OFFICE OF INSPECTOR GENERAL 

Catalyst for Improving the Environment 

 Evaluation Report 

Progress Report on EPA’s 

Nonroad Mobile Source 

Emissions Reduction Strategies 

 Report No. 2006-P-00039

 September 27, 2006 
Report Contributors: 

Abbreviations 

CO 

EPA 

MARPOL 

NOx 

OIG 

OTAQ 

PM2.5 

PM10 

PM 

PPM 

SOX 

STAPPA/ALAPCO 

THC 

VOC 

John Bishop 

 Gwen Butler

 Jennifer Dwyer

 Sarah Fabirkiewicz

 Bill Nelson 

 Rick Beusse 

Carbon Monoxide 

U.S. Environmental Protection Agency 

International Convention for the Prevention of Pollution from Ships 

Nitrogen Oxides 

Office of Inspector General 

Office of Transportation and Air Quality 

Fine Particulate Matter 

Particulate Matter up to 10 micrometers in diameter 

Particulate Matter 

Parts Per Million 

Sulfur Oxides 

State and Territorial Air Pollution Program Administrators/ 

 Association of Local Air Pollution Control Officials 

Total Hydrocarbons 

Volatile Organic Compound 

Cover photos: Various types of nonroad mobile sources of emissions (photos courtesy EPA). 
U.S. Environmental Protection Agency 2006-P-00039

Office of Inspector General September 27, 2006 

At a Glance


Catalyst for Improving the Environment 

Why We Did This Review 

Emissions from nonroad 

mobile sources can present 

significant health and

environmental hazards. The 

U.S. Environmental Protection 

Agency (EPA) projects that 

emissions from these sources 

will decrease in some 

categories but increase in

others. As such, we examined 

EPA’s efforts to reduce 

nonroad mobile source 

emissions, opportunities for 

additional reductions, and 

challenges to addressing

nonroad emissions problems. 

Background 

Nonroad mobile sources 

include marine vessels, 

locomotives, aircraft, farm and 

construction machinery, lawn 

and garden equipment, 

recreational vehicles, and 

outdoor power equipment. 

Nonroad mobile sources 

produce particulate matter and 

ozone-forming nitrogen oxides 

and volatile organic 

compound emissions, as well 

as toxic air pollutants, which 

contribute to a host of health 

and environmental hazards. 

Progress Report on EPA’s Nonroad Mobile 

Source Emissions Reduction Strategies 

What We Found 

EPA has issued nonroad mobile source emissions control regulations that, when 

fully implemented, should result in significant reductions in such emissions. 

However, more emission reduction efforts are needed and some challenges 

remain. 

Until the mid-1990s, emissions from nonroad mobile sources were largely 

uncontrolled. In the 1990 Clean Air Act Amendments, Congress directed EPA to 

study the contribution of nonroad sources to ozone and other air pollutants, and to 

issue regulations if problems were found. EPA has since issued 14 regulations to 

control pollutants from nonroad mobile sources, with a total of 20 standards for 

various nonroad categories. The most recent regulation, the 2004 Nonroad Diesel 

Engines rule, is based on a systems approach involving a combination of engine 

modifications, reduced sulfur content in diesel fuel, and exhaust controls. 

There are approximately 5 million nonroad diesel engines in the United States 

today, many of which are not subject to EPA emissions standards. These engines 

have the potential to continue to produce high levels of pollution over the next 

20 years or more. Agency projections show that substantial emissions reductions 

have already been made for some source categories. However, the full benefits of 

EPA’s regulations may not be realized until 2020-2030, when the standards are 

expected to be fully implemented. Projected benefits assume engine turnover and 

replacement – activities that may be influenced by cost, lead time, and overall 

feasibility. EPA has encouraged emission reductions for existing engines through 

voluntary efforts and incentive programs. Although a mandatory retrofit program 

may achieve increased health protection sooner, such a requirement from the 

Federal level can only come through a change in the Clean Air Act. 

EPA faces significant challenges in addressing nonroad emissions, particularly 

among the marine, aircraft, and small gasoline engine categories. The role that 

other government entities and international communities play in regulating 

emissions from these source categories hinders EPA’s progress in achieving 

reductions. Technical challenges, including the availability of low sulfur fuel, the 

diversity of nonroad engines, and the wide range of applications, also must be 

addressed to meet air quality standards and emission reduction goals. 

This report provides information on the progress of EPA’s efforts to address 

nonroad emissions and makes no recommendations. 

For further information, 

contact our Office of 

Congressional and Public 

Liaison at (202) 566-2391. 

To view the full report, 

click on the following link: 

www.epa.gov/oig/reports/2006/ 

20060927-2006-P-00039.pdf 
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF 

INSPECTOR GENERAL

September 27, 2006 

MEMORANDUM 

SUBJECT: Progress Report on EPA’s Nonroad Mobile Source 

Emissions Reduction Strategies 

Report No. 2006-P-00039 

TO: William L. Wehrum 

Acting Assistant Administrator for Air and Radiation 

This is a report on the subject evaluation conducted by the Office of Inspector General (OIG) of 

the U.S. Environmental Protection Agency (EPA). The report examines current and projected 

nonroad mobile source emissions and how Agency actions have affected those emissions to date, 

and are projected to affect emissions in the future. This report represents the opinion of the OIG 

and the findings in this report do not necessarily represent the final EPA position. Final 

determinations on matters in the report will be made by EPA managers in accordance with 

established procedures. 

The estimated cost of this report – calculated by multiplying the project’s staff days by the 

applicable daily full cost billing rates in effect at the time – is $453,376. 

Action Required 

This report does not include recommendations. Therefore, you are not required to respond to 

this report. 

We appreciate the efforts of EPA managers and staff in working with us to develop this report. 

If you or your staff have any questions regarding this report, please contact me at (202) 566-0847 

of roderick.bill@epa.gov, or Wade Najjum at (202) 566-0827 or najjum.wade@epa.gov. 

Sincerely, 

 Bill A. Roderick 

 Acting Inspector General 
Progress Report on EPA’s Nonroad Mobile Source Emissions Reduction Strategies 

Table of Contents 

Chapters 

1 Introduction ........................................................................................................... 1 

Purpose .......................................................................................................... 1 

Background .................................................................................................... 1 

Scope and Methodology................................................................................. 4 

2 Despite Regulatory Progress, More Work Needed 

to Achieve Emissions Reductions....................................................................... 5 

EPA Making Regulatory Progress for New Nonroad Engines........................ 5 

EPA Undertakes Non-Regulatory Efforts to Reduce Emissions 

 from Existing Diesel Engines..................................................................... 6 

Data Not Yet Available to Measure Actual Emissions Reductions 

and Health Benefits ................................................................................... 8 

Further Controls Needed In Nonattainment Areas and 

for Certain Nonroad Categories ................................................................ 11 

Conclusions.................................................................................................... 12 

Agency Response and OIG Evaluation.......................................................... 13 

3 Challenges Remain to Achieve Emissions Reductions .................................... 14 

Challenges Exist to Controlling Emissions from Certain Categories.............. 14 

Nonroad Diesel Engines Rule Presents Technical Challenges...................... 17 

Conclusions.................................................................................................... 18 

Agency Response and OIG Evaluation.......................................................... 19 

Status of Recommendations and Potential Monetary Benefits................................. 20 

Appendices 

A Details on Scope and Methodology..................................................................... 21 

B EPA’s Regulatory Schedule for Nonroad Engines............................................. 24 

C Agency Response to Draft Report....................................................................... 27

D Agency Memo on Projected Near-Term Nonroad Emissions Reductions....... 28 

E Distribution ............................................................................................................ 30 
Chapter 1

Introduction 

Purpose 

Emissions from nonroad engines contribute significantly to air pollution and 

health problems. The U.S. Environmental Protection Agency (EPA) projects that 

emissions from some nonroad engines will continue to increase and contribute 

large amounts of particulate matter and ozone precursor emissions,1

 while 

emissions from other source categories have begun to decrease. Concerned with 

growth in emissions from these air pollution sources, EPA has issued 14 

regulations to control pollutants from nonroad engines, particularly nitrogen 

oxides (NOx), a precursor to the formation of ozone, and particulate matter (PM). 

Because emissions from existing engines will be a concern for many years, we 

reviewed the status of EPA’s efforts to reduce emissions from nonroad sources. 

Chapter 2 presents EPA’s overall approach to reducing nonroad mobile source 

emissions, the progress the Agency has made in taking actions to reduce 

emissions, and additional opportunities for nonroad ozone and particulate matter 

emissions reductions. Chapter 3 notes some of the major challenges EPA faces in 

effectively addressing nonroad emissions. 

Background 

Mobile sources are divided into two categories: onroad and nonroad. The onroad 

category includes cars and light trucks, motorcycles, and heavy-duty vehicles, 

such as trucks and buses. Nonroad categories cover a variety of engine 

configurations and applications and are divided into several sub-categories, as 

listed in Table 1-1. 

