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1
Overview
Small particles—about one nanometer to tens of presentations that highlighted new advances in character-
microns—are ubiquitous in the natural and engineered izing small particles.
worlds. They are in the air, soil, and water on Earth, as well This document summarizes the presentations and discus-
sions that took place during the workshop.1 Where possible,
as at the farthest reaches of the universe. One of the major
buzz words over the past 10 years, nanotechnology, involves background references have been provided to support state-
the creation of nanoscale materials with the promise of new ments made or data described. The reader is urged to follow
and revolutionary properties. Given the size and abundance up with individual guest speakers and their institutions for
of small particles, however, there is relatively little under- further clarification of statements made during the workshop
standing about their properties and chemical composition, or to obtain additional reference materials.
which limits our ability to understand, predict, and control
their applications and impacts in both natural and engineered
WORKSHOP OVERVIEW
systems. At the same time, information may be available
that just needs to be shared across disciplinary boundaries
Why Small Particles Matter
to increase understanding of small particles.
The workshop began with an introduction by co-chair
Barbara Finlayson-Pitts, University of California, Irvine,
ABOUT THIS DOCUMENT
who noted the importance of and challenges associated
with characterizing small particles in the atmosphere. Steve
The National Academies’ Chemical Sciences Roundtable
Schwartz, Brookhaven National Laboratory, continued this
(CSR) held a workshop on October 25-26, 2010, to explore
new opportunities, challenges, and approaches to character- theme with a more thorough discussion of the many roles that
izing small particles and understanding their impacts. In atmospheric aerosols play in determining climate. Aerosol
many scientific and engineering domains, a lack of under- particles act as the seeds for cloud formation, reflect sunlight
standing about the properties and chemical composition of away from Earth’s surface, and serve as catalytic sites for
small particles limits our ability to understand, predict, and atmospheric chemical processes. He also described efforts
control their applications and impacts. to characterize atmospheric aerosols and model how they
The workshop, “Challenges in Characterizing Small influence, or force, climate.
Mort Lippmann, New York University, discussed some
Particles: Exploring Particles from the Nano- to Microscales,”
explored the critical importance of small particles in environ- of the health impacts caused by airborne particles, which are
mental science, materials and chemical sciences, biological also known as particulate matter. In particular, he described
science, and engineering, and the many challenges involved how the size of these particles, along with the chemicals they
in characterizing materials at the nano- and microscales. The pick up on their surfaces, relates to the negative impacts on
discussions on characterization included static, dynamic,
experimental, computational, and theoretical characteriza- 1About Open Discussions: All but one chapter (Chapter 4) in this
tion. The workshop also included several “research tool” document ends with a summary of discussion topics introduced by speakers
and participants in the immediate session, as well as all preceding sessions.
1
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2 CHALLENGES IN CHARACTERIZING SMALL PARTICLES
endanger the environment or human health. Yi Qiao, 3M
human health that accompany prolonged exposure to par-
ticulate matter smaller than 10 microns in diameter. Michael Corporate Research Process Laboratory, discussed some
Hochella, Virginia Polytechnic and State University, then of the challenges facing those who need to characterize
noted that nanoparticles are everywhere in the environment nanoparticle dispersions used in industrial applications. He
and that the mass of nanoparticles that nature puts into the noted that to meet the needs of a manufacturing environment,
environment will always dwarf the mass that humans will a measurement technique must be fast enough to provide
ever produce. He discussed some of the ways in which feedback on a meaningful timeframe, have few restrictions
nanoparticles enter the environment, including volcanic concerning sample preparation in terms of nanoparticle con-
eruptions and salt spray, and the effects of human activities centration and purity, and be able to distinguish “good” from
on levels of potential toxic nanoparticles found in soil and “bad” so that a line operator can make necessary adjustments
water. to the manufacturing process in real time. He then described
With his presentation on the ways in which small par- two techniques that meet these requirements.
ticles interact with cells, Gary McDermott, University of Rhonda Stroud, Naval Research Laboratory, concluded
California, San Francisco, brought this session to a close. He this session by describing how the techniques used to charac-
described methods for imaging small particles inside cells terize terrestrial particles can be applied to the characteriza-
and showed how they could be used to help with the design tion of the 40,000 tons of extraterrestrial dust that enter the
of new therapeutic drugs to treat human disease. planet’s upper atmosphere annually.
