NOx Emissions of In-Use Trucks
Motivation
The estimated contribution of on-road heavy-duty diesel vehicles to the total NOx emission in California was ~32% in 2016, which is considerably higher than the US average (~16-18% in the past decade).
Objective
This work used on-board NOx sensor data to assess the real-world nitrogen oxides (NOx) emissions from heavy-duty diesel vehicles equipped with Selective Catalytic Reduction (SCR) in California.
Main Conclusions
Although substantial progress has been made in controlling NOx emissions from heavy-duty diesel vehicles since 2010, a large fraction of the fleet could have much higher than expected in-use NOx emissions due to insufficient SCR performance. Potential reasons for insufficient SCR performance include low operation temperature, catalyst malfunction, and insufficient dosing of diesel exhaust fluid (DEF).
Peer-Reviewed Publications
Impact on CARB programs
Results will help understand in-use NOx emissions from heavy-duty diesel vehicles, and inform the revision of heavy-duty OBD requirements. It also helps to identify specific vehicle types that may be malfunctioning on-road. For example, real-world emissions data helped lead to the recall of Cummins engine aftertreatment devices.