Grantee Research Project Results
2005 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, 2004 through August 14, 2005
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 project, we are developing and applying a thermodenuder-Aerodyne Aerosol Mass Spectrometer (TD-AMS) technique for ambient organic fine particle analysis. The objectives of the 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 (i.e., combustion of gasoline, diesel fuel, and wood; and meat cooking) and the major sources of fine particle organics (i.e., oxidation of aromatics, alkanes and alkenes, and biogenic compounds by OH and NO3 radicals and O3). A field study will be conducted 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, and the TD-AMS data will be analyzed using the source database developed in this study. The results of this project will lead to a powerful new technique for the chemical characterization of atmospheric organic PM2.5, which through its application will improve the understanding of organic aerosol formation mechanisms and sources, and add valuable new data for use in source apportionment modeling.
Progress Summary:
During Year 1 of this project, the major accomplishments were that a TD system was designed, constructed, and tested at Aerodyne, further evaluated at the University of Colorado–Boulder (CU), and then deployed by the CU group in front of an AMS in a preliminary study as a part of the New England Air Quality Study–Intercontinental Transport and Chemical Transformation (NEAQS-ITCT) at Chebogue Point, Nova Scotia, for 3 weeks in July 2004. The results demonstrated the potential utility of the TD-AMS technique, and pointed to improvements that needed to be made.
During Year 2 of this project, a second TD was designed and constructed by Aerodyne, with several design modifications based on experience gained using the first unit. In particular, a problem identified with the first unit was that the time scale for changing temperatures was too long, on the order of 1 hour. This was a serious obstacle to the rapid scanning of the TD, which is especially important during field experiments. The second TD was built with less insulation, a fan that could blow air in the insulation chamber to shorten the cool-down period and a 3-zone automatic temperature control system.
The CU group further improved on the TD design and operation by implementing a valve and temperature control system in software (Labview and Visual Basic 5.0). The valve system allows for switching between ambient air that either bypasses or passes through the TD, for constant time periods. The temperature control system was programmed to step through several temperatures repeatedly and has demonstrated transition times between different temperature settings of 10 minutes or less. During the Riverside field study (described below), the TD was stepped to the following temperatures: 50, 75, 100, 125, 150, 175, and 200°C in 20-minute intervals. For the first 10 minutes after switching temperatures, the temperature was allowed to stabilize while the AMS sampled ambient air that bypassed the TD. For the next 10 minutes, the AMS sampled air that passed through the TD. The procedure was then repeated. This procedure was automated and employed 24/7 during the Riverside campaign.
The University of California–Riverside (UCR) conducted studies on a series of standard compounds and secondary organic aerosol (SOA) formed in an environmental chamber using a TD (the first version constructed by Aerodyne) interfaced with the thermal desorption particle beam mass spectrometer (TDPBMS, equivalent to TD-AMS). The standards that were analyzed included a variety of monocarboxylic and dicarboxylic acids, dioctyl sebacate, diesel lubricating oil (as a surrogate for primary aerosol), ammonium sulfate, and SOA formed from reactions of cyclohexene and a-pinene with O3, and pentadecane with OH/NOx. TD desorption profiles were obtained and compared with temperature-programmed thermal desorption (TPTD) profiles (these involve collecting aerosol on a cooled TDPBMS vaporizer and then desorbing with a slow temperature ramp). The TPTD technique has been used for many years by the UCR group to obtain compound vapor pressure information, and is being used here as an aid in interpreting the volatility information contained in TD profiles. These results also were used to establish appropriate TD-AMS temperature settings for the Riverside field studies. Analyses of laboratory measurements made thus far indicate that there is a close correspondence between TD and TPTD profiles, such that the midpoint temperature for sample desorption in the TD is approximately 20°C higher than for TPTD. It appears that the midpoints can be used to estimate component vapor pressures. The desorption behavior of many of the analyzed components was sufficiently different from one another that the TD technique can provide at least partial, and sometimes complete, separation for mass spectral analysis.
A major accomplishment of Year 2 was the SOAR-1 (Study of Organic Aerosol in Riverside) field campaign. This study was organized by Professors Jimenez and Ziemann to evaluate the performance of the TD-AMS. It was conducted at UCR, which is a polluted region downwind of Los Angeles that is heavily impacted by both primary and secondary aerosol. Although it was originally intended that this study would include only the UCR and CU groups, as word of our intentions spread, many other research groups became interested in making measurements with a variety of complementary methods during this period. As a result, during the SOAR-1 study (around July 15 to August 15) approximately 50-60 scientists from 15 universities and research institutes and companies participated in what is probably the most complete analysis of organic aerosols performed to date. More detailed information on the participants and measurements can be found at http://cires.colorado.edu/jimenez-group/Field/Riverside05/.
During SOAR-1, the TD system was used by the CU group in front of a new high-resolution time-of-flight aerosol mass spectrometer (ToF-AMS) and a scanning mobility particle sizer (SMPS). This system was used to continuously analyze ambient particles, and to analyze secondary organic aerosol (SOA) formed in five reactions [pentadecane + OH/NOx, α-pinene + O3, 3-methyl-2-butenal + OH/NOx, toluene + OH/NOx, gasoline + OH/NOx] conducted in the environmental chamber in the Ziemann laboratory. The UCR group employed their TDPBMS system for a number of comparisons with the AMS of real-time mass spectra at vaporizer temperatures of around 150-200 oC, which demonstrated that the two systems yield similar mass spectra when operated under similar conditions. This correspondence enhances the utility of a large library of TDPBMS SOA mass spectral data that is available for interpreting AMS ambient measurements. The UCR group also performed real-time and TPTD analysis of ambient aerosol by sampling through a VACES particle concentrator developed and operated by Professor Sioutas’ group from the University of Southern California.
