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Final US EPA emission standards for heavy-duty diesel engines

7 October 1997

The US EPA adopted today a new combined emission standard for oxides of nitrogen (NOx) and hydrocarbons (HC) for model year 2004 and later heavy-duty diesel engines used in trucks and buses. The new standard represents a 50% reduction in NOx from the 1998 and later model year NOx standard. In 2020, EPA projects a reduction of 1.1 million tons per year of ozone precursors due to the new standard. In addition, the reduction of NOx emissions will also result in a reduction of secondary nitrate particulate matter, which forms in atmosphere when NOx combines with ammonia, of about 43,000 tons per year.

The standard is in the form of combined non-methane hydrocarbons (NMHC) plus NOx and is presented in units of grams emitted per brake horsepower-hour (g/bhp-hr). Manufacturers have the choice of certifying their engines to either 2.4 g/bhp-hr NMHC + NOx or 2.5 g/bhp-hr NMHC + NOx with a limit of 0.5 g/bhp-hr on NMHC.

EPA also proposed the above standard for gasoline-fueled engines, but is not finalizing the standard at this time. The Agency is planning a supplemental rulemaking to address gasoline-fueled engines specifically.

Nitrogen oxides from diesel engines are a major contributor to the formation of ground-level ozone and particulate matter. Ozone reduces lung function and aggravates existing respiratory problems such as asthma. It can also cause a breakdown in a person's ability to fight off infectious bacteria. Particulates become lodged in the lungs' most sensitive tissue and may result in premature death. In addition, ozone, particulate matter and nitrogen oxides cause crop damage, acid rain, and reduction in visibility.

EPA estimates the new standard will cause a near term retail price increase of $260-$470 per vehicle, with cost decreasing to half that amount in five years. The near term increase represents a 2 to 4% increase in engine price and less than 1% of the price of most new heavy duty vehicles. EPA does not expect any increase in fuel consumption due to the new rule. The long term cost effectiveness of the final rule is estimated to be $100 - $200 per ton of NOx plus HC.

The new standard reflects the provisions of the Statement of Principles (SOP) signed in July 1995 by the EPA, California Air Resources Board and the manufacturers of heavy duty diesel engines. Following the SOP, EPA issued an Advanced Notice of Proposed Rulemaking (ANPRM) on 31 August 1995, and formally proposed the standard on 27 June 1996. According to the EPA, stakeholders continued their support for the new standard during the comment period for the rulemaking.

See the DieselNet Emission Standards section (US Heavy-Duty Truck and Bus Engines) for more details on the new regulations.