CARB Launches Rulemaking for Heavy-Duty Engine Low NOx Standard

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On November 3, the California Air Resources Board (CARB) announced plans for a new low-nitrogen oxide (NOx) standard for heavy-duty engines sold in the state.  CARB intends to adopt the new NOx standard—of 0.02 grams per brake horse power-hour (g/bhp-hr)—in 2019.  This standard would apply beginning with 2023 model year engines sold in California.  CARB stated that this new rulemaking will combine amendments to:

  • The heavy-duty engine NOx standards, including a low load certification cycle;
  • The Not-to-Exceed in-use compliance program;
  • The useful life and durability requirements in certification;
  • Warranty period requirement; and
  • Emission Warranty Information Reporting

The stringent NOx standards are likely to pose significant challenges for industry.   As discussed in our blog on the federal Phase 2 emission standards, and earlier blog on this expected 0.2 g/bhp-hr NOx standard, coupling a lower NOx emission standard with greenhouse gas (GHG) emission reductions comes with trade-offs.  As companies implement GHG controls to meet the Phase 2 emission standards, NOx emissions will increase.  Specifically, industry expects some after-treatment configurations, proposed by CARB to meet NOx standards, to lead directly to GHG increases.

NOx is a precursor to ozone, and the state of California is required to meet ozone and particulate matter (PM) attainment levels in the South Coast and San Joaquin Valley.  The state is not required, however, to specifically reduce these criteria pollutant emissions by reducing NOx from heavy-duty engines.  To the extent there is a direct trade-off between reduction in NOx and increasing GHG, the  overall clean air benefits to the state appear minor compared to the expense required for industry compliance.

EPA is likely to also adopt a NOx standard, but it’s expected to be less stringent, and have a longer timeframe for implementation, i.e. a coordinated effort is not expected.   In the end, if California adopts a stringent standard, it matters very little what EPA does.  While the California standard will be more onerous, engine manufacturers will likely certify all of their engines to the stricter California standards, rather than manufacturing two different sets of engines.