Challenges in Chemical Analysis and Challenges in Analyzing Nanoparticles in
Imaging of Small Particles Complex, Real-World Mixtures
Over the course of two sessions, speakers described In this session, three speakers addressed some of the
the challenges of characterizing small particles and some challenges in measuring and predicting the properties and
o f the real-world needs for developing new analytical behavior of complex nanoparticle formulations and dis-
technologies applicable to small particles. Alla Zelenyuk, cussed the often surprising findings that come from studying
nanomaterials as they occur in the real world. James Lister,
Pacific Northwest National Laboratory, discussed her
team’s use of single particle laser ablation time-of-flight Purdue University, talked about particles in the micron and
mass spectrometry to characterize atmospheric aerosols and submicron size ranges that are used in industrial applications,
to study how other atmospheric components influence the with a specific focus on the delivery forms for these particles.
morphology and particle chemistry of atmospheric aerosols. In particular, he addressed some of the methods for charac-
James Smith, National Center for Atmospheric Research, terizing the processes used to create delivery forms such as
addressed the phenomenon of new particle formation in the catalyst pellets and drug tablets. He also described how these
atmosphere and the recent progress that his group has made characterization tools can provide insights into how manu-
in quantifying the composition of these spontaneously gener- facturing processes impact the final properties of these
ated atmospheric nanoparticles. delivery forms, such as dissolubility and chemical stability.
In his presentation, Ralph Nuzzo, University of Illinois, Pedro Alvarez, Rice University, then discussed his work
Urbana-Champaign, discussed the rich toolbox that is avail- on characterizing how nanoparticles interact with micro-
able for characterizing heterogeneous catalysts at the atomic organisms in the environment. He explained that bacteria,
level. This information is leading to a better understanding the foundation of all ecosystems, provide a convenient
of how these particles assemble and how particle structure model for studying the potential toxicity of engineered
nanoparticles. Vicki Grassian concluded the session by
impacts particle properties. Continuing on the catalysis
theme, Abhaya Datye, University of New Mexico, stressed describing methods used to understand the transformations
the importance of nanoscale characterization for understand- and surface chemistry of mineral dust, a major component
ing how the interactions between catalytic nanoparticles of atmospheric aerosols. Using these methods, she and her
and bulk-scale supports affect catalytic activity, information colleagues have been able to show how mineral dust can
that could lead to the development of improved industrial catalyze a wide range of chemical reactions occurring in the
heterogeneous catalysts. atmosphere.
Lee Silverman, DuPont Central Research and Develop-
ment Laboratory, continued this industrial theme by discuss -
Modeling and Simulation of Small Particles
ing the tools needed to characterize composite polymeric
In the workshop’s final scientific session, Angela Violi,
materials containing nanoscale particle additives. Silverman
University of Michigan, and Douglas Tobias, University of
noted that the information generated using these tools can
play a role in the development of new materials that will not California, Irvine, described the use of several computational
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3
OVERVIEW
ORGANIZATION OF THIS WORKSHOP SUMMARY
approaches to modeling nanoparticles to provide insights
into how structure and function are related. Violi spoke about
This document was prepared by rapporteurs Tina
a hybrid modeling technique that works at an atomistic level
Masciangioli and Joe Alper for the Chemical Sciences
to follow the growth of particles produced during the incom-
Roundtable as a factual summary of what occurred during the
plete combustion of different hydrocarbon-based fuels. She
workshop. In accordance with the CSR’s policies, the sum-
also described a computational model of the cell membrane
mary does not attempt to establish any conclusions or recom-
that can follow how carbonaceous particles, such as those
mendations about needs and future directions, focusing instead
produced during combustion, impact the natural flow of
on issues identified by the speakers and workshop participants.
lipids in the cell membrane.
This summary is organized according to the four main ses-
Tobias then spoke about an atomistic computational
sions. Overview presentations highlighted the critical impor-
model that is providing insights into the interactions between
tance of small particles in environmental science, materials
a particle’s reactive surface and compounds impinging on
and chemical sciences, biological science, and engineering.
that surface. He also described a coarse-grained model for
Technical sessions focused more on the research tools used
studying the atmospheric chemistry of sea salt particles that
to characterize small particles, such as sampling, nucleation
improves the prediction of the geographical distribution of
and growth, and chemical imaging. Poster abstracts are pro-
ozone production in a polluted urban environment.
vided in Appendix B.
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