Real-World Emissions from Modern Heavy-Duty Diesel, Natural Gas, and Hybrid Diesel Trucks Operating Along Major California Freight Corridors
Emiss. Control Sci. Technol.
Real-World Emissions from Modern Heavy-Duty Diesel, Natural Gas, and Hybrid Diesel Trucks Operating Along Major California Freight Corridors
David C. Quiros 0 1 2
Arvind Thiruvengadam 0 1 2
Saroj Pradhan 0 1 2
Marc Besch 0 1 2
Pragalath Thiruvengadam 0 1 2
Berk Demirgok 0 1 2
Daniel Carder 0 1 2
Adewale Oshinuga 0 1 2
Tao Huai 0 1 2
Shaohua Hu 0 1 2
0 Monitoring and Laboratory Division, California Air Resources Board , 1927 13th, Sacramento, CA 95811 , USA
1 South Coast Air Quality Management District , 21865 Copley Drive, Diamond Bar, CA 91765 , USA
2 Mechanical and Aerospace Department, West Virginia University , 395 Evansdale Drive, Morgantown, WV 26506 , USA
Emissions were measured from seven heavy-duty (HD) on-road vehicles that were operated along six common route types used for freight transport in California. All vehicles had engines that were certified to the 0.01 g/bhp-h particulate matter (PM) and either a 0.2, 0.3, or 2.3 g/bhp-h nitrogen oxide (NOx) standard. Diesel vehicles had low carbon monoxide (CO) and total hydrocarbon (THC) emissions below brake-specific standards, with route averages ranging from 0.24 to 3.35 g CO/ mi and from 0.02 to 0.45 g THC/mi. Diesel vehicles equipped with selective catalytic reduction (SCR) had route average NOx emissions ranging from 0.58 to 3.99 g/mi (0.16 to 0.96 g/bhp-h). NOx emissions were less route-dependent for the one vehicle with a 12-L compressed natural gas (CNG) engine and threeway catalyst (TWC), with route averages ranging from 0.16 to 0.46 g/mi (0.06 to 0.13 g/bhp-h). The ranking of certification NOx emissions for the seven engines reported during enginedynamometer-based certification was not maintained during real-world testing; for example, highway driving NOx emissions were lower than certification values for some engine families and higher than certification values for others. Route-average gravimetric particulate matter (PM) emissions ranged from 4 to 12 mg/ mi, which on a brake-specific basis were at least two times below the 0.01 g/bhp-h standard. Ion speciation of PM emissions indicated that the most prevalent species were sulfate (SO42−) for the model year (MY) 2007 diesel vehicle equipped with a diesel particulate filter (DPF) and no SCR, nitrate (NO3−) for conventional diesel vehicles with a DPF and SCR, and sodium (Na+) was the most abundant species for the CNG vehicle. NOx and PM emissions were compared to, and show generally good agreement with, the latest California mobile source model (EMFAC2014).
Heavy-duty truck; Portable emission measurement system; Nitrogen oxides; Selective catalytic reduction; Diesel particulate filter; On-road testing; Freight; Greenhouse gas
1 Introduction
Extensive human epidemiological and animal exposure studies
have demonstrated short-term and chronic health effects from
exposure to both ozone [1, 2] and fine particulate matter (PM)
[3–6]. Emissions reductions for nitrogen oxides (NOx) and PM
are needed in many areas of California and the USA, especially
in regions that are in nonattainment of the National Ambient Air
Quality Standards (NAAQS) for ozone and fine PM [7–9].
Onroad heavy-duty (HD) trucks are not only responsible for the
largest fraction of freight emissions in California, which
statewide is responsible for 50 % of diesel PM, 45 % of the nitrogen
oxides (NOx), and 6 % of the greenhouse gas (GHG) emissions
[10] but also are the category of mobile sources with the greatest
fuel consumption in the USA [11]. New HD on-road engines
manufactured to the model year (MY) 2010 standard have 97 %
lower NOx and PM emissions than engines manufactured to the
MY 1987 emission standard; these current limits are 0.2 g NOx/
bhp-h and 0.01 g PM/bhp-h when tested over the Federal Test
Procedure (FTP) and Supplemental Emission Test (SET) cycles.
However, additional stringency is needed to achieve several air
quality goals in the coming decades, most notably, attainment of
ambient air quality standards for ozone. Near-term strategies to
reduce criteria pollutant emissions in California over the next
5 years include turning over the heavy-duty fleet through
implementation of the Statewide Truck and Bus Regulation, adopting
more stringent certification, in-use compliance, and warranty
reporting requirements [12, 13]. Thereafter, additional in-use
regulations or incentive programs may be needed to accelerate the
adoption of newer technologies and adopting more stringent
certification standards [14].
In-use programs that are used to accelerate the adoption of
newer technologies into the long-lived fleet are important
because the median lifetime mileage accrual for a heavy-HD
(HHD, >33,000 lbs gross vehicle weight rating, GVWR)
vehicle operating in the USA is nearly 800,000 mi (1,290,000 km)
[12]. Accordingly, the California Air Resources Board (CARB)
adopted the Truck and Bus Regulation in 2008 [15], which
requires phasing-out older equipment and the adoption of MY
2010 or newer (...truncated)