American Association for Aerosol Research - Abstract Submission

AAAR 36th Annual Conference
October 16 - October 20, 2017
Raleigh Convention Center
Raleigh, North Carolina, USA

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Effects of After-Treatment Emission Control Technologies on In-Use Heavy-Duty Diesel Trucks under Two Different Driving Modes

CHELSEA V. PREBLE, Troy Cados, Robert Harley, Thomas W. Kirchstetter, University of California, Berkeley

     Abstract Number: 430
     Working Group: Urban Aerosols

Abstract
Heavy-duty diesel trucks (HDDT) are a major source of nitrogen oxides (NOx) and black carbon (BC) in urban environments, contributing to persistent ozone and particulate matter air quality problems. Recently, diesel particle filter (DPF) and selective catalytic reduction (SCR) emission control systems have become standard equipment on new HDDT. DPFs can also be installed as a retrofit. Prior work has shown that in-use DPF and SCR systems effectively reduce BC and NOx emission rates by up to 90% and 80%, respectively (Preble et al., ES&T 2015). There is concern that DPFs may promote the formation of ultrafine particles (UFP) and can increase tailpipe nitrogen dioxide (NO2) emissions. SCR systems may form nitrous oxide (N2O), a potent greenhouse gas.

To evaluate the in-use performance of DPF and SCR systems, pollutant emissions from thousands of HDDT were measured over several years at the Port of Oakland and the Caldecott Tunnel in the San Francisco Bay Area. Gas- and particle-phase pollutants in the exhaust plumes of individual HDDT were measured at high time resolution (≥1 Hz) as trucks passed under an emissions lab stationed on an overpass. Fuel-based emission factors (g kg-1) were calculated on a truck-by-truck basis and linked via recorded license plates to vehicle attributes, including engine model year and installed after-treatment controls.

DPFs reduced the BC emission rate by up to 95% at both locations. SCR systems were more effective at reducing NOx emissions under the uphill, highway driving conditions at the Tunnel compared to the flat, arterial roadway near the Port. The impact on co-emitted species NO2, UFP, and N2O showed driving mode dependence. Some aging DPF systems showed evidence of deterioration (i.e., failure), leading to BC emission rates greater than the average for trucks without filters.