Grantee Research Project Results
2008 Progress Report: The Impact of Aerosols, Clouds, and Ozone on Surface UV and Photochemistry in Houston, TX
EPA Grant Number: R832837Title: The Impact of Aerosols, Clouds, and Ozone on Surface UV and Photochemistry in Houston, TX
Investigators: Phares, Denis J.
Institution: University of Southern California
EPA Project Officer: Chung, Serena
Project Period: January 1, 2006 through December 31, 2010
Project Period Covered by this Report: January 1, 2008 through December 31,2009
Project Amount: $356,500
RFA: Continuous Measurement Methods for Particulate Matter Composition (2005) RFA Text | Recipients Lists
Research Category: Particulate Matter , Air , Air Quality and Air Toxics
Objective:
The objective of this project is to provide in-situ quantitative chemical analysis targeting intact organic molecules present within the fine and ultrafine size fractions of ambient aerosol. Using soft ionization of the parent molecules, and subsequent measurement of molecular shape as well as mass, we aim to facilitate a more definitive identification, and to use the new techniques as diagnostic tools to probe primary and secondary organic aerosol formation within the Los Angeles basin.
Progress Summary:
Year 3 of the project focused on continued instrument characterization and calibration, and preliminary field measurements. The project is currently under a one-year no-cost extension in order to allow for continued field measurements, data analysis, and manuscript submission.
Specific accomplishments from year 3 include:
Verification of the size-resolved collection of aerosols on the inlet
The performance of the inlet for the size-resolved collection of aerosols onto a heating filament for subsequent thermal desorption was verified theoretically and experimentally. Experimentally, the collection efficiency was determined by vaporization of the particles from the filament, chemical ionization of the vapor, and low-pressure ion mobility spectrometry of the ionized sample. Measurements were made at atmospheric pressure and at 18 Torr. The data demonstrated that the device is indeed size selective, and the collection efficiency curves agree with model predictions.
Thermal-desorption chemical-ionization ion mobility spectrometry of organic gases and aerosols
Ion mobility spectra were obtained for a variety of organic compounds, including gas-phase compounds and aerosols. The ion mobility cell was able to detect nanogram quantities of aerosol collected on the heating filament in the aerosol inlet.
Thermal-desorption chemical-ionization mass spectrometry of organic gases and aerosols
Chemical ionization TOF mass spectra were obtained for a variety of gas-phase and aerosol standards. It was found that fragmentation was minimal, even for longer chain hydrocarbons that typically feature extensive fragmentation patterns under photon ionization or electron beam impact ionization.
Figure 1: Mass spectrum acquired during thermal desorption of oleic acid particles from heating filament. The prominent peak at 283 Da is the protonated oleic acid parent ion.
Characterization of field-dependent ion clustering and fragmentation
It was observed that water clustering and sample ion clustering (at high sample pressures) could be eliminated by collision in the gas skimmer region of the instrument. Sample ion fragmentation could also be induced by the same mechanism. These measurements demonstrate the usefulness of tuning the electric field strength for analysis of collision-induced fragments.
Acquisition of preliminary field data
Atmospheric aerosols were sampled from the University of Southern California campus in downtown Los Angeles. Although analysis is minimal at this point, there are several notable observations. There are a series of complex organic compounds having a characteristic spacing of 14 amu indicative of - CH2 – group additions. Larger peaks corresponding to masses over 350 Da are evident during certain times. At this point, these peaks are unidentified and may have resulted from polymerization of gas phase species in the atmosphere.
Future Activities:
- Obtain aerosol mass spectra in the lab from well-controlled combustion sources.
- Obtain a data set in downtown Los Angeles, near the 110 freeway.
- Obtain a data set at another deployment site (Long Beach, 710 freeway, or Riverside)
- Incorporate ion mobility cell and obtain mobility/mass spectra from gas phase organics.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 5 publications | 2 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Phares DJ, Collier S. Direct collection of aerosols by electrostatic classification for size-resolved chemical analysis. Aerosol Science & Technology 2010;44(3):173-181. |
R832837 (2008) R832837 (2009) R832837 (Final) |
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Supplemental Keywords:
Organic aerosols, Chemical Analysis, Aerosol mass spectrometry, Combustion, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Environmental Engineering, particulate organic carbon, atmospheric measurements, model-based analysis, source apportionment, chemical characteristics, emissions monitoring, environmental measurement, airborne particulate matter, air quality models, air quality model, air sampling, speciation, particulate matter mass, analytical chemistry, modeling studies, monitoring of organic particulate matter, real-time monitoring, aerosol analyzers, chemical speciation sampling, particle size measurementProgress 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.