US EPA, California ARB, reveal plans on new HD diesel emission standard

7 October 1999

Environmental regulatory authorities in the USA revealed their planned new emission standards for new heavy-duty highway engines, which target emission levels of about 0.5 g/bhp-hr for oxides of nitrogen (NOx) and 0.01 g/bhp-hr for particulate matter (PM). These plans were presented by the federal Environmental Protection Agency (EPA) and the California Air Resources Board (ARB) during the SAE Clean Diesel TOPTEC, held last week in Florida, and during the "Exploring New Technologies For Clean Air" symposium in California earlier this week.

The new standard is expected to require exhaust gas aftertreatment technologies, including diesel particulate traps and NOx trap/catalyst systems. Ultra low sulfur diesel (ULSD) fuel will play a key "technology enabler" role in making the standard feasible. ULSD fuels improve the emission reduction effectiveness and durability of diesel oxidation catalysts and are expected to enable future, advanced emission controls.

Diesel fuel sulfur levels of between 5 - 40 ppm are considered by the EPA, while the ARB pointed at the 30 ppm mark. Current US standards allow for up to 500 ppm of sulfur in highway diesel fuel. The final fuel sulfur specification will depend on aftertreatment technology needs for NOx and PM control, refinery production technology feasibility, costs, ability to maintain fuel quality in the distribution system, and testing tolerances.

Ultra low sulfur diesel regulation for HD engines would be also beneficial for light-duty vehicles, which need to use the same aftertreatment technologies to meet the proposed Tier 2 standard.

EPA sees a potential for 70-90% reduction in PM emissions and 60-90% reduction in NOx emissions, relative to today's standards. That translates to about 0.01 g/bhp-hr PM standard, down from current 0.1 g/bhp-hr, and about 0.5 g/bhp-hr NOx standard, down from today's 4 g/bhp-hr (about 2 g/bhp-hr in 2004). Both standards are considered by the EPA as forcing exhaust gas aftertreatment in heavy-duty diesel engines.

The Clean Air Act requires a 3-year stability period between new emission standards. Since the latest adopted HD diesel emission standard comes to power in 2004, the earliest introduction of the new federal standards is possible in the year 2007. The EPA expects a phased-in beginning of the standard in 2007. In California, the ARB Chairman Alan Lloyd has directed the ARB staff to develop a program to reduce emissions from new heavy-duty diesel engines to the above levels beginning in 2007.

A Notice of Proposed Rule Making (NPRM) on the new federal HD standards is expected to be published in early 2000.

Both the EPA and ARB indicated they would also regulate substantial reductions in PM emissions from non-road diesel engines. The federal non-road engine regulation, expected in 2001 (ANPRM in early 2000), would also consider a non-road fuel quality standard similar to the current highway requirement of 500 ppm sulfur cap.