2006 Progress Report: Characterization and Source ApportionmentEPA Grant Number: R832415C001
Subproject: this is subproject number 001 , established and managed by the Center Director under grant R832415
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Rochester PM Center
Center Director: Oberdörster, Günter
Title: Characterization and Source Apportionment
Investigators: Hopke, Philip K. , Prather, Kimberly A.
Current Investigators: Hopke, Philip K. , Gelein, Robert , Prather, Kimberly A.
Institution: Clarkson University , University of California - San Diego
Current Institution: Clarkson University , University of California - San Diego , University of Rochester
EPA Project Officer: Chung, Serena
Project Period: October 1, 2005 through September 30, 2010 (Extended to September 30, 2012)
Project Period Covered by this Report: October 1, 2005 through September 30, 2006
RFA: Particulate Matter Research Centers (2004) RFA Text | Recipients Lists
Research Category: Health Effects , Air
Research Core 1 (Characterization & Source Apportionment) performs the measurements and characterization of UF and fine PM to understand the link between physicochemical properties (EC/OC, inorganics, surface reactive oxygen species, EPR), sources, and health effects.
The specific aims of this core were:
- To understand the evolution of ambient particle compositions as they are transported from the sources to the receptor site with particular emphasis on the concentrations of particle-bound reactive oxidative species (ROS).
- To develop methods to characterize the sources and nature of reactive oxidative species associated with the ambient PM2.5 and PM0.1 particle aerosol.
- To identify and apportion sources of the ambient aerosol in locations where epidemiological studies are being made and collect samples for in vitro and in vivo studies.
- To apportion the sources that contribute to the concentrated ambient particles (CAPs) that are used for human and animal exposures and for in vitro studies.
Characterization of Particle-Bound ROS
There is a need to reproducibly generate particles containing ROS for method development and animal exposures. We can use ozone to oxidize a reactive VOC like α-pinene to produce peroxide species as indicated by Docherty, et al. (2005). The schematic diagram of the ROS particle generator is shown in Figure 1. The charcoal denuder removes both the hexane and the residual ozone to provide a particle size distribution shown in Figure 2. The stability of the generator in hour-by-hour samples is shown in Figure 3. The ROS was measured using the dichlorofluorescein (DCFS) system we have previously used for ambient particle measurements (Venkatachari, et al., 2005). This generator system appears to provide reasonable reproducibility and further work to improve its stability is in progress. A system has been provided to the animal studies core for use in animal exposures.
Figure 1. Schematic Diagram of the ROS-Bearing Particle Generator
Figure 2. Particle Size Distribution of Particles Produced by the ROS-Bearing Particle Generator
Figure 3. ROS Concentrations Measured for 1 Hour Intervals With the Particle Generator
Work is in progress to characterize the nature of the ROS species. Methods need to be developed to make such a characterization. Our current approach is to stabilize the radicals using molecular spin-traps. We will then identify chemical nature using high resolution EPR (UCSD) and separate and identify the nature of the stabilized ROS using LC/MS (Clarkson University).
We have begun to establish protocols for collection of particles and EPR spectroscopy on these particles. We have worked with different spin trapping agents to determine the best ones for characterizing ambient particles. In addition, we are working on sampling particles directly into solution containing the spin trap. This will eliminate many artifacts associated with loss of spins between sampling analysis, as well as those associated with extracting the particles from the filters.
A study was conducted in Riverside, CA, during the summer and fall of 2005. This was a large field study focused on PM2.5 organic aerosols. In addition to standard gas, aerosol, and PM measurements, as part of this project, ultrafine particles were measured using a UF-ATOFMS for 3 weeks during both of these studies. In addition to standard ambient sampling and characterization, ambient particles were size selected using an SMPS. The aerodynamic sizes of these particles were measured in the ATOFMS. These two sizes can be used to determine the density and shape of ambient EC particles. It was determined that most of the particles in the summer had different densities on different days and times of the day. These densities were strongly dependent on the atmospheric water content. The higher the water content, the lower the particle density. This suggested the Riverside summer aerosol was highly processed, allowing significant uptake of water. The curve showing the relationship between atmospheric water content and particle density for ambient summer particles is shown in Figure 4.
