2002 Progress Report: Characterization of the Chemical Composition of Atmospheric Ultrafine Particles

EPA Grant Number: R827354C001
Subproject: this is subproject number 001 , 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: Airborne PM - Rochester PM Center
Center Director: Oberd√∂rster, G√ľnter
Title: Characterization of the Chemical Composition of Atmospheric Ultrafine Particles
Investigators: Cass, Glen , Prather, Kimberly A. , Hopke, Philip K. , Dillner, Ann
Institution: Georgia Institute of Technology , Arizona State University - Main Campus , Clarkson University , University of California - Riverside
EPA Project Officer: Chung, Serena
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 2002 through May 31, 2003
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air


The objective of this research project is to provide an improved understanding of the chemical and physical nature of the ultrafine ambient aerosol. Relatively little data are available that provide distinct information on particles in the size range of less than 100 nm. Because of the relatively small amount of particle mass in this size range, sampling and chemical analysis are difficult. However, such physical and chemical data provide critical information to the epidemiological and toxicological studies to help guide their investigations of the relationships of the ultrafine particles and adverse health effects. Initially, the focus of this research has been on the development of effective methods to sample and analyze ultrafine particles. These methods now are being applied to characterize the ultrafine aerosol in a number of locations across the country to assess the variations that exist in the nature of the ultrafine particles.

Progress Summary:

Summary of Progress to Date (Years 1-3 of the Project)

In the early stage of this project, the Cass/Dillner group collected ultrafine particle samples in field experiments in a south central U.S. city (Houston, TX) and in a West Coast city (Riverside, CA) and used automated equipment to measure ultrafine aerosol size distributions. The Prather group completed the development of an improved aerosol time of flight mass spectrometry (ATOFMS) instrument to measure the chemical composition of single atmospheric particles smaller than 100 nm in particle diameter. An ultrafine particle ATOFMS instrument has been constructed incorporating an aerodynamic lens system, which allows transmission of ultrafine particles into the instrument. An effective method for detecting ultrafine particles in the systems is being developed.

Activities for Year 4 of the Project

Instrumentation Development and Characterization. An improved ATOFMS equipped with an aerodynamic lens inlet and an enhanced light scattering system was developed to provide higher detection efficiencies for fine and ultrafine particles. The particle sizing efficiency (product of particle transmission efficiency and particle scattering efficiency) was determined to be approximately 0.5 percent for 95 nm polystyrene latex (PSL) particles and approximately 47 percent for 290 nm PSL particles. The particle detection efficiency (product of particle sizing efficiency and particle hit rate) was measured to be approximately 0.3 percent for 95 nm PSL particles and 44 percent for 290 nm PSL particles, respectively. In addition, the beam profiles for PSL particles of various sizes were measured in the ion source of the ATOFMS and follow a Gaussian distribution with a full width at half maximum of approximately 0.35 mm. A publication describing the optimization and characterization of the improved ultrafine-ATOFMS instrument has been submitted for publication in Analytical Chemistry (Su, et al., submitted, 2003). The results from ambient sampling in San Diego, CA are detailed. In this progress report, the capabilities of this improved ATOFMS for characterizing single fine and ultrafine ambient particles represent ambient measurements made in Rochester, NY and Atlanta, GA. Under typical ambient sampling conditions with particle number concentrations between approximately 100 and 1,000 particles/cm3, approximately 30,000 particles with aerodynamic diameter of 50-300 nm were detected with 24 hour hit rates varying between 10-35 percent. Benefiting from higher sizing and detection efficiencies, this ATOFMS instrument is capable of detecting single fine and ultrafine particles with 30-60 minute temporal resolution, even at low number concentrations of less than 10 particles/cm3. This advancement, allowing the rapid determination of particle composition at smaller sizes with higher efficiency, opens new research opportunities for ultrafine analysis in a number of areas, including environmental and material sciences, health effects studies, industrial hygiene, and national security.

Ambient Ultrafine Aerosols and Homogeneous Nucleation

From the end of November 2001, the number concentrations of ultrafine particles have been measured at the New York State (NYS) Department of Environmental Conservation (DEC) monitoring site on the central fire station in downtown Rochester, NY. Particle size distributions are being measured using a scanning mobility particle sizer (SMPS) comprised of a differential mobility analyzer (DMA) and a condensation particle counter (CPC). In the diameter range of 10 to 500 nm, ambient particles are classified by a DMA (TSI 3071) and counted with a CPC (TSI 3010) every 5 minutes. This work was originally supported by the NYS Energy Research and Development Authority, but at the end of that support, we have continued this work with Center support. We have 1.5 years of data providing information on the number distributions of particles between 10 and 500 nm. In addition, the DEC site monitors SO2, CO, particulate matter (PM2.5), and meteorological variables. The results of these measurements have been submitted for publication in Atmospheric Environment (Jeong, et al., 2003a).

