United States Air and Radiation EPA420-F-95-008a
Environmental Protection September 1995
Agency
Office of Mobile Sources
vvEPA Environmental
Fact Sheet
TIGHTER CONTROLS EVALUATED
FOR NOx, HC AND PM EMISSIONS
FROM HEAVY-DUTY ENGINES
In response to public health concerns, the Environmental
Protection Agency (EPA) has published an Advance Notice of
Proposed Rulemaking which explores a national program to
reduce emissions of oxides of nitrogen, hydrocarbons, and
particulate matter from heavy-duty engines. Despite great
progress in reducing emissions from stationary and mobile
sources, continued growth in the mobile sector threatens to offset
the effect of current controls. Tighter engine emission standards
would assist States in meeting and maintaining National Ambient
Air Quality Standards.
BACKGROUND
Poor air quality represents a serious threat to the health and well-being
of millions of Americans and a large burden to the U.S. economy. This threat
exists despite the fact that, over the past two decades, great progress has been
made at local, state, and national levels in controlling emissions from many
sources of air pollution. However, continued industrial growth and expansion
of motor vehicle usage threaten to offset the effect of technological progress in
emission controls. Today, many states are still finding it difficult to deliver the
quality of air their citizens need and expect in the long-term. Furthermore,
other states which are approaching or have reached attainment of National
Ambient Air Quality Standards (NAAQS) may see those gains lost if current
growth trends persist.
In recent years, efforts to improve air quality have focused largely on
ground-level ozone and its main precursors, oxides of nitrogen (NOx) and vola-
tile organic compounds (VOCs), consisting mostly of hydrocarbons (HC). In
addition, airborne particulate matter (PM) has been a major air quality concern
in many regions. NOx, ozone, and PM have all been linked to a range of seri-
ous respiratory health problems and a variety of adverse environmental effects.
-------
Air Quality Trends
Ozone levels remain unacceptably high in many areas. For many years,
control of VOCs was the main strategy employed to reduce ground-level ozone.
VOC reductions were more cost-effective (on a per-ton basis) and more readily
achievable than NOx reductions. In addition, it was generally believed that
greater ozone benefits could be achieved through VOC reductions. More re-
cently, it has become clear that NOx control is also critical to ozone reduction
efforts, especially where ozone is high over a large region (as in the Midwest
and Northeast). As a result, attention has turned to NOx emissions as a key to
improving air quality in many areas of the country.
Current projections show a slight decrease in total NOx emissions during
the next few years as stationary and mobile source control programs promul-
gated under the 1990 Clean Air Act (CAA) are phased in. However, downward
trends in NOx pollution will begin to reverse and NOx emission inventories will
begin to rise by the early 2000s, due to growth in stationary and mobile source
activity. Emissions from heavy-duty highway and nonroad engines are pro-
jected to represent a significant fraction of these mobile source NOx emissions
by the middle of the next decade. In some areas, the rise in NOx emissions can
be expected to be accompanied by a significant increase in ground-level ozone.
Levels of PM are also expected to rise for two reasons. First, the number of PM
sources is expected to increase. Second, NOx is transformed in the atmosphere
into fine acidic nitrate particles (a phenomenon known as "secondary particu-
late formation") which account for a substantial fraction of the airborne par-
ticulate matter in some areas of the country.
Given these expected trends, and in the absence of new emission control
incentives, some of the nation's hard-won air quality improvements will begin
to be seriously threatened in the early 2000s. In response to widespread urg-
ing by the states, municipalities, and health officials in virtually every region of
the country, EPA is intensifying its efforts to understand and respond to
today's stubborn air quality challenges. Over the past decade, ambient air
measurements and computer modeling studies have demonstrated that ozone
and its precursors, NOx and VOC, are transported across large distances.
Thus, while there is a role for all levels of government to address these issues,
EPA's state and local partners generally agree that long-term clean air goals
can only be achieved with new initiatives at the regional and national level.
Integration of Stationary and Mobile Source Controls
The CAA assigns states jurisdiction for implementing most stationary
source emission controls. In most regions of the country, states are imple-
menting stationary source NOx control options (as well as stationary source
VOC controls) for the control of acid rain, ozone, or both. In many areas, how-
ever, these controls will not be sufficient for reaching and maintaining the
ozone standard without significant additional NOx reductions from mobile
-2-
-------
sources. Those charged with delivering cleaner air to the citizens of their states
look to a national mobile source emission control program as a necessary
complement to their efforts to reduce NOx, PM, HC, and other emissions.
Common emission standards for mobile sources across the nation are
also strongly supported by heavy-duty engine (HDE) manufacturers, which
often face serious production inefficiencies when different requirements apply
to engines/vehicles sold in different states or areas. States may have different
standards for the same vehicle or engine type because the CAA grants Califor-
nia the authority to establish emission control standards for mobile sources,
and other states may adopt California's programs. Therefore, national HDE
controls make compliance simpler and less burdensome for the HDE manufac-
turing industry by harmonizing California's standards for HDEs with federal
requirements.
