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Final Report: Measurement of the “Effective” Surface Area of Ultrafine and Accumulation Mode PM (Pilot Project)
EPA Grant Number: R827352C003Subproject: this is subproject number 003 , established and managed by the Center Director under grant R827352
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Southern California Particle Center and Supersite
Center Director: Froines, John R.
Title: Measurement of the “Effective” Surface Area of Ultrafine and Accumulation Mode PM (Pilot Project)
Investigators: Friedlander, Sheldon , Sioutas, Constantinos
Institution: University of California - Los Angeles , University of Southern California
EPA Project Officer: Stacey Katz/Gail Robarge,
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
RFA: Airborne Particulate Matter (PM) Centers (1999)
Research Category: Particulate Matter
Description:
Objective:Topic A: Studies Emphasizing Investigation of the Biological Mechanisms of Particulate Matter (PM) Effects in Relation to PM Physical and Chemical Characteristics
The ultrafine particle size range (dp < 0.1 μm) of the atmospheric aerosol is composed of both primary and secondary particulate matter. The primary component, emitted directly from sources, often includes agglomerates of 10 to 50 nm particles. (Note that the term “primary” in this context differs from its use to designate the individual particles that compose aerosol aggregate structures.) The secondary component is composed of particulate matter formed in the atmosphere, including sulfuric acid and sulfates, and organic reaction products of low volatility. Particles that form in the atmosphere tend to evaporate in the electron microscope, our principal observational method. Animal studies indicate that freshly formed agglomerate structures may have adverse health effects (Warheit, et al., 1990). Thus it is important to be able to characterize this component of the atmospheric aerosol.
With support from other sources, our Laboratory developed novel methods for the sampling and analysis of ultrafine atmospheric agglomerates. We applied our technology in a collaborative study with Dr. Constantinos Sioutas. Our goal was to determine whether the condensation and evaporation processes that precede aerosol concentration in the VACES alter the structure of agglomerates in the ultrafine particle size range. In the set of measurements described in methodology below, we found that the agglomerates were concentrated without substantial changes in their structure. The results of our study were described in the following publication:
Kim S, Jaques PA, Chang M, Barone T, Xiong C, Friedlander SK, Sioutas C. Versatile Aerosol Concentration Enrichment System (VACES) for simultaneous in vivo and in vitro evaluation of toxic effects of ultrafine, fine and coarse ambient particles. Part II: Field evaluation. Journal of Aerosol Science 2001;32(11):1299-1314.
Summary/Accomplishments (Outputs/Outcomes):Methodology
Atmospheric ultrafine particles and those concentrated by the VACES were sampled using the low-pressure impactor (LPI) at the UCLA campus, in west Los Angeles. Measurements for the ambient air and concentrated particles from the VACES were made within minutes of each other. Concentrated ultrafine aerosols generated by the VACES were sampled after they were dried by diffusion. The LPI is an eight-stage single jet impactor equipped with a critical orifice that maintains a flow rate of 1 L/min under the appropriate pressure drop (Hering, et al., 1978; 1979). The stages have 50% efficiency cutoffs for aerodynamic diameters of 4.0, 2.0, 1.0, 0.5, 0.26, 0.11, 0.075, and 0.05 μm for stages one to eight, respectively. The particles were collected on a nickel transmission electron microscope (TEM) grid. To minimize the effects of particle bounce, only one stage at a time had a grid attached for sampling; the grid was secured at the center of a 25 mm diameter glass stage, while the other glass stages were coated with apiezon grease to trap the larger particles. Air was drawn through the impactor by a vacuum pump for 5 minutes per stage for aerosols coming from the concentrator and 10 minutes for the ambient air samples. Agglomerates were collected on LPI stages 7 and 8, which have aerodynamic diameter ranges of 0.075–0.11 mm and 0.05–0.075 μm, respectively. TEM photomicrographs of the grids were taken using a JEOL 100CX and 2000FX TEM at a magnification of 105. To compare the morphologies of the atmospheric agglomerates and those concentrated by the VACES, we made use of fractal concepts. The fractal characteristics determine agglomerate transport and deposition from the atmosphere and in the lung. They may also affect the interaction of agglomerates with cellular surfaces. More details on fractal analysis conducted in our Laboratory can be found in Xiong (2000).
