AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Effects of After-Treatment Control Technologies on Heavy-Duty Diesel Truck Emissions
CHELSEA PREBLE, Timothy Dallmann, Nathan Kreisberg, Susanne Hering, Robert Harley, Thomas Kirchstetter, University of California, Berkeley
Abstract Number: 555 Working Group: Urban Aerosols
Abstract Diesel engines are the largest source of nitrogen oxides (NO$_x) emissions nationally and a major contributor to the black carbon (BC) fraction of fine particulate matter (PM). Recently, diesel particle filter (DPF) and selective catalytic reduction (SCR) emission control systems that target exhaust PM and NO$_x have become standard equipment on new heavy-duty diesel trucks. There is concern that DPFs may promote the formation of ultrafine particles (UFP) and increase total particle number emissions while reducing PM mass emissions. Also, the deliberate catalytic oxidation of engine-out nitric oxide (NO) to nitrogen dioxide (NO$_2) in continuously regenerating DPFs may lead to increased tailpipe emission of NO$_2 and near-roadway concentrations that exceed the new 1-hour national ambient air quality standards. Increased NO$_2 emissions can also promote formation of ozone and secondary PM.
We report results from ongoing on-road studies of heavy-duty diesel truck emissions at the Port of Oakland and the Caldecott Tunnel in California’s San Francisco Bay Area. Emission factors (g pollutant per kg of diesel) were linked via recorded license plates to individual truck attributes, including engine model year and installed after-treatment controls. At the Port of Oakland, average NO$_x, BC, and UFP emission factors from new trucks equipped with both DPF and SCR emission controls were 69 ± 15%, 92 ± 32%, and 66 ± 35% lower, respectively, than modern trucks without these emission control devices. DPF use significantly increased the NO$_2/NO$_x emission ratio. DPFs also significantly increased NO$_2 emissions when installed as retrofits on older trucks with higher baseline NO$_x emissions. SCR systems effectively reduce total NO$_x emissions and mitigate these undesirable DPF-related NO$_2 emissions, but such systems can lead to the emission of N$_2O, a potent greenhouse gas.