Summarizing the results from the first year of measurements, more than 70 percent of total number concentration was associated with particles in the size range 11 to 50 nm, and 20 percent was associated with particles 50 to 100 nm. The differences of ultrafine particles in the size range 11 to 50 nm between weekdays and weekends clearly suggest that the sources of ultrafine particles are strongly associated with human activities, such as the traffic hour, whereas there was no relationship between fine particle in the size range 100 to 470 nm and human activities. The monthly variations of the number concentrations of particles and ambient temperature suggest that the mean concentrations were inversely proportional to ambient temperature.

One of the surprising findings in recent studies of the urban aerosol is the discovery of relatively frequent homogeneous nucleation events in urban areas. For many years, it was believed that there was too much surface area in the existing aerosol to permit the formation of new particles in the urban atmosphere by vapor-liquid nucleation. The morning rush hour traffic can be seen as a concentration peak at about 9:00 AM. This peak tends to correlate well with the CO concentration measured at the same location. Evening traffic can be observed between 6:00 PM and 9:00 PM.

A second type of pattern of particle size distributions shows a nucleation and growth event. Following the morning rush hour peak, there are a large number of very small (~10 nm) particles appearing just after noon in this figure. These particles grow rapidly through the early afternoon into particles in the 50 to 75 nm size range. The evening rush hour traffic shows some additional peaks in the late afternoon. Thus, the shift toward early afternoon is the result of the onset on more frequent nucleation events during the summer when photochemical processes are more intense.

In addition to these nucleation events, where there are sufficient particles to observe subsequent growth, there can be nucleation events. Thus, there are two distinct forms of nucleation events that have been observed in Rochester. Important questions then are what is nucleating and what is the source of this material. To examine this question, the time variation of the other measured variables can be compared. In the case of the second type of event, there is a strong correlation between the occurrence of the events and the SO2 concentration that also is measured at the same site. There also is a strong relationship with wind direction. These events appear to be the result of the plume from a local coal-fired power plant on the northwestern side of the city. However, for the nucleation with growth events, it appears that these events are more widely spatially distributed based on results from Pittsburgh, Florence, and Philadelphia, PA in July 2001. The nature of the nucleation and growth processes are not well understood in terms of the species that are nucleating and the source of the substantial amount of condensable mass needed to support the observed growth. These nucleation and growth events produce particles over a wide geographical area in sizes that could be a source of adverse health effects.

These data are similar to those that have been previously accumulated in Erfurt, Germany by research project R827354C002 researchers. We anticipate developing a comparable data set that will permit a collaborative project to be developed examining the role of ultrafine particles in causing adverse health effects in Rochester.

Particle Characterization Measurements

During this year, we have developed the methodology for determining the total peroxide content of aerosol samples using the method described by Hung and Wang, 2001. A fluorimeter has been procured and initial laboratory experiments have shown that we can make these measurements.

Field Studies in Rochester, NY

A coordinated measurement program was mounted at the University of Rochester Medical Center to characterize the composition of ultrafine and fine particles. The sampling systems included particle size distribution measurements using a SMPS, several micro-orifice uniform deposit impactors (MOUDI), including nano-MOUDIs to extend the measurement range to 10 nm. The ATOFMS with the aerodynamic lens was brought to Rochester. In addition, several semicontinuous measurements of PM2.5 mass and composition were made.

Size segregated, speciated ambient and concentrated aerosol data were obtained in Rochester, NY during June 2002. Each day, from June 4 to 8, one 6-hour sample of concentrated ultrafine aerosol was collected in three size bins (10-56 nm, 56-100 nm, and 100-180 nm) along with ambient and concentrated number size distributions. From June 11 to 17, four 48-hour ambient MOUDI samples (six size bins with sizes 0.056–1.8 µm) and PM1.8 samples were collected along with number size distribution data. In addition, one 8-day ambient sample for ultrafines with three size bins (10-56 nm, 56-100 nm, and 100-180 nm) were collected during this time. All substrates and filters were analyzed for organic carbon (OC)/elemental carbon (EC), inorganic ions, and trace elements.

