Primary Emissions and Secondary Aerosol Formation from In-use Heavy-Duty Diesel and Natural Gas Vehicles
SAHAR GHADIMI, Hanwei Zhu, David R. Cocker III, Thomas D. Durbin, Georgios Karavalakis,
University of California, Riverside Abstract Number: 373
Working Group: Aerosol Chemistry
AbstractHeavy-Duty Vehicles (HDVs) are major contributors to urban air pollution due to elevated tailpipe nitrogen oxide (NOx) and particulate matter (PM) emissions. Fuel type, driving conditions, and exhaust aftertreatment technologies are known to impact vehicle primary emissions, but less is known about their effect on secondary aerosol (SA) formation. In this study, tailpipe emissions and SA formation from in-use HDVs were assessed. The diesel-powered HDVs were operated with ultra-low sulfur diesel (ULSD) and hydrogenated vegetable oil (HVO), while the natural gas HDVs were operated with compressed natural gas (CNG). Testing was conducted on a chassis dynamometer over the Urban Dynamometer Driving Schedule (UDDS), the Refuse Truck Cycle, the Goods movement cycle, and the CARB HHDDT cruise mode cycle.
In summary, CNG vehicles produced higher ammonium nitrate containing secondary aerosols (up to ~450 mg/mile) compared to diesel HDVs. Inadvertent lubricant oil consumption (confirmed by AMS analysis) in two CNG vehicles was the major source of organic aerosols (up to ~80 mg/mile). HVO fuels resulted in lower precursor emissions and ultimately lower SOA formation compared to ULSD. Generally, secondary aerosol mass production during photochemical aging significantly exceeded primary tailpipe PM emissions. Our results suggest that diesel HDVs with functioning DOC/DPF aftertreatment systems will likely decrease SOA precursor emissions. The use of renewable and aromatics-free HVO will result in lower SOA formation than petroleum diesel. CNG vehicles will likely have a greater contribution to urban SOA formation than current technology diesel vehicles, with a significant contribution to secondary inorganic aerosol.