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ABSTRACT - TOPIC #2

Analytical Challenges

Topic Leader: Monica Mazurek
Contributor: Berndt Simoneit and Michelle Schantz

Detection and measurement of organic compounds at the molecular level is now a routine practice for many air quality ambient monitoring studies. Molecular tracer analysis provides a powerful approach for linking major emissions with observed concentrations of fine particles. Quantitative estimates of major emissions to observed fine particle ambient mass concentrations are developed by using mass ratios of marker concentrations to the total organic aerosol ambient mass. Rogge et al., (1993) first described the molecular marker approach for fine particle apportionment work using ambient marker concentrations and emissions profiles measured for metropolitan Los Angeles. Further development of the mathematical model was published by Schauer et al., (1996) linking emissions inventories, emissions sources chemical compositions, and ambient concentrations of organic molecular tracers. Identification of molecular markers in ambient fine particles is incorporated into current research and monitoring activities on the sources and compositions of fine particles, including the current Supersites project funded by the U.S. Environmental Protection Agency.

Typically, a single molecular marker compound comprises only a minute fraction of the organics fine particle mass fraction with ambient ratios of marker mass to total organics in units of ng m-3 and mg m-3, respectively. For example, ambient mass ratios of hopane fossil fuel biomarkers to organics range can range from [0.08-2.14]x10-3 for metropolitan New York City (Mazurek et al, 2004) to [0.87-3.50]x10-3 for metropolitan Los Angeles (Schauer et al., 1996). Consequently, the analytical protocol for detecting and quantifying a molecular marker within ambient particulate matter must be sensitive and precise.

This workshop session addresses the current state-of-the-science for molecular maker analysis in aerosol complex mixtures. Nearly two decades have passed since the gas chromatography/mass spectrometry based analytical protocol was developed by Mazurek and coworkers and applied to ambient fine particle samples (Mazurek et al., 1987; Mazurek and Simoneit, 1981; Rogge et al., 1993)and emission source samples (Mazurek et al, 1989, 1993; Hildemann et al., 1991) over the period 1982 to 1984 in metropolitan Los Angeles. Many innovations in molecular level analysis have occurred since this time involving advances in instrumentation, separation of complex organic mixtures, improvements in measurement accuracy and precision, and in strategies for improved interpretation mass spectrometric data for target marker compounds. Invited presentations in “Session 2. Analytical Challenges” focus on 1) components of the collection and analytical protocol necessary for identification and quantitation of molecular markers in fine particle samples; 2) standard reference materials, new standards for aerosol marker compounds, and results of intercomparison laboratory trials for molecular markers in urban dust standard matrix reference material; and 3) advanced mass spectrometric interpretation methods for target compounds in complex organic mixtures from airborne particles. Individual abstracts for the invited presentations are presented in the following section.

1) A Critical Assessment of the Molecular-Level Analytical Protocol for Ambient Fine Particles

Monica A. Mazurek, Department of Civil and Environmental Engineering, Rutgers University, 623 Bowser Road, Piscataway, NJ, 08854-8014.

Organic molecular tracers in fine particulate matter constituent only a minute fraction of aerosol mass. Given the sub parts-per-billion concentrations of organic marker compounds present in most urban atmospheres, the analytical protocol for detection and measurement is detailed and requires high precision and accuracy. An essential feature of the molecular analysis protocol involves a thorough quality assurance/quality control (QA/QC) plan. The QA/QC plan examines sampling, and filter handling and preparation steps evaluated also at the molecular level with identical instrumentation for compound detection and quantification. Typically, quadrupole electron-impact mass detection is used with pre-separation by high resolution gas chromatography.

Although the GC/MS molecular marker technology was developed in the early 1980’s, no general criteria have been developed for how accurately and precisely a marker compound must be measured, what are critical detection limits, or what surrogate analytes must be incorporated into a sample to monitor method, instrument, and analyst performance. Each of these factors is critical for producing molecular marker measurements of known quality (Budde, 2001). Finally, additional method validation steps, including laboratory duplicate sample aliquots, performance check standards, and field duplicate samples, generally are not conducted for molecular marker characterization work, but are essential to improving ambient mass concentration measurements. This presentation addresses these analytical protocol elements as key challenge areas for molecular marker measurement and identification in fine particle samples.

2) Reference Material and Quality Assurance Needs to Support Organic Speciation Measurements in Air Particulate Matter

Stephen A. Wise and Michele M. Schantz, National Institute of Standards and Technology (NIST), Analytical Chemistry Division, 100 Bureau Drive Stop 8392, Gaithersburg, MD 20899-8392; Joellen Lewtas, USEPA, NERL, Manchester Lab, 7411 Beach Dr. E., Port Orchard, WA 98366.

