Research Projects

Project at a Glance

Project Status: complete

Title: Development of methods and procedures for monitoring ambient concentrations of oxygenated hydrocarbons.

Principal Investigator / Author(s): Fitz, Dennis & Kochy Fung

Contractor: AeroVironment, Inc. and AtmAA, Inc.

Contract Number: 92-306


Research Program Area: Atmospheric Processes

Topic Areas: Chemistry & Reactivity


Abstract:

Oxygenated hydrocarbons (OHCs) in the ambient air are of concern because of their health effects and because they are a precursor to ozone. Since the introduction of methyl tertiary butyl ether (MTBE) as an addition to gasoline, the importance of measuring OHCs has increased. Previous measurements for OHCs have used gas chromatography (GC) methods that have made quantification and qualification of OHCs difficult, as these methods do not separate the OHCs from the rest of the volatile organic compounds (VOCs). In order to have a method for better determining OHCs in ambient air. the Air Resources Board (ARB) sponsored this ambient OHC collection and analysis development program.

The goal of this project was to develop and evaluate a method for measuring ambient air concentrations of oxygenated hydrocarbons (including carbonyls, alcohols and ethers) at the ppb level. The method developed involved collecting a sample on a sorbent tube, extracting the sample with a solvent, and analyzing the sample through injection into a two-dimensional gas chromatography with intem1ediate cryogenic trapping and detection by an oxygen specific detector (O-FID). With this method all of the relevant oxygenated hydrocarbons can potentially be analyzed on one sample medium with a single analysis. he samples are easily collected at variable intervals in a routine field monitoring program and may be stored indefinitely.

In general, results of the project indicate that routine analysis of OHCs is possible using the developed methodology. The methodology was tested using six OHC species, representing all of the target OHC classes. and a combination of charcoal and silica gel sorbent tubes. The six species were acetaldehyde. methanol, acetone, MTBE, butanal, and methyl ethyl ketone. With the possible exception of methanol, all of the species were accurately detected using the methodology. The detection of methanol using the silica gel tubes showed considerable variability at lower concentrations, most likely due to high methanol background concentrations in the elution solvent. Methanol detection may be improved by finding ways to lower the background concentrations in the solvent.

While the investigated methodology appeared to work satisfactorily, O-FID analysis is more labor and resources intensive than traditional FID analysis. The O-FID detector must be regularly primed with hydrocarbons, and large amount of N2 and H2 are required to operate the system. Thus, to remain economically feasible, the described methodology should be limited to large batch jobs, during which the system can be continuously operated. In addition, an O-FID provides specificity to the method, but at a greatly reduced sensitivity for OHCs of two or more carbons. Continued investigation into the use of O-FID detectors is recommended.


 

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