Experiments and computer simulations have shown that fractal concepts can often be applied to agglomerates of nanometer primary particles (Forrest and Witten, 1979; Witten and Sander, 1981). Such agglomerates can be described by the following relationship (Weber, et al., 1995):
(1)
where Df is the fractal dimension, Np is the number of primary particles in the agglomerate, A is the fractal pre-factor, Ro is the average primary particle radius and Rg is the radius of gyration. The radius of gyration is defined by the expression:
Rg = [(1/M)∑(miri2)]1/2 (2)
where mi is the mass of the ith primary particle, M is the total mass given as ∑mi, and ri is the distance of the ith primary particle from the center of mass. Values of Df and A for agglomerates sampled from ambient air and from the concentrator exit air were obtained from a log-log plot of the number of primary particles as a function of distance from the center of mass to the edge of the agglomerate. The fractal dimension was determined from the slope of this diagram, and the prefactor from the intercept of the line representing the least squares fit.
Conclusions:Changes in agglomerate structure were investigated by comparing values for Df and A for 38 agglomerates sampled from ambient air to 39 from the concentrator exit. Figures 1 and 2 show the Df distributions for concentrated and ambient aerosols, respectively. The count median Df was very similar (between 1.6 and 1.8) for both concentrated and ambient particles. The average value of A for the particles collected from the VACES was 2.73 and for the atmospheric agglomerates 2.83.
Figure 1. Fractal Dimension Distribution for Agglomerates From the VACES. The count mean Df value was found to be between 1.8 and 2. Samples were taken at the Center for Health Sciences at UCLA on 8/22/00 using a LPI.
Figure 2. Fractal Dimension Distribution for Agglomerates Sampled From the Ambient Aerosol. The count mean Df value was found to be between 1.6 and 1.8. Samples were taken at the Center for Health Sciences at UCLA on 8/22/00 using a LPI.
Previous studies suggest that chain agglomerates may become more compact when subjected to condensation and evaporation processes (Colbeck, et al., 1990; Hallet, et al., 1989; Wells, et al., 1976). In a study of diesel chain agglomerates (Huang, et al., 1994), the fractal dimension increased from 1.56 to 1.76 for mid-sulfur fuels and 1.40 to 1.54 for low-sulfur fuels, after condensation and evaporation processes. These were somewhat larger changes than we found. A possible explanation is that in the study by Huang, et al., the agglomerates underwent up to three cycles of condensation and evaporation while in our study they only went through one cycle. We therefore conclude that for the one set of measurements conducted by our Laboratory, the condensation and evaporation process used with the VACES did not cause significant changes in agglomerate structure as measured by Df and A. However, both the sources of the fractal-like structures and associated trace gases may affect this phenomenon. Since the measurements were made for only one sampling site, more experiments will be needed at different sites to generalize these conclusions.
References:
Colbeck DV, Sizto R. Hospital admissions and air pollutants in Southern Ontario; the acid summer haze effect. Environmental Health Perspectives 1989;21:527-538.
Forrest SR, Witten TA. Long-range correlations in smoke-particle aggregates. Journal of Physics 1979;A12:L109-117.
Hallet J, Hudson JG, Rogers CF. Characterization of combustion aerosol for haze and cloud formation. Aerosol Science and Technology 1989;10:70-83.
Hering SV, Flagan RC, Friedlander SK. Design and evaluation of new low-pressure impactor. Environmental Science & Technology 1978;12:667-673.
Hering SV, Friedlander SK, Collins JJ, Richards LW. Design and evaluation of a new low-pressure impactor, 2. Environmental Science & Technology 1979;13:184-188.
