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(ISEA) MOLECULAR MARKER ANALYSIS OF DEARS SAMPLES
Citation:
MCDOW, S. R., D. A. OLSON, L. STOCKBURGER, AND J. TURLINGTON. (ISEA) MOLECULAR MARKER ANALYSIS OF DEARS SAMPLES. Presented at International Society of Exposure Analysis Conference, Tucson, AZ, October 30 - November 03, 2005.
Impact/Purpose:
1) Develop a TOA protocol that meets the basic assumptions of the method and peer review of the method, 2) understand the role of sampling, analysis, and blank subtraction on the differences between the IMPROVE and STN OC and EC results 3) Evaluate the use of light absorbance methods to estimate EC on human exposure samples, 4) develop a sensitive analytical method suitable for analysis of STN and micro-environmental samples for organic molecular markers, and 5) develop an optimum list of organic molecular markers for source apportionment of particulate matter.
Description:
Source apportionment based on organic molecular markers provides a promising approach for meeting the Detroit Exposure and Aerosol Research Study (DEARS) objective of comparing source contributions between community air monitoring stations and various neighborhoods. Source apportionment of ambient particulate matter has been frequently achieved by comparing its elemental composition to major source emissions. This approach is difficult if sources are dominated by organic species, as for automobiles, biomass burning, and commercial cooking. For these sources, organic molecular markers such as polycyclic aromatic hydrocarbons, hopanes, unsaturated fatty acids, alkanes, and pyrolyzed sugars provide a more suitable alternative to elemental composition. Their recent measurement in major sources has led to several successful molecular marker based source apportionment efforts for ambient particulate matter.
The greatest challenge for micro-environmental neighborhood samples is the high sensitivity required. In all previous ambient studies, samples were collected at relatively high flow rates and composited for extraction and analysis. A Tisch TE-1202 sampler widely used for molecular marker sample collection is in use at the air monitoring station. However, for micro-environmental samples flow rates are lower than in previous studies, but daily concentrations are still desired to adequately represent temporal variability.
To increase sensitivity, a high volume injection method was implemented for analysis by gas chromatography/mass spectrometry. Highly linear calibrations were obtained with detection limits below 20 pg/m3 for all markers for low volume 24-hour samples. Recoveries of greater than 85% were obtained for high pressure solvent extraction of all molecular markers. Preliminary tests to verify that molecular markers can be detected in actual samples of smaller than 200 micrograms particulate mass are in progress.
Preliminary results from the community air monitoring station will be presented. Performance of the high volume injection method will be described using preliminary results from other studies. Preliminary information on marker concentrations, potential source contributions, and method performance will be used to evaluate the use of molecular markers for comparing source contributions between the monitoring station and neighborhood samples. Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.