Mapping chemical concentrations indoors using open-path FTIR spectroscopy and computed tomography: chamber studies

This paper presents studies conducted in an indoor exposure chamber, on the detection and mapping of chemical concentrations using open-path FTIR (Fourier Transform Infrared) spectroscopy and computed tomography. A vertical flow indoor air chamber having roller tracks at the periphery was used. The source and detector of an open-path FTIR spectrometer were mounted on separate tables place on the tracks. Sulfur hexafluoride was injected from the floor of the chamber and the plume was scanned using the FTIR spectrometer. Different ray configurations were used to scan and map the plume on a 2D plane. To test the validity of the FTIR/computed tomography system for mapping gases, point samples from within the chamber were drawn remotely from ports and were analyzed using an electron capture detector. The concentrations indicated by the gas samples at different points were compared to the tomographically mapped concentrations. A comparison of mapped concentrations with point sampled concentrations were made with respect to position, and concentration of the chemical peak. A comparison of different algorithms for mapping chemical concentrations was performed.