 Table 1-1: Nonroad Engine Categories 

Category Application 

Land-Based Diesel 

Engines 

Backhoes, tractors, material handling equipment, airport service vehicles, 

generators, and pumps 

Land-Based SparkIgnition Engines 

Small Spark-Ignition Engines: Lawnmowers, string trimmers, leaf blowers, and 

chain saws fueled with gasoline 

Large Spark-Ignition Engines: Forklifts, generators, compressors, and welders 

fueled with liquefied petroleum gas, gasoline, or natural gas 

Recreational Vehicles: Off-highway motorcycles, all-terrain vehicles, and 

snowmobiles fueled with gasoline 

Marine Engines and 

Vessels 

Marine Spark-Ignition Engines: Outboard engines, personal water craft, and 

gasoline-fueled sterndrive and inboard engines 

Marine Diesel Engines: Recreational yachts, fishing boats, tug and towboats, 

dredgers, and coastal and ocean-going vessels 

Locomotives Diesel-powered engines used in freight and passenger rail, line-haul, local, and 

switch-yard service 

Aircraft All types of aircraft (ground support equipment not included) 

Source: EPA, Mobile Source Emissions: Past, Present and Future 

1 Ozone is formed by a complex atmospheric chemical reaction of oxides of nitrogen (NOX) and volatile organic compounds 

(VOCs) in the presence of sunlight and heat. NOX and VOCs are known as precursor emissions for ozone. 

1 
As illustrated in Table 1-1, some nonroad sources operate with the use of diesel 

engines and others operate with gasoline, liquefied petroleum gas, or natural gas 

(also known as spark ignition engines). Unlike gasoline engines, diesel engines 

have no spark plug, but take in air and compress it; the fuel is then injected 

directly into a combustion chamber and the heat of the compressed air ignites the 

fuel in the engine. While both engines produce air pollutants, diesel engines 

produce substantially more NOx and particulates, and spark-ignition engines 

generally produce more volatile organic compounds (VOCs). 

Until the mid-1990s, emissions from nonroad mobile sources were largely 

unregulated. In the 1990 Clean Air Act Amendments, Congress directed EPA to 

study the contribution of nonroad sources to ozone and other air pollutants, and to 

issue regulations for nonroad sources found to contribute to air pollution. In 

1991, EPA concluded that nonroad engines contributed significantly to air quality 

problems related to ozone-forming NOx and VOCs, PM, and other pollutants. 

Subsequently, in 2001, EPA found that nonroad and onroad engines also 

contributed to air pollution from 21 air toxics. EPA defines air toxics as “those 

pollutants that are known or suspected to cause cancer or other serious health 

effects or adverse environmental effects.” From 1994 to 2004, EPA issued 14 

regulations to control pollutants from nonroad engines. 

Nonroad Emissions Pose Significant Air Quality and Health Concerns 

Nonroad engines emit significant amounts of diesel exhaust, which has been 

designated a probable human carcinogen. EPA’s most recent data2 indicate that 

nonroad engines produce about 66 percent of the nation’s fine particulate matter 

(PM2.5) from all mobile sources. These nonroad engine emissions contribute 

significantly to air pollution affecting about 88 million Americans living in areas 

that violate PM2.5 air quality standards. Exposure to fine particulate matter has 

been linked to premature death rates and the incidence of cardiovascular and 

respiratory illnesses. Particulate matter is a mixture of solid particles and liquid 

droplets found in air, and comes in a wide range of sizes. Particles less than 

2.5 micrometers in diameter are referred to as fine particles, or PM2.5, and because 

of their small size pose the greatest health risk compared to other particulates. 

These fine particles – about 1/30th of the thickness of a human hair – can lodge 

deeply into the lungs and may even get into the blood stream. Additionally, fine 

particles are the major source of haze. Unless otherwise specified, this report 

focuses on PM2.5 when addressing particulate matter. 

NOx and VOCs combine in the presence of heat and sunlight to form one of the 

most pervasive air pollution problems for major urban areas – ground level ozone. 

Ozone pollution is linked to illnesses such as asthma and heart disease. 

Environmental effects of ozone include crop damage, damage to trees, decreased 

crop yields that cost the agriculture industry billions of dollars, acid deposition, 

2

 EPA 2005 Technology Transfer Network Clearinghouse for Inventories & Emissions Factors: National Emissions 

Inventory Air Pollutant Emissions Trends Data. 

2 
and nutrient overloads in coastal waters. Nonroad engines produce about 

36 percent of NOx and 37 percent of VOC emissions,3

 two ozone precursors 

contributing significantly to air pollution affecting about 159 million Americans 

living in areas that exceed EPA’s 8-hour ozone standard. 

Overall Nonroad Mobile Source Emissions Decreasing, 

But Some Categories Continue to Increase 

Prior to EPA’s 1994 regulations, emissions from nonroad mobile sources (PM, 

and ozone-forming NOx and VOCs) were steadily increasing. Since the nonroad 

regulations came into effect, PM2.5 and VOC emissions have generally declined, 

while NOx emissions have generally begun to level off. However, EPA projects 

that emissions from nonroad sources such as aircraft, marine, and locomotive 

diesel engines will continue to increase. EPA estimates that by 2030, without 

new controls, locomotive and marine diesel engines, as a subset of mobile source 

emissions, will contribute about 27 percent of NOx and 45 percent of fine diesel 

PM. While aircraft emissions contribute 1 percent of these NOx emissions 

nationwide, some cities with greater airport traffic see larger NOx emissions and 

these emissions levels are expected to grow. 

Figures 1-1 through 1-3 illustrate the NOx, PM2.5, and VOC emissions for nonroad 

sources from 1990 to 2002. As shown, emissions for all three steadily increased 

prior to EPA’s nonroad regulatory actions, which began to be implemented in 

1996. 

 Figure 1-1: Change in Nonroad Mobile Figure 1-2: Change in Nonroad Mobile

 Source NOx Emissions From 1990 to 2002 Source PM2.5 Emissions From 1990 to 2002 

4, 40 0 

4, 20 0 

ons 4, 00 0 

T

3, 80 0 

3, 60 0 

3, 40 0 

90 

92 

4 

19

199

96 

8 

19

199

00 

02 

19

20

20

Year 

32 0 

31 5 

31 0 

30 5 

ons 

30 0 

29 5 

 T

29 0 

28 5 

28 0 

27 5 

27 0 

0 

2 

4 

6 

8 

0 

2 

199

199

199

199

199

200

200

Year

3

 EPA 2005 Technology Transfer Network Clearinghouse for Inventories & Emissions Factors: National Emissions 

Inventory Air Pollutant Emissions Trends Data. 

3 
 Figure 1-3: Change in Nonroad Mobile Source

 VOC Emissions From 1990 to 2002 

3,000 

2,900 

Tons 2,800 

2,700 

2,600 

2,500 

2,400 

1990

1992 

4

6

199

199

98 

0

19

200

02 20

Year 

Source for Figures 1-1 through 1-3: 

EPA, 2005 National Emission Inventory Air Pollutant 

Emissions Trends Data 

Scope and Methodology 

To assess EPA’s efforts to reduce nonroad mobile source emissions, we reviewed 

EPA reports, regulations, and guidance, and EPA and external stakeholder 

analyses and studies of emissions from nonroad diesel engines. We also 

performed limited analyses from EPA’s National Emissions Inventory Air 

Pollutant Emissions Trends Data, and interviewed officials and representatives 

from the EPA Office of Air and Radiation’s Office of Transportation and Air 

Quality (OTAQ), Ann Arbor, Michigan. In addition, we conducted interviews 

with external stakeholder organizations, including State and local organizations, 

and environmental and industry groups. We also reviewed pertinent sections of 

the Clean Air Act, as amended. Our work was conducted from April 2005 

through February 2006. We conducted our evaluation in accordance with 

Government Auditing Standards, issued by the Comptroller General of the United 

States. Additional details on our scope and methodology are in Appendix A. 

4 
Chapter 2

Despite Regulatory Progress, More Work Needed 

to Achieve Emissions Reductions 

Since 1994, EPA has issued 14 regulations to control emissions from nonroad 

mobile sources. A number of these regulations include multiple tiers of standards, 

with a total of 20 standards for the various nonroad categories. Twelve of the 

standards have already taken effect, seven are in the process of being phased-in, 

and one will not begin to phase-in until 2008. There are approximately 5 million 

nonroad diesel engines in the United States today, many of which are not subject 

to any EPA diesel engine emissions standards. These engines have the potential 

to operate for the next 20 to 30 years and continue to produce high levels of 

pollution. EPA officials are aware of the need to reduce emissions from these 

existing engines, and have encouraged reductions through voluntary initiatives, 

grant awards, and technical guidance. EPA and others have identified 

locomotive, marine, and aircraft engines as increasingly significant sources of 

emissions that will require additional controls. According to EPA, when the full 

inventory of older nonroad engines has been replaced, the nonroad diesel program 

will annually prevent up to 12,000 premature deaths, 1 million lost work days, 

15,000 heart attacks, and 6,000 children's asthma-related emergency room visits. 

