Examples of Active FT-IR Monitoring Applications     

  The pictures below are from volcano plume monitoring investigations on Mt. Etna in Sicily, the island of Vulcano in the Mediterranean Sea, and Mt. Erebus in Antarctica (left to right, respectively).

    In addition to whatever is spewed out during actual eruptions, hundreds of non-erupting volcanoes are constantly degassing, collectively introducing an enormous amount of pollutants into the atmosphere each year.  Open-path FT-IR air monitoring has been used to directly measure the composition of the plumes from a few volcanoes, with the hopes that such information may provide a better understanding of the impact of volcanic contributions on the global atmospheric budget and possibly provide a predictive technique for impending eruptions.

    The spectra below show the absorbance bands of sulfur dioxide, silicon tetrafluoride, hydrogen chloride, and carbon monoxide in typical open-path FT-IR spectra collected during the investigations pictured above. The ratios of the various gases were determined in hundreds of spectra such as these at each of the volcanoes monitored.  Gas ratios were desired because it is believed that the composition of volcanic plumes changes prior to an eruption.  Gas ratios involving sulfur dioxide are especially useful for another reason.  Total sulfur dioxide flux can be accurately determined via another spectroscopic technique (COSPEC) and ratio information relating sulfur dioxide to other analytes allows flux information to be calculated for many of the other relevant gases.
       

    The results of our work on the Italian volcanoes have been published in a few different journals.

    For information on the FT-IR aspects of the work we suggest you read "Infrared Analysis of Volcanic Plumes: A Case Study in the Application of Open-Path FT-IR Monitoring Techniques," C.T. Chaffin, T.L Marshall, W.G. Fateley, R.M. Hammaker, Spectroscopy Europe, 7/3, 18-24 (1995).

    For information on the volcanic aspects of the results, try "SO2:HCl ratios in the plumes from Mt. Etna and Vulcano determined by Fourier transform spectroscopy," P.W. Francis, A. Maciejewski, C. Oppenheimer, C.T. Chaffin, and T. Caltobiano, Geophysical Research Letters, 22,13, 1717-1720 (1995).

    Travelling to exotic locations around the globe to measure volcanic plumes is great but we've also been able to find some interesting (if somewhat less glamorous) applications of our air monitoring technology in our own backyard.  The pictures below were taken during active FT-IR air monitoring we performed recently at a local hog farm.

    The owners of these type of farms are interested in finding ways to control odors so they can be better neighbors.  Since the farmers tend to become somewhat accustomed to the odor, a device is sought that can objectively measure downwind odor.  Our goal with this investigation was to see if any compound in the fugitive emissions from the farm operation could be spectroscopically detected and used as an indicator of odor levels.  To look for such a compound, we went straight to the source of most odors on these type of large-scale farming operations - the waste lagoon.  As we said earlier, this was not one of our more glamorous projects.

    We were able to use a short pathlength in this case since we knew exactly where any fugititive emissions of interest would be originating.  The wind was fairly consistent but a couple of different pathlengths were used over a period of about six hours to take best advantage of the conditions.  We also collected spectra over beam paths of similar length upwind of the site for use as background spectra.  As is often the case in this type of monitoring, we found we were able to produce better information by using spectra collected over the same path as the sample spectra as backgrounds rather than the spectra collected upwind.  Changes in wind speed, wind direction, and rate of fugitive emissions allow this same-path background approach to work well in many cases, provided the analyst is willing to do a little extra work with the manipulation and interpretation of the data.  The spectrum below is typical.
 

    In addition to the infrared signatures of water and carbon dioxide that are found in all open-path FT-IR spectra, the spectra collected over and immediately downwind of the lagoon displayed the infrared signatures of methane and ammonia, quite strongly in some spectra.  The ammonia and methane levels were seen to vary somewhat over time and we're now interested in pursuing a long term monitoring project to determine if these compounds can be correlated to odor levels.  If they can, a small, simple, and relatively inexpensive device might be developed as a fenceline monitor to keep odors from such operations in check.

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