California Air Resources Board

Principal Investigator/Author: Kent Johnson

Contractor: University of California, Riverside

Contract Number: 23RD009

Project Status: Active

Relevant CARB Programs: Heavy-Duty Vehicles, Mobile Source Emissions Research Program

Topic Areas: Air Pollution, On-Road Heavy-Duty Vehicles

Research Summary:

Reducing emissions from mobile sources remains one of the most important environmental challenges in the near term and extending out over the next few decades. The California Air Resources Board (CARB) has been a leader in developing and implementing regulations to deal with both air pollutants, such as nitrogen oxides (NOx), and carbon dioxide (CO2) emissions, as the primary greenhouse gas (GHG) of concern. This is being carried out through a range of different regulatory programs that include both increasing tighter emissions standards, as well as the monitoring of heavy-duty diesel vehicle (HDDV) performance and emissions using sensors and the vehicles on-board diagnostic (OBD) system.

Recently, CARB funded one of the largest emissions measurements studies of over 200 HDDVs (CARB contract 16RD012). One interesting finding from the 200 heavy-duty vehicles emission study is that there may be leaks in exhaust systems that may contribute to excess emissions that have not been previously accounted for. Exhaust leaks prior to the aftertreatment system (ATS) in particular can lead to considerably higher emissions, as the exhaust pollutants have not been treated by the ATS prior to being released into the atmosphere.

Given the potential impact of exhaust leaks on emissions inventories in urban areas, it is important to understand the extent to which they are occurring in the real world. The objective of this research is to evaluate the potential extent of exhaust leaks in the in-use HDDV fleet, to characterize the levels of these exhaust leaks, and to better understand their potential impacts. This would include testing exhaust leaks for fleet in-use vehicles. This information will in turn be used to characterize the fraction of vehicles in the on-road and off-road fleet that have leaky ATS and evaluate the potential in-use impacts of these leaks.

Keywords: unfiltered exhaust leaks, NOx emissions, particulate matter emissions, aftertreatment system maintenance, heavy-duty vehicles