EPA Making Regulatory Progress for New Nonroad Engines 

The first of the 14 regulations that EPA has issued since 1994 to control nonroad 

mobile emission sources went into effect in 1996, and the last is to go into effect 

in 2008. EPA has generally taken a phased-in approach when adopting these 

regulations and has issued multiple tiers for certain engine categories, with a total 

of 20 standards promulgated as of April 2006. To illustrate, EPA issued four tiers 

of land-based diesel engine emissions standards, with each tier requiring more 

stringent emissions reductions than the previous one. For example, Tier 4 of the 

land-based standards first goes into effect in 2008 and is expected to take until 

2015 to achieve its 90-percent reduction goal. Additional information on EPA’s 

nonroad emissions regulatory schedule is in Appendix B. 

According to OTAQ officials, at least one set of regulations has been issued for 

each nonroad category, with the exception of stern-based marine engines. 

OTAQ is working on the following nonroad regulations/activities: 

• Implementing land-based diesel engine emission standards (Tiers 3 and 4). 

• Future gasoline control standards. 

• Future standards for locomotive and marine diesel engines. 

• Mobile source air toxics rulemaking. 

5 
• Sulfur Oxides (SOX) Emission Control Area under the 1997 Amendments 

to the International Convention for the Prevention of Pollution from Ships 

(MARPOL-Annex VI). 

• Adopting 2004 NOx standards approved for aircraft by the International 

Civil Aviation Organization. 

• Pursuing international standards for ocean-going marine vessels. 

In 2004, EPA developed the Control of Emissions of Air Pollution From Nonroad 

Diesel Engine and Fuel (Tier 4 standards) – commonly referred to as the Nonroad 

Diesel Engines rule – to reduce emissions from nonroad diesel engines by 

combining engine and fuel controls as a system to increase emissions reductions. 

This concept of integrating engine and fuel controls as a system was 

unprecedented in nonroad regulations. 

The 2004 standards apply to land-based diesel engines, which are typically used 

in construction, agricultural, and industrial equipment. The standards are expected 

to reduce NOx emissions by 90 percent and PM2.5 emissions by 95 percent. EPA 

estimates that by 2030, these reductions will result in a variety of public health 

benefits, including the prevention of 12,000 premature deaths, 1 million lost work 

days, 15,000 heart attacks, and almost 6,000 emergency room visits by children 

due to asthma attacks. The sulfur fuel component of this rule applies to land 

based diesel engines, commercial and recreational marine diesel engines, and 

locomotives, and is expected to reduce sulfur levels by 99 percent. EPA’s 

Nonroad Diesel Engines rule calls for a nationwide transition from diesel fuel 

containing about 3,000 parts per million (ppm) of sulfur today to 500 ppm of 

sulfur in 2007, and eventually to 15 ppm of sulfur by 2010. Low sulfur levels in 

diesel fuel will allow engine manufacturers to use advanced emission control 

technologies that allow emissions reductions for PM2.5 and NOx, and, more 

importantly, address health and environmental risks associated with these 

pollutants. 

EPA Undertakes Non-Regulatory Efforts to Reduce Emissions 

from Existing Diesel Engines 

There are approximately 5 million nonroad diesel engines in use in the United 

States today. Many of these are not subject to any EPA diesel engine emissions 

standards. Because diesel engines are durable and likely to continue operating 

over the next 20 years or more, high levels of pollution from these engines will 

persist throughout the life of these engines. 

An OTAQ official highlighted the need to reduce emissions from these engines, 

and noted that EPA had established a goal of reducing emissions from the existing 

11 million onroad and nonroad diesel engines by 2014. Reducing emissions from 

6 
these diesel engines is one of three main priorities that OTAQ plans to address.4 

According to the EPA Region 9 Administrator, reducing emissions from older 

diesel engines is “one of the most important air quality challenges facing the 

country.” To meet the goal of reducing emissions from existing engines, a 

subcommittee of the Clean Air Act Advisory Committee – the Mobile Source 

Technical Review Subcommittee Clean Diesel and Retrofit Working Group – was 

established to: 

• Address how to assess fleets to determine diesel emissions reduction 

strategies suitably, 

• Evaluate in-use performance of retrofit technology, 

• Educate the public on emissions reduction strategies, and 

• Address how to establish national incentives for cleaner diesel strategies. 

Voluntary Diesel Retrofit Program and 

National Clean Diesel Campaign 

To address the challenge of reducing emissions from existing engines, EPA 

established the Voluntary Diesel Retrofit Program and the National Clean Diesel 

Campaign. Established in 2000, the Voluntary Diesel Retrofit Program verifies 

new retrofit technologies, awards grants, and provides technical guidance. In 

2004, EPA established the National Clean Diesel Campaign, which promotes 

retrofit incentives and technical assistance to help reduce pollution from these 

engines and equipment. The campaign also established voluntary programs in the 

marine and construction nonroad sectors – the Clean Ports and Clean 

Construction USA initiatives – to encourage the use of emissions control 

technology, replacement of older equipment, and use of cleaner fuels. Today, the 

National Clean Diesel Campaign is the overall umbrella for EPA’s diesel retrofit 

activities. 

The National Clean Diesel Campaign promotes regional collaborations and 

partnerships, such as the West Coast Diesel Emissions Reductions Collaborative. 

This collaborative is a joint effort with EPA and other Federal, State, local, and 

non-profit and private sector partners to reduce air pollution emissions from diesel 

engines along the West Coast. The collaborative, for example, supported the 

Oregon Construction Equipment Emissions Reduction Project to reduce diesel 

emissions from construction equipment in the City of Portland through diesel 

engine retrofits, cleaner fuels, and engine idle reduction policies. Although a 

mandatory retrofit program may achieve increased health protection sooner, such 

a requirement from the Federal level can only come through a change in the Clean 

Air Act. Concerned with nonroad emissions, some States have implemented their 

own mandatory programs. 

4 EPA outlined three priorities for OTAQ: (1) to successfully implement the diesel programs; (2) focus on 

locomotives, marine diesel engines, mobile source air toxics rule, and programs for small engines; and (3) focus on 

addressing existing diesel engines. 

7 
EPA has worked to encourage emissions reductions through voluntary initiatives, 

grants, and technical guidance. Although some funding is currently available to 

reduce emissions from existing engines, the Acting Director, Compliance and 

Innovative Strategies Division, OTAQ, said additional resources are needed. 

OTAQ has also focused on guidance and technical support to encourage 

emissions reductions. 

Data Not Yet Available to Measure Actual Emissions Reductions 

and Health Benefits 

The Clean Air Act provides EPA with the authority to establish emissions 

standards only for new engines; therefore, nonroad engine emissions standards 

phase in over time as older engines undergo turnover and replacement. Twelve of 

the standards have already taken effect, seven are in the process of being phasedin, and one will not begin to phase-in until 2008. Table 2-1 shows the emissions 

reductions estimates for some nonroad standards; for a complete list, see 

Appendix B. 

Table 2-1: Emissions Reductions Estimates for Existing nonroad regulations 

Regulation 

Implementation 

Date Estimated Results 

Tier 1 standards for landbased diesel engines 

1996-2000 By 2025, 30% reduction in 

NOX emissions 

Phase 1 standards for small 

spark-ignition engines 

1997 By 2020, 32% reduction in 

hydrocarbon emissions 

Gasoline outboard & personal 

watercraft Phase 1 

1998-2006 By 2025, 75% lower 

hydrocarbon emissions on 

average 

Tier 2 standards for land 

based diesel engines 

2001-2006 By 2020 50% NOX and 

40% PM reduction from Tier 1 

levels 

Tier 2 standards for Category 

1 and 2 marine diesel engines 

2004-2007 By 2030, 24% reduction in 

NOX, 12% reduction in PM 

Tier 4 standards for land 

based diesel engines 

2008-2015 By 2030, 95% reduction PM 

and 90% reduction in NOX, 

and 99% reduction SOx levels 

Source: EPA, Federal Register Environmental Documents and EPA OTAQ 

The full benefits of EPA’s regulations may not be realized until 2020-2030, when 

the standards are expected to be fully implemented. These benefits assume engine 

turnover and replacement, behavior which may be influenced by cost and lead 

time, and overall feasibility. For example, EPA estimates that the full emissions 

reductions from the Phase 1 standards (small spark-ignition engines) will be 

achieved by 2020, at which time the existing fleet of engines is expected to have 

turned over. An OTAQ official noted that “even during the phase-in of new 

standards, emission reductions are being seen, since the engines complying with 

the newer standards are being introduced into commerce.” OTAQ provided the 

OIG with projected near-term emission reductions, presented in Table 2-2. 

