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Measurements and Standards Intercomparison (MSI) GroupMSI Group members:
As of August, 2006, the MSI Group is now part of the Community Airborne Research (CARI) Group
Summary of Activities:
This year the Trace Organic Gas Analyzer (TOGA) instrument was developed and deployed during the MIRAGE and IMPEX campaigns. This is a one-of-a-kind instrument based on gas chromatography/mass spectrometry designed to measure in-situ , with high accuracy and precision, a suite of the key organic compounds (process intermediaries, oxidation products, and tracers of anthropogenic and biogenic activity) throughout the troposphere including the UT/LS region. These measurements are targeted to increase the understanding of a number of factors that influence atmospheric processes, including:
The TOGA has been designed to continuously measure oxygenated volatile organic compounds (OVOCs), non-methane hydrocarbons (NMHCs) and halocarbons via preconcentration/mass spectrometry
A number of innovations were required to allow the instrument to produce data at the desired time resolution. These included a gas chromatograph with very rapid heating and cooling rates and an efficient and fast preconcentration system. New designs were incorporated and proved to be successful during the recent MIRAGE and IMPEX field campaigns. This instrument represents a giant innovative step forward for the VOC measurements community as it has demonstrated unsurpassed sensitivity (less than 1 pptv LOD for select species and less than 10 pptv for all species) and selectivity for a wide variety of VOC species. Figure 1 shows a partial chromatogram that illuminates the potential of the instrument. Because compounds are chromatographically separated and mass selected, the instrument literally has the potential to quantify up to 100 VOC compounds per analysis. Each analysis cycle presently occurs every 2.5 minutes. However, recent work has shown that this can be improved to 1.5 minutes.
Figure 2 shows an example of data recently collected during the MIRAGE field campaign. The top panel shows a trace of the altitude along with continuous CO measurements. The middle panel shows a trace of a subset of non-methane hydrocarbons and the lower panel shows a trace of a subset of the oxygenated volatile organic compounds that were quantified during the experiment. The major advantage of this instrument is ultimately in the interpretation of field data as continuous and simultaneous analyses are obtained for a wide variety of atmospherically important species. Data such as these will be extremely valuable to this as well as future field campaigns and similar technology will be applied to the HIAPER instrument.
Figure 3 shows the utility of the instrument for measuring important atmospheric tracer species at very low levels. Methyl tertiary butyl ether (MTBE) is a compound which can be added to gasoline to increase the oxygenated content of the fuel. Because of environmental concerns, this compound has been phased out of the gasoline supply in the Western US and Canada. However it is still used as an additive in Asia. Because of its lifetime of approximately 3.5 days, this presents an opportunity for using it as a tracer for pollution from Asia provided that the instrument sensitivity is high enough to detect it in very small quantities. Back trajectories from this flight show that air from Asia was potentially impacting North America. The simultaneous observation from TOGA of benzene and MTBE confirms that this was indeed the case. MTBE and other tracers will be used to interpret results from both the MIRAGE and INTEX-B campaigns.
This work was partially funded by NASA.
Collaborators:
Figure 1.
Figure 2.
Figure 3.
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