Grantee Research Project Results
2007 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, 2007 through December 31, 2008
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:
The second year of the project resulted in significant instrument modification and refinement. We have overhauled the ion focusing region and the data acquisition system. These changes have successfully resulted in our first chemical ionization time-of-flight mass spectra. We have tested the system using a number of organics, and have characterized the spread of kinetic energy of ions entering the extraction region in the TOF-MS, and the fragmentation of various organics. This has allowed us to tune the system to minimize fragmentation of the organics during ionization and transmission to high vacuum, thus aiding in their identification.
Specific accomplishments from year 2 include:
Establishment of data acquisition system: We have acquired a time-to-digital converter and constructed a fast preamplifier in order to allow for individual ion counting using the microchannel plate detector with high time resolution.
Refinement of the ion focusing region and mass spectrometer: We have implemented new models, using SIMION, to include collisions between ions and neutral molecules in the ion focusing region. We have also experimentally examined ion mobility and mass effects in the transmission to high vacuum, due to these collisions. Focusing region parameters, such as orifice plate/skimmer spacing, deflection voltages, and ion optics ions/second were obtained in the extraction region of the mass spectrometer.
Charaterization of the instrument: We have acquired mass spectra for a variety of organics and under a wide range of conditions, in order to minimize clustering and fragmentation (see Fig. 1). Ion kinetic energy into vacuum was found to be related to the extent of fragmentation. The ion reflector in the mass spectrometer was used to select specific ion kinetic energies, and the resulting mass spectra allowed for determination of the extent of fragmentation.
Figure 1: Chemical ionization mass spectra of acetone and isopropanol.
Future Activities:
During Year 3 of the project, we will 1)publish a series of papers documenting the performance of the instrument, 2) obtain chemical ionization mass spectra of atmospheric aerosols in L.A., and 3) incorporate the ion mobility cell into the chemical ionization mass spectrometer.
Journal Articles:
No journal articles submitted with this report: View all 5 publications for this projectSupplemental Keywords:
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.