Regulatory Background on the U.S. Mobile Source Emission Control Program

U.S. EPA Clean Air Nonroad Diesel Rule

On May 11, 2004, the U.S. Environmental Protection Agency (EPA) issued their final comprehensive national program to reduce emissions from nonroad diesel engines. Based in large part on the 2007 highway diesel program, the proposal sets out: 1) new engine exhaust emissions standards and emissions test procedures, including not-to-exceed requirements, for nonroad engines used in most kinds of construction, agricultural, and industrial equipment, and 2) sulfur control requirements for nonroad, locomotive, and marine diesel fuel.

EPA states that exhaust standards associated with the nonroad rule will result in particulate matter (PM) and nitrogen oxide (NOx) emissions levels that are in excess of 95 percent and 90 percent, respectively, below comparable levels today. These standards will begin to take effect in the 2008 model year, with a phase-in of standards across five different engine power rating groupings. Diesel fuel used in nonroad, locomotive, and marine applications would meet a 500 ppm sulfur cap starting in June 2007, a reduction of approximately 90 percent. In June 2010, sulfur levels in nonroad diesel fuel (excluding locomotive or marine diesel fuel) would meet a 15 ppm cap, for a total reduction of over 99 percent.

EPA expects the entire nonroad diesel engine inventory to comply with these new nonroad standards by 2030 (based on estimated fleet turnover). The program's estimated environmental benefits include reductions of 738,000 tons of NOx and 129,000 tons of particulate emissions annually by 2030. The anticipated health benefits of these emission reductions are enormous and include the annual prevention of 12,000 premature deaths, 15,000 heart attacks, and more than 280,000 cases of respiratory symptoms in children. EPA has estimated the costs of the program to average from one to three percent of the total purchase price of most nonroad diesel equipment, with the net cost of ultra-low sulfur fuel averaging about four cents per gallon.

Important provisions of the final rule are summarized below.

Exhaust Emission Standards

Tables 1 and 2 show the proposed "Tier 4 emission standards" for PM, NMHC, and NOx for different rated power categories of nonroad diesel engines. Table 3 summarizes the phase-in schedule for Tier 4 NMHC and NOx emission standards as a function of engine rated power. The emission levels and phase-in requirements contained in these tables are identical to those originally proposed by EPA in April 2003.

 

Table 1. Tier 4 PM Emission Standards (g/bhp-hr)

 

Rated Power
2008
2009
2010
2011
2012
2013
<25 hp
0.30
-
-
-
-
-
25 to <75 hp
0.22
-
-
-
-
0.02
75 to <175 hp
-
-
-
-
0.01
-
175 to 750 hp
-
-
-
0.01
-
-

 

 

Table 2. Tier 4 NOx and NMHC Emission Standards (g/bhp-hr)

 

Rated Power
NOx
NMHC
25 to <75 hp
3.5 NMHC+NOx
3.5 NMHC+NOx
75 to <175 hp
0.30
0.14
175 to 750 hp
0.30
0.14

 

 

Table 3. Tier 4 NOx and NMHC Phase-In Schedule

 

Rated Power
2011
2012
2013
2014
25 to <75 hp
-
-
100%
-
75 to <175 hp
-
50%
50%
100%
175 to 750 hp
50%
50%
50%
100%

 

All proposed Tier 4 PM standards would require 100 percent compliance in the model year shown in Table 1. Manufacturers may also choose to skip the 2008 0.22 g/bhp-hr PM standard for 50-75 hp engines and instead meet the more severe 0.02 g/bhp-hr PM standard for these same engines in 2012, one year earlier than the 2013 compliance requirement shown in Table 1. The 0.02 g/bhp-hr and 0.01 g/bhp-hr PM standards are expected to require the use of particulate filter technology over all nonroad diesel engines with rated power of 25 hp or greater. The 0.22 g/bhp-hr and 0.30 g/bhp-hr PM standards for smaller engines that would be implemented in 2008 are expected to be met with either advanced engine designs, the application of diesel oxidation catalysts, or the combination of advanced engine designs with oxidation catalysts.

