-046), December 1999.
Emission Standards for New Gasoline Marine Engines (EPA420-
F-96-012), August 1996.
Emission Standards for New Spark-Ignition Marine Engines:
Information for the Marine Industry (EPA420-F-96-013), August 1996.
Boating Pollution Prevention Tips (EPA420-F-96-003), July
1996.
Marine Diesel Engines:
Emission Standards Adopted for New Marine Diesel Engines
(EPA420-F-03-001), January 2003. This fact sheet describes the MAR-
POL Annex VI standards and their application to engines with per-
cylinder displacement over 2.5 liters. These are the only standards that
apply to Category 3 engines.
MARPOE 73/78 Annex VI Marine Diesel Engine Requirements
(EPA420-F-99-038), October 1999.
Emission Standards for New Nonroad Engines (EPA420-F-02-
037), September 2002. This fact sheet describes new emission standards
for recreational vehicles, Large SI engines, and recreational marine diesel
engines.
Frequently Asked Questions from Owners of Recreational Boats
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with Diesel Engines (EPA420-F-02-042), September 2002.
Emission Standards for new Commercial Marine Diesel Engines
(EPA420-F-99-043), November 1999. This fact sheet describes the Tier 2
standards that apply to Category 1 and Category 2 marine diesel engines.
Emission Standards for Marine Diesel Engines: Scope of Appli-
cation (EPA420-F-00-006), February 2000.
Responsibilities for Marine Vessel Operators with EPA-Certified
Engines (EPA420-F-99-044), December 1999.
Organization of Gasoline and Diesel Marine Engine Emission
Standards (EPA420-F-99-046), December 1999.
Reducing Marine Vessel and Port Emissions in the South Coast
(EPA420-F-96-011), July 1996.
Locomotives:
Final Emission Standards for Locomotives (EPA420-F-97-048),
December 1997.
Requirements for Railroads Regarding Locomotive Exhaust
Emission Standards (EPA420-F-99-036), September 1999.
Applicability of Locomotive Emission Standards (EPA420-F-99-
037), September 1999.
Federal Preemption of State and Local Control of Locomotives
(EPA420-F-97-050), December 1997.
Environmental Benefits of Emission Standards for Locomotives
(EPA420-F-97-049), December 1997.
Emission Factors of Locomotives (EPA420-F-97-051), December
1997.
Aircraft:
Evaluation of Air Pollutant Emissions from Subsonic Commer-
cial Aircraft (EPA420-R-99-013), April 1999.
Reducing Aircraft and Airport Emissions in the South Coast
(EPA420-F-96-010), July 1996.
Adopted Aircraft Engine Emission Standards (EPA420-F-97-
010), April 1997.
1 This fact sheet also describes emission standards that apply to
aircraft engines, even though EPA does not consider these to be nonroad
engines under the Clean Air Act.
EPA refers to the combined set of highway and nonroad engines
as mobile sources. This does not include engines used in stationary
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applications, which are regulated by separate programs, usually at the
state level.
3 Diesel engines may also be referred to as compression-ignition or
CI engines. These engines typically operate on diesel fuel, but other fuels
may be also be used. In contrast, spark-ignition (or SI) engines generally
operate on gasoline, natural gas, or liquefied petroleum gas.
4 The U.S. Mine Safety and Health Administration sets require-
ments related to emissions from underground mining equipment.
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