8 
Table 2-2: Projected Near-Term Emissions Reductions Resulting from All 

EPA Nonroad Standards, Except Aircrafta 

Pollutant 

2006 

Tons 

Reduced 

Percent 

Reduced 

2010 

Tons 

Reduced 

Percent 

Reduced 

THC 1,590,089 33% 2,449,807 47% 

NOx 913,055 21% 1,558,322 33% 

PM10 73,143 21% 117,147 33% 

CO 3,145,113 10% 4,718,399 14% 

THC: Total hydrocarbons 

PM10: Particulate matter up to 10 micrometers in diameter 

CO: Carbon monoxide a If the aircraft category was included in Table 2-2, slightly greater emission reductions 

would result, in particular for NOx. 

Source: EPA OTAQ 

The 2004 Nonroad Diesel Engines rule is viewed by environmental, industry, and 

State and local stakeholders as a successful EPA rulemaking. Similar to other 

nonroad regulations, emissions reductions and the resultant health benefits 

continue to phase-in until 2030. EPA has projected that PM2.5 emissions will be 

reduced by 95 percent and NOx emissions by 90 percent for the land-based diesel 

engine category of nonroad engines by 2030. 

According to OTAQ’s 2004 Final Regulatory Analysis, the Nonroad Diesel 

Engines rule5 will ultimately yield the public health benefits shown in Table 2-3 

by 2030. The timeframe for EPA's analysis reflects engine turnover (existing 

engines being replaced by new, cleaner ones) beginning in 2007 and extending 

through 2030. 

Table 2-3: Projected Public Health Benefits When the Fleet of Older Nonroad 

Engines Has Fully Turned Over (by 2030) 

Full Implementation of Rule Will Annually Prevent Projected Amount 

Premature deaths 12,000 

Hospitalizations 8,900 

Heart attacks 15,000 

Children’s asthma-related emergency room visits 6,000 

Cases of respiratory problems in children 280,000 

Work days lost 1,000,000 

Cases of asthma symptoms in children 200,000 

Source: EPA, Clean Air Nonroad Diesel Rule – Facts and Figures 

5 EPA (2004a), Final Regulatory Analysis: Control of Emissions from Nonroad Diesel Engines, EPA420-R-04-007 (May 2004), 

Table 9-16. 

9 
As shown in Figure 2-1, both the monetized health benefits (shown by the pink 

line) and the tons of PM2.5 emissions reduced (shown by the blue line) are 

projected to appear gradually. EPA projects that health benefits will begin to 

appear in 2007, when the first phase of the low-sulfur diesel fuel requirements 

takes effect for nonroad engines. 

Figure 2-1: Projected PM-2.5 Emissions Reductions and Public Health Benefits Resulting 

from the 2004 Nonroad Diesel Rule 

Projected tons PM2.5 Reduction and Monetized

Health Benefits

21,692 

53,072 

85,808 

110,043 

128,350 

3.61% 

13.4% 

31.7% 

60.82% 

100% 

0 

20,000 

40,000 

60,000 

80,000 

100,000 

120,000 

140,000 

Tons Reduced 

0 

20 

40 

60 

80 

100 

Percent 

2010 2015 2020 2025 2030 

Years 

tons reduced % total monetized health benefits 

Source: EPA, Final Regulatory Analysis: Control of Emissions from Nonroad Diesel Engines 

For the nonroad diesel engine standards, implementation will occur in stages: 

reductions in sulfur content of nonroad diesel fuel will occur first, and then 

adoption of controls on most new nonroad engines. Because full turnover of the 

fleet of nonroad diesel engines will not occur for many years, the emission 

reduction benefits of the standards will not be fully realized until many years after 

the reduction in fuel sulfur content. According to EPA, the overall quantifiable 

benefits will total over $83 billion annually by 2030, with a 30-year net present 

value of $805 billion. 

EPA’s “NONROAD” emission inventory model has limitations that could affect 

the validity of emission reduction projections. The NONROAD model is used to 

estimate emissions from nonroad equipment. This model calculates past, present, 

and future emissions inventories for all nonroad categories, but does not currently 

have the capability to estimate emissions from aircraft, commercial marine 

vessels, and locomotive engines. Also, the emissions data are based on laboratory 

testing instead of actual field testing of in-use applications. In the future, the 

aircraft, locomotive, and commercial marine source categories will be included in 

EPA’s new emissions model – Motor Vehicle Emission Simulator (MOVES) – 

which is currently under development. 

10 
According to an OTAQ official, because the regulations are phased in and 

projections are long term, it is difficult to capture emissions reductions data in the 

short term. Unlike highway vehicles, nonroad engines are not registered, and the 

difficulty in measuring the activity of nonroad vehicles creates a challenge for the 

Agency and the States to collect sufficient reliable data for the NONROAD 

model. 

Further Controls Needed In Nonattainment Areas and for 

Certain Nonroad Categories 

EPA’s deadlines to meet ozone and PM2.5 standards by 2010 are critical to 

meeting human health goals in nonattainment areas. Also, OTAQ officials and 

outside stakeholders identified locomotive, marine, and aircraft engines as sources 

of significantly increasing emissions that will require additional emissions 

controls. 

Nonattainment Areas 

Emissions from nonroad diesel engines are significant contributors to the 

pollution in areas that do not meet National Ambient Air Quality Standards 

(nonattainment areas). EPA's Green Book of nonattainment areas for criteria 

pollutants identifies areas of the country where air pollution levels exceed the 

national ambient air quality standard and are designated as nonattainment. Recent 

data from EPA’s Green Book show that about 159 million Americans live in 126 

ozone nonattainment areas. Additionally, about 88 million Americans live in 208 

counties not meeting EPA’s PM2.5 standards, and EPA’s deadlines to meet PM2.5 

standards by 20106 are critical in these areas. 

Nonattainment areas are required to reduce ozone and PM2.5 emissions as part of 

State Implementation Plans. The 2004 Nonroad Diesel Engines rule is expected 

to begin providing emissions results by 2008, but will not be fully implemented 

until 2015. Therefore, these States will need to look elsewhere for additional 

ozone-forming NOx and PM2.5 reductions. 

Category 1 and 2 Marine Diesel and Locomotive Engine Emissions 

EPA estimates that by 2030, without new controls, locomotive and marine 

(Category 1 and 2) diesel engines will contribute about 27 percent of mobile 

source NOx and 45 percent of mobile source diesel PM emissions. Currently, 

marine diesel engines contribute about 8 percent of mobile source NOx and 

9 percent of mobile source diesel PM emissions, although their relative 

contribution is greater around commercial ports. 

6 With appropriate justification, States are allowed an extension of up to 5 years, or until February 2015, to reach full 

attainment for PM2.5. 

11 
A representative from OTAQ’s marine and locomotive group said that because 

the first standards for marine diesel engines did not take effect until January 2004, 

large projected emissions reductions have not yet been achieved. Additionally, 

this representative said that emissions certification data from engine 

manufacturers indicate they are producing and distributing cleaner engines to 

meet the new standards. However, according to EPA documents, the Tier 1 

marine standards are equivalent to the international emissions standards, which 

are considered less stringent regulations by key OTAQ officials. 

EPA estimates that locomotives currently contribute about 7 percent of NOx and 

5 percent of PM mobile source emissions. Typically, a locomotive engine will 

remain in service 40 years or more before it is scrapped. During that time an 

engine may be remanufactured every 5 to 7 years to restore it to an “as new” 

condition and may travel a million miles between remanufactures. According to 

EPA, locomotive engines have relatively modest emissions standards, and 

continue to emit large amounts of NOx and PM. Emissions requirements issued in 

1997 were considered adequate at the time, but EPA is now considering more 

protective regulations. EPA included sulfur fuel requirements for locomotives in 

the 2004 Nonroad Diesel Engines rule to reduce emissions from these engines and 

improve the ability to use advanced aftertreatment systems. 

OTAQ reported that they are talking with locomotive and marine engine 

manufacturers to develop a strategy to implement more stringent regulations for 

both locomotive and marine engines based on advanced aftertreatment 

technologies. OTAQ expects to issue a notice of proposed rulemaking by 

December 2006 and a final rule in 2007. 

Aircraft Engine Emissions 

Aircraft engine emissions are increasing at a time when other mobile source 

categories are being reduced. Aircraft emissions contribute 0.7 percent of NOx 

emissions from mobile sources nationwide, but some cities with greater airport 

traffic see a larger contribution of NOx emissions from these engines, and these 

emissions are expected to grow. For example, EPA estimates that NOx emissions 

from commercial aircraft in the Atlanta, Georgia area are expected to double by 

2010 and contribute as much as 10 percent of mobile source NOx emissions in 

that area. Nationally, the Federal Aviation Administration projects that 

commercial air travel is expected to increase 45 percent from 2002 to 2020. 