Figure 4. Relationship Between Atmospheric Water Content and Effective Density of the Aerosols Sampled in Riverside, CA, During August 2005
In the Fall, the aerosols showed more diversity in composition and density for a given mobility diameter. This was due to the fact that the particles were less aged. Figure 5 shows size selected ambient particles at a mobility diameter of 450 nm. One can see that several distinct aerodynamic modes exist. The particles with the smallest aerodynamic diameter (~100 nm) had the lowest effective densities. These are primarily EC particles. This suggests particles with this aerodynamic diameter had extremely low effective density (<< 1) and thus were highly fractal in nature. As particles age and become coated, their fractal shape collapses to a sphere as we showed in our lab coating experiments. Thus these EC particles are fresh vehicle emissions. These particles were only detected in the morning periods. They showed relatively quick processing in the Riverside aerosol.
Figure 5. Aerodynamic Diameters of Ambient Aerosols Sampled During the Fall in Riverside, CA. These particles had mobility diameters of 450 nm. Each of the modes has a distinct density and shape which can be calculated from the mobility and aerodynamic diameters.
In support of the Cardiac Rehabilitation Panel study, particle size distributions are being measured inside and outside of the Rehab Center and at the New York State Department of Environmental Conservation (NYS DEC) site. Prior data have been analyzed using positive matrix factorization (PMF) and sources have been tentatively identified (Ogulei and Hopke, in review). These methods are then available to apply to the size distribution data collected during the panel study.
Studies will be conducted on the stability of spin trapped radicals as a function of storage time and temperature. Initial EPR and chemical separation approaches will be developed and tested. We expect to refine the laboratory studies to provide samples of radicals that can be used to test the methods and to collect field samples in a number of locations for ROS studies, as well as support in vitro studies at Rochester. We will participate in the Center-wide analysis intercomparison exercises currently being organized. We will continue to collect and analyze the particle size distribution data in Rochester to support the cardiac rehabilitation panel study.
We have developed software algorithms that allow us to source apportion ambient particles “on the fly.” This advance will allow us to measure ambient particles with ATOFMS and use this information to selectively collect size-fractionated ambient particles on filters for in-vivo and in-vitro analysis. Preliminary plans are to sample during periods with fresh emissions, aged particles, and metal “events.” Different composite samples will be collected over several days when these distinct particle types are present. Size cuts will be sub-200 nm, PM1, and PM2.5.
Docherty KS, Wu W, Lim Y, Ziemann PJ. Contributions of organic peroxides to secondary aerosol formed from reactions of monoterpenes with O3. Environmental Science & Technology 2005;39:4049-4059.
Venkatachari P, Hopke PK, Grover BD, Eatough DJ. Measurement of particle-bound reactive oxygen species in Rubidoux aerosols. Journal of Atmospheric Chemistry, 2005;50:49-58.
Ogulei D, Hopke PK. Modeling source contributions to submicron particle number concentrations measured in Rochester, NY. Aerosol Science and Technology (in review, 2006).
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other subproject views:||All 19 publications||13 publications in selected types||All 13 journal articles|
|Other center views:||All 190 publications||156 publications in selected types||All 143 journal articles|
||Spencer MT, Shields LG, Prather KA. Simultaneous measurement of the effective density and chemical composition of ambient aerosol particles. Environmental Science & Technology 2007;41(4):1303-1309.||
Supplemental Keywords:ATOFMS, source apportionment, reactive oxygen species, particle size distributions,, RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, Health Risk Assessment, Biochemistry, airway epithelial cells, atmospheric particles, cardiopulmonary responses, chemical characteristics, fine particles, airborne particulate matter, aerosol composition, human exposure
Progress and Final Reports:Original Abstract
Main Center Abstract and Reports:R832415 Rochester PM Center
Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R832415C001 Characterization and Source Apportionment
R832415C002 Epidemiological Studies on Extra Pulmonary Effects of Fresh and Aged Urban Aerosols from Different Sources
R832415C003 Human Clinical Studies of Concentrated Ambient Ultrafine and Fine Particles
R832415C004 Animal models: Cardiovascular Disease, CNS Injury and Ultrafine Particle Biokinetics
R832415C005 Ultrafine Particle Cell Interactions In Vitro: Molecular Mechanisms Leading To Altered Gene Expression in Relation to Particle Composition