The 48-hour ambient PM1.8 concentrations ranged from 17 to 32 µg/m3 with more than one-half of the mass composed of organic compounds and an additional significant contribution from sulfate. A comparison of fine (PM1.8) and ultrafine (PM0.1) was conducted to discern the relative potential toxicity of fine and ultrafine aerosol. Although the concentration of EC in the ultrafine (0.032 ± 0.011 µg/m3) is much less than the concentration of fine EC (0.63 ± 0.35 µg/m3), the percentage to total mass is much higher for ultrafine than for the fine aerosol. A similar pattern holds true for trace metals, indicating that potentially toxic materials, trace metals, and EC are found in greater abundance in the ultrafine than in the fine aerosol.

Inductively coupled plasma-mass spectrometry quantified 29 elements in the ambient samples. The composition of the trace metals varies by particle. Both the smallest (0.056 - 0.10 µm) and the largest (1.0 - 1.8 µm) particle sizes have similar percentages of iron and copper. Ultrafine particles have a higher percentage of chromium and arsenic; the 1.0 - 1.8 µm particles have a higher percentage of zinc and titanium. Studies of trace metals in ultrafine aerosols in two other cities, Los Angeles, CA, and Houston, TX, show that iron is one of the most abundant trace metals in urban areas. These results suggest that iron is commonly observed in the ambient ultrafine aerosol and, thus, it is useful to examine health effects in the toxicological studies being conducted (as described in Annual Report R827354C004).

Continuous or semicontinuous concentrations of PM2.5, OC, EC, black carbon (BC), and sulfate were measured. Quartz filter samples were analyzed for filter-based OC/EC and sulfate. Two-hour integrated and 24-hour integrated OC and EC were measured using thermal-optical transmittance methods. Sulfate was determined using a high-time resolution sulfate analyzer and ion chromatography (IC). BC was analyzed using a two-wavelength aethalometer. Semicontinuous OC and continuous sulfate accounted for more than 57 percent and 20 percent, respectively, to the PM2.5 mass with a mean of 14.9 µg-3. Comparison of the continuous sulfate analysis with the filter-based IC analysis showed very good correlation between the two measurements. Good agreement was found between the reconstructed chemical composition mass based on the filter samples and the real-time PM2.5 mass. These results have been submitted for publication (Jeong, et al., 2003b).

Single Ultrafine Particle Characterization

The size and chemical composition of individual concentrated and nonconcentrated ambient fine (100-300 nm) and ultrafine (< 100 nm) particles were obtained in Rochester, NY during June 2002. During a 17-hour sampling experiment on June 6 and June 7, 14,166 particles with an aerodynamic diameter of lower than 300 nm, including 2,964 ultrafine (< 100 nm) particles, were sized and chemically analyzed. After the concentrator experiment, the ATOFMS was used to sample ambient particles directly (nonconcentrated). During 8 days of continuous ambient measurements from midnight June 10 to midnight June 18, 2002, 96 nonconcentrated particles with aerodynamic diameters of less than 300 nm, including 10,489 ultrafine particles (Da < 100 nm), were sized and chemically analyzed.

The improved ATOFMS was located in the annex of the University of Rochester Medical Center, and used to directly sample ambient fine and ultrafine particles about 2.5 m from Elmwood Avenue, a moderate traffic road located about 3 miles away from downtown Rochester. EC rich-type particles are dominant in the ultrafine (< 100 nm) range; OC rich particles are the most significant in the fine (100-300 nm) mode. The major source of the EC and OC particles is vehicular emissions from cars during this study. The temporal variations of the major particle types observed in Rochester and apportionment to sources currently are being conducted.

Field Studies in Atlanta, GA

Three modified nano-MOUDIs, a PM1.8 sampler, and SMPS were used during a 10-day period at the Atlanta Supersite in parallel with an ultrafine ATOFMS. The modified nano-MOUDIs were used to collect two 5-day samples of fine and ultrafine aerosol. The two nano-MOUDI sampling events were midnight-to-midnight August 6-10, 2001, and August 11-15, 2001. The PM1.8 sampler was used to collect PM1.8 filters each 24-hour period during the 10-day sampling event. Filters and substrates were analyzed for inorganic ions, EC/OC, and trace elements. The SMPS ran continuously to obtain number size distribution data.

For the Atlanta study, 212,016 particles in the fine size mode (particles with aerodynamic diameters between 100 and 300 nm) and 21,859 particles in the ultrafine size mode (particles with aerodynamic diameters between 50 and 100 nm) were analyzed. The ATOFMS sampled approximately 500-2,000 particles per hour at sizes below 300 nm. The ultrafine particles (50-100 nm) observed consisted of EC, OC, and a mixture of EC and OC (EC/OC) as a result of vehicular, industrial, and biogenic emissions with a high correlation to relative humidity. EC was found to be dominant in the ultrafine mode, whereas OC (most likely coated on EC particle cores) was dominant for particles between 100 nm and 300 nm. A greater fraction of particles containing OC compared to EC increases with increasing size. These ultrafine particles grow into the fine mode through agglomeration and/or condensation of organic species on the particles, and contribute to the fine mode where particles with organic species (most likely masking smaller EC cores in some cases) dominate the particles observed by the ATOFMS.