Conclusions 

EPA has issued several nonroad mobile source emissions control regulations that 

will require significant reductions in nonroad source emissions. The full benefits 

of EPA’s regulations may not be realized until 2020-2030 when the standards are 

expected to be fully implemented. However, these regulations have already 

achieved reductions in emissions from some emission source categories. These 

12 
benefits assume engine turnover and replacement – activities which may be 

influenced by cost, lead time, and overall feasibility. 

According to EPA there are approximately 5 million existing nonroad diesel 

engines in the United States, many of which are not subject to EPA diesel engine 

emission standards. EPA has acknowledged the need to reduce emissions from 

existing engines and has introduced voluntary programs and grants to encourage 

emissions reductions from these engines. Although a mandatory retrofit program 

may achieve increased health protection sooner, such a requirement from the 

Federal level can only come through a change in the Clean Air Act. 

This report provides information on the progress of EPA’s efforts to address 

nonroad emissions and makes no recommendations. We plan to perform 

additional reviews of mobile source issues in the future, including an in-depth 

review related to existing engines. 

Agency Response and OIG Evaluation 

In addition to the memorandum sent to the OIG with Agency comments to the 

draft report, the Agency also submitted more specific comments on the draft 

report. These comments were documented in the margins of the draft. A 

summary of the key additional comments follows: 

(1) The draft report should include information on the substantial reductions 

that have already occurred as a result of EPA’s nonroad emissions 

standards. To demonstrate projected emissions reductions in the nearterm, OTAQ prepared data for the OIG using the NONROAD model to 

show projected emissions for the years 2006 and 2010. 

(2) Tier 4 standards incorporated a great deal of flexibility to allow 

manufacturers the lead time necessary to develop and apply aftertreatment 

device technology. 

We agree with the Agency’s key comments, and revisions to the draft report were 

made accordingly. The Agency also provided technical comments to the draft 

report; we made changes based on these comments as appropriate. In both its 

memorandum as well as the comments it provided within the margins of the draft, 

the Agency asked that the OIG include information regarding near-term projected 

emissions reductions to demonstrate the progress that has already been made due 

to EPA’s nonroad emissions standards. To address this comment, the OIG 

incorporated data on projected emissions reductions for 2006 and 2010 in 

“Table 2-2: Projected Near-Term Emissions Reductions Resulting from All EPA 

Nonroad Standards, Except Aircraft” of the report. 

The Agency’s comments are in Appendix C. Appendix D contains a separate 

memo with information that EPA provided to supplement Table 2-2. 

13 
Chapter 3

Challenges Remain to Achieve Emissions Reductions 

Although EPA has made substantial progress in developing regulations to reduce 

nonroad mobile source emissions, challenges remain in regulating the aircraft, 

marine, and small gasoline engine categories. These challenges may hinder 

EPA’s progress in achieving emissions reductions from nonroad engines and in 

protecting public health. In particular: 

• EPA faces significant challenges in issuing regulations for aircraft and 

large ocean-going marine vessels because other government entities and 

international organizations play significant roles in regulating those 

categories of nonroad sources. 

• Small gasoline engines are the largest contributor of nonroad gasoline 

NOx emissions, and while EPA is required to issue new regulations for 

small gasoline engines, technical challenges exist related to lawn and 

garden equipment that must be addressed first. 

• Technical challenges also exist related to the diversity of nonroad engines 

and the wide range of applications of those engines. 

Challenges Exist to Controlling Emissions from Certain Categories 

Large Ocean-going (Category 3) Marine Diesel Engine Emission 

Challenges 

The commercial marine engine sector is particularly challenging because marine 

diesel engines have a long service life (as long as 20 to 30 years), and there are 

limited Federal incentives for retrofitting these engines prior to the end of their 

useful life. Also, most large ocean-going vessels (category 3 diesel engines) are 

subject to international standards rather than U.S. standards. EPA estimates that 

commercial marine diesel vessels annually emit about 1,000,000 tons of ozoneforming NOx, 40,000 tons of PM2.5, and 160,000 tons of sulfur dioxide. 

EPA has set engine emissions (Tier 1) standards for large ocean-going marine 

(Category 3) vessels flagged in the United States. The International Maritime 

Organization sets the engine emissions standards for foreign-flagged ocean-going 

vessels. As noted in Chapter 2, Tier 1 marine standards are equivalent to the 

international emissions standards and considered less stringent. However, OTAQ 

staff said that the standards are based on the technology available at the time the 

standards were adopted, and there have been technological advancements within 

14 
the nonroad diesel sector since then that OTAQ hopes to apply to the marine 

sector. 

EPA must continue to work with the international community to regulate 

emissions from these engines. The International Maritime Organization was 

established under the United Nations to address safety, navigation, and pollution 

prevention for ships involved in international trade. According to EPA 

documents, foreign-flagged vessels account for about 97 percent of calls on 

U.S. ports, and it is likely that the contribution of U.S. vessels with Category 3 

engines to local air pollution is small compared to foreign vessels. Because most 

of these ships are subject to International Maritime Organization standards rather 

than U.S. standards, EPA faces significant legal issues regarding its authority to 

regulate these vessels under the Clean Air Act. 

From an environmental perspective, International Maritime Organization 

standards that are particularly useful are the 1997 Amendments to the 

International Convention for the Prevention of Pollution from Ships (MARPOL - 

Annex VI), which address air emissions such as ozone-depleting substances, 

onboard incinerators, emissions from tanker operations, and NOx and SOX 

emissions from ship engines. MARPOL-Annex VI went into effect in May 2005, 

and 28 countries have signed it. In April 2006, the United States Senate gave its 

advice and consent to the ratification of MARPOL-Annex VI, but has not yet 

ratified the treaty. According to OTAQ staff, some of the potential benefits of the 

United States joining the MARPOL-Annex VI agreement are related to the 

designation of SOX Emission Control Areas, since it would help prevent, reduce, 

and control air pollution from SOX emissions. Additionally, MARPOL-Annex VI 

would give the United States authority to inspect foreign ships entering U.S. ports 

for compliance with MARPOL-Annex VI standards. 

OTAQ staff also noted they are working with the international community and 

other stakeholders to develop a second tier of more stringent marine diesel 

standards. In July of 2005, the International Maritime Organization formally 

agreed to begin deliberations regarding a potential second tier of emission 

standards for ocean-going marine vessels. OTAQ and EPA’s Office of 

International Affairs staff are actively working with the International Maritime 

Organization to establish aggressive future standards for ocean-going vessels, 

according to OTAQ representatives. 

Aircraft Engine Emissions Challenges 

Similar to marine diesel and locomotive engines, the long service life of aircraft 

engines is a substantial challenge to reducing these emissions, and there are no 

Federal incentives for retrofitting these engines prior to the end of their useful life. 

As mentioned in Chapter 2, emissions from commercial aircraft are a growing 

segment of mobile source emissions. Some aircraft engines have a life span of 

about 30 years and account for about 45 percent of total emissions among all 

15 
airport operations. Further, shared authority for regulating aircraft emissions, 

both internationally and within the Federal Government, add additional 

challenges. 

EPA and the Federal Aviation Administration have joint authority for regulating 

aircraft emissions. An OTAQ official told us that sharing joint authority has been 

challenging because the two agencies have different missions and approaches. 

OTAQ officials said the Federal Aviation Administration focuses on aircraft 

safety, and their emissions agenda is more consistent with that of the airline 

industry than EPA’s emissions agenda. 

In addition, the International Civil Aviation Organization is the international 

governing body for the aviation industry, seeking to ensure safety, equality, and 

consistency among the international aircraft community through the development 

of standards and procedures for aircraft engines. A final rule for the control of 

pollution from aircraft was issued last year to adopt the Organization’s current 

standards, but an OTAQ official told us that these standards are essentially a 

codification of the existing EPA aircraft standards, and are not technologyforcing. Currently, about 90 percent of aircraft engines in use already meet these 

standards. Further, the official said EPA has tried on numerous occasions to 

adopt more stringent aircraft emissions regulations but has not been successful. 

Small Gasoline Engine Challenges 

Small gasoline engines such as lawn and garden equipment are the largest 

contributor of nonroad gasoline NOx emissions (44 percent), and the second 

largest contributor of PM2.5 emissions (31 percent) among nonroad gasoline 

sources nationwide. Thus, small gasoline engines are another nonroad engine 

emissions source in need of emissions reductions. One specific challenge, 

described next, exists with respect to reducing emissions from small gasoline 

engines less than 50 horsepower. 

