AP-107

Instrumentation

MEASUREMENTS OF CHEMICAL EMISSIONSUSING FTIR SPECTROSCOPY

by Hue Phan and Jerry Auth Introduction Recently, toxic volatile organic air pollution has become a source of major health concern becauseof its widespread presence in the atmosphere. Chemical dump sites, landfills, industrial sites, chemical spills, auto and rocket exhaust are the usual sources of volatile organic compounds (VOC). There is growing interest in monitoring ambient air for these toxic compounds. Among the many instrumental techniques that have been developed for environmental monitoring, FTIR spectroscopy is one that has unique advantages. This paper describes the application of open path Fourier Transform Infrared Spectroscopy (FTIR) for measurements of ambient air volatile organic compounds. It is important to have a stable spectrometer manufacturer system with high sensitivity so that the compounds of interest may easily be identified and quantified. This experiment focuses on measuring the controlled release of volatile gas over a grass covered athletic field at the University of Kansas. The instrument used was a Midac portable emission spectrometer. This paper describes the Midac open path Ft ir spectrometer for on-site pollution analysis and presents various IR gas traces that were measured using a long path configuration. The FTIR instrument used in this experiment was the Midac Outfielder
tm (M2400) portable emissionspectrometer. It is the combination of a Midac interferometer and a liquid nitrogen cooled mercury cadmium telluride (MCT) detector. The Midac spectrometer is capable of 0.5cm
-1 resolution and iscontrolled by an IBM compatible AT computer. The optical unit was mounted on a basic tripod which was placed on the sampling path at the athletic field of the University of Kansas. The infrared source (a 1660K silicon carbide glower) was located across the field about 100 meters away from the spectrometer. The beam was collimated into the optical unit and subsequently through the interferometer to the detector. For this test, a telescope was not used in conjunction with the spectrometer system. However, for infrared measurement with pathlengths longer than 100 meters, coupling a telescope with the spectrometer system is recommended. The signal-to-noise ratio of the spectral data would increase by a factor of two with the use of a telescope (a 10 inch Newtonian telescope). The source and FTIR spectrometer setup was aligned by hand; the source was moved using the sighting scope until the center of the beam struck the spectrometer. The spectrometer was then aligned by adjusting the position of the gear head mounted on the tripod. This fine alignment was being done while the spectrometer was continuously scanning (Spectra Calc's
tm "align" mode). A series of 200 scans was collected for each run. The samples were collectedat 1cm
-1 resolution. The data acquisition
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