2006 Progress Report: Application of Thermal Desorption GCMS (TD-GCMS) for the Analysis of Polar and Non-Polar Semi-Volatile and Particle-Phase Molecular Markers for Source AttributionEPA Grant Number: R831088
Title: Application of Thermal Desorption GCMS (TD-GCMS) for the Analysis of Polar and Non-Polar Semi-Volatile and Particle-Phase Molecular Markers for Source Attribution
Investigators: Schauer, James J. , Sheesley, Rebecca J. , Simoneit, Bernd R.T.
Institution: University of Wisconsin - Madison , Oregon State University
Current Institution: University of Wisconsin - Madison
EPA Project Officer: Chung, Serena
Project Period: January 1, 2004 through December 31, 2006 (Extended to December 31, 2007)
Project Period Covered by this Report: January 1, 2006 through December 31, 2007
Project Amount: $449,687
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
The overall goal of the proposed project is to fully develop, validate, and employ a cost-effective thermal desorption gas chromatography mass spectrometry (TD-GC-MS) technique for the analysis of semi-volatile and particle-phase organic compounds, which can be applied to both atmospheric and source samples.
Briefly, Year 3 efforts on the TD-GC-MS focused on finalizing development and validation of the two polar derivatization methods for atmospheric particulate matter analysis. The diazomethane derivation method combines analysis of both polar acid compounds— such as aromatic and aliphatic mono and diacids and the full suite of non-polar compounds including polyaromatic hydrocarbons (PAHs), hopanes, steranes, and alkanes—and has been used for the Study of Organic Aerosols at Riverside (SOAR study), which was a U.S. Environmental Protection Agency (EPA) and California Air Resources Board (CARB)-funded field study of organic aerosol composition that took place in July and August 2005, on the campus of the University of California, Riverside. The second polar method uses a silylation derivatization to quantify alcohols and polyols including levoglucosan, cholesterol, mono palmitin, glucose, and sucrose and is being used in the analysis of samples from Fresno, CA collected in the winter of 2007. The non-polar (no derivatization) method was employed as well for several studies which focused on motor vehicle emissions, including a personal exposure study of workers at a trucking terminal and several projects from the Southern California Particle Center.
The SOAR samples were collected in Riverside, CA, in the summer of 2005 with 24-hour and higher time-resolved 6-hour samples. Samples were collected on 90-mm quartz fiber filters at a flow rate of 92 lpm. A single 1.45 cm2 punch was used for this analysis, which conserved most of the filter for future analysis. The initial analysis used the 24-hour samples and provided consistent non-polar data with a volatility-limited list of polar acids (Figure 1). It is often helpful to compare results roughly with previous studies in the same region. The hopanes are in the same range as measured in the Los Angeles area by Fine, et al. (2004) and the reported acids (methyl phthalic and azelaic) are in the same range as reported in a central California study (Rinehart, et al., 2006). These data illustrate that the non-polar compounds continue to be measured in a rigorous manner, even when combined with the diazomethane derivatization. Additionally, the day of the week information has been included on the X axis to illustrate the potential utility of these data in assessing weekday/weekend trends; although the data are reported in ambient concentration and have not yet been normalized by organic carbon concentration.
Additional developmental work was done with the diazomethane method to improve recovery and quantification of aliphatic diacids, which are higher volatility. The GC method was modified to enhance detection of these more volatile compounds. One week of 6-hour SOAR samples is currently being analyzed using the improved diazomethane method to focus on time-of-day fluctuations in the full list of polar acids and non-polar compounds. The 24-hour SOAR samples quantified azelaic and sebacic acids (nonanedioic and decanedioic acids), while the modified method will allow quantification of aliphatic diacids with molecular weights as low as succinic acid (butanedioic acid). Measurement of acidic compounds, such as the aliphatic and aromatic diacids, combined with non-polar tracers, such as hopanes, is essential to understanding the sources and secondary processing occurring in ambient particulate matter. The results of the SOAR study will be published as part of a method development paper on the diazomethane TD-GC-MS method and are also being used as part of an intercomparison study with in situ GC-MS analysis collocated at the SOAR site.
Validation of the diazomethane method consists of extensive duplicate analysis, matrix spike (standard spike directly onto ambient samples) recovery analysis, and intercomparison with solvent extraction GC-MS using ambient particulate matter samples collected in Mexico City during the 2006 Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign.
The silylation TD-GC-MS method has made significant progress in Year 3. It had been mentioned in previous progress reports that the method was not ideal for large projects due to instrument wear and tear resulting from high inputs of the silylation reagent. Much time was devoted to method development to limit the amount of reagent in the system, including dilution of the reagent and increased instrument cleaning and maintenance. Additionally, the Markes TD unit has been modified and updated with cooperation from Markes, which has made it more durable for high-temperature particulate matter analysis and conducive to repeated silylation analysis. The silylation method is being developed as a separate stand-alone method for the analysis of select polar compounds including levoglucosan, sterols, monoglycerides, and simple carbohydrates. Samples have been collected in Fresno, CA during the winter 2007 season to analyze by the silylation method. Four 6-hour samples were collected each day using a 92-lpm medium volume sampler equipped with a 90-mm quartz fiber filter. The first round of sample analysis provides a limited look at the mass of these polar compounds per filter (Figure 2). The simple carbohydrate concentrations were quite low for this sampling set, but these illustrate the low detection limits that can be achieved with the method. Levoglucosan concentrations were at the other extreme; although these numbers are preliminary, they indicate the unique condition of very high wood smoke contribution in the San Joaquin Valley in the winter time.
Figure 1. Methylated TD GCMS results for SOAR study, Riverside, CA 2005
Figure 2. Silylation TD-GCMS and OC results for Fresno, CA Winter 2007 Study
As the diazomethane method is now fully established and the silylation method development is nearing completion, efforts are being directed at writing up and publishing the methods and results for the diazomethane method and SOAR study and the silylation method with the Fresno study. Additionally, development of a TD-GC-MS method using aluminum substrates is in process specifically geared to the analysis of Micro-Orifice Uniform Deposit Impactor (MOUDI) and nano-MOUDI substrates.
Fine PM, Chakrabarti B, Krudysz M, Schauer JJ, Sioutas C. Diurnal variations of individual organic compound constituents of ultrafine and accumulation mode particulate matter in the Los Angeles basin. Environmental Science & Technology 2004;38(5):1296-1304.
Rinehart LR, Fujita EM, Chow JC, Magliano K, Zielinska B. Spatial distribution of PM2.5 associated organic compounds in central California. Atmospheric Environment 2006;40(2):290-303.