15 April 2003 | updated 25 April 2003

The US Environmental Protection Agency (EPA) signed today proposed Tier 4 emission standards and diesel fuel regulation for nonroad diesel engines. The proposed standards—which reduce emissions of particulate matter (PM) and oxides of nitrogen (NOx) in various engine categories by as much as 90% and more—would be phased-in over the period 2008-2014.

The proposed emission standards apply to new mobile nonroad diesel engines, such as those used in construction, agricultural, and industrial equipment. The standards do not apply to locomotive, marine, or mining engines (EPA will issue a proposal for the next tier emission standards for locomotives and marine engines by Spring 2004; mining engine emissions remain under the jurisdiction of MSHA).

The fuel program included in the proposal limits the sulfur content in diesel fuel used for nonroad engines, as follows:

  • 500 ppm effective 2007 for fuels used in nonroad, locomotive and marine engines
  • 15 ppm effective 2010 for nonroad fuel (but not for locomotive or marine fuels)

Proposed Tier 4 emission standards for PM and NOx and their implementation dates (phase-in periods) are listed below.

Proposed Tier 4 Emission Standards, g/kWh (g/bhp-hr)
Rated Power, P Year PM NOx
P < 19 kW (25 hp) 2008 0.40 (0.30) -
19 ≤ P < 56 kW (75 hp) 2013 0.03 (0.022) 4.7* (3.5)
56 ≤ P < 130 kW (175 hp) 2012-2014 0.02 (0.015) 0.40 (0.30)
130 ≤ P < 560 kW (750 hp) 2011-2014 0.02 (0.015) 0.40 (0.30)
P ≥ 560 kW (750 hp) 2011-2014 0.02 (0.015) 0.40 (0.30)
* NOx + NMHC

The proposal also introduces an interim Tier 4 PM standard of 0.30 g/kWh (0.22 g/bhp-hr) for engines of 19-56 kW, effective 2008.

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With the exception of engines below 19 kW (25 hp), the proposed exhaust emission standards are similar in stringency to the 2007-2010 requirements for engines used in highway trucks and buses. They will require the use of diesel particulate filters and NOx control catalysts. The ultra low sulfur fuel (15 ppm S) would enable the introduction of several catalyst based emission control devices (such as catalytic particulate filters and NOx adsorber/catalysts) that otherwise would be deactivated by sulfur. Considering that nonroad engines have currently more relaxed standards than highway engines, implementation of the proposed Tier 4 standards may present a bigger technological challenge than it is the case with the 2007-2010 standards for highway engines. Added complexity is also presented by the great diversity in nonroad engines—there are currently 650 nonroad engine families in the USA from some 60 manufacturers, compared to only 107 highway engine families from 10 manufacturers.

The EPA estimated that affected nonroad diesel engines currently account for about 44% of total diesel PM emissions and about 12% of total NOx emissions from mobile sources nationwide. By 2030, 9,600 premature deaths would be prevented annually due to the implementation of the proposed standards.

EPA estimated the cost of producing 500 ppm fuel to be on average 2.5 cents per gallon. Average costs for 15 ppm fuel are estimated to be an additional 2.3 cents per gallon, for a combined cost of 4.8 cents per gallon.

The estimated costs for added emission controls vary depending on equipment size and application. For the vast majority of equipment, EPA estimated the cost of meeting emission standards at 1-2% compared with the typical retail price. For example, for a 175 hp bulldozer that costs approximately $230,000 it would cost an additional $2,600 to add the advanced emission controls and to design the bulldozer to accommodate the modified engine.

The Tier 4 proposal in only partially harmonized with European regulations. The new EPA transient test cycle is identical to that introduced with the EU Stage III nonroad standards proposal this January. The PM standards, however, are different, with the EU Stage IIIB of 0.025 g/kWh compared to the Tier 4 of 0.02 g/kWh. The EU has not yet proposed aftertreatment-forcing standards for NOx.

Public hearings concerning the Tier 4 proposal will be held on 10 June 2003 in New York, NY; on 12 June 2003 in Chicago, IL; and on 17 June 2003 in Los Angeles, CA. The comment period for the proposed rule expires on 20 August 2003.

Source: US EPA (Tier 4 page)