Grantee Research Project Results
2001 Progress Report: Ultrafine Oil Aerosol Generation for Inhalation Studies
EPA Grant Number: R827354C008Subproject: this is subproject number 008 , established and managed by the Center Director under grant R827354
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC (1989) - Northeast HSRC
Center Director: Sidhu, Sukh S.
Title: Ultrafine Oil Aerosol Generation for Inhalation Studies
Investigators: Veranth, John
Institution: University of Utah
EPA Project Officer: Chung, Serena
Project Period: June 1, 1999 through May 31, 2004 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 2000 through May 31, 2001
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air
Objective:
The objective of this research project is to design and validate an ultrafine aerosol generator for hydrocarbon aerosols to use in inhalation studies using laboratory animals. The particle generator is used in a controlled exposure experiment, exposing rats to organic carbon aerosol, a surrogate for the organic component of internal combustion engine tailpipe emissions. Because particulate matter (PM) is very small, it is easily inhaled and trapped in the lungs, causing various cardiovascular health problems. In May 2001, the Rochester Airborne Particulate Matter Center's external Science Advisory Committee recommended animal inhalation studies of ultrafine organic aerosol. This exposure study, in response to the Committee’s recommendation, examines ultrafine aerosol derived from used motor oil. The specific objective of this research project is to produce a number concentration greater than 1 x 106 particles/cm3 of hydrocarbon mixture particles, derived from used motor oil, with a number mode between 20 and 100 nanometers (nm), with the majority of the particle volume (mass) distribution in the submicron range.
Progress Summary:
Much of the previous work in laboratory aerosol generation has been directed toward generation of either monodisperse supermicron aerosols for instrument calibration (Fuchs, et al., 1966; Willeke, 1980; Chen, et al., 2001) or the generation of ultrafine aerosols of metal or salt for nucleation and coagulation studies (Husar, 1971; Bartz, 1987). In a review of prior aerosol generation efforts, no references were found that reported laboratory generation of organic aerosols in the ultrafine size range (Ristovski, 1998). Use of a small diesel engine as an aerosol source was considered but rejected as infeasible for the current project. Difficulties included the heat, noise, and vibration of an engine in a biomedical laboratory setting, and the need to remove copollutants such as soot, CO, and NOx if the aim was to study the effects of ultrafine organic aerosol alone. Concurrent efforts to generate a suitable aerosol using an electrospray generator were attempted by TSI, Inc., but were not successful as the electrospray requires a conducting fluid (Rulison, 1994). Attempts to operate the electrospray with water-oil emulsions also were unsuccessful (Gomez, 1998).
The literature review suggests that a vaporization-condensation particle generator based on the classical Sinclair-LeMer generator (Fuchs, 1966; Rapaport, 1955) should be capable of generating a suitable organic aerosol if operating conditions were optimized. This type of particle generator is a two-step process, where nuclei of a very high boiling point compound are produced, then the lower boiling aqueous or organic compound is condensed on the nuclei. Several weeks have been spent testing nuclei generation methods and reviewing the vaporization-condensation aerosol generation literature to develop a quantitative understanding of the factors affecting nucleation rate and subsequent particle growth (Barrett, 2000; Koch, 1993). Initial work was conducted with pure hydrocarbons, and various configurations were tried to introduce into the gas stream the proper amount of salt nuclei and hydrocarbon to achieve the target aerosol number concentration and size. By the end of April 2001, an ultrafine aerosol composed of triacontane (C30H62 n-alkane) condensed on NaCl nuclei had been produced in demonstration experiments. However, additional testing in November to determine reproducibility of the system when running used motor oil showed that the NaCl nuclei generation was unnecessary when running at the high aerosol concentrations desired for the inhalation studies. The ultrafine particle generation efforts were successful and an aerosol that met the original specification was generated for a 6-hour inhalation study of saline-treated and LPS-treated rats.
The number and size of the aerosol was measured with a TSI, Inc. (St. Paul, MN) Model 3071A Scanning Mobility Particle Sizer (SMPS), and a Model 3022A Condensation Particle Counter (CPC). At various times in the study, the SMPS operated at 2 liters-per-minute (Lpm) aerosol with 20 Lpm sheath flow to obtain a resolution below 10 nm. Alternatively, the SMPS operated at 0.3 Lpm aerosol and 3 Lpm sheath to resolve both the nucleation and accumulation modes. The instrument was set up according to the TSI operating manual, and flows were checked with a bubble flow meter. The mass distribution of particles larger than the SMPS cutoff was determined using a cascade impactor (In-Tox Products, Albuquerque, NM).
