ARB Research Seminar

This page updated March 26, 2019

In-Use Performance of Diesel Particle Filters and Selective Catalytic Reduction Emission Control Technologies

Photo of Thomas Kirchstetter, PhD.

Thomas Kirchstetter, Ph.D., University of California, Berkeley

March 26, 2019
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


Pollutant emissions from thousands of on-road trucks in California were measured in 2014, 2015, and 2018 at the Caldecott Tunnel in the San Francisco Bay Area to quantify the in-use performance of diesel particle filters (DPFs) and selective catalytic reduction (SCR) emission control technologies. Compared to baseline measurements made in 2010, the median truck model year observed in 2018 increased by 9 years, and DPF and SCR penetration increased from 15 to 91% and 2 to 59%, respectively. Over this period, fleet-average emission rates of BC and NOx decreased by 79 and 57%, respectively. NO2 emission rates remained about the same, despite the intentional oxidation of engine-out NO to NO2 in DPF systems, due to the effectiveness of SCR systems in reducing NOx emissions and mitigating the DPF-related increase in primary NO2 emissions. Fleet-average emissions of NH3 and N2O increased from near-zero to levels that are comparable to NH3 emissions from three-way catalyst-equipped light-duty cars, and to levels about equal to the N2O emission limit for heavy-duty trucks. The g kg-1 reduction in the emissions of NOx is about 150 times the increase in NH3, which is a precursor to atmospheric formation of ammonium sulfate and ammonium nitrate. The reduced BC emissions from DPF- equipped trucks and the ~4% fuel economy gained with the addition of SCR outweigh effect of the N2O global warming potential increase.

Truck license plates were recorded, transcribed, and matched to entries in state- maintained databases to link the emission profiles of individual trucks to engine model year and emission control technology. BC emissions from trucks with 2010+ engines were 97% lower than from trucks with 1965-2003 engines. Furthermore, 2010+ engines equipped with both DPF and SCR emitted on average 82% less BC than 2007-2009 engines that have DPFs only, even though both categories of trucks are expected to meet the same exhaust PM emission standard. A 57% increase in BC emissions from 2007-2009 DPF-equipped engines between 2014 and 2015 raised concerns about the durability of DPF systems installed on some heavy-duty trucks. However, the BC emission factor for the 2007-2009 engines was no higher in 2018 than in 2014, and lower in 2018 than in 2015, possibly due to repair or replacement of some high-emitting trucks. In the spring of 2018, ~10% of the on-road truck fleet was either exempt from or noncompliant with the Truck and Bus Regulation; nearly 60% of the remaining on-road BC emissions comes from these trucks.

Speaker Biography

Dr. Kirchstetter is a Senior Scientist, the Director of the Energy Analysis and Environmental Impacts Division, and the Head of the Sustainable Energy and Environmental Systems Department at Lawrence Berkeley National Laboratory. He holds a concurrent appointment as an Adjunct Professor in Civil & Environmental Engineering at UC Berkeley, where he teaches courses and mentors undergraduate and graduate student researchers. Kirchstetter has served as an editor of the journals Aerosol Science & Technology and Atmospheric Chemistry & Physics and organizer of the International Conference on Carbonaceous Particles in the Atmosphere.

Kirchstetter entered the DOE national laboratory system as a student intern at Brookhaven National Lab in 1992. After earning a PhD in Environmental Engineering at UC Berkeley, Kirchstetter won the DOE Alexander Hollaender Distinguished Postdoctoral Fellowship in 1998 and began conducting atmospheric aerosol research under the mentorship of Tihomir Novakov at Lawrence Berkeley National Lab. Kirchstetter is well known for his research on the optical properties of carbonaceous aerosols and the quantification of emissions from motor vehicles. His current research interests in air pollution science and technology include the in-use performance and durability of vehicle emission controls, the environmental impact of freight transport, inventing and benchmarking air pollution sensors, and evaluating the benefits and barriers to the scale-up of municipal solid waste-to-energy.

Kirchstetter lives in Oakland, California with his wife and three kids and enjoys playing music, fishing, hiking, and cooking

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