A rider enacted in the 2004 VA-HUD7 appropriations bill preempts any State 

(with the exception of California8

) from adopting or enforcing standards relating 

to the control of emissions from new nonroad spark-ignition engines smaller than 

50 horsepower. Section 209(e)(B) of the Clean Air Act Amendments of 1990 

provided States flexibility in choosing between Federal emission standards or 

7

 Appropriations Bill for the Department of Veterans Affairs and the Department of Housing and Urban 

Development 8

 There appears to be a typographical error in the VA-HUD Appropriation language which states that “[t]he 

prohibition in subsection (e) does not apply to or restrict in any way the authority granted to California under 

Section 209(e) of the Clean Air Act (42 U.S.C. 7543(e)).” Subsection (e) does not expressly contain any 

prohibition, but rather contains language regarding the effect of these provisions on the enforcement by States of 

California standards enacted prior to September 1, 2003. We conclude that in referring to “the prohibition in 

subsection (e),” the drafters intended to reference subsection (c), which includes the following prohibition: “[n]o 

state or political subdivision thereof may adopt or attempt to enforce any standard or other requirement applicable to 

spark ignition engines smaller than 50 horsepower.” 

16 
California’s more protective standards. Now, because of the 2004 VA-HUD 

rider, States are prohibited from adopting (under section 209(e) of the Clean Air 

Act Amendments) the stricter California standards for this subset of small 

nonroad vehicles or engines. 

EPA had previously issued two sets of regulations – Phase 1 and 2 Emissions 

Standards Engines at or Below 19 kW – to control emissions from new small 

spark-ignition (small gasoline) engines less than 25 horsepower in 1997 and 2000, 

and did not intend to issue additional regulations for these engines in the near 

future. Since States are preempted from adopting California’s regulations for 

small engines less than 50 horsepower, Congress directed EPA to issue revised 

small gasoline engine emissions regulations by December 2004. EPA did not 

meet the 2004 deadline, which an OTAQ official said was unrealistic. In June 

2005, the Senate approved a provision requiring EPA to conduct a safety study on 

the effects of installing new emission controls on lawnmowers (a small gasoline 

engine) and their potential to cause fires and burns, which could have impacted 

the development of the revised rule. Congress required EPA to complete the 

study by February 2, 2006, and prohibited the Agency from publishing proposed 

or final regulations until after the study was complete. EPA completed the study 

in March 2006, and concluded that adding emission control technologies would 

not increase the risk of fire and burns to consumers. Now EPA can begin the 

rulemaking process for the Phase 3 emission standards. 

Nonroad Diesel Engines Rule Presents Technical Challenges 

The diversity of nonroad engines presents several technical challenges to the 

successful implementation of the most recent rule. The 2004 Nonroad Diesel 

Engines rule is based on a systems approach in which emissions reductions will 

be accomplished through a combination of engine modifications, reduced content 

of sulfur in diesel fuel, and exhaust aftertreatment devices. EPA and other key 

stakeholders described this systems-based approach as technology-forcing, 

requiring technological advancements or new applications, and combinations of 

existing technology to meet required emissions standards. To meet these 

challenges, EPA will need to address: (1) diversity of nonroad engine 

applications, (2) integration of aftertreatment technology, and (3) availability of 

low sulfur fuel. Details on each follow. 

Diversity of Nonroad Engine Applications 

The nonroad diesel engine sector covers a diverse range of equipment and engine 

applications, from tractors to generators. EPA believes the emissions reduction 

technology currently used for the onroad sector can be transferred to the nonroad 

sector, but transferring this technology to the diverse engine types and sizes in the 

nonroad sector, in some cases, may be challenging. While onroad engines operate 

under a narrow range of sizes and designs, each nonroad diesel engine application 

17 
involves different mechanical and duty cycle demands, resulting in a variety of 

engine designs and configurations. 

Integration of Aftertreatment Technology 

Exhaust aftertreatment technology or retrofit devices are used to control engine 

emissions, such as PM and NOx, before they leave the tailpipe. Examples of these 

devices include oxidation catalysts, selective catalytic reduction devices, 

particulate filters, and NOx catalysts. The integration of aftertreatment devices in 

nonroad equipment presents a challenge due to the variation in operating 

temperatures and space constraints. For example, PM aftertreatment devices must 

be operated above a certain temperature, while NOx aftertreatment devices have 

both a low and high temperature requirement. Further, the technology for 

controlling PM emissions is more mature than that for controlling NOx. 

Nonroad equipment also has safety and visibility requirements that must be taken 

into account when designing aftertreatment devices. For example, nonroad 

equipment operators must have a clear view of the operating area for equipment 

attachments, such as shovels and buckets, without being blocked by the engine 

compartment. While some equipment using a particular engine may have 

sufficient space to accommodate aftertreatment devices, the same engine used on 

another piece of equipment may not have enough room. 

To help address these challenges, EPA incorporated flexibilities into the Tier 4 

nonroad diesel rule to allow manufacturers the lead time necessary to develop and 

apply aftertreatment device technology. In certain cases, this flexibility extends 

for some manufacturers until 2020. 

Availability of Low Sulfur Fuel 

The use of aftertreatment devices to control NOx and PM emissions will depend 

on the availability of ultra low sulfur diesel fuel. Currently, diesel fuel contains 

sulfur levels of about 3,400 ppm. EPA’s sulfur fuel standards in the 2004 

Nonroad Diesel Engines rule should enable the use of new technology to reduce 

PM and NOx emissions and, more importantly, address health and environmental 

risks associated with these pollutants. These standards require refineries to reduce 

the sulfur content of diesel fuel to 500 ppm by 2007 and to 15 ppm by 2010. 

Thus, the availability of 15 ppm ultra low sulfur diesel fuel is critical. 

Conclusions 

EPA emissions control regulations exist for almost all nonroad engine categories, 

but challenges to reducing emissions from these engines remain. These 

challenges involve the development of regulations with other Federal Government 

entities and international organizations, as well as other issues generally outside 

of EPA’s control. These challenges may hinder EPA’s progress in achieving 

18 
emissions reductions from nonroad engines and protecting public health. 

Technical challenges exist related to the diversity of nonroad engines and the 

wide range of applications of those engines, and will require creating a wide 

variety of engine designs and sizes to accommodate emissions controls. Further, 

operating constraints, varying temperature ranges, and equipment sizes create a 

challenge regarding the placement of aftertreatment devices. 

Agency Response and OIG Evaluation 

See Agency Response and OIG Evaluation section at the end of Chapter 2, along 

with Appendices C and D. 

19 
Status of Recommendations and 

Potential Monetary Benefits 

POTENTIAL MONETARY 

RECOMMENDATIONS BENEFITS (in $000s) 

Planned 

Rec. No. 

Page 

No. Subject Status1 Action Official 

Completion 

Date 

Claimed 

Amount 

Agreed To 

Amount 

No recommendations 

20 
Appendix A 

Details on Scope and Methodology 

We conducted our work from April 2005 through February 2006 in accordance with Government 

Auditing Standards issued by the Comptroller General of the United States. This report presents 

information based on results from preliminary research; field work was not conducted because a 

follow-on evaluation is planned in the near future. This report focused on EPA’s efforts to 

reduce emissions from nonroad sources, and not those of States or environmental and industry 

groups. Nonetheless, we interviewed officials from associations representing air pollution 

control agencies across the United States, as well as officials from selected State and local 

agencies, and environmental and industry groups, to ascertain their views on EPA’s nonroad 

emissions reduction efforts. We selected these stakeholders based on their involvement in EPA’s 

nonroad rulemaking efforts and involvement in the nonroad sector. 

To review EPA’s approach to reducing nonroad mobile source emissions, the progress made, and 

what opportunities and challenges exist in implementing actions that could lead to greater 

emissions reductions, we reviewed several documents. These documents included applicable 

Agency rulemakings, policies, guidance, and other documentation regarding planning, 

implementation, and oversight of programs to reduce emissions from nonroad mobile sources. 