A comparison in the chemical composition of ultrafine and fine particles observed in Atlanta and Rochester shows that there is a smaller fraction of elemental carbon particles detected in Rochester. The greater contribution of EC particle found in Atlanta can be attributed, in part, to the diesel emissions originating from the Greyhound bus maintenance facility located near the sampling site and other nearby diesel traffic. Because the combustion process from diesel engines is less efficient, it is expected that diesel emissions produce a greater fraction of soot particles. Roadside measurements taken in Rochester mostly were coming from spark engine vehicles that could also account for the greater fraction of OC, polycyclic aromatic hydrocarbon (PAH)-rich, and amine-rich particles in the ultrafine particles. In both cities, OC dominates the fine mode. There also is a greater fraction of vanadium-rich particles in Rochester observed in the fine mode. Transition metals such as vanadium and iron were observed in association with organic particles. This particle type is indicative of vehicular traffic. In Atlanta, throughout the entire size range of particles detected, there was a greater fraction of potassium-rich particles. The source of these particles is unknown.

Concentrator Experiment

A prototype Harvard ultrafine particle concentrator, located at the University of Rochester Medical Center, was designed for particle health effects and toxicological studies. After completing the ambient aerosol studies described above, additional measurements were made of the particles entering and exiting the concentrator. During the study, the concentrator was not operating optimally, and the exit air stream was at high relative humidity rather than having been returned to typical ambient level. The ambient particles thus experienced saturation, condensation, and desolvation/evaporation processes inside the particle concentrator, but may not have been fully restored to their original condition. Because the toxicity of ambient particles is closely related to their size, number and mass concentrations, and chemical composition, the improved ATOFMS and the nano-MOUDI were used to characterize the concentrated particles. The results from the concentrator experiments were compared with those obtained by direct (nonconcentrated) ambient measurement to evaluate whether the animal and human models were exposed to real-world ambient particles. The results were reported in several posters at the 2003 American Association of Aerosol Research Meeting on Particulate Matter: Atmospheric Sciences, Exposure, and the 4th Colloquium on PM and Human Health. The results of this preliminary study have led us to create additional studies of the more developed form of the ultrafine concentrator described below.

Exposure System for “Truck Study”

Recent studies have shown particle number concentrations over urban roadways are higher than roadside and much higher than downwind. In fact, on-road number concentrations often are higher than provided by concentrator systems. People in passenger cars and trucks are directly exposed to these particles that are present on highways at high concentrations. Thus, an on-road exposure system was developed, in which laboratory animals were transported on active roadways to provide exposures to fresh ultrafine aerosols. The University of Minnesota’s Mobile Emissions Laboratory has been used extensively to make on-road emission measurements. It was adapted for use as both an emission laboratory and exposure system. An inlet brings the on-road aerosol from in front of the truck into the laboratory in the truck bed’s cargo container, where measurements and animal exposures are performed. In these experiments, some of the equipment was removed to make room for the animal exposure system. An air delivery system was built to provide exposures for three groups of animals: whole highway aerosol; filtered air with the gaseous pollutants present; and clean air without particles, volatile organic compounds, CO, or NOx. The cages held 10 animals each; thus, 30 animals could be used for a given experiment. Rats of old age were used, with and without preexposure to endotoxin or human influenza virus, as well as spontaneously hypertensive rats, with telemetric electrocadiogram and blood pressure implants. The truck was then driven on highways around Rochester under varying conditions to provide a range of exposures to the animals. The results of this experiment are described in Annual Report Summary R827354C004.

Hung H-F, Wang C-S. Experimental determination of reactive oxygen species in Taipei aerosols. Journal of Aerosol Science 2001;32(10):1135-1233.

Kim E, Larson TV, Hopke PK, Slaughter C, Sheppard LE, Claiborne C. Source identification of PM2.5 in an arid northwest U.S. city by positive matrix factorization. Atmospheric Research 2004;66(4):291-305.

Kim E, Hopke PK, Larson TV, Covert DS. Analysis of ambient particle size distributions using UNMIX and positive matrix factorization. Environmental Science and Technology 2004;38(1):202-209.

Jeong C-H, Lee D-W, Kim E, Hopke PK. Measurement of real-time PM2.5 mass, sulfate, and carbonaceous aerosols at multiple monitoring sites. Atmospheric Environment (submitted, 2003a).

