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Nonroad diesel engines are used in machines that perform a wide range of important jobs in our economy. They also contribute greatly to air pollution in many of our nation's cities and towns. Examples of land-based nonroad applications using diesel engines include construction equipment such as backhoes, agricultural equipment such as tractors, material handling equipment such as heavy forklifts, industrial equipment such as airport service vehicles, and utility equipment such as generators and pumps.

Nonroad engines being produced today must meet relatively modest emission requirements and therefore continue to emit large amounts of nitrogen oxides (NOx) and particulate matter (PM), both of which contribute to serious public health problems. Recent data show that nearly 160 million people live in nonattainment areas for ground-level ozone, also called smog, which is formed by NOx and other pollutants. About 65 million people live in areas that violate air quality standards for PM. Reducing nonroad emissions is a critical part of the effort by federal, state, local, and tribal governments to reduce the adverse health impacts of air pollution.

In May 2004, as part of its Clean Diesel Programs, EPA finalized a comprehensive rule to reduce emissions from nonroad diesel engines by integrating engine and fuel controls as a system to gain the greatest emission reductions. The new engine standards will reduce PM and NOx emissions by 90 percent. Closely linked to these engine provisions are new fuel requirements that will decrease the allowable levels of sulfur in fuel used in nonroad diesel engines, locomotives, and marine vessels by more than 99 percent. These fuel improvements will create immediate and significant environmental and public health benefits by reducing PM from engines in the existing fleet of nonroad equipment. It also makes it possible for engine manufacturers to use advanced emission control technologies, similar to those upcoming for highway diesel trucks and buses. These reductions in NOx and PM emissions from nonroad diesel engines will provide enormous public health benefits. EPA estimates that by 2030, controlling these emissions will annually prevent 12,000 premature deaths, 8,900 hospitalizations, and one million work days lost. The overall benefits ($80 billion annually) of this rule outweigh the costs by a ratio of 40 to 1. This final rule is one of a suite of interrelated rules known as the Clean Air Rules of 2004 which address ozone and fine particle pollution, nonroad diesel emissions, and power plant emissions of sulfur dioxide, nitrogen oxides and mercury.

In 1994, EPA adopted the first set of emission standards ("Tier 1") for all new nonroad diesel engines greater than 37 kilowatts (kW) (50 horsepower [hp]), except those used in locomotives and marine vessels. The Tier 1 standards were phased in for different engine sizes between 1996 and 2000, reducing NOx emissions from these engines by 30 percent.

In 1998, EPA adopted more stringent emission standards ("Tier 2" and "Tier 3") for NOx, hydrocarbons (HC), and PM from new nonroad diesel engines. This program includes the first set of standards for nonroad diesel engines less than 37 kW (phasing in between 1999 and 2000), including marine engines in this size range. It also phases in more stringent "Tier 2" emission standards from 2001 to 2006 for all engine sizes and adds yet more stringent "Tier 3" standards for engines between 37 and 560 kW (50 and 750 hp) from 2006 to 2008.

The latest emission standards and diesel fuel sulfur reductions complement the similar program reducing emissions and fuel sulfur for highway diesel engines and fuel for 2007. The engine manufacturing industry had made great technical strides in adapting efficient emission controls from highway diesel to nonroad applications. At the same time, the manufacturers of this equipment that use these engines have responded by creatively incorporating the new engines and emission controls into their machines. These improvements will continue as stringent new emission standards come into effect in the coming years, coupled with the elimination of most of the sulfur from the diesel fuel used in nonroad equipment.

For further information or assistance regarding this Web page, please contact the ASD Information Line at (734) 214-4636 or email: asdinfo@epa.gov.

This page is maintained by EPA's Office of Transportation and Air Quality (OTAQ).
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