One of the first environmental matrix Standard Reference Materials (SRMs) developed by the National Institute of Standards and Technology (NIST) for determination of organic species was SRM 1649 Urban Dust, an ambient total suspended particulate matter sample collected in Washington DC in the late 1970’s. Since SRM 1649 was issued in 1981, it has found widespread use in the particulate matter (PM) measurement community, and NIST has assigned values for over 100 organic species in this material. However, there is a growing need for additional reference materials to support organic speciation of PM, particularly for the fine particulate matter fraction and representative of contemporary combustion sources. NIST is collaborating with the U.S. Environmental Protection Agency (EPA), with input from a group of investigators involved in EPA’s PM research program and related studies, to develop additional SRMs and to provide interlaboratory comparison exercises to improve the accuracy and comparability of organic speciation measurements. SRM activities include development of both PM matrix and calibration solution SRMs for organic species of interest in PM characterization. For development of a future PM-matrix SRM, efforts are underway to obtain a suitable quantity of a fine PM either through collection of fine PM or size fractionation of existing total suspended particulate material to provide fine particulate fraction. We are also assessing the suitability of a fine PM on filter media SRM, which was developed for carbon measurements, for organic speciation measurements. Calibration solution SRMs containing a wide range of organic species are under development including: polycyclic aromatic hydrocarbons (PAHs) (two redesigned solutions with an expanded list of 53 PAHs and alkyl-substituted PAHs), aliphatic hydrocarbons, nitro-substituted PAHs (redesigned and expanded list of compounds), hopanes/steranes, and 13C-labeled levoglucosan for use as an internal standard. In addition to the SRMs developed in conjunction with EPA, several additional PM-matrix SRMs for organic speciation are currently in progress including: SRM 2585 Organic Contaminants in House Dust and SRM 1650b Diesel Particulate Matter. In addition to the SRM development activities, two NIST/EPA interlaboratory comparison studies have been conducted to assess and improve the comparability measurements of organic species in PM. This presentation will discuss these SRM and quality assurance activities and their potential impact on improving the accuracy of organic speciation measurements for PM characterization.

This work has been funded in part by the U S Environmental Protection Agency. It has been subjected to Agency review and approved for publication.

3) Characterization of novel organic tracers in aerosols by mass spectrometry

Berndt R. T. Simoneit, Oceanic and Atmospheric Sciences, Oregon State University, 104 Oceanography Administration Building, Corvallis, OR 97331-5503.

Organic compounds in aerosols are useful as tracers for assessment of sources, alteration and fate in indoor, urban and global air sheds. Indoor and urban pollution research has been reported mainly in the U.S. and European literature and both organic and inorganic tracers have been applied. Although, this meeting is focused on urban air pollution, it should be emphasized that aerosol particulate matter (PM) is also of global concern in climate change research and organic matter plays a key role. Initial studies of long-range transport of organic compounds in continental aerosols over the oceans were in the Atlantic (Simoneit, 1977) and Pacific (SEAREX program). The subsequent hiatus is currently followed by new major programs of global change research (i.e., ACE-Asia) and organic tracers are an important aspect.

Progress in defining new organic tracers in aerosols was mainly due to instrument development (GC-MS sensitivity) and the applications of the biomarker compounds elucidated in the geologic record by organic geochemists, the natural compounds characterized by natural product chemists, and the synthetic compounds from the chemical industry (Simoneit,1999). Mass spectrometry (MS) is the analytical method of choice and compound identifications must be coupled initially with comparisons to authentic standards or structure proofs by MS, NMR and syntheses. It is now routine to analyze total extracts (both organic or aqueous) directly by GC-MS after suitable derivatization of the polar compounds. Preparation of separated polarity fractions (by LC or TLC) remains an option for selected samples to gain additional functional group information. Derivatization is typically carried out by methylation and /or trimethylsilylation. This can involve MS interpretation because the derivatives (especially TMS) are not necessarily in the library or the free compound or acetate derivative MS may be archived. High temperature GC-MS can also be applied for high molecular weight compound identification ( e.g., wax esters to C40, alkanes to C100).

