General Audience Oral Presentations Abstracts

TOPIC #6

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1. New Mass Spectrometric Tools and Their Application to Organic Aerosol Characterization

Murray V. Johnston, Michael P. Tolocka, Berk Oktem, Matthew Dreyfus
Chemistry and Biochemistry Department, University of Delaware, Newark, DE 19716

The organic fraction of airborne particulate matter is a complex mixture of compounds with a combined concentration on the order of 1 to 10 micrograms per cubic meter. Thousands of compounds may be present in a sample, with individual concentrations between about 0.1 and 10 nanograms per cubic meter. The complexity and low concentration levels associated with ambient samples present a significant analytical challenge. We have been exploring the use of new methods for off-line and on-line analysis of organic matter in particles to study aerosol reactions.

Off-line analysis is performed with electrospray ionization and matrix-assisted laser desorption ionization in combination with exact mass measurements and tandem mass spectrometry. These methods have allowed us to characterize hundreds of high molecular weight compounds formed by secondary polymerization of the primary products of a-pinene ozonolysis. Aerosols were produced by the reaction of a-pinene and ozone in the presence of acid seed aerosol and characterized by exact mass measurements and tandem mass spectrometry. Oligomeric products between 200 and 900 u were detected with both electrospray ionization and matrix-assisted laser desorption ionization. The exact masses and dissociation products of these ions were consistent with various combinations of the known primary products of this reaction (“monomers”) with or without the expected acid-catalyzed decomposition products of the monomers. Chemical reactions leading to oligomer formation provide a reasonable answer to a difficult problem associated with secondary organic aerosol production in the atmosphere. It is unlikely that monomers alone play an important role in the formation and growth of nuclei in the atmosphere as their Kelvin vapor pressures are too high for them to significantly partition into the particle phase. Polymerization provides a mechanism by which partitioning to the particle phase becomes favored. These methods are also being used by our group to characterize biological material in ambient filter samples. Preliminary results will be presented at the meeting.

On-line measurements are made with a field-deployable photoionization aerosol mass spectrometer (PIAMS) that provides relatively “soft” ionization of both aliphatic and aromatic compounds. Soft ionization is needed to reduce the spectral congestion that is normally observed from complex samples when separation prior to mass analysis is not performed. With PIAMS, we are able to distinguish various sources of ambient organic aerosol (diesel and gasoline emissions, meat cooking, wood burning, cigarette smoke) by the distribution of compounds detected. The mass spectra are consistent with previous off-line measurements by gas chromatography mass spectrometry. The current detection limit per “compound” (includes all isomers and isobars at a single m/z) is in the range 7-70 ng/m3 for a 1 minute time average. We have used PIAMS for real-time characterization of organic aerosols in flames and smog chambers on this timescale. Instrumental improvements are underway to increase sensitivity and thereby facilitate ambient measurements.

References
B. Oktem, M.P. Tolocka, M.V. Johnston, “On-Line Analysis of Organic Components in Fine and Ultrafine Particles by Photoionization Aerosol Mass Spectrometry”, Analytical Chemistry (2004) Jan. 15 issue.

M.P. Tolocka, M.Jang, J.M. Ginter, F.J. Cox, R.M. Kamens, M.V. Johnston, “Formation of Oligomeric Species in Secondary Organic Aerosols”, Environmental Science and Technology (2004) in press.

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2. Primary Biopolymer Associations with Fine Particulate Matter: Comparisons of Protein, Carbohydrate and Endotoxin content of Temperate Urban PM2.5 with Selected Sources

Lisa Clarke1, Lars Angenent2, Allen Robinson3, and Mark Hernandez1
1Department of Civil, Environmental, and Architectural Engineering, University of Colorado at Boulder, Boulder, Colorado
2Department of Chemical Engineering & Environmental Engineering Science Program, Washington University in St. Louis, St. Louis, Missouri
3Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania

From July 2001 to August 2002, high-volume samplers collected fine airborne particulate matter (PM2.5) from a site in the Pittsburgh metropolitan on 37 mm polycarbonate filters. The particulate matter impacted on these filters was composited over 24 hour periods, and analyzed for carbohydrate, protein and endotoxin content. After eluting the samples into sterile, pyrogen-free water, the following methods were used to quantify common biopolymers: (i) a colorimetric, dextrose-standardized acid digestion for carbohydrate measurement; (ii) a fluorometric, albumen-standardized intercalating assay for protein measurements; and (iii) a commercially standardized enzyme assay for endotoxin measurements. Carbohydrates were measurable and correlated with airborne particulate matter (detection limit c.a. 0.1 mg/m3) during approximately 90% of the monitoring period, and seasonal trends emerged where the averaged levels monitored during the summer and fall months were markedly higher than those monitored in the winter and spring. During this period, PM-associated carbohydrate levels varied between 0.2 and 2.2 mg/m3, and comprised between 2% and 60% of the total organic carbon on an averaged mass basis. Proteins were also measurable and correlated with airborne particulate matter (detection limit c.a. 0.05 mg/m3) during about 74% of days observed, and seasonal trends emerged where the averaged levels monitored during the fall and winter months were markedly higher than those monitored during the spring and summer months. Throughout this time, PM-associated protein levels varied between 0.006 and 1.3 mg/m3 and comprised between 0.5 and 7.5% of the total organic carbon on an averaged mass basis. Endotoxin analyses were executed for the four mid-season months – July 2001, October 2001, January 2002, and April 2002. Endotoxin levels were always lower than 5 EU/m3 during these months, and were consistent with outdoor levels reported elsewhere. These results suggest that microscopic primary biological materials may have a significant contribution to airborne organic carbon levels, and be seasonally associated with airborne particulate matter in this region.

For comparison to the ambient recoverires, samples of diesel exhausts, wood smokes, and vegetative detritus were collected in this same metropolitan area between May and September 2003 and were analyzed for their biopolymer content. These source samples were collected on filters with a design loading of 200 mg of fine particulate matter; actual loading was based on mass concentration estimates from a Scanning Mobility Particle Sizer (SMPS). The diesel exhausts did not yield any proteins or carbohydrates above method detection limits. Wood smoke generated a range of carbohydrates, and moderate levels of proteins, depending on the smoke source (e.g. flaming or smoldering). Vegetative detritus produced extremely high levels of carbohydrates, beyond the upper detection limit of the method (150 mg/m3), and moderate levels of proteins. These results suggest that common sources of primary biological materials may promote biopolymer associations with airborne particulate matter, and may be a noteworthy component of particle-associated organic carbon.

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