Grantee Research Project Results
2004 Progress Report: Advancing ATOFMS to a Quantitative Tool for Source Apportionment
EPA Grant Number: R831083Title: Advancing ATOFMS to a Quantitative Tool for Source Apportionment
Investigators: Prather, Kimberly A. , Hopke, Philip K.
Institution: University of California - San Diego , Clarkson University
EPA Project Officer: Chung, Serena
Project Period: October 1, 2003 through September 30, 2006 (Extended to September 30, 2007)
Project Period Covered by this Report: October 1, 2003 through September 30, 2004
Project Amount: $450,000
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter
Objective:
The objective of this research project is to further explore the aerosol time-of-flight mass spectrometry (ATOFMS) data to determine if single particle mass spectrometry can:
- quantitatively measure the carbonaceous component of the ambient aerosol, including organic carbon (OC) and elemental carbon (EC), and ascertain if it is possible to develop a quantitative and universal calibration that provides results comparable to time-resolved OC/EC measurements;
- provide key markers that distinguish among sources of carbonaceous aerosol, including diesel and spark-ignition vehicles, mobile and stationary sources, fossil fuel sources versus biomass burning, and primary biological and/or secondary organics;
- and provide insights into atmospheric processes that can then be better represented in air-quality models such as the relationship of secondary OC with primary particle types.
Progress Summary:
We have established unique mass spectral ion marker combinations in ATOFMS data for primary and secondary carbonaceous species, including EC and OC. Unique markers in the mass spectra of these particle types make it possible to distinguish between EC, OC, and OC on EC cores at the single particle level. These markers are observed consistently in ambient field studies, as well as source combustion studies of spark ignition and diesel vehicle emissions with extremely reproducible ion intensities. We have used the mass spectral data to establish a correlation between the measured relative ion intensities and the mass fractions of OC and EC in individual particles as a function of size, which represents a significant advance in our ability to be quantitative for these species with ATOFMS. In addition, because individual particle compositions are measured, we can directly assess the mixing state (or chemical associations) between EC and OC and other (primarily) secondary species such as ammonium, nitrate, and sulphate. The EC particle trends measured using ATOFMS in the 50-200 nm size range show strong correlations with the temporal evolution of gas phase carbon monoxide in a study conducted near a major freeway, a species indicative of fresh vehicle emissions. From a source apportionment perspective, EC signatures from cars and trucks are almost identical; however, the single particle associations with other chemical species such as calcium and phosphate (both indicators of engine oil observed in diesel exhaust) and certain metals vary from source to source. The overall fingerprints used for apportioning single particles are based on the presence of a combination of ion markers for EC, OC, calcium, and phosphate (and/or lack of some of these species) and show distinctions between these carbonaceous species from different sources.
Using the results from the flow tube laboratory studies conducted as part of this project, the quantitative OC/EC measurements were used to quantify the amount of transformations occurring on particles after passing through an ultrafine particle concentrator system used for health effects studies as part of the University of Rochester Particulate Matter Center project. Finally, scaling procedures have been developed to transform ATOFMS particle concentrations acquired in measurements made at the Fresno Supersite to mass concentrations. These scaled mass concentrations compare well (R2 ~ 0.8) with standard PM2.5 mass concentration measurements acquired with a beta attenuation monitor. Scaled size- and temporal-resolved concentrations of particles as a function of single particle composition are derived using these scaling factors for an urban location in Fresno and compared with ATOFMS data acquired at a rural location in central California (Angiola) located outside of Fresno. This study was conducted in the winter and thus the Fresno particles were dominated by biomass burning aerosols. In contrast, the Angiola particulate matter concentrations are lower and show ion markers, indicating they have undergone fog processing and gas-to-particle conversion upon transit to the Angiola site. The results obtained to date show great promise for using ATOFMS as a tool for performing time- and size-resolved source apportionment of ambient aerosols, which will be important for establishing control strategies to meet compliance. Also, characterizing the composition changes on shorter time scales allows for comparisons to be made between ATOFMS and other gas and particle phase measurements, which will allow us to better understand aerosol processing in the atmosphere.
Future Activities:
We will further subdivide the carbonaceous particle types into different types, including gasoline (cars), diesel (trucks), and biomass burning aerosols. The mass fractions of carbonaceous particles as a function of size will be obtained for other studies conducted with the ATOFMS in North Carolina, Boston, and Atlanta. In Year 1 of the project, we laid the groundwork for understanding the different signatures from OC and EC in ambient and source particles and performed source apportionment using simplistic fingerprint matching techniques developed at the University of California–San Diego. The next phase of this project will involve extending the analysis to include multivariate approaches for source apportionment using the tools being developed in Professor Hopke’s group.
Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
PM2.5, OC/EC, secondary organic aerosol, ATOFMS, continuous measurements, sources, Supersite, air, ecosystem protection, environmental exposure, risk, analytical chemistry, atmospheric sciences, environmental chemistry, environmental engineering, environmental monitoring, monitoring/modeling, physics, air toxics, particulate matter, aerosol analyzers, aerosol particles, aerosol time-of-flight mass spectrometry, air quality model, air sampling, atmospheric dispersion models, atmospheric measurements, atmospheric particulate matter, carbon particles, emissions, human exposure, human health effects, mass spectrometry, measurement methods, modeling, modeling studies, monitoring stations, particle phase molecular markers, particulate matter mass, secondary organic aerosols,, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, air toxics, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Environmental Engineering, atmospheric particulate matter, atmospheric dispersion models, atmospheric measurements, source apportionment, aerosol particles, human health effects, secondary organic aerosols, air quality models, monitoring stations, air sampling, carbon particles, air quality model, emissions, modeling, particulate matter mass, human exposure, secondary organic aerosol, particle phase molecular markers, transport modeling, modeling studies, aerosol analyzers, measurement methodsRelevant Websites:
Progress and Final Reports:
Original AbstractThe 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.