The processes of MS interpretation and data evaluation (identification of the compounds in a mixture analyzed by GC-MS) will be illustrated here with some examples. Smoke from burning of contemporary (biomass, refuse, etc.) and fossil fuels is a global problem and the mass spectrometric identification of tracers for this process is discussed (Simoneit el al., 1999). Soil resuspension and erosion is another unquantified emission source and its contribution to the ACE-Asia aerosols is presented in another example (Simoneit et al., 2003). Also, a brief discussion of what not to do with organic tracer analyses is included (Simoneit, 2003). The total extract GC-MS analysis method with selected derivatization is a powerful tool for determining aliphatic homologous lipids, natural products, fossil fuel components, secondary oxidation products, PAH, UCM, phenols, saccharides, etc. and thus attaining an overview of the major and key organic tracers in aerosol PM.

References

Budde, William L. Analytical Mass Spectrometry: Strategies for Environmental and Related Applications. American Chemical Society, Washington, DC. 386 pp., 2001.

Hildemann, L. M., M. A. Mazurek, G. R. Cass, and B. R. T. Simoneit, Quantitative characterization of urban sources of organic aerosol by high-resolution gas chromatography, Environ.Sci.Technol., 25, 1311-1325, 1991.

Mazurek, M. A., G. R. Cass, and B. R. T. Simoneit, Interpretation of high-resolution gas chromatography and high-resolution gas chromatography/mass spectrometry data acquired from atmospheric organic aerosol samples, Aerosol Science Technology, 10, 408-420, 1989.

Mazurek, M. A., L. M. Hildemann, G. R. Cass, B. R. T. Simoneit, and W. F. Rogge, Methods of analysis for complex organic aerosol mixtures from urban emission sources of particulate carbon, in Measurement of Airborne Compounds: Sampling, Analysis, and Data Interpretation, edited by E. D. Winegar, pp. 177-190, American Chemical Society Symposium Series, CRC Press, Inc., Boca Raton, FL, 1993.

Mazurek, M. A., M. Li, S. McDow, J. Graham, D. Felton, C. Pietarinen, A. Leston, S. Bailey, Speciation of Organics for Apportionment of PM2.5 (SOAP) in the New York City Metropolitan Area, presented at the Mid-Atlantic Regional Air Management Association 2004 Science Meeting, January 27-29, 2004, Baltimore Maryland.

Mazurek, M. A. and B. R. T. Simoneit, Characterization of biogenic and petroleum-derived organic matter in aerosols over remote, rural and urban areas, in Identification and Analysis of Organic Pollutants in Air, edited by L. H. Keith, pp. 353-370, Ann Arbor Science/Butterworth, Boston, MA, 1984.

Mazurek, M. A., B. R. T. Simoneit, G. R. Cass, and H. A. Gray, Quantitative high-resolution gas chromatography and high-resolution gas chromatography/mass spectrometry analyses of carbonaceous fine aerosol particles, Int.J.Environ.Anal.Chem., 29, 119-139, 1987.

Rogge, W. F., M. A. Mazurek, L. M. Hildemann, G. R. Cass, and B. R. T. Simoneit, Quantification of urban organic aerosols at a molecular level: Identification, abundance and seasonal variation, Atmos.Environ., 27A, 1309-1330, 1993.

Schauer, J. J., W. F. Rogge, L. M. Hildemann, M. A. Mazurek, and G. R. Cass, Source apportionment of airborne particulate matter using organic compounds as tracers, Atmospheric Environment, 30, 3837-3855, 1996.

Simoneit, B.R.T. Organic matter in eolian dusts over the Atlantic Ocean. Marine Chemistry 5, 443-464. 1977.

Simoneit, B.R.T. A review of biomarker compounds as source indicators and tracers for air pollution. Environ. Sci. and Pollut. Res. Int. 6, 159-169, 1999.

Simoneit, B.R.T. Polemic response to Mayol-Bracero et al. (2001) Atmos. Environ. 36, 5259-5263, 2002.

Simoneit, B.R.T., J.J. Schauer, C.G. Nolte, D.R. Oros, V.O. Elias, M.P. Fraser, W.F. Rogge and G.R. Cass. Levoglucosan, a tracer for cellulose in biomass burning and atmospheric particles. Atmos. Environ. 33, 173-192, 1999.

Simoneit, B.R.T., Kobayashi, M., Kawamura, K. et al., Saccharides, lipids and oxidation products in Asian dust and marine aerosols of the East Asia/Pacific region. Geochim. Cosmochim. Acta 67, A437, #2003

The Organic Speciation International Worskhop is sponsored by the Western Regional Air Partnership/Western Governors Association. APACE is seeking support from the US Dept. of Energy, US EPA Office of Air Quality Planning and Standards, and the National Science Foundation.