UCLA, ARB, WVU measure on-road particle numbers for heavy-duty diesel and CNG trucks in California

In a new study, a team from UCLA, with colleagues from the California Air Resources Board (ARB) and West Virginia University, measured total particle number emission factors (PNEFs) from six newly certified heavy-duty vehicles (HDVs) powered by diesel and CNG totaling over 6,800 miles of on-road operation in California. They calculated distance-, fuel- and work-based PNEFs for each vehicle. A paper describing their findings is published in the ACS journal Environmental Science & Technology.

They found that distance-based PNEFs of the vehicles equipped with original equipment manufacturer (OEM) diesel particulate filters (DPFs) in the study had decreased by 355–3,200 times compared to a previous retrofit DPF dynamometer study. Fuel-based PNEFs were consistent with previous studies measuring plume exhaust in the ambient air. On-road PNEFs showed route and technology dependence. . . .

The team selected the vehicles in the study to represent four emission technology groups currently prevalent in California:

• One MY 2007 (Vehicle Nº 1) diesel engine with no SCR and certified to a 2.3 g/bhp-hr NOx family emission limit (FEL);
  
  Two MY 2013 (Nº 2 and Nº 5) and a MY 2014 (Nº 4) diesel engines equipped with SCR;
  
  One MY 2013 compressed natural gas (CNG) (Nº 3) 12-L engine with a three-way catalyst (TWC) certified to the 0.2 g/bhp-hr NOx standard; and
  
  One hybrid diesel vehicle (Nº 6) with a MY 2011 engine with no SCR and certified to a 0.47 g/bhp-hr NOx FEL.

All diesel vehicles were equipped with a DOC and a DPF.

Six route types represented real-world driving conditions associated with freight operation in California, including steep hill climb; highway speed; congestion; stop-and-go operations at ports and rail yards; and urban “last-mile” delivery routes. . . .

Broadly, they found that for vehicles with OEM DPFs and Selective Catalytic Reduction Systems, PNEFs under highway driving (i.e., 3.34 × 1012 to 2.29 × 1013 particles/mile) were larger than those measured on urban and drayage routes (i.e., 5.06 × 1011 to 1.31 × 1013 particles/mile). . . .

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