NISTIR 6888
Technology Adoption Indicators Applied to the ATP Flow-Control Machining Project

Appendix A
EPA Phase 1 and Phase 2 Regulations on
Nonroad Nonhandheld Small Engines

Under the Clean Air Act (1990), the Environmental Protection Agency was directed to study and regulate the emissions of nonroad engines (engines used in vehicles not driven on roadways). The EPA found that nonroad engines contributed significantly to pollution, emitting nitrogen oxides (NOx), hydrocarbons (HC), nonmethane hydrocarbons (NMHC), carbon monoxide (CO), and particulate matter (PM). Subsequently, under Phase 1 in 1997, lower emissions were required for new nonroad engines less than 19 kW (25 HP). In March 1999, the EPA finalized Phase 2 emissions standards for new nonroad non-handheld spark-ignition engines at or below 19 kW that phase in between 2001 and 2007.⁽³⁶⁾   The Phase 2 emissions standards also addressed handheld engines (such as those used in leaf blowers and lawn-and-garden-type trimmers and edgers). The EPA plans to propose regulations for nonroad engines in recreational uses as well as nonroad engines larger than 19 kW (25 HP) in 2001.

The Phase 2 emissions limits are defined by engine displacement class. Displacement categories, measured in cubic centimeters (cc) for engine classes I and II, are shown in Table 8.⁽³⁷⁾   Most walk-behind lawnmowers use engines that fall into engine Class I, and the remaining larger mowers fall in engine Class II.

In 1997, Phase 1 emissions standards addressed the total hydrocarbons and oxides of nitrogen (HC + NOx) exhaust emissions in engine classes I and II. Phase 1 standards were applied to a newly manufactured engine. New Class I engines were allowed to emit up to 16.1 g/kW·h of HC + NOx, measured at a steady state. Class II engines were allowed to emit up to 13.4 g/kW·h or HC + NOx, measured at a steady state. Classes I and II were not to exceed carbon monoxide (CO) emissions of 519 g/kW·h.

Phase 2 regulations added new emissions test limits using a new test method. Tests are to be done after the engine's service accumulation period (based on the engine's useful life) so that emissions are stabilized. Engine Class I was subject to Phase 2 regulations in 2003 and 2007, as shown in Table 9. Limits on emissions of nonmethane hydrocarbons plus oxides of nitrogen (NMHC + NOx) are applied only to engines fueled by natural gas, and take the place of the limits on HC + NOx emissions. Regulations on Class II engines were phased in from 2001 to 2005, as shown in Table 10.

Table 9 . Phase 2 (1999) Emissions Regulations for Engine Class I

Table 10 . Phase 2 (1999) Emissions Regulations for Engine Class II

_____________________
36. The March 1999 Phase 2 emissions standards are detailed in the Code of Federal Regulations Title 40: Protection
of Environment Volume 14, which includes Section I: Environmental Protection Agency, Part 90, “Control of
emissions from nonroad spark-ignition engines,” dated July 1, 2000 (GPO 2000). Part 90 has 13 subparts, A through
M, that address different aspects of the regulation. The sections numbered 90.1 through 90.7 fall under subpart A,
those numbered 90.103 through 90.126 fall under subpart B, numbers 90.201 through 90.220 under subpart C, and
so on, culminating with subpart M, containing sections 90.1201 through 90.1249. Part 90, in its entirety, requires
129 pages in the Federal Register (pages 166 to 294 in Title 40 Volume 14).

37. Throughout this report, the abbreviation “cc” is used to denote cubic centimeters (cm3). The use of “cc” is
standard industry practice when measuring the displacement of engines, and is therefore followed in this report.

Go to Appendix B or return to Table of Contents.

Date created: June 11, 2003
Last updated: August 3, 2005

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