Grantee Research Project Results
2006 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, 2005 through August 1, 2006
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 overall objective of this Science To Achieve Results (STAR) project is to develop an innovative particle sampler that can be coupled to pre-existing commercial or research-grade analytical instruments for on-line, size-resolved analysis of individual organic species in ambient aerosol particles. This coupling will enable:
(1) High efficiency separation of particles from the gas phase.
(2) Concentration of collected aerosol on a cryo-cooled surface under high vacuum (avoiding problems associated with filter sampling and solvent extractions).
(3) 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 (MIT), Department of Chemical Engineering, and Dr. Douglas R. Worsnop at Aerodyne Research, Inc. (ARI).
Progress Summary:
The following improvements were introduced and the following experiments were performed to characterize the particle sampler during Year 3:
- It was found that the valve between the chamber and the collector was not working properly. This valve is controlled with an automated stepper motor and at the beginning of the sample stage it opened properly. But sometimes electronic interference from the switching of the liquid nitrogen valve caused the stepper motor to make additional steps during the sampling period. Therefore, for long sampling times the stepper motor sometimes made so many steps that the valve was closed during the sampling period. This problem was solved by resetting the sampling valve after every switching of the liquid nitrogen valve in the ACM program.
- A Proton Transfer Reaction/Mass Spectrometer (PTR/MS), which is owned by Pacific Northwest National Laboratory (PNNL), was shipped to Aerodyne for 1 week and was connected to the ACM. Experiments were performed with different parameters, such as, temperatures of valves and lines and times of different stages of a sampling cycle. Figure 1 shows the results for motor oil for two different temperatures of the Valco valves and the transfer line. The higher temperature leads to a more rapid transfer of material to the detector.
Figure 1. Motor Oil Detected With the PTR/MS at Two Different Temperatures of the Valves and the Transfer Line (Red Graph 150° C, Blue Graph 200° C)
- Experiments with the PTR/MS with faster sampling time suggested that some of the sample is sticking and desorbing in the transfer line. By coating the transfer line with Silcosteel from Entech Instruments, it was possible to get more reproducible results.
- The success of coating the transfer line led to a consideration of what other parts could be coated. The normal fused silica coatings used in gas chromatography (GC) applications cannot be used to coat the collector because it consists mainly of copper. For this reason, the collector was first coated with Kisscote, a special silicon compound. The results of these experiments were more reproducible, but after several experiments the sensitivity decreased. After re coating the collector, the sensitivity was improved again. In addition, traces of silicon compounds were apparent in the chromatograms of experiments and blanks, indicating that the Kisscote also is desorbed at these temperatures and in vacuum.
- A new collector was designed in stainless steel, which can be coated with the normally used fused silica coatings, and this collector was coated with Siltek from Restek. Experiments were performed to investigate the behavio r of the collector when it was heated in the desorption stage. It was found that there was no significant difference in the time needed to heat the collector from the cold temperature in the collection stage to the hot temperature in the desorption stage between the copper/stainless steel collector and the stainless steel collector. Experiments with this new collector showed better reproducibility.
- Blank and memory effects were investigated using a GC/MS as the detector. In most of the experiments several blanks had to be made to clean the system. It was found out that a cleaning of the collector in the vacuum by opening the valve between vacuum chamber and collector is more efficient than cleaning in backflush with carrier gas.
- Experiments also were made with oleic acid (C18H34O2, MW = 282 amu) because it is a good surrogate for ambient aerosol. More mass than expected was needed to give a measurable response because part of the oleic acid decomposes, which was shown by GC/MS mass spectra where the majority of the ion intensity is low molecular weight fragments (< 90 amu). Also, significant levels of CO2 formed by de carboxylation of the oleic acid were observed. This shows that thermal decomposition may be a limiting factor for this technique. However, ambient aerosol contains hundreds of other compounds that can be detected with the ACM.
- Experiments with a candle flame as a combustion source were performed to show the potential of the ACM for multi-component samples. Figure 2 shows the chromatogram from one of these experiments in which many (> 15) individual components can be resolved. With the National Institute of Standards and Technology M ass S pectral Library, most of these peaks are identified as polyaromatic and aliphatic hydrocarbons (tri-, tetra-, penta-, and hexadecane, benzene, and naphthalene derivatives). A cryotrap at the head of the column is not necessary because the sample is collected at the head of the cold column during the desorption stage and is desorbed after heating the column in the particular GC method used here.
Figure 2. Chromatogram of Soot From a Candle Flame
Summary
The reproducibility of the particle sampler for on-line sampling was enhanced by the use of a coated transfer line and a coated collector. To use the coatings normally used in GC/MS applications, which showed the best results in the experiments with the ACM, the collector cannot be of copper. For this reason, a collector of stainless steel was developed and introduced successfully.
The experiments with the PTR/MS show the possibility of us ing the ACM with different detectors, which is one of the goals of this project.
The experiments with the candle flame show the use of the ACM for samples with many compounds. It is possible to resolve several components with the GC/MS. A cryotrap at the head of the column is not necessary because the sample is adsorbed at the head of the column and desorbed from there when the column is heated during the GC/MS cycle. This qualitative result shows the power of this technique for on-line compound separation and identification without costly post- collection analysis procedures.
Future Activities:
After getting the no -cost extension, further experiments are in progress to finish the characterization of the particle sampler and to demonstrate the detection of ambient aerosol. In particular, the following tasks will be performed during the fourth year of the project:
- Experiments with laboratory aerosol to optimize temperatures and times for the different stages and check linearity. The aerosol will be generated with an atomizer and a DMA and will be characterized with a CPC and later in a smog chamber. Also, comparisons with an Aerodyne aerosol mass spectrometer (AMS) will be made. The AMS provides real-time chemically speciated mass loadings for aerosol particles and can be used to quantify the particle sampler results.
- More experiments with a PTR/MS to get results with the optimized system. The PTR/MS will be coupled again to the particle sampler and experiments with laboratory generated aerosol particles will be performed.
- Experiments with ambient aerosol in urban and rural sites.
Journal Articles:
No journal articles submitted with this report: View all 6 publications for this projectSupplemental Keywords:
PM2.5, on-line analysis, particle sampler, organic speciation, GC/MS,, 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.