CARB Staff Release White Paper to Provide Response to Manufacturers Regarding NOx Requirements

CARB staff released a white paper in April to respond to engine manufacturers requests for feedback regarding NOx requirements for Model Year (MY) 2022 and newer engines. Engine manufacturers are preparing their design and development plans to meet Phase 2 Greenhouse House Gas (GHG) requirements and want feedback from CARB on proposed NOx requirements, so they can include in their design and development plans. 

The NOx standard has gone from 6.00 grams per brake horsepower hour (g/bhp-hr) in 1990 to 0.20 g/bhp-h in 2010. Even with a significantly lower NOx standard, CARB believes NOx levels are still a major contributor to poor air quality. They find that heavy duty trucks are still responsible for 70% of NOx from on-road mobile sources. To further lower NOx levels, CARB developed optional low NOx standards in 2013 and passed the 2016 State Strategy for the State Implementation Plan (SIP). The SIP requires NOx emission standards to be 90% lower then they are curently. Since the SIP was approved in 2017, CARB staff have been working on how they can make this a requirement a reality and will be required to present a plan to the board in the First Quarter of 2020. 

The white paper emphasized that their assessment is, "strictly staff's current assessment of what is currently considered as technically achievable and cost effective for 2022 and subsequent model years." The assessment may change if new information becomes available. 

In their assessment, CARB staff does not think new NOx standards need to be implemented for 2022 and 2023 MY engines. However, they do think that stricter NOx standards should be developed for 2024 through 2026 MY engines. They believe it is technically achievable and cost effective for NOx standards to be brought down from .20 g/bhp-h to .05 - .08g/bhp-h for 2024 through 2026 MY engines. The NOx standards for these MY engines would align with Phase 2 GHG requirements. 

CARB staff does not think there is enough information to determine the NOx standards for 2027 and newer MY engines, but believes this information will be available in the near future. CARB plans to introduce a more strict NOx standard for 2027 and newer MY engines once sufficient data becomes available. They also mentioned that the stricter standards would align with the final phase of the GHG requirements. 

For Transport Topics summary of the CARB white paper, click here. 
To read the white paper, click here.