Huang P, Turpin BJ, Pipho MJ, Kittelson DB, McMurry PH. Effects of water condensation and evaporation on diesel chain-agglomerate morphology. Aerosol Science and Technology 1994;25:447-459.
Warheit DB, Seider WC, Carakostas MC, Hartsky M. Attenuation of perfluoropolymer fume pulmonary toxicity: effect of filters, combustion method, and aerosol age. Experimental and Molecular Pathology 1990;52:309-329.
Weber AP, Thorne JD, Friedlander SK. Microstructure of agglomerates of nanometer particles. Materials Research Society Symposium Proceedings 1995;380:87-92.
Wells AC, Venn JB, Heard MJ. In: Inhaled Particles: Proceedings of an International Symposium Organized by the British 1 Occupational Hygiene Society 1976;4:175-189.
Witten TA, Sander LM. Diffusion-limited aggregation, a kinetic critical phenomenon. Physical Review Letters 1981;47:1400-1403.
Xiong C. Chemical and morphological studies of marine and urban aerosols. M.S. Thesis. University of California, Los Angeles, 2000.
Journal Articles on this Report: 1 Displayed | Download in RIS Format
| Other subproject views: | All 1 publications | 1 publications in selected types | All 1 journal articles |
| Other center views: | All 136 publications | 135 publications in selected types | All 135 journal articles |
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Kim S, Jaques PA, Chang M, Barone T, Xiong C, Friedlander SK, Sioutas C. Versatile aerosol concentration enrichment system (VACES) for simultaneous in vivo and in vitro evaluation of toxic effects of ultrafine, fine and coarse ambient particles. Part II: Field evaluation. Journal of Aerosol Science 2001;32(11):1299-1314. |
R827352 (2004) R827352 (Final) R827352C003 (Final) R827352C014 (Final) R826232 (2000) |
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Relevant Websites:
Progress and Final Reports:
2002 Progress Report
2003 Progress Report
Original Abstract
Main Center Abstract and Reports:
R827352 Southern California Particle Center and Supersite
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R827352C001 The Chemical Toxicology of Particulate Matter
R827352C002 Pro-inflammatory and the Pro-oxidative Effects of Diesel Exhaust Particulate in Vivo and in Vitro
R827352C003 Measurement of the “Effective” Surface Area of Ultrafine and Accumulation Mode PM (Pilot Project)
R827352C004 Effect of Exposure to Freeways with Heavy Diesel Traffic and Gasoline Traffic on Asthma Mouse Model
R827352C005 Effects of Exposure to Fine and Ultrafine Concentrated Ambient Particles near a Heavily Trafficked Freeway in Geriatric Rats (Pilot Project)
R827352C006 Relationship Between Ultrafine Particle Size Distribution and Distance From Highways
R827352C007 Exposure to Vehicular Pollutants and Respiratory Health
R827352C008 Traffic Density and Human Reproductive Health
R827352C009 The Role of Quinones, Aldehydes, Polycyclic Aromatic Hydrocarbons, and other Atmospheric Transformation Products on Chronic Health Effects in Children
R827352C010 Novel Method for Measurement of Acrolein in Aerosols
R827352C011 Off-Line Sampling of Exhaled Nitric Oxide in Respiratory Health Surveys
R827352C012 Controlled Human Exposure Studies with Concentrated PM
R827352C013 Particle Size Distributions of Polycyclic Aromatic Hydrocarbons in the LAB
R827352C014 Physical and Chemical Characteristics of PM in the LAB (Source Receptor Study)
R827352C015 Exposure Assessment and Airshed Modeling Applications in Support of SCPC and CHS Projects
R827352C016 Particle Dosimetry
R827352C017 Conduct Research and Monitoring That Contributes to a Better Understanding of the Measurement, Sources, Size Distribution, Chemical Composition, Physical State, Spatial and Temporal Variability, and Health Effects of Suspended PM in the Los Angeles Basin (LAB)