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.

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 (NAAGS) 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 volatile 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 serious 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 recently, 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 promulgated 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 projected 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 particulate formation”) which account for a substantial fraction of the airborne particulate 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 urging 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 implementing stationary source NOx control options (as well as stationary source VOC controls) for the control of acid rain, ozone, or both. In many areas, however, these controls will not be sufficient for reaching and maintaining the ozone standard without significant additional NOx reductions from mobile 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 California 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 manufacturing 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 growing 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 standards. 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. Similarly, 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 reductions. 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 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 differences in application and usage can complicate direct translation of the technology, technology transfer from highway to nonroad represents a future avenue for additional mobile source emission reductions.

In response to the need for additional pollution reduction measures at the national level, EPA held a series of discussions with the California Air Resources Board (CARB) and representatives of the HDE manufacturing industry to exchange views on the appropriateness and feasibility of new emission standards 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 industry/ 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 continue discussions with others with the goal of signing a similar SOP with respect 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 consider additional reductions from nonroad HDES. For purposes of this ANPRM, the Agency is primarily interested in nonroad sources greater than 50 horsepower (37 kilowatts). The ANPRM provides an early focus for an open and comprehensive discussion of the issues involved in achieving additional emission reductions from HDEs and makes the SOP available for public comment.

EPA invites comment from all interested parties on the need and potential 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.

Please submit comments no later than October 2, 1995, 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 modem; 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/OMSWVW/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

Source: US EPA

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Last Update – 21-Mar-97