ARB Research Seminar

This page updated June 19, 2013

Toxicity of Emissions from Heavy Duty Diesel Engines with Retrofit Controls

Photo of Constantinos Sioutas, Sc.D.

Constantinos Sioutas, Sc.D., Department of Civil and Environmental Engineering, University of Southern California

May 05, 2011
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


The objective of this 4 year project was to enhance a planned ARB vehicle emissions study with the research component to determine the physicochemical and toxicological properties of particulate matter (PM) from heavy duty vehicles operating with and without emissions control technologies. Our goal was to determine the physicochemical and toxicological properties of the semi-volatile and non-volatile fractions of PM from heavy duty diesel vehicles operating with and without emissions control technologies. With the exception of uncontrolled diesel, the majority of PM emitted by these vehicles is semi volatile in nature, formed by condensation of super saturated vapors as they cool in the ambient atmosphere. Measurements of the relative toxicity of these particles compared to the more refractory (non volatile mode) PM are valuable in terms of assessing the need for additional control strategies.

As part of this study, we assessed the PM-related oxidative activity from a wide variety of vehicles to represent the in-use fleet, including diesel vehicles with and without advanced PM emission control technologies. We investigated different driving cycles, since engine operation is known to affect the concentration, relative amounts and chemical composition of the nucleation and accumulation PM modes emitted. The oxidative activity of the collected particles was measured by two independent assays: 1) the DTT assay, and 2) the macrophage ROS assay. The effect of semi-volatile species on DTT assay was determined by comparing the DTT activity for PM samples collected at both ambient and elevated temperature, while the contribution of transition metals in ROS activity was assessed by chelating the PM samples using a Chelex® complexation method.

The study demonstrated that despite generally similar reductions in PM mass emissions from diesel vehicles by various control technologies, the intrinsic oxidative activity (both DTT and ROS) of the emitted particles may vary dramatically with retrofit types. Although, mass based levels (g/mg of PM) increased with the application of after-treatment devices, a significant reduction was observed in the overall oxidative activity (per km for cruise and UDDS and per hr for idle) for retrofitted configurations, compared to the baseline vehicle. A substantial fraction of DTT activity of DEPs was associated with the semi-volatile fraction of the particles as demonstrated by a significant reduction in the activity (by 50-100%) observed for thermally-denuded PM. On the other hand, non-volatile transition metals drive the response of ROS assay as indicated by a substantial removal (=70 %) of the ROS activity after Chelex treatment of the PM samples. A univariate regression analysis further supported that DTT activity is strongly associated (R=0.94) with the water soluble organic carbon (WSOC), while Fe is responsible for most of the variability (R=0.93) in ROS levels. An important caveat of the toxicological findings of this study is that they are all based on molecular or cellular assays that examine the toxicity of the PM suspension collected from a given vehicle and driving configuration based on PM mass. By their nature and design, these investigations did not take into account important parameters determining the toxicity and overall health effects attributable to the inhalation of an aerosol, such as particle size. The substantial reduction in the overall particle size distribution of newer vehicles creates an aerosol with a much higher lung deposition fraction than the baseline vehicle, and with vastly different toxicokinetics inside the human body once inhaled. Such important investigations can only be addressed by in vivo inhalation exposure studies to these aerosols, whether using animal models or human volunteers (or both), and are greatly needed in order to provide a more complete perspective to the results of this study.

Speaker Biography

Constantinos Sioutas, Sc.D., is currently the first holder of the Fred Champion Professorship in Civil and Environmental Engineering at the University of Southern California (USC) and the Co-Director and Co-Principal Investigator of the Southern California Particle Center and Supersite (SCPCS). The SCPCS is a recently renewed 12-year research program, established in early 2000 by the US Environmental Protection Agency (USEPA) for an initial award of about $40 million. Dr. Sioutas's research has followed an integrated approach to the problem of the well-publicized and significant effects of particulate air pollution on health and the environment. His research has focused on investigations of the underlying mechanisms that produce the health effects associated with exposure to air pollutants generated by a variety of combustion sources, such as traffic (including light and heavy-duty vehicles, natural gas buses, and biodiesel vehicles), harbor and airport operations, power plants, and photochemically induced atmospheric reactions. He was the PI in one of the first and most highly cited studies on exposures to vehicular emissions and the decrease of pollutants with distance to freeways. During his faculty career, he has directed, as either a Principal or Co-Principal Investigator, some 40 research grants exceeding $40 million (USC's share $16 million), many of which extend through 2012 and beyond. He has authored about 220 peer-reviewed journal publications, 5 book chapters and holds 13 U.S. patents in the development of instrumentation for aerosol measurement and emissions control. His published work has received over 5,100 citations according to the ISI Web of Science, he is among the top 1% authors worldwide in Engineering according to the Institute of Scientific Information. Results from his publications have been used by the US Environmental Protection Agency (EPA) in their National Air Quality Criteria document in promulgating stricter air quality standards in the US. He has advised 15 PhD students, and mentored 18 postdoctoral fellows at USC. He is co-editor in chief of the journal of Aerosol & Air Quality Research and a member of the editorial board of Atmospheric Environment.

Dr. Sioutas received his undergraduate education in mechanical engineering at the Aristotle University of Thessaloniki, Greece, where he was born. He came to the U.S. in the fall of 1986 as a Fulbright Foundation fellow to pursue graduate studies. He received MS degrees in Mechanical Engineering and in Aerospace Engineering, both from the University of Minnesota. He worked as an Advanced Product Development Engineer for 3M for two years, prior to continuing his doctoral studies at Harvard School of Public Health in the department of Environmental Engineering, where he received his Doctor of Science degree in 1994. He started his academic career in 1995 as an Assistant Professor of Aerosol Science at the Harvard, prior to joining the faculty of the University of Southern California (USC) in January 1998.

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