The test hydrocarbon was "used commercial motor oil" collected from a Honda automobile. The used motor oil was dark and opaque. Solids settled out from the mixture and only the supernatant was used. Preliminary testing also used C25 (pentacosane), C30 (triacontane), C40 (tetracontane) straight-chain alkanes (Aldrich, Milwaukee WI) and light paraffin oil (EM Science).
The aerosol generation system used in the rat inhalation studies was made up of flow rates, system geometry, line sizes, operating temperatures, and organic feed, arrived at by a combination of design calculations and empirical experimentation, which iteratively lead to aerosol that met the specifications. Preliminary testing indicated that NaCl nuclei were needed to form an ultrafine aerosol when operating at low organic feed rates, but nuclei were not needed when the organic feed rate was increased. The carrier gas for organic vaporization was argon because preliminary experiments with long-chain n-alkanes showed partial oxidation of the hydrocarbon, leading to deposits and changes in aerosol size with time.
The feed rate of used commercial motor oil (with solids settled out from the oil and only the supernatant used) proved to be the most critical variable controlling aerosol size and number. Material balance calculations indicated that a very small feed rate was required.
During preliminary demonstration runs, the final aerosol generator configuration was able to produce a well-defined particle number distribution between 30-100 nm, with a count median diameter (CMD) between 40-50 nm. The concentration in the 30-liter inhalation chamber was 1 to 2 x 106/cm3, and the integrated volume from 13 to 789 nm was 2.8 nm3/cm3, which is about 200 µg/m3.
Figure 1. Number Distribution at 20-Minute Intervals During Inhalation Exposure
Figure 2. Volume Distribution at 20-Minute Intervals During Inhalation Exposure
The data showed that the animal exposure study met the aerosol criteria that had been set based on the Science Advisory Committee recommendation. The exposure went as planned; starting at 9:55 a.m. and ending at 3:55 p.m. on December 3, 2001. The SMPS statistics for the exposure period from 10:10 a.m. to 3:55 p.m. (excluding transient after opening the chamber to insert the rats) are shown below. The number and volume distributions are shown graphically in Figures 1 and 2.
Average |
Standard Dev |
Units |
|
Count Median | 39.9 |
3.5 |
nm |
Geometric Standard Deviation | 1.46 |
.02 |
-- |
Integrated Number Conc. | 1.13 E6 |
0.3 E6 |
N / cm3 |
CPC Direct Number Count | 2.84 E6 |
0.5 E6 |
N / cm3 |
Volume Median | 100.9 |
10 |
nm |
Integrated Volume | 1.36 E11 |
0.5 E11 |
nm3 / cm3 |
The systematic difference in total number concentration between the number
computed by TSI software from the SMPS readings and the total measured by a
CPC directly has also been noted in previous work, but the issue remains unresolved.
In addition, the generator was tested with different organic feeds and produced similar aerosol size distributions using clear paraffin oil and triacontane (C30H62) dissolved in hexane. This indicates that the aerosol is not dependent on unique properties of the used motor oil, such as trace contaminants serving as nuclei. Based on both calculations from aerosol theory and these demonstration experiments, it is likely that other low volatility hydrocarbons can generate an ultrafine aerosol with an appropriate adjustment of operating setpoints.
The particle generator produced larger median diameter particles as the total
amount of aerosol increased, which is consistent with aerosol formation theory.
A material balance calculation showed that the concentration of oil aerosol
produced by the particle generator is approximate to what would be found
from an engine that emitted 1 quart of unburned oil smoke per 10,000 miles.
The average mass concentration of the oil aerosol in the inhalation chamber, calculated
from SMPS data assuming 0.8 solid geometry spheres, was 110 µg/m3, which
is less than 2 times the PM2.5 air quality standard.
The particles derived from the used motor oil are relevant to real-world exposures but allow testing of the effect of ultrafine organic particles free from the soot, metal oxides, and gas-phase pollutants found in engine exhaust.
The ability of the aerosol generator to work with both complex mixtures, such as used motor oil and single-component hydrocarbons, suggests that future studies can be designed using a range of environmentally relevant organic aerosols. These could include controlled mixtures of relatively benign aliphatic hydrocarbons with known biologically active species such as polycyclic aromatic hydrocarbons (PAH). Further, the condensation organic particle generator can be combined with a nuclei generator to create mixtures of organic compounds and carbon or metal oxides. This opens the way to a reductionist approach to studying the toxicology of engine emissions by hypothesis-driven inhalation studies of single components and of mixtures of components found in real engine exhaust.
An unresolved issue is the lower limit of organic particles that can be generated by a vaporization-condensation generator. The relevance is that diesel engines have been reported to generate a particle mode around 10 nm, which is smaller that was achieved in this study. (Abdul-Khalek 1998, Shi 1999, Abdul-Khalek 1999) As the organic feed rate is decreased the particle size decreases until the CMD is 25-30 nm then the size stays nearly constant but the particle number drops. The relative importance of vapor pressure (Kelvin effect) and mass transfer kinetics has not been fully evaluated.
