example, nonroad emissions are emitted from a wide variety of engines, including land-based diesel engines (tractors, backhoes, and generators), land-based spark ignition engines (chain saws, lawn mowers, airport ground-service equipment, and motorcycles), marine engines, jet and propeller aircraft engines, and diesel locomotives. In most cases, individual emission-control strategies need to be devised for each engine type and for widely varying use and performance cycles.10 Although control of many new nonroad engines, such as portable power equipment and construction vehicles, can follow implementation and jurisdiction patterns similar to those used for on-road vehicles, the control of substantial emissions from aircraft and engines used in international maritime commerce is made much more difficult by the diverse international jurisdictions under which these vehicles fall.

The 1990 CAA Amendments directed EPA to prepare a study of the scope and sources of nonroad emissions and to regulate them if they were found to make a substantial contribution to O3 or CO nonattainment. The EPA report did not make a formal determination of a significant effect, but it contained an inventory of emissions from nonroad sources and concluded, “because nonroad sources are among the few remaining uncontrolled sources of pollution, their emissions appear large in comparison to the emissions from sources that are already subject to substantial emission-control requirements” (EPA 1991). EPA regulations for some of these engines and vehicles started in 1995, and subsequent regulations continue to bring new classes of engines and vehicles under regulation while more stringent regulations are being prepared to replace existing control requirements. In 2002, EPA finalized regulations for a number of nonroad engines and vehicles, including large spark-ignition engines and recreational vehicles (67 Fed. Reg. 68242 [2002]). In April 2003, the agency proposed a national program to reduce emissions from nonroad diesel engines by combining engine and fuel controls. It is expected that engine manufacturers will meet proposed emission standards by producing new engines with advanced emission-control technologies. Because these control devices can be damaged by sulfur, EPA is also proposing to reduce the allowable level of sulfur in nonroad diesel fuel. The proposed exhaust emission standards would apply to diesel engines used in most kinds of construction, agricultural, and industrial equipment and are expected to reduce emissions by


A performance or test cycle is where a vehicle or engine is run over a prespecified range of conditions to create repeatable emission-measurement conditions. Test cycles, such as the federal test procedure, are linked to the certification process to verify and ensure compliance with new-equipment emission standards. As described in this chapter, it is difficult to ensure that all possible driving conditions are represented within the new-vehicle emissions certification process.

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