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COMPOSITION OF PM 2.5 DURING THE SUMMER OF 2003 IN RESEARCH TRIANGLE PARK, NORTH CAROLINA
Citation:
Lewandowski, M, T E. Kleindienst, M. Jaoui, AND E O. Edney. COMPOSITION OF PM 2.5 DURING THE SUMMER OF 2003 IN RESEARCH TRIANGLE PARK, NORTH CAROLINA. Presented at American Association of Aerosol Research 2004 Annual Conference, Atlanta, GA, October 4-8, 2004.
Impact/Purpose:
1. Using laboratory and field study data generated during FY99-FY04, develop a science version of a PM chemistry model for predicting ambient concentrations of water, inorganics, and organics in PM2.5 samples. The model will include the Aerosol Inorganic Model for predicting concentrations of inorganic compounds and a computational chemistry-based method for predicting concentrations of organic compounds.
2. Identify and evaluate methods for analyzing the polar fraction of PM2.5 samples.
3. Carry out short term field studies in Research Triangle Park, North Carolina in the summer and the winter to determine the composition of the organic fraction of ambient PM2.5 samples, with special emphasis placed on identifying and determining ambient concentrations of polar compounds.
4. Conduct laboratory studies to establish the chemical composition of secondary organic aerosol (SOA) and to determine source signatures for aromatic and biogenic SOA.
5. Conduct laboratory and theoretical investigations of thermodynamic properties of polar organic compounds.
6. Evaluate the science version of the PM chemistry model using laboratory and field data generated under this task as well as other available data in the literature.
7. Conduct PM chemistry-related special studies for OAQPS
Description:
Ambient PM2.5 contains a complex mixture of organic and inorganic compounds which may be derived from primary emission to the atmosphere or from secondary reaction processes. Determining the relative contributions of primary emissions versus secondary production and understanding the sources of secondary products are of great importance for the development of effective control strategies for reducing ambient PM2.5 levels.
A short-term field study was carried out in Research Triangle Park to examine the inorganic and organic components of PM2.5. Samples were collected during seven 48-hour periods between July and September of 2003. The general composition of the collected PM2.5 was evaluated using a combination on gravimetric analysis, ion chromatography, and a thermal-optical method for the determination of carbon content. The ambient PM2.5 mass concentrations measured in this summer field study ranged between 6.1 and 33.7 µg/m3, with an average value of ~20 µg/m3. On average, the PM2.5 samples contained 6.4 µg/m3 sulfate, 2.2 µg/m3 ammonium, very little nitrate (0.01 µg/m3), and 5.8 µg/m3 total carbon.
For structural characterization of the organic fraction, the collected ambient PM2.5 was solvent extracted and derivatized using a single, double, or triple derivatization technique based upon the BF3-methanol, BSTFA, and PFBHA techniques. The resulting derivatives were analyzed by GC-MS in EI and methane-CI modes. Interpretation of the EI and CI mass spectra provide important information, leading to unambiguous identification of compounds comprising PM2.5. GC-MS analyses of the field samples showed the presence of seven compounds that we have tentatively identified in laboratory irradiations of monoterpence/NOx that could serve as tracer compounds for monoterpene SOA: 3-isopropyl pentanedioic acid, 3-acetyl pentanedioic acid, 3-carboxy heptanedioic acid, 3-acetyl hexanedioic acid, 3-(2-hydroxy-ethyl)-2,2-dimethyl-cyclobutane-carboxylic acid, and two triol compounds. GC-MS analysis also revealed two additional compounds, 2,3 dihydroxy-4-oxopentanoic acid and ,3-dihydroxy-4-oxobutanoic acid, which are observed in laboratory irradiations of toluene/NOx and may serve as tracer compounds for aromatic SOA.
This work has been funded wholly or in part by the United States Environmental Protection Agency under Contract 68-D-00-206 to ManTech Environmental Technology, Inc. It has been subjected to Agency review and approved for publication.