Grantee Research Project Results
2006 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, 2006 through December 31, 2007
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 project to date has consisted of extensive instrument development, fabrication, and modeling involving the various components of the proposed aerosol mobility/mass spectrometer. These include: (1) the aerosol inlet; (2) the low-pressure chemical ionization chamber; (3) the ion gate; (4) the ion mobility cell; (5) the gas skimming/ion focusing chamber; and (6) the mass spectrometer. A primary focus has been resolution of the arcing, discharge, and aerosol diffusional loss issues associated with operating the inlet, chemical ionization region, and mobility cell between 1 and 10 Torr. Such pressures are necessary to minimize ion clustering and maximize ion transmission into high vacuum. These issues have been resolved through design modification and some trial and error. Every component of the instrument is now operational and undergoing calibration in the laboratory. Specific accomplishments from year 1 include:
Completion and Modeling of the Aerosol Inlet
The aerosol collection inlet resembles a cylindrical differential mobility analyzer (DMA) operated at low pressure. The low pressure increases the likelihood of arcing between the high-voltage cylinder and ground, as well as diffusional broadening of the collection efficiency function. The operating parameters have been established and the effect of diffusion quantified using a combination of finite element modeling and Lagrangian analysis of particle trajectories. Three separate heating elements and their respective housings—a thin strip, a wire, and a coil—have been constructed.
Manufacture and Testing of a Series of Novel Bradbury-Nielsen-Type Ion Gates
Ion gates are important for introducing a short pulse of ions into the mobility cell so that they may be separated based on mobility. The gates have been tested and the optimum geometry determined experimentally for inclusion into the final instrument. We have also completed the electronics necessary to apply high voltage pulses, shorter than 100 μs in width, to the gate.
Design and Construction of the Ion Mobility Cell and Ion Focusing Region
This part of the project entailed an extensive modeling study using the commercial codes, FLUENT and SIMION. The aim here was to maximize ion transmission efficiency through the mobility cell and into the mass spectrometer, while at the same time providing a large pressure drop between the mobility cell and mass spectrometer and maintaining sufficient mobility resolution. After several design iterations, the ion focusing region (i.e., the interface region between the mobility cell and mass spectrometer where the drop to high vacuum occurs) has been completed and sufficiently tested. The ion mobility cell has also been constructed and tested, and its performance was adequate. We are in the process of applying further SIMION computations in order to increase the mobility resolution. In order to do this more efficiently, we have constructed a separate vacuum chamber with the specific purpose of optimizing this portion of the instrument.
Modeling and Modification of the Mass Spectrometer
The orthogonal reflectron time-of-flight mass spectrometer provides high-resolution mass analysis of the ions that have been separated based on mobility. The ions enter the mass spectrometer with an initial energy that is determined by the geometry of, and high-voltage applied to, the ion-focusing region. We have modeled the mass spectrometer to determine the optimal reflectron mounting angle as a function of the initial kinetic energy and have made the necessary modifications to the mass spectrometer.
Future Activities:
During Year 2 of the project, we will: (1) deploy a low-pressure chemical ionization time-of-flight mass spectrometer at the port of Los Angeles; (2) continue modeling and initiate experimental optimization of the ion mobility cell using a specially constructed test chamber; and (3) incorporate the ion mobility cell into the chemical ionization mass spectrometer in preparation for deployment of the mobility/mass spectrometer.
Journal Articles:
No journal articles submitted with this report: View all 5 publications for this projectSupplemental 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.