We also examined external stakeholder reports, including the following: 

Policies, Guidance, and Reports Reviewed 

• Clean Air Act Amendments of 1977 and 1990, Sections 110 , 209, 213, and 231 

• 1991 Nonroad Mobile Sources Study 

• 2004 Control of Emissions of Air Pollution From Nonroad Diesel Engines and Fuel Rule 

• Agency Strategic Plans 

• Regulatory announcements for various nonroad diesel engine categories 

• Various State and local environmental group reports pertaining to nonroad diesel engine emissions 

• NONROAD emissions inventory model 

• EPA National Emissions Inventory Air Pollutant Emissions Trends Data, 2005 

• Clean Air Act Advisory Committee, Mobile Sources Technical Review Subcommittee 

meeting notes and presentations 

• Clean Air Act Advisory Committee, Mobile Sources Technical Review Subcommittee – 

Clean Diesel and Retrofit Working Group 

• National Clean Diesel Campaign 

• EPA Voluntary Diesel Retrofit Program 

• 2005 Diesels Emissions Reduction Act 

• Congestion, Mitigation, and Air Quality Program 

• State and local incentive and grant emission reduction programs 

• EPA marine and locomotive regulations 

• International Maritime Organization regulations 

• EPA aircraft regulations 

• Outdoor Power Equipment Institute 

We also interviewed key air program officials and representatives at OTAQ, which is part of 

EPA’s Office of Air and Radiation. We also interviewed the following external stakeholders 

21 
from State and local environmental organizations, environmental groups and associations, and 

industry: 

Key Stakeholders Contacted 

EPA • Clean Air Act Advisory Committee – Clean Diesel and Retrofit Working Group 

• Clean Air Act Advisory Committee – Mobile Sources Technical Review 

Subcommittee, Ports Sector Working Group staff 

• OTAQ Officials

9 Marine Diesel Engine staff 

9 NONROAD Model Staff 

9 Voluntary Diesel Retrofit Program

External • Association of Equipment Manufacturers 

• Association of Local Air Pollution Control Officials 

• California Air Resources Board 

• Diesel Technology Forum 

• Engine Manufacturers Association 

• Environmental Defense 

• Manufacturers of Emission Controls Association 

• Natural Resources Defense Council 

• Northeast States for Coordinated Air Use Management 

• Puget Sound Clean Air Agency 

• Resources for the Future 

• State and Territorial Air Pollution Program Administrators / 

 Association of Local Air Pollution Control Officials 

To determine EPA’s approach to reduce nonroad mobile source emissions and progress made, 

we identified EPA’s goals and strategies for controlling nonroad emissions from 1994 to the 

present. We identified EPA’s rulemaking status for all nonroad engine categories, including 

effective dates and the expected emission reductions. We reviewed EPA’s regulatory authority 

to address emissions from new and existing engines. To identify EPA’s efforts to address 

emissions from new and existing engines, we reviewed EPA regulations and programs to address 

emissions from nonroad engines, interviewed Agency staff and interested stakeholders, and 

analyzed supporting documentation. We reviewed PM and NOx emission trends. 

To answer the question of what additional opportunities exist for nonroad ozone precursor and 

PM emission reductions, we interviewed OTAQ staff, State officials, local environmental groups 

and associations, and industry stakeholders. This included discussing whether additional 

regulations were needed to address nonroad emissions. We reviewed EPA and other reports on 

the health and air quality impacts of nonroad sectors identified in need of additional emission 

reductions. We reviewed EPA and external documentation to identify nonroad categories with 

projected emissions growth. We identified external stakeholder reports on State and local 

emission reduction programs. We reviewed several Bills/Laws/Acts, such as: 

22 
• The Federal Highway Administration’s Congestion, Mitigation, and Air Quality program, 

signed into law on August 10, 2005, as part of the Safe, Accountable, Flexible, Efficient 

Transportation Equity Act. 

• Diesel Emissions Reduction Act of 2005, signed into law August 2, 2005, as part of the 

Energy Policy Act of 2005. 

To answer the question of what challenges EPA faces in effectively addressing nonroad 

emissions, we interviewed key EPA officials and external stakeholders to ascertain their 

perspective on the regulations for foreign-flagged (Category 3) marine vessels as well as aircraft, 

and the roles of the International Maritime Organization and International Civil Aviation 

Organization in addressing harmful emissions. We reviewed documentation on foreign-flagged 

marine vessels and aircraft emissions. We interviewed EPA and external stakeholders to 

understand EPA’s progress in revising rules for small gasoline engines. We reviewed 

Congressional reports and documentation regarding small gasoline engines. 

This report provides information on the progress of EPA’s efforts to address nonroad emissions 

and makes no recommendations. We plan to perform additional reviews of mobile source issues 

in the future, including an in-depth review related to existing engines. 

Management Controls 

This report provides information on the status of EPA’s efforts to address nonroad emissions, 

and makes no recommendations for Agency action due to the limited scope discussed above. As 

such, a review of EPA management control systems was not conducted. To fully assess EPA’s 

nonroad emission reduction strategies related to existing nonroad engines, the Office of Inspector 

General plans further work regarding EPA’s programs to reduce emissions from nonroad diesel 

sources. 

Data Quality 

We reviewed EPA’s 2005 National Emissions Inventory Air Pollutants Emissions Trends Data 

for PM2.5, NOx, and VOCs, but did not conduct a data reliability assessment of the inventory as 

this was not the focus of our objectives. 

Prior Reports 

The EPA Office of Inspector General has not issued any reports specific to nonroad emissions 

reductions efforts. During the course of our evaluation, we reviewed the following Government 

Accountability Office reports related to airport emissions: 

• Aviation and the Environment: Airport Operations and Future Growth Present 

Environmental Challenges (GAO/RCED-00-153), August 2000 

• Aviation and the Environment: Strategic Framework Needed to Address Challenges 

Posed by Aircraft Emissions (GAO-03-252), February 2003 

23 
Appendix B 

EPA’s Regulatory Schedule for Nonroad Engines 

Equipment 

Category 

Rule Making and Date 

Final Rule Established 

Phases/Tiers of 

Emissions 

Standards 

Implementation 

Date of 

Emissions 

Standards 

Actual/ Planned 

Emissions 

Reductions 

Land-Based 

Diesel Engines 

Control of Air Pollution; 

Amendments to Emission 

Requirements Applicable to New 

Nonroad Compression-Ignition 

Engines at or Above 37 kW: 

Provisions for Replacement 

Compression-Ignition Engines and 

the Use of On-Highway 

Compression-Ignition Engines in 

Nonroad Vehicles (published 

November 12, 1996) 

Control of Emissions of Air Pollution 

from Nonroad Diesel Engines 

(published October 23, 1998) 

Control of Emissions of Air Pollution 

From Nonroad Diesel Engines 

(published June 29, 2004) 

Tier 1 

Tier 2 

Tier 3 

Tier 4 

1996-2000 

2001-2006 

2006-2008 

2008-2015 

Tier 1: 30% reduction 

in NOX and 37% 

reduction by 2025 

Tiers 2 and 3: By 2020 

exceed 50% NOX and 

40% PM reduction 

By 2030 , 95% 

reduction in PM and 

90% reduction in NOX 

And 99 % reduction 

sulfur fuel levels 

Land-Based 

Spark-Ignition 

Engines 

Small SparkIgnition 

Control of Pollution; Emission 

Standards for New Nonroad SparkIgnition Engines At or Below 19kW 

(published July 3, 1995) 

Phase 2 Emission Standards for 

new Nonroad Spark-Ignition 

Nonhandheld Engines At or Below 

19kW (published March 30, 1999) 

Phase 2 Emission Standards for 

New Nonroad Spark-Ignition 

Handheld engines At or Below 

19kW and Minor Amendments to 

Emission Requirements Applicable 

to Small Spark-Ignition Engines and 

Marine Spark-Ignition Engines 

(published April 25, 2000) 

Phase 1: <25 hp 

Phase 2: <25 hp 

non-handheld 

engines 

Phase 2: <25 hp 

handheld 

engines 

1997 

2001-2007 

2002-2007 

Phase 1: 32% 

reduction in HC by 

2020 

Phase 2: 60% 

reduction in HC and 

NOX from Phase 1 

level 

Phase 2: 70% 

reduction in HC and 

NOX from Phase 1 

level 

24 
Equipment 

Category 

Rule Making and Date 

Final Rule Established 

Phases/Tiers of 

Emissions 

Standards 

Implementation 

Date of 

Emissions 

Standards 

Actual/ Planned 

Emissions 

Reductions 

Large SparkIgnition 

Control of Emissions from Nonroad 

Large Spark-Ignition Engines, and 

Recreational Engines (Marine and 

Land Based) (published November 

8, 2002) 

> 25 hp 2004-2007 By 2030, 75% 

reduction in HC, 82% 

reduction in NOX. 

61% reduction CO, 

60% reduction in PM 

Recreational 

Vehicles 

ATVs & 

Motorcycles 

Snowmobiles 

Control of Emissions from Nonroad 

Large Spark-Ignition Engines, and 

Recreational Engines (Marine and 

Land Based) (published November 

8, 2002) 

The regulation 

does not include 

tiers of standards 

2006-2007 

(ATVs & 

Motorcycles) 

2006-2012 

(Snow Mobiles) 

67% reduction in HC 

28% reduction in CO 

Marine Engines 

and Vessels 

Marine SparkIgnition 

Control of Air pollution for New 

Gasoline Spark-Ignition Engines: 

Exemptions for New Nonroad 

Compression Ignition Engines at or 

Above 37 Kilowatts and New 

Nonroad Spark-Ignition Engines at 

or Below 19 Kilowatts (published 

October 4,1996) 

Tier 1: Outboard 

& personal water 

craft 

1998-2006 By 2025 ,75% lower 

HC emissions on 

average 

Marine Diesel 

Engines 

Small Engines Control of Emissions of Air Pollution 

from Nonroad Diesel Engines 

(published October 23, 1998) 

Tier 1 

Tier 2 

1999 or 2000a 

2004 or 2005a 

Tier 1 and Tier 2: 

exceed 50% NOX and 

40% PM reduction 

These are the same 

as the Tier 2 and 3 

Land Based Diesel 

Engine standards 

Commercial diesel 

marine engines, 

Categories 1 and 2 

Control of Emission from New 

Marine Compression-Ignition 

Engines at or Above 30 Liters per 

Cylinder (published February 28, 

2003)b 

Control of Emission of Air Pollution 

from New Marine CompressionIgnition Engines at or Above 37 kW 

(published December 29, 1999) 

Tier 1 

Tier 2 

2004 

2004-2007a 

Not available 

24% reduction in NOX, 

12% reduction in PM 

in 2030 

Commercial 

marine diesel 

engines, Category 

3 vessels flagged 

or registered in the 

U.S. 