Analysis of the CU and UCR results from the SOAR-1 campaign is ongoing. Analysis of the CU data was delayed by the need to develop data analysis software for the ToF-AMS, which is now available. In general, qualitative results are consistent with the known relative volatilities of aerosol species: ammonium nitrate > organics > ammonium sulfate. There have been, however, some surprises: during several days in SOAR-1, high volatility sulfur-containing species were observed that were probably hydroxymethane sulfonate. This contrasts with the low volatility of ammonium sulfate, the most common sulfate aerosol species. These two components would have been very difficult to separate without the TD. Data analysis is now focusing on the volatility behavior of hydrocarbon-like and oxygenated organic aerosols (HOA and OOA) identified from custom principal component analysis of AMS spectra.
Our work to date is successfully meeting the original goals of the project. We have completed Task 1 of this project, which was to construct two TD systems. We also have completed most of Task 2, which was to characterize the TD. Some additional tests are needed to verify particle passing efficiencies. Tasks 3–through 6 are all underway. For Task 3, a number of pure organic compounds have been analyzed using the TD and TPTD methods, while studies of standard mixtures remain. The TD (interfaced with both the TDPBMS and AMS) and TPTD methods also have been used to analyze SOA formed from a series of environmental chamber reactions, although other systems remain to be studied by the UCR group to complete Task 4. Thus far, the results of analyses of diesel lubricating oil have been used as a surrogate for organic combustion aerosol, prior to planned Task 5 studies by the CU group. The SOAR-1 campaign was the focus of Task 6, and the large amounts of data from those studies are now being analyzed.
The results of this project are demonstrating that the TD-AMS technique will be a powerful new approach for characterizing the chemical composition of atmospheric organic PM2.5. We have demonstrated that the TD can provide a significant degree of separation of components based on volatility, which improves mass spectral identification and yields information on component vapor pressures. The information obtained by the AMS has previously come from the dependence of aerosol mass spectra on particle size and time. Addition of the desorption temperature as a new correlation parameter for characterization will significantly enhance the power of the AMS method. Through its application, it is expected to provide improved data for understanding organic aerosol formation mechanisms and sources, and for use in source apportionment modeling. Such data can aid in the evaluation of the effects of fine particulate matter on human health and the environment, and can be used to develop more accurate air pollution models. This will allow for more efficient targeting of aerosol sources in pollution control strategies.
Also, it is worth noting an important practical application of this project. One of the original reasons the TD technique was selected as the means for gaining aerosol volatility information with an AMS was that a TD is easily interfaced to an AMS. It was expected that once the power of the TD-AMS technique was demonstrated, the TD would become a desired addition to current and future AMS instruments. Because of the widespread use of the AMS (> 40 currently in use), the impact of the TD technique (and this project) would therefore be greatly amplified. The TD technique already has generated considerable interest in the AMS community, especially after results were presented by Professor Jimenez at the 6th Annual AMS Users Meeting. Aerodyne reports that four groups have inquired about the possibility of ordering a TD from Aerodyne to interface with their AMS.
Future Activities:
The plans for Year 3 for the CU group include: (1) participation in SOAR-2 (around November 1-15, 2005), which will involve TD-AMS analysis at UCR under less polluted conditions; (2) further TD laboratory characterization, especially more detailed mapping of the passing efficiency versus particle size and temperature for nonvolatile aerosols; (3) deployment of the TD in front of two ToF-AMSs and an SMPS for 1 month in the upcoming Mexico City field campaign (MCMA-2006, March 2006) [this is a target of opportunity]; and (4) TD-AMS characterization of combustion particles generated with a burner, as well as car exhaust. During Year 3, the UCR group will continue laboratory studies of standard aerosol particles as well as SOA using the TD-TDPBMS and TPTD analysis. The standard particles of interest are primarily mixtures of organics and organics/inorganics that are representative of ambient aerosol. The SOA systems to be studied include aromatics, monoterpenes, and alkanes, reacting with O3 and OH/NOx. Reactions will be carried out with and without seed particles, including acidic particles that can initiate heterogeneous oligomerization reactions. One important goal is to determine whether a particular SOA system can be identified as the source of the large m/z 44 signal that generally appears in AMS ambient mass spectra and is indicative of a large contribution from oxidized organic aerosol.
In addition, we are working on two manuscripts presenting the results of the work conducted to date. A first paper will focus on describing and characterizing the TD-AMS technique. We aim to submit this paper around June 2006. A second paper will present and compare the results of the several ambient-sampling field campaigns in which the TD-AMS system has been deployed: Nova Scotia in summer 2004, Riverside in summer and fall 2005, and Mexico City in spring 2006.
Journal Articles:
No journal articles submitted with this report: View all 39 publications for this projectSupplemental Keywords:
ambient air, tropospheric, air pollution, particulates, particulate matter, environmental chemistry, monitoring, carbonaceous particles, combustion aerosols, source apportionment,, RFA, Scientific Discipline, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, 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
http://www.aerodyne.com Exit
http://cires.colorado.edu/jimenez-group/Field/Riverside05/ 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.