Grantee Research Project Results
2005 Progress Report: Particle Sampler for On-Line Chemical and Physical Characterization of Particulate Organics
EPA Grant Number: R831077Title: Particle Sampler for On-Line Chemical and Physical Characterization of Particulate Organics
Investigators: Smith, Kenneth A. , Worsnop, Douglas R.
Institution: Massachusetts Institute of Technology , Aerodyne Research Inc.
EPA Project Officer: Chung, Serena
Project Period: October 1, 2003 through August 1, 2006 (Extended to September 30, 2007)
Project Period Covered by this Report: October 1, 2004 through August 1, 2005
Project Amount: $410,000
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 develop an innovative particle sampler that can be coupled to pre-existing commercial or research-grade analytical instruments for online, size-resolved analysis of individual organic species in ambient aerosol particles. This coupling will enable:
- High efficiency separation of particles from the gas phase.
- Concentration of collected aerosol on a cryo-cooled surface under high vacuum (avoiding problems associated with filter sampling and solvent extractions).
- Direct injection of desorbed species from particle sample into analytical instruments.
This program is a collaborative effort between the research groups led by Professor Kenneth A. Smith at the Massachusetts Institute of Technology , Department of Chemical Engineering, and Dr. Douglas R. Worsnop at Aerodyne Research, Inc.
Progress Summary:
The following improvements were introduced and the following experiments were performed to characterize the particle sampler during Year 2 of the project.
The particle sampler was connected to a commercial gas chromatograph–mass spectrometer (GC/MS, Agilent 5890 Series & Agilent 5973) for experiments. Two 4-port valves were used for the necessary flow cycles of particle sampling and analysis. Experiments were performed with different temperatures and durations for the four stages of a sampling cycle (backflush, sampling, vaporization/desorption, and transfer/injection) to optimize these parameters. Experiments were performed with vaporization/desorption in vacuum as well as in the carrier gas (high purity helium).
A new kind of inlet (Volatile Interface G2319-64000 from Agilent) was installed to introduce the sample into the GC. With the volatile interface inlet, the reproducibility of the sample retention time was increased and losses in the transfer to the GC were decreased.
A significant leak between the aerosol collection chamber and the vacuum system was identified and repaired resulting in lower background signals in the chromatograms.
The carrier gas path was improved and the heating rate was increased (using a heater with 40 W output) to 230°C in 1 minute.
An interrupt driven C program was written to control the parameters of the particle sampler. With this program, the temperatures and durations of the stages of the sampling cycles could be chosen and the valves switched automatically. The GC/MS is a slave in this program, so it is possible to start the GC/MS temperature program and the flow control of the volatile interface automatically at the right time.
Experiments were performed with the particle sampler using a hydrocarbon standard (ASTM) with several components. The chromatograms of these experiments show some of the components of the standard. The associated peaks were very well resolved and sharp, indicating efficient desorption and transfer to the GC. Which peaks appeared depended on the chosen desorption temperature. Other experiments were performed where a liquid sample of the ASTM standard was injected directly into the GC instead of via the particle sampler to investigate the transfer characteristics of the particle sampler. The chromatograms from these experiments yielded more individual components than the experiments using the particle sampler. This shows that the smaller hydrocarbons (for example hexane) are too volatile to be detected with the particle sampler. Furthermore, the largest molecular weight components decompose in the particle sampler.
Experiments with monodisperse aerosol (pristane in trichloroethane) were performed. Particles were generated with an atomizer (TSI, Model 3076) and then dried using a charcoal filter. The dried particles were introduced into a DMA (TSI, Model 308100) and part of the resulting monodisperse aerosol was sent to the particle sampler and the other part to a condensation particle counter (CPC, TSI, Model 3022A) to count the particles. Monodisperse pristane particles were sampled for 1 minute (size 300 nm, CPC: 8000 particles/cm3, flow 5 cm3/s), which is equivalent to approximately 10 ng. A typical ion chromatogram from one of these experiments and the corresponding mass spectrum are shown in Figure 1.
Figure 1. Chromatogram and Corresponding Mass Spectrum of a Sample of a Monodisperse Aerosol Corresponding to 10 ng Pristane
Summary
The prototype particle sampler for on-line sampling was partially characterized and a sample of less than 10 ng was detected. The signal height was equivalent to a detection limit of less than 1 ng. The system was not highly reproducible, however, so it was not possible to determine the exact detection limit. The resolution observed for the several peaks of the hydrocarbon standard and the sharpness of the peaks in the chromatograms suggest that it will be possible to resolve different organic species in ambient aerosol particles. With the interrupt driven C program, autonomous data collection is possible.
Future Activities:
Further experiments are in progress to get better reproducibility and to demonstrate the detection of ambient aerosol. In particular, the following tasks will be performed during Year 3 of the project:
- Experiments with laboratory aerosol to improve reproducibility and check linearity.
- Experiments with ambient aerosol in urban and rural sites.
- Experiments with a Proton Transfer Reaction/Mass Spectrometer (PTR/MS) to show that the particle sampler operates with different detectors.
- Data analysis and quantification of the results.
Journal Articles:
No journal articles submitted with this report: View all 6 publications for this projectSupplemental Keywords:
PM2.5, particulate matter, air pollution, online analysis, particle sampler, organic speciation, GC/MS, atmospheric dispersion models, gas chromatography, modelling,, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, RESEARCH, particulate matter, Environmental Chemistry, Monitoring/Modeling, Monitoring, Environmental Monitoring, Ecological Risk Assessment, particle size, atmospheric dispersion models, atmospheric measurements, analysis of organic particulate matter, chemical characteristics, human health effects, air quality models, monitoring stations, gas chromatography, air quality model, air sampling, modeling, analytical chemistry, particulate matter mass, particle sampler, modeling studies, aerosol analyzersProgress 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.