Jeong C-H, Hopke PK, Utell M, Chalupa D. Characteristics of nucleation and growth events of ultrafine particles measured in Rochester, NY. Atmospheric Environment (submitted, 2003b).

Su YX, Sipin MF, Furutani H, Prather KA. Development and characterization of an ATOFMS with improved detection efficiency for individual fine and ultrafine particle analysis. Analytical Chemistry (submitted, 2003).

Future Activities:

Future activities for the ATOFMS data include comparison of the mass spectral signatures to ion markers identified in ATOFMS source characterization studies to determine the particle emission sources in the ambient experiments. To have representative number mass concentrations, the data will be scaled to number concentrations obtained by a SMPS, and to mass concentrations obtained by MOUDI measurements taken along side in Atlanta by Arizona State University. These results will be developed into publications based on the Rochester and Atlanta field measurements. Further data analysis on these two data sets from the East Coast, and comparison to the results from West Coast field measurements, will provide signatures of fine and ultrafine particles on the East and West coasts of the United States.

Measurements of peroxide concentrations will be made and samples will be collected for morphometric examination in Rubidoux, CA during July 2003 in conjunction with experiments being conducted by Professor Delbert Eatough of Brigham Young University. We also anticipate making measurements in January 2004 in Philadelphia and/or New York City in conjunction with winter intensive studies being conducted in those locations.

We will conduct studies of the current generator of Harvard Ultrafine Concentrator during August 2003. Given our initial results suggesting that there were observable changes in the aerosol characteristics between the inlet and the outlet of the concentrator, it is important to determine exactly what is happening in the later designs of these systems. There is substantial use of concentrators to provide exposure of animals and humans to concentrated airborne particles and it is necessary to fully understand the nature of that exposure and its relationship to actual ambient aerosol exposures. Experiments will be conducted at the Harvard School of Public Health using both the improved ATOFMS, semicontinuous instruments, and a nano-MOUDI. These systems will be used to collect and characterize the aerosol composition at the inlet and exit of the concentrators. The semicontinuous instruments will include a Sunset field OC/EC analyzer, a two-wavelength aethalometer, and a sulfate analyzer. The nano-MOUDI will use collection media that will permit the analysis of OC and EC.

Subsequently, in conjunction with Dr. Robert Devlin of the National Health of Environmental Effects Research Laboratory/U.S. Environmental Protection Agency, we will examine the concentrator that the U.S. EPA has in its human exposure chamber at the University of North Carolina. At the present time, we are trying to arrange additional tests of ultrafine concentrators to be able to better characterize the exposure being provided to a variety of animal and human subjects.

We have begun increased collaboration with the epidemiological research group (R827354C002). In May, Professor Hopke visited Dr. Wichmann at the GSF in Munich. During the first week of June, Matthias Stotzel of the GSF visited Professor Hopke’s laboratory at Clarkson University to learn the use of positive matrix factorization for particle source apportionment. During the coming year, we will be looking to expand this collaboration to examine the use of apportioned source contributions in epidemiological studies.

Journal Articles:

No journal articles submitted with this report: View all 30 publications for this subproject

Supplemental Keywords:

pollution prevention, urban air pollution, atmosphere, air, health, atmospheric sciences, environmental chemistry, incineration, combustion, combustion engines, air toxics, tropospheric ozone, PM2.5, particulates, ultrafine particles, particulate matter, particle exposure, particle size, aerosol, metals, ambient air, ambient air monitoring, ambient air quality, atmospheric, fine particles, human exposure, human health, human health effects, environmental health effects, inhalation toxicology, lung, lung inflammation, stratospheric ozone,, RFA, Health, Scientific Discipline, Air, Geographic Area, particulate matter, Environmental Chemistry, Health Risk Assessment, Epidemiology, State, Risk Assessments, Biochemistry, ambient air quality, particle size, particulates, sensitive populations, cardiopulmonary responses, chemical characteristics, fine particles, human health effects, morbidity, ambient air monitoring, pulmonary disease, susceptible populations, epidemelogy, particle exposure, environmental health effects, nano differential mobility analyzer, human exposure, chemical kinetics, particulate exposure, Texas (TX), PM, mortality, urban environment, aerosols, chemical speciation sampling, human health risk

Relevant Websites:

Relevant Web Sites: http://www2.envmed.rochester.edu/envmed/ Exit

Progress and Final Reports:

Original Abstract
  • 1999 Progress Report
  • 2000 Progress Report
  • 2001 Progress Report
  • 2003 Progress Report
  • 2004 Progress Report
  • Final Report

  • Main Center Abstract and Reports:

    R827354    Airborne PM - Rochester PM Center

    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