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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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