Grantee Research Project Results
2004 Progress Report: Development and Application of a Mass Spectra-Volatility Database of Combustion and Secondary Organic Aerosol Sources for the Aerodyne Aerosol Mass Spectrometer
EPA Grant Number: R831080Title: Development and Application of a Mass Spectra-Volatility Database of Combustion and Secondary Organic Aerosol Sources for the Aerodyne Aerosol Mass Spectrometer
Investigators: Ziemann, Paul J. , Worsnop, Douglas R. , Jimenez, Jose-Luis
Institution: University of California - Riverside , Aerodyne Research Inc. , University of Colorado at Boulder
EPA Project Officer: Chung, Serena
Project Period: October 1, 2003 through August 14, 2006 (Extended to September 30, 2007)
Project Period Covered by this Report: October 1, 2003 through August 14, 2004
Project Amount: $409,922
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:
In this 3-year experimental research program, we are developing and applying a Thermodenuder-Aerodyne Aerosol Mass Spectrometer (TD-AMS) technique for ambient organic fine particle analysis. The objectives of this research project are to: (1) construct and couple a TD to the AMS and evaluate and optimize its performance; (2) use the TD-AMS technique in laboratory studies to develop a mass spectra-volatility database for the major atmospheric sources of combustion, aerosol and secondary organic aerosol; and (3) apply the database to a TD-AMS study of organic aerosol in the Los Angeles Air Basin.
The TD-AMS system will be evaluated and optimized using standard particles and then used to develop a database of mass spectra-volatility signatures for interpreting ambient organic aerosol TD-AMS data. TD-AMS measurements will be made on laboratory-generated organic aerosols from the major primary sources (combustion of gasoline, diesel fuel, and wood, and meat cooking) and the major sources of fine particle organics (oxidation of aromatics, alkanes and alkenes, and biogenic compounds by OH and NO3 radicals and O3). A field study then will be carried out in the Riverside area of the Los Angeles, California, metropolitan area under conditions when both primary and secondary organic aerosols are expected to be present. The TD-AMS data will be analyzed using the source database developed in this study. The results of this research project will lead to a powerful new technique for the chemical characterization of atmospheric organic PM2.5. The application of this technique will improve the understanding of organic aerosol formation mechanisms and sources and add valuable new data for use in source apportionment modeling.
Progress Summary:
A TD system was designed based on a model published by Wehner, et al. (2002) and constructed and tested at Aerodyne Research, Inc. A University of Colorado at Boulder (CU) graduate student (Alex Huffman) participated in the testing at Aerodyne. The instrument then was shipped to CU for further characterization. The first tests were designed to confirm that the instrument was working similarly to specifications set by the authors of the design. The heating tube was tested for performance and optimized to flatten the temperature profile over the desired heating stage. Based on results indicating that vapor recondensation could introduce significant errors into the analysis, some aspects of the system are being redesigned to keep the temperature elevated to an optimal level until the vaporized material is able to interact with the activated charcoal adsorbent. Passing efficiencies also were measured to verify that particles pass through the instrument with minimal losses resulting from diffusion and thermophoresis. These tests outlined areas of suboptimal temperature and passing performance that are being investigated and optimized further.
Although the design of the TD is not yet optimal, it operates sufficiently well and was deployed in front of an AMS as a part of the New England Air Quality Study-Intercontinental Transport and Chemical Transformation at Chebogue Point, Nova Scotia, for 3 weeks in July 2004. This was the first time the TD-AMS system was used for ambient particle analysis. In addition to using the study to add the volatility dimension to the data set, it was important to employ the instrument under field study conditions to help determine design aspects that could be improved. The TD was added inline to the sampling line before a TSI Model 3010 Condensation Particle Counter (CPC) and AMS. A computer-controlled solenoid valve was used to switch automatically between sampling by the AMS/CPC alone (no TD) and through the TD. The TD was run at 50, 100, and 175ºC temperatures at different times, with the lower two temperatures cycled more frequently through the campaign.
