Long-Term Fuel-Specific NO x and Particle Emission Trends for In-Use Heavy-Duty Vehicles in California

• Published in: Environmental science & technology Vol. 52; no. 10; pp. 6070 - 6076
• Main Authors: Haugen, Molly J, Bishop, Gary A
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.05.2018
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.8b00621

Two California heavy-duty fleets have been measured in 2013, 2015, and 2017 using the On-Road Heavy-Duty Measurement System. The Port of Los Angeles drayage fleet has increased in age by 3.3 model years (4.2–7.5 years old) since 2013, with little fleet turnover. Large increases in fuel-specific particle emissions (PM) observed in 2015 were reversed in 2017, returning to near 2013 levels, suggesting repairs and or removal of high emitting vehicles. Fuel-specific oxides of nitrogen (NO x ) emissions of this fleet have increased, and NO x after-treatment systems do not appear to perform ideally in this setting. At the Cottonwood weigh station in northern California, the fleet age has declined (7.8 to 6 years old) since 2013 due to fleet turnover, significantly lowering the average fuel-specific emissions for PM (−87%), black carbon (−76%), and particle number (−64%). Installations of retrofit-diesel particulate filters in model year 2007 and older vehicles have further decreased particle emissions. Cottonwood fleet fuel-specific NO x emissions have decreased slightly (−8%) during this period; however, newer technology vehicles with selective catalytic reduction systems (SCR) promise an additional factor of 4–5 further reductions in the long-haul fleet emissions as California transitions to an all SCR-equipped fleet.