Controlling mobile source emissions is a key strategy for reducing ambient particulate matter (PM) emissions and to comply with the National Ambient Air Quality Standards (NAAQS). The California Air Resources Board (ARB) has adopted new regulations, strengthened existing regulations, and implemented control programs for reducing emissions of PM from light-duty vehicles (LDV) and heavy-duty diesel trucks (HDDT). Since model year (MY) 2007, all HDDTs are certified to a stringent PM emissions standard of 0.01 g PM per brake-horsepower-hour using diesel particulate filter (DPF) aftertreatment. Recently, ARB adopted the Low Emission Vehicle (LEV) III regulations, which will reduce the PM emissions for LDVs over the Federal Test Procedure (FTP) to 3 mg/mi beginning with MY 2017, and to 1 mg/mi beginning with MY 2025. This dissertation discusses and investigates some of the key issues for reducing PM emissions from both HDDTs and LDVs. It is subdivided into the following five chapters: an introduction (Chapter 1), three chapters of original research (Chapters 2-4), and a discussion of the implications and conclusions of the work (Chapter 5).
Chapter 2 evaluates PM emissions during a process called diesel particulate filter (DPF) regeneration, which is the periodic oxidization of accumulated soot into mostly carbon dioxide. The PM emissions released during this process are noteworthy and need to be controlled. However, the total PM emissions, following equal treatments of loading, decreased by over an order of magnitude between the MY 2007 and 2010 HDDT.
Chapters 3 and 4 evaluate particle size distribution, effective density, and an alternative method called Integrated Particle Size Distribution (IPSD) to further support measurement of PM from vehicles emitting below 1 mg/mi. The evaluation of the IPSD method provided a better understanding of the variability of PM emissions of vehicles meeting the LEV III standards. The implementation of the 1 mg/mi standard is currently scheduled to begin with MY 2025 vehicles, and serves to prevent emissions backsliding associated with the introduction of newer and more fuel-efficient engine designs that could result in excess PM emissions.
At the time of filing, Chapter 2 has been published in the Journal of Aerosol Science (JAS), Chapter 3 has been submitted to JAS, and Chapter 4 is in preparation for submission to Environmental Science & Technology.