Future Activities:
We will continue to design and validate an ultrafine aerosol generator for hydrocarbon aerosols to use in inhalation studies using laboratory animals.
References:
Abdul-Khalek IS, Kittelson DB, Graskow BR, Wei Q, Brear F. Diesel exhaust particle size: measurement issues and trends. Society of Automotive Engineers Transactions 1999;108(4):638-696.
Shi JP, Harrison RM. Investigation of ultrafine particle formation during diesel exhaust dilution. Environmental Science and Technology 1999;33(21):3730-3736.
Abdul-Khalek ID, Kittelson, Brear F. The influence of dilution conditions on diesel exhaust particle size distribution measurements. Society of Automotive Engineers Transactions 1999;108(4):563-571.
Fuchs NA, Sutugin AG. The generation and use of monodisperse aerosols. In: Davies CN, eds, Aerosol Science. 1966, Academic Press. New York, NY, pp 1-30.
Willeke K, ed. Generation of Aerosols and Facilities for Exposure Experiments. Ann Arbor Science. Ann Arbor, MI, 1980.
Chen BT, John W. Instrument calibration. In: Baron PA, Willeke K, eds. Aerosol Measurement: Principles, Techniques, and Applications. John Wiley and Sons. New York, NY, 2001.
Husar RB. Coagulation of Knudsen aerosols. Ph.D. Thesis, University of Minnesota, 1971.
Bartz H, Fissan H, Liu BYH. A new generator for ultrafine aerosols below 10 nm. Aerosol Science and Technology 1987;6(2):163-171.
Ristovski ZD, Morawska L, Bofinger ND. Investigation of a modified Sinclair-LeMer aerosol generator in the submicrometer range. Journal of Aerosol Science 1998;29(7):799-809.
Rulison AJ, Flagan RC. Electrospray atomization of electrolytic solutions. Journal of Colloid and Interface Science 1994;167(1):135-145.
Gomez A, Bingham D, de la Mora J, Tang K. Production of protein nanoparticles by electrospray drying. Journal of Aerosol Science 1998;29(5/6):561-574.
Rapaport E, Weinstock SE. A generator for homogeneous aerosols. Experientia 1955;11:363-364.
Barrett JC, Baldwin TJ. Aerosol nucleation and growth during laminar tube flow: maximum saturations and nucleation rates. Journal of Aerosol Science 2000;31(6):633-650.
Koch W, Windt H, Karfich N. Modeling and experimental evaluation of an aerosol generator for very high number currents based on a free turbulent jet. Journal of Aerosol Science 1993;24(7):909-918.
Supplemental Keywords:
ultrafine organic aerosol, aerosol, motor oil, hydrocarbon aerosol, inhalation, animal., RFA, Health, PHYSICAL ASPECTS, Scientific Discipline, Air, Waste, particulate matter, Air Pollution, Air Pollutants, Environmental Chemistry, Health Risk Assessment, air toxics, Epidemiology, Air Pollution Effects, Risk Assessments, Physical Processes, Biochemistry, Atmospheric Sciences, Molecular Biology/Genetics, Incineration/Combustion, ambient air quality, particle size, particulates, atmospheric, health effects, risk assessment, sensitive populations, cardiopulmonary responses, fine particles, human health effects, ambient air monitoring, lung, exposure, cardiovascular vulnerability, pulmonary disease, susceptible populations, animal model, epidemelogy, ambient air, environmental health effects, particle exposure, ambient monitoring, human exposure, particulate exposure, lung inflamation, pulmonary, coronary artery disease, inhalation toxicology, combustion engines, PM2.5, urban air pollution, urban environment, aerosol, cardiopulmonary, human health, human health risk, aerosols, cardiovascular disease, ultrafine particlesProgress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R827354 HSRC (1989) - Northeast HSRC Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R827354C001 Characterization of the Chemical Composition of Atmospheric Ultrafine Particles
R827354C002 Inflammatory Responses and Cardiovascular Risk Factors in Susceptible Populations
R827354C003 Clinical Studies of Ultrafine Particle Exposure in Susceptible Human Subjects
R827354C004 Animal Models: Dosimetry, and Pulmonary and Cardiovascular Events
R827354C005 Ultrafine Particle Cell Interactions: Molecular Mechanisms Leading to Altered Gene Expression
R827354C006 Development of an Electrodynamic Quadrupole Aerosol Concentrator
R827354C007 Kinetics of Clearance and Relocation of Insoluble Ultrafine Iridium Particles From the Rat Lung Epithelium to Extrapulmonary Organs and Tissues (Pilot Project)
R827354C008 Ultrafine Oil Aerosol Generation for Inhalation Studies
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.