Control of Emission from New 

Marine Compression – Ignition 

Engines at or Above 30 Liters per 

Cylinder (published February 28, 

2003) 

Tier 1 2004 Not available 

25 
Equipment 

Category 

Rule Making and Date 

Final Rule Established 

Phases/Tiers of 

Emissions 

Standards 

Implementation 

Date of 

Emissions 

Standards 

Actual/ Planned 

Emissions 

Reductions 

Category 3 vessels 

– foreign flagged 

vessels 

MARPOL-Annex VI 

(international marine standards) 

The regulation 

does not include 

tiers of standards 

2000 20% NOX reduction 

Recreational 

Control of Emissions from New 

Marine Compression-Ignition 

Engines at or Above 30 Liters per 

Cylinder (published February 28, 

2003) 

Tier 1 2004 Not available 

Control of Emission from Nonroad 

Large Spark-Ignition Engines, and 

Recreational Engines (Marine and 

land-Based) (published November 

8, 2002) 

Tier 2 2006-2009 Not available 

Locomotives 

Emission Standards for 

Locomotives and Locomotive 

Engines (published April 19,1998) 

Tier 0: engines 

originally 

manufactured 

1973-2001 

Tier 1: engines 

originally 

manufactured 

and thereafter, 

2002-2004 

Tier 2: engines 

originally 

manufactured 

2005 or later 

2001-2005 By 2040, 59% 

reduction in NOX and 

(41% reduction by 

2010) 

46% reduction in PM, 

43% reduction in HC 

Aircraft 

Control of Air Pollution from Aircraft 

and Aircraft Engines; Emission 

Standards and Test Procedures, 

(published November 17, 2005) 

The regulation 

does not include 

tiers of standards 

December 19, 

2005 

Approximately 16% 

reduction in NOX 

emissions 

CO: Carbon Monoxide 

HC: Hydrocarbons a

 Effective dates depend on Engine Size. b This rule also applies the Tier 1 standards to Category 1 and Category 2 engines with a displacement of 

2.5 liters/cylinder and greater. The Tier 1 standards are equivalent to the MARPOL-Annex VI NOx and 

began in 2004. Beginning in 2007, Category 1 and Category 2 engines must comply with the Tier 2 

standards. 

Source: EPA, Program Update: Reducing Air Pollution from Nonroad Engines, April 2003 

26 
Appendix C 

Agency Response to Draft Report 

September 8, 2006 

MEMORANDUM 

SUBJECT: Comments on OIG’s “Progress Report on EPA’s Nonroad Mobile Source 

Emissions Reduction Strategies” 

FROM: William L. Wehrum 

Acting Assistant Administrator 

TO: J. Rick Beusse, Director 

Office of Inspector General 

I am writing to provide you with the Office of Air and Radiation’s comments on the draft 

Inspector General Report, “Progress Report on EPA’s Nonroad Mobile Source Emissions 

Reduction Strategies,” (No. 2005-001206, May 16, 2006). Thank you for the extended 

opportunity to review and comment on this report. 

The report has identified a number of important challenges for EPA as we try to reduce 

air pollution from the few remaining categories of nonroad equipment where we have yet to 

effect meaningful control. I am very concerned, however, as I discussed with Acting Inspector 

General Bill Roderick on July 31, that the report does not reflect the important progress that we 

have achieved thus far. 

The first task OIG set out for this report was to determine “the effectiveness of EPA’s 

efforts to reduce nonroad mobile source emissions, particularly ozone precursor emissions.” The 

draft report, however, provides little evaluation or analysis of the enormous progress EPA has 

made in reducing ozone precursors (and other pollutants) from nonroad sources. Since the Clean 

Air Act Amendments of 1990, EPA has implemented standards for nearly every nonroad source 

category. Millions of engines, vehicles and equipment have been introduced into commerce in 

the past decade that are cleaner because of these standards, resulting in substantial reductions in 

air pollution. This has helped states meet the National Ambient Air Quality Standards for ozone, 

particulate matter and carbon monoxide, in addition to providing meaningful public health and 

welfare benefits. The report does not quantify these reductions, but instead indicates that EPA’s 

efforts to date will not have any impact for 20 to 30 years. This is an important issue which 

should be addressed. 

Please see the attached mark-up of the draft report for additional detailed comments. 

I trust these comments will be helpful in completing your work on this report. Please feel 

free to contact me or Bill Charmley (734-214-4466) if you have any questions about our 

comments or if we can provide additional information. 

Attachments 

27 
Appendix D 

Agency Memo on Projected Near-Term Nonroad 

Emissions Reductions

August 25, 2006 

MEMORANDUM 

SUBJECT: Impact of EPA Nonroad Rules on Emissions for 2006 and 2010. 

FROM: Craig Harvey and Penny Carey 

Assessment and Standards division 

TO: John Koupal, Director, Air Quality and Modeling Center 

Assessment and Standards Division 

This memorandum documents the emission reductions for calendar years 2006 and 2010 

projected to occur from all existing EPA nonroad emission standards, except aircraft standards. 

The NONROAD emission inventory model was used for all nonroad source categories except 

aircraft, commercial marine, and locomotive engines. For the two years selected, 2006 and 

2010, NONROAD was used to estimate the national emissions inventory for total hydrocarbons 

(THC), oxides of nitrogen (NOx), particulate matter less than 10 micrograms (PM10) and carbon 

monoxide (CO). For each year, annual emission inventories were estimated for two scenarios. 

First, inventories were estimated with no EPA emission standards in place. Second, emission 

inventories were estimated with the current status quo, that is, with all EPA emission standards 

which have been finalized as of August, 2006 assumed. 

NONROAD does not currently have the capability to estimate emissions from aircraft, 

commercial marine and locomotive engines. Emission estimates for these categories have 

historically been done using spread-sheet models. For locomotive engines, the uncontrolled fuelspecific emission factors contained in the 1997 locomotive final rule were used together with the 

2006 and 2010 locomotive fuel use estimates in the 2004 Clean Air Nonroad Diesel Rule to 

calculate the locomotive inventories with no EPA emission standards in place. The control 

inventories in the 2004 Clean Air Nonroad Diesel Rule incorporate all EPA locomotive 

standards which have been finalized to date, so these were used directly for the second scenario. 

For commercial marine engines, the inventories with no EPA emission standards in place were 

taken from the 1999 final rule affecting Category 1 and 2 engines, and the 2003 final rule 

affecting Category 3 engines. The control inventories in the 2004 Clean Air Nonroad Diesel 

Rule incorporate all EPA commercial marine standards which have been finalized to date, so 

these were used directly for the second scenario. 

28 
The inventories for the source categories were then combined for each scenario. The outputs of 

these two scenarios were then compared and are summarized in Table 1. 

Table 1: Emission reductions from all EPA nonroad standards, except aircraft 

2006 2010 

Pollutant Tons Reduced Percent Reduced Tons Reduced Percent Reduced 

THC 1,590,089 33% 2,449,807 47% 

NOx 913,055 21% 1,558,322 33% 

PM10 73,143 21% 117,147 33% 

CO 3,145,113 10% 4,718,399 14% 

The results of this analysis show, for example, that in 2006, EPA’s existing emission standards 

for nonroad sources are projected to have resulted in a 33% reduction in total hydrocarbons, a 

reduction of 1.5 million tons, excluding the aircraft category. 

In the future, the aircraft, locomotive, and commercial marine source categories will be included 

in EPA’s new emissions model, MOVES. If the aircraft category was included in Table 1, it 

would show slightly greater emission reductions, in particular for NOx. 

29 
Appendix E 

Distribution 

Office of the Administrator 

Acting Assistant Administrator for Air and Radiation 

Deputy Assistant Administrator for Air and Radiation 

General Counsel 

Agency Followup Official (the CFO) 

Agency Followup Coordinator 

Audit Followup Coordinator, Office of Air and Radiation 

Associate Administrator for Congressional and Intergovernmental Relations 

Associate Administrator for Public Affairs 

Director, Office of Transportation and Air Quality 

Deputy Director, Office of Transportation and Air Quality 

Audit Liaison, Office of Transportation and Air Quality 

Acting Inspector General 

30