Detailed Speciation and Quantification of Toxic Organic Pollutants on the Particulate Matter from Diesel Engine Exhaust Emissions, 08-R9641Printer Friendly Version
Inclusive Dates: 07/01/06 Current
Background - Fine particulate matter (PM or soot) found largely in diesel engine exhaust emissions tends to remain suspended in the air for extended periods of time, and as such poses a great threat to human beings. Specifically, the PM10 (less than 10 micron PM), and more so the PM2.5 (less than 2.5 micron PM), can be easily inhaled by humans. The toxic chemicals adsorbed on the aforementioned PM have the potential to be leached into lung tissues and carried to various organs, where they will eventually exert their potentially deadly effects.
In recent years, many studies have focused on the size and number of PM produced by diesel engines. Although some studies have been performed concerning the speciation (identification) and quantification of the chemical species adsorbed on the PM, these studies have had limited applications. The extraction and analytical methods as well as the lack of appropriate chemical standards have made the results of previous studies doubtful at best. Under such conditions, it is difficult to assess accurately the potential hazards that PM poses to human health.
Furthermore, 2007 and 2010 diesel emission standards require additional reduction in the amount of PM allowed from diesel-fueled, on-road engines. This requirement makes the speciation and quantification of the compounds associated with PM a tremendous challenge. Good extraction, speciation, and quantification methodologies are urgently needed for current and future PM studies.
Approach - Four different extraction techniques will be used to extract the PM on Teflon-coated glass fiber filters, and the extraction efficiency of these methods on PM will be compared. The four different extraction techniques are Soxhlet extraction, sonication, microwave extraction, and accelerated solvent extraction (ASE). Two solvents or solvent systems will be used with each extraction method.
A 60-meter DB-5ms (or equivalent) gas chromatography column with 25mm id and 25um film thickness will be used to separate the semi-volatile organic compounds (SVOC) in the PM extracts. Both high and low resolution mass spectrometers will be used along with electron impact and chemical ionization techniques. Other techniques such as spectral background subtraction and mass spectral library search will be used to help identify unknown SVOCs. An isotope dilution technique will be developed to quantify identified SVOCs. Special emphasis will be placed on polycyclic aromatic hydrocarbons (PAH), alkyl-PAHs, nitro-PAHs, oxygenates, and hopanes and steranes (biomarkers for oil contamination).
Accomplishments - More than 150 SVOCs has been identified and quantified. Some 30 SVOCs detected and quantified at higher concentrations using a gas chromatography/ mass spectrometry full-scan technique were used for the comparison of the extraction efficiency of the four extraction methods. Data indicate that the four extraction methods produced very similar results. However, further analysis of PAHs and N-PAHs using gas chromatography/mass spectrometry/selected ion monitoring technique indicated that the order of extraction efficiency was ASE > Microwave > Soxhlet > sonication. And the order of extraction efficiency of the four solvent systems was ethanol/toluene (30/70, v/v) > ethanol/benzene (30/70, v/v) > DCM > acetone/hexane (50/50, v/v). More data will be presented in future publications.