Grantee Research Project Results
Final 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 Amount: $356,500
RFA: Continuous Measurement Methods for Particulate Matter Composition (2005) RFA Text | Recipients Lists
Research Category: Particulate Matter , Air Quality and Air Toxics , Air
Objective:
There were two main goals of this project. The first goal was the development of novel instrumentation aimed at optimizing the real-time identification of organic compounds in ambient aerosols segregated by size. The second goal was the deployment of the instrumentation within the Los Angeles basin. The general project design was aimed at incorporating technologies that demonstrated the potential for molecular analysis that minimized fragmentation and clustering of parent molecules. The selected methods were electrostatic collection of particles, thermal desorption of the collected particles, low-pressure proton transfer ionization of the desorbed molecules, ion mobility separation of the ions, and, finally, time-of-flight mass spectrometry of the mobility-separated ions. In addition to the identification of organic compounds, the desired characteristics of the device were: (1) it must be deployable, (2) it must provide a time-resolution on the order of minutes, and (3) it must have the potential for automation.
Summary/Accomplishments (Outputs/Outcomes):
Development and Characterization of Size-Resolved Aerosol Collection/Desorption Systems
- A cylindrical aerosol collector was designed and fabricated for the size resolved collection and thermal desorption of ambient fine and ultrafine aerosols.
- A model for the collection efficiency of the cylindrical aerosol collector was developed.
- A series of experiments was designed and performed to test the collection efficiency at atmospheric pressure and low pressure.
- An electrostatic nano-aerosol collector was developed and modeled.
- The nano-aerosol collector was tested experimentally using aerosol standards.
Development and Characterization of Low-pressure Chemical Ionization Chamber
- A radioactive source chemical ionization chamber was designed and built.
- A corona discharge chemical ionization chamber was designed and built.
- Experiments were designed and performed to determine the ion production rate and ion transmission through the system.
Development and Characterization of Ion Mobility Drift Cell
- A model was applied to compute the optimized design for a low-pressure ion mobility drift cell.
- The ion mobility drift cell was fabricated and tested with organic compounds.
- The drift cell was used to calibrate the aerosol collector at low pressure.
- The response of the ion mobility cell to a variety of organic compounds was modeled and compared with laboratory data.
Development and Deployment of Thermal Desorption CI-TOFMS Instrument
- The sensitivity of the instrument was determined through experiments involving the controlled flow of organic vapor.
- Experiments aimed at determining the extent of clustering and fragmentation of organic standards were designed and completed.
- The response of the of the CI-TOFMS to organic aerosol standards was determined, and conditions were optimized to retain only parent ions during analysis.
- Measurements of ambient gas-phase and aerosol-phase organic compounds were made through deployment of the optimized TD-CI-TOFMS instrument.
Development and Testing of a Combined IMS/MS System for Analysis of Aerosols
Incorporating the ion mobility drift cell into the TD CI-TOF instrument represents the final step in terms of instrument development for this project. Progress in this step currently is hindered by the control/data acquisition system. Although the hardware obtained during the project is capable of acquiring the two-dimensional mobility/mass spectra, there remain software issues in terms of accessing the raw data from the data acquisition board (Ortec model 9353). This data access is required to bin the ion counts with respect to their mobility, rather than just summing them into a single mass spectrum.
TD-CIMS mass spectra of aerosol standards and ambient aerosols
Atmospheric aerosols were sampled from the roof of Tutor Hall on the University of Southern California campus in downtown Los Angeles. In Figure 2, a mass spectrum was obtained from an aerosol sample that was size-selected using a differential mobility analyzer, passed through a denuder, vaporized in a temperature-controlled stainless steel hot tube set to 450º C, and analyzed by the TOF-MS. There are several notable features in the figure. First, the water cluster reagent ions, labeled in the figure, represent the largest peaks. Second, there is series of complex organic compounds evident between roughly 100 and 250 amu, having a characteristic spacing of 14 amu indicative of - CH2 – group additions. Third, larger peaks corresponding to larger masses are clearly evident near 280, 350, 410 and 490 amu.
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| Other project views: | All 5 publications | 2 publications in selected types | All 2 journal articles |
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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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Phares DJ, Collier S, Zheng Z, Jung HS. In-situ analysis of the gas-and particle-phase in cigarette smoke by chemical ionization TOF-MS. Journal of Aerosol Science 2017;106:132-141. |
R832837 (Final) |
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Supplemental Keywords:
air, engineering, chemistry, physics, environmental chemistry, environmental monitoring, chemical detection techniques, chemical composition, aerosol particles, air sampling, atmospheric aerosols, monitoring, air quality field measurements, particulate matter chemistry, field monitoring, ion mobility spectrometer, RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Air, particulate matter, Air Quality, Environmental Chemistry, Monitoring/Modeling, Environmental Engineering, Environmental Monitoring, air sampling, chemical characteristics, airborne particulate matter, emissions monitoring, atmospheric chemistry, real-time monitoring, speciation, modeling studies, environmental measurement, particulate matter mass, air quality model, particulate organic carbon, aerosol analyzers, source apportionment, chemical speciation sampling, particle size measurement, air quality models, analytical chemistry, atmospheric measurements, monitoring of organic particulate matterProgress 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.