Heavy-Duty Engines
Motor vehicle emission control programs have a history of technological
success that, in the past, has largely offset the pressure from constantly grow-
ing numbers of vehicles and miles traveled in the U.S. The per-vehicle rate of
emissions from new passenger cars and light trucks has been reduced to very
low levels. As a result, increasing attention is now being focused on heavy-
duty trucks (ranging from large pickups to tractor-trailers), buses, and nonroad
equipment.
Since the 1970s, manufacturers of highway HDEs have developed new
technological approaches in response to increasingly stringent emission stan-
dards. However, the technological characteristics of HDEs, particularly diesel
engines, have to date prevented the achievement of emission levels comparable
to today's light-duty gasoline vehicles. While diesel engines provide advantages
in terms of fuel efficiency, reliability, and durability, control of NOx emissions
is a much greater challenge for diesel engines than for gasoline engines. Simi-
larly, control of PM emissions, which are at very low levels for gasoline engines,
represents a substantial challenge for diesel engines.
Despite these technological challenges, there is emerging agreement that
highway HDEs offer the potential for large additional emission reductions. In
their successful efforts to reach lower NOx and PM levels over the past 20
years, heavy-duty highway diesel engine manufacturers have identified new
technologies and approaches that today offer promise for significant new reduc-
tions. New technological options are available to manufacturers of heavy-duty
gasoline engines as well.
Many engines used in highway trucks have similar counterparts that are
used in nonroad equipment applications. The first emission control regulations
covering these nonroad HDEs have been only recently established; these new
-3-
-------
standards are less stringent than current standards for highway HDEs. A
strong potential exists for transfer of some current highway engine emission
control technology to certain heavy-duty nonroad engines. Even though differ-
ences in application and usage can complicate direct translation of the technol-
ogy, technology transfer from highway to nonroad represents a future avenue
for additional mobile source emission reductions.
EPA REEVALUATES CURRENT STANDARDS
In response to the need for additional pollution reduction measures at
the national level, EPA held a series of discussions with the California Air Re-
sources Board (CARB) and representatives of the HDE manufacturing industry
to exchange views on the appropriateness and feasibility of new emission stan-
dards for HDEs. Based on these discussions, a Statement of Principles (SOP)
regarding highway HDEs has been signed by these parties.
The SOP addresses: (1) NOx, PM, and non-methane HC standards for
highway HDEs; (2) the important role that fuel may play in achieving these
standards; (3) a procedure to reevaluate the appropriateness of these standards
in 1999; (4) the intent of the parties to undertake development of a joint indus-
try/government research program aimed at meeting and exceeding the NOx
and PM levels discussed in the SOP; and (5) the intent of the parties to con-
tinue discussions with others with the goal of signing a similar SOP with re-
spect to nonroad HDEs.
EPA has published an Advance Notice of Proposed Rulemaking (ANPRM) which
reviews the need and potential for additional reductions in NOx, HC, and PM
emissions. It also announces the Agency's intent to establish new emission
controls for highway HDEs starting in model year 2004 and describes EPA's
plans to work cooperatively with engine and equipment manufacturers to con-
sider additional reductions from nonroad HDEs. For purposes of this ANPRM,
the Agency is primarily interested in nonroad sources greater than 50 horse-
power (37 kilowatts). The ANPRM provides an early focus for an open and
comprehensive discussion of the issues involved in achieving additional emis-
sion reductions from HDEs and makes the SOP available for public comment.
EPA SEEKS PUBLIC INVOLVEMENT
EPA invites comment from all interested parties on the need and poten-
tial for additional reduction of NOx, HC, and PM emissions from HDEs and
EPA's plans to achieve such reductions. After reviewing the comments, EPA
intends to issue a Notice of Proposed Rulemaking (NPRM) proposing standards
for highway HDEs in accordance with the SOP. In addition, comments received
regarding reduction in emissions from nonroad HDEs will inform any EPA
discussions with manufacturers regarding additional emission reductions.
-4-
-------
Please submit comments by following the instructions in the Federal
Register notice (8/31/95, 60FR45579). The ANPRM is available electronically
on EPA's electronic bulletin board system, the Technology Transfer Network
(TTN). The service is free of charge, except for the cost of the phone call. Users
are able to access and download TTN files using a personal computer and mo-
dem: for TTN, call (919) 541-5742; for the voice helpline, call (919) 541-5384.
This information is also posted on the EPA Office of Mobile Sources' World
Wide Web homepage on the Internet. The address is: http://www.epa.gov/
OMSWWW/omshome.htm.
For further information, please call the NOx/PM Heavy-Duty Engine
voice mailbox at (313) 741-7887, or write to:
U.S. Environmental Protection Agency
National Vehicle and Fuel Emissions Laboratory
NOx/PM Initiative Team
2565 Plymouth Road
Ann Arbor, Michigan 48105
-5-
------- |