The data from this campaign are only beginning to be analyzed, but preliminary analysis shows that the volatility signature of the particles changed during different particle episodes. For example, in some episodes, the AMS mass loading for organic and nitrate species decreased at the same rate, and there was successively greater loss of particle mass for these species at each temperature step. Mass loadings for ammonium and sulfate, however, did not decrease significantly until the 175ºC step, showing that these species had lower volatility. This is consistent with ammonium sulfate particles, which have a high vaporization temperature. In other episodes, all particle species lost mass at the same rate. This seems to show, albeit very roughly, that the TD-AMS system is able to vaporize and denude ambient particle species as a function of volatility, and this ability adds volatility to the set of particle properties already accessible with the AMS/CPC system. During this study, we also determined that the time for switching to lower temperatures is too long (> 1 hour) for our needs, and we now are redesigning part of the heating unit to allow faster cooling and thus speed up the overall time resolution achievable with the system. Overall, however, the TD worked well in the field and produced reasonable particle volatility results. A thermal desorption gas chromatography/mass spectrometry (GC-MS) system (TAG) operated by Allen Golstein’s group (University of California at Berkeley) also was sampling aerosol composition with a time resolution of 1 hour during this field experiment. We plan to jointly analyze the TD-AMS and TAG data, especially for the unresolved complex mixture that contains most of the GC-MS signal. Because the elution time in the GC-MS column is directly related to volatility, the joint analysis of these two data sets may lead to insights that benefit our understanding of both systems.
Thus far, studies at the University of California at Riverside have employed a Thermal Desorption Particle Beam Mass Spectrometer (TDPBMS), which has a number of similarities to the AMS, to investigate the effect of vaporizer temperature (100, 150, 200, 250, and 300ºC) on mass spectra for a variety of pure inorganic compounds (i.e., ammonium sulfate and ammonium nitrate) and organic compounds and mixtures (i.e., stearic acid, adipic acid, benzoyl peroxide, dioctyl phthalate, dioctyl sebacate, octacosane, and diesel oil). As expected, the extent of fragmentation generally increases with increasing temperature such that high-mass ion intensities decrease, whereas low-mass ion intensities increase. These results will be compared in detail with similar measurements to be made with the AMS at CU to determine optimal vaporizer temperatures for obtaining high-mass and low-mass peak information. Both types of spectra are useful for extracting composition information. This also will aid the understanding of field data when we are able to collocate the instruments.
Future Activities:
The TD has gone through an initial testing in the laboratory and field campaign. We now understand aspects of the instrument that need minor modifications, which currently are underway. We also will begin a more detailed analysis of the Nova Scotia field data in November 2004. Recently, the TD has been shipped to the University of California at Riverside, where it is being interfaced to the TDPBMS. An extensive series of studies are planned (beginning in the next month) to obtain mass spectra-volatility information on secondary organic aerosol formed in environmental chamber reactions. These data will be compared with volatility profiles obtained using the temperature-programmed thermal desorption method normally employed with the TDPBMS in secondary organic aerosol studies. Later in the spring, we plan to begin characterization of organic combustion aerosols using the TD-AMS system at CU to further develop the volatility-MS database. A field study currently is planned for around May 2005 in Riverside, California, where we will co-locate the TD-AMS system with the TDPBMS. The exact dates of this study will depend on the progress made in the laboratory studies.
Journal Articles:
No journal articles submitted with this report: View all 39 publications for this projectSupplemental Keywords:
ambient air, tropospheric, air pollution, particulates, environmental chemistry, monitoring, carbonaceous particles, combustion aerosols, source apportionment,, RFA, Scientific Discipline, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, Air Quality, particulate matter, air toxics, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Incineration/Combustion, Engineering, Chemistry, & Physics, Environmental Engineering, carbon aerosols, air quality modeling, particle size, atmospheric particulate matter, combustion byproducts, particulate organic carbon, aerosol particles, atmospheric particles, mass spectrometry, carbon, chemical characteristics, PM 2.5, air modeling, air quality models, airborne particulate matter, air sampling, gas chromatography, thermal desorption, carbon particles, air quality model, emissions, secondary organic aerosol, particulate matter mass, ultrafine particulate matter, PM2.5, modeling studies, mass spectra volatility database, particle dispersion, aerosol analyzers, aerosol mass spectrometry, measurement methods, combustion contaminants, chemical speciation samplingRelevant Websites:
http://www.chem.ucr.edu/faculty/ziemann/ziemann.html Exit
http://cires.colorado.edu/jimenez Exit
Progress 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.