The Tier 4 NOx and NMHC standards shown in Table 2 for engines rated at 75 hp and larger are similar in stringency to the final standards included in the 2007 highway diesel program and are expected to require the use of high-efficiency NOx emission control technology systems (e.g., NOx adsorbers or SCR catalysts) to ensure compliance. EPA is phasing in many of these standards over a period of three years in order to address lead time, workload, and feasibility considerations. This phase-in approach for NMHC and NOx is modeled after the NOx phase-in provisions of the 2007-2010 highway diesel program. The final program does not include any Tier 4 NOx standards for the smallest categories of engines (<75 hp), but the program does include provisions for a technology review in 2007 to review the feasibility of tighter NOx emission standards on these smaller engines. This 2007 technology review will also consider if a more stringent, long-term PM standard for engines under 25 hp is appropriate.

For the largest nonroad engine segment (over 750 hp), EPA has established the emission standards summarized in Table 4 that require 100 percent compliance for new engines in 2011 and 2015, depending on whether these engines are used as stationary power generators or in mobile machinery.

 

Table 4. Tier 4 Emission Standards for Engines over 750 hp (g/bhp-hr)

 

Application Class
2011 PM
2011 NOx
2011 NMHC
2015 PM
2015 NOx
2015 NMHC
Generator sets up to 1200 hp
0.075
2.6
0.30
0.02
0.50
0.14
Generator sets >1200 hp
0.075
0.50
0.30
0.02
0.50
0.14
Mobile machinery
0.075
2.6
0.30
0.03
2.6
0.14

 

For these largest engines, the 0.50 g/bhp-hr NOx standard is expected to require the use of NOx-based emission controls (e.g., NOx adsorbers or SCR), while the 2.6 g/bhp-hr NOx level is expected to be achieved using engine-based controls. The 0.02 and 0.03 g/bhp-hr PM standards that are required in 2015 are expected to require the use of PM-based emission controls. All application segments would be expected to use particulate filter technologies starting in 2015. The choice of a 0.03 g/bhp-hr PM standard for mobile machinery is based on EPA's prediction that these large vehicles will rely on wire or fiber mesh-based particulate filter technology rather than ceramic-based wall-flow filters. EPA indicates in the final rule that it will continue to consider evaluating the appropriateness of a more stringent long-term NOx standard for mobile machinery.

CO emission standards for all ranges of engine power remain unchanged from Tier 3 levels.

Nonroad Diesel Fuel Sulfur Levels

Nonroad diesel fuel currently has sulfur levels of about 3,400 ppm on average. Beginning June 1, 2007, refiners will be required to produce nonroad, locomotive, and marine diesel fuel that meets a maximum sulfur level of 500 ppm. This does not include diesel fuel for home heating, industrial boiler, or stationary power uses or diesel fuel used in aircraft. Then, beginning in June 1, 2010, fuel used for nonroad diesel applications (excluding locomotive and marine engines) will be required to meet a maximum sulfur level of 15 ppm since all 2011 and later model year nonroad diesel-fueled engines with advanced emission control technology must be refueled with this new ultra-low sulfur diesel fuel. This sulfur standard is based on EPA's assessment of the impact of sulfur on advanced exhaust emission control technologies and a corresponding assessment of the feasibility of ultra-low sulfur fuel production and distribution.

In the final rule, EPA indicates that, with respect to locomotive and marine application, it is their intent to propose new future emission standards for these engines that could require the use of high efficiency exhaust emission control technology and thus the use of 15 ppm sulfur diesel fuel. EPA did, however, choose to include in the final nonroad rule the requirement for the production of ultra-low sulfur diesel fuel for locomotive and marine applications starting in June 2012, two years after the introduction of 15 ppm sulfur fuel for other nonroad applications.

For More Information

The EPA final nonroad rule and related documents are available at: www.epa.gov/nonroad-diesel/2004fr.htm.