|Increasing epidemiological and toxicological evidence
links cardio-respiratory health effects with exposures to ultrafine particles (diameter < 0.1 µm). Emission
inventories suggest that motor vehicles may be primary direct emission sources of ultrafine particles to urban
atmospheres. Given the amount of traffic in the Los Angeles Basin, it is important to understand how ultrafine
particles behave after emission as they are transported away from busy roadways. Understanding the characteristics
of ultrafine particle volatility and how these traffic-emitted ultrafine particles penetrate indoor environments
is also vital.
The goals of our research undertaken by the Southern California Particle Center and Supersite were to create an
extensive inventory on what is known about the physical and chemical characteristics of atmospheric ultrafine particles.
Utilizing a mobile particle concentrator, researchers set about characterizing the physical and chemical PM characteristics
and volatility on/near freeways, in source and receptor areas of the Los Angeles Basin, the impact of mobile sources
on indoor environments as well as ultrafine PM characteristics and emission factors in roadway tunnels with light-duty
or heavy-duty vehicles.
The data provided an increased understanding of how physical and chemical characteristics of ultrafine particles
change on/near heavily trafficked areas; this information is necessary to better understand exposure outcomes.
Relative concentrations of CO, black carbon and particle number decreased exponentially and tracked each other
well as one moves away from the freeway.
Our studies also showed that particles emitted from vehicles are externally mixed; different particles of the same
size can have different chemical compositions. Depending on ambient conditions, between 70-90% of the particles
by number, and 10-30% by mass consisted of semi-volatile material originating from condensation of organic vapors
from fuel and lube oil. The non-volatile portion is known to primarily consist of elemental carbon, which is often
coated with more volatile organic species. The volatility of these particles explains the more rapid decay in their
concentration with respect to distance from a roadway, compared to that of non-labile PM species (such as EC) or
gaseous co-pollutants such as CO and NOx, the concentration decrease of which would be affected mostly my atmospheric
Also, our studies showed that the volatile component of these particles may likely be present in its gaseous phase
in indoor environments, causing particle shrinkage and-or compete evaporation as they infiltrate indoors. In future
research, given that the majority of people's exposure during commute will be dominated (at least based on particle
numbers) to these particles, it would be useful to know whether the non-volatile or semi-volatile material is more
A better understanding of ultrafine particle characteristics and their volatility allows for the narrowing of the
search for the most toxic PM components, and would also suggest new emissions control technologies that better
protect the public health. Current particle traps remove non-volatile soot particles but not the precursors of
the smaller semi-volatile particles. An unintended result of this reduction of the larger, non-volatile particles
from the exhaust is the potential increase in the formation/emission of the smaller, semi-volatile PM as seen in
our experiments performed at the Caldecott tunnel in which we determined size fractionated emission factors for
heavy and light duty vehicles and compared them to those of previous studies in the same location.
|Costas Sioutas, Ph.D., is currently Professor of Civil and Environmental Engineering
at USC and the Co-Director and Co-Principal Investigator of the Southern California Particle Center and Supersite
(SCPCS). The SCPCS is recently renewed 11-year research program, established in early 2000 by the US Environmental
Protection Agency (USEPA) for an initial award of about $28 million. Dr. Sioutas and his group have developed technologies
for measuring the physico-chemical characteristics of air pollutants and determining their toxic properties. These
technologies are used by toxicologists and immunologists in the several institutions around the world to expose
human volunteers, animals or human cell cultures to concentrated, real -world particulates and study the effects
of chemical composition on toxicological outcomes. Personal monitor devices also developed by Dr. Sioutas's group
are used by epidemiologists to measure population exposures to air pollutants and determine how their exposure
relates to lung growth and exacerbation of early asthma. Several of these technologies are also being used by agencies
such as the US. EPA, as well as the National Institutes of Public Health of the Netherlands, Canada, Taiwan and
Several publications resulting from the work of Dr. Sioutas and his group have been cited in EPA' s National Air
Quality Criteria document and earned him a position in the Air Quality Advisory Committee on Particulate Matter
of the State of California and the advisory board of the South Coast Air Quality Management District. Dr. Sioutas
is also a member of the NRC Committee on models for testing interventions against aerosolized bio-terrorism agents.
Dr. Sioutas came to the U.S. in the fall of 1986 as a Fulbright Foundation fellow to pursue his graduate studies.
He received Master of Science degrees in Mechanical Engineering and in Aerospace Engineering, both from the University
of Minnesota. He then 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. Dr. Sioutas 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.
Since 1993, Dr. Sioutas has authored over 140 peer-reviewed journal publications, and holds 11 U.S. patents in
development of aerosol instrumentation. He is a Fulbright Fellow (1986), a recipient of the 3M Circle of Technical
Excellence Award (1991) and a recipient of the USC School of Engineering Outstanding Research Faculty Award (2000).
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