September 16, 2019
Emissions Regulations

The emission standards included new, very stringent limits for PM and NOx. The PM emission standard took full effect in 2007. The NOx standard was phased-in for diesel engines between 2007 and 2010. The phase-in was defined on a percent-of-sales basis: 50% from 2007 to 2009 and 100% in 2010 (gasoline engines are subject to these standards based on a phase-in requiring 50% compliance in 2008 and 100% compliance in 2009). In practice, very few engines meeting the NOx limit appeared before 2010. In the 2007-2009 period, most manufacturers opted to meet a NOx family emission limit (FEL) for most of their engines. Because of this compliance path during the NOx limit phase-in period, engines produced during 2007-2009 were technologically very different from those required to comply in 2010 and later when all engines needed to comply with the NOx limit. While it is common to refer to “2010 standards” in a way that implies they are different from “2007 standards”, legally, there was not a standard for 2010 that differed from 2007.

Starting in 2007, manufacturers could choose to chassis certify complete heavy-duty diesel vehicles (HDV) with GVWR as an option to engine certification. The emission limits applicable to Otto cycle heavy-duty vehicles with the same GVWR applied. Diesel engines optionally certified as complete vehicles were not allowed to be included in any averaging, banking, or trading program for criteria emissions. However, they were included in the phase-in calculations that required 50% of engines to comply with the final 2010 NOx limit. Diesel engines thus certified were legally equivalent to a NOx engine provided they met the 2008 Otto-cycle HDV limits. After 2011, all manufacturers of complete HDVs with GVWR (primarily heavy pick-ups and utility vans) adopted this optional chassis certification approach because of the heavy-duty vehicle GHG regulations coming into effect in 2014.

In addition to the FTP testing, emission certification requirements include:

  • SET test, with limits equal to the FTP standards, and
  • NTE limits of 1.5 × FTP standards (or 1.25 × FTP for engines with NOx FEL > 1.5 g/bhp·hr).

The diesel fuel regulation limited the sulfur content in on-highway diesel fuel to 15 ppm (wt.), down from the previous 500 ppm. Refiners were required to start producing the 15 ppm S ultra-low sulfur diesel (ULSD) fuel beginning from June 2006. The ULSD fuel has been introduced as a “technology enabler” to pave the way for sulfur-intolerant exhaust emission control technologies, such as catalytic diesel particulate filters and NOx catalysts that have been widely introduced to meet the 2007/2010 emission requirements.

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Go to for information about the United States Environmental Protection Agency.

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