Heavy-Duty Low NOx

This page last reviewed November 1, 2016


Nonattainment Map A key measure in the Mobile Source Strategy is the establishment of low oxides of nitrogen (NOx) engine emission standards that result in a 90 percent reduction in NOx emissions compared to the emissions of todayís diesel engines.  This measure is critical for attaining federal health-based air quality standards for ozone in 2023 and 2031 in the South Coast and San Joaquin Valley air basins, and fine particulate matter (PM2.5) standards in the next decade.  Under this measure, staff also plans to develop regulatory amendments to improve the certification requirements to better reflect emission control under low load urban driving operations, to improve engine and emission control system durability, and to expand and improve the in-use compliance testing program. These supplemental actions include:

  • Amending the warranty period;
  • Adopting a new low load certification test cycle;
  • Amending the useful life and durability demonstration provisions within the certification requirements for heavy-duty engines; and
  • Amending the Not-to-Exceed (NTE) in-use compliance program.
In 2013, California established optional low-NOx standards with the most aggressive being 0.02 g/bhp-hr, which is 90 percent below the current standard.  The optional NOx standards were developed to pave the way for mandatory standards by encouraging manufacturers to develop and certify low NOx engines and incentivizing the purchase of certified low NOx engines. Currently, Cummins has certified two natural gas engine families to the optional low-NOx standards.  An 8.9 liter engine has been certified to the optional 0.02 g/bhp-hr standard, and a 6.7 liter engine has been certified to the optional 0.10 g/bhp-hr NOx standard. Both engines are currently commercially available.

Need for federal action:  As vehicles purchased outside the state account for a majority of the heavy-duty vehicle miles travelled in the South Coast on any given day, federal NOx engine emission standards are necessary in order to achieve emission reductions from vehicles operating in California that were purchased outside the state.  In the preamble to the Heavy-Duty GHG Phase 2 Final Rule, U.S. EPA affirmed their commitment to consider developing low NOx emission standards for on-road heavy-duty engines. ARB plans on coordinating its regulatory development efforts with U.S. EPA.  ARB Board action on a lower NOx standard for on-road heavy-duty engines is expected in 2019.

Research Activities:  ARB is currently funding a $1.6 million research contract with Southwest Research Institute (SwRI) to assess the feasibility of lower NOx emissions through a combination of engine calibration, exhaust thermal management strategies, and advanced aftertreatment systems (ARB-SwRI Low NOx Project), as described further at: https://www.arb.ca.gov/research/veh-emissions/low-nox/low-nox.htm.  As a follow-on project to the current ARB-SwRI Low NOx Project, ARB is also funding a $1.05 million research contract with SwRI to optimize diesel engine calibrations for low load duty cycles, and develop a low-load certification cycle.

What's New

Posted November 1, 2016:

The agenda and presentations for the November 3, 2016 workshop, as well as the descriptions of workgroups have been posted on the workshops section of this page. The workshop is also available via webcast.

Posted October 5, 2016:

ARB invites you to participate in a public workshop to learn more about potential regulatory measures to reduce NOx emissions from new on-road heavy-duty vehicles.   Additional details can be found in this public notice.


Thursday, November 3, 2016


1:00 p.m. – 5:00 p.m.


South Coast Air Quality Management District
21865 Copley Drive
Diamond Bar, California 91765


Date/Time Description Documents
November 3, 2016
1:00 p.m. - 5:00pm
Public Workshop to Discuss Potential Changes to the Heavy-Duty Engine and Vehicle Emission Standards, Test Procedures, Warranty, and Other Related Heavy-Duty Programs
Workshop Notice



Email List

For more information on ARBís heavy-duty low NOx efforts, please sign up for the Heavy-Duty Low NOx Email List