Timothy L. Marshall

FT-IR remote sensing of industrial atmospheres for spatial characterization

Two identical Fourier transform infrared (FT-IR) field monitoring systems have been used to investigate differences in apparent plume concentrations as a function of height. The two systems also have been used to monitor the same plume simultaneously at the same height to estimate the precision that can be expected. The data collected suggest that IR beam height may play a significant role in the measured concentrations of plume constituents.

Infrared detection and analysis of vapor plumes using an airborne sensor

An airborne infrared (IR) line-scanner and a Fourier transform infrared (FT-IR) spectrometer operating in the 3- 5micrometers and 8-12micrometers spectral regions provide a rapid wide- area surveillance capability. The IR scene containing target vapors is mapped remotely with the wide fields of view (FOV) multi-spectral IR line-scanner using 14 bands. The narrow FOV FT-IR spectrometer permits remote verification of target vapor plume contents within the IR scene. The IR image and FT-IR interferogram analysis supply a near real-time detection that provides visual monitoring of potential downwind vapor hazards. This capability is demonstrated using the target vapor methanol. An active mono-static FT-IR configuration furnishes ground-truth monitoring for methanol released from an industrial stack and a nearby ground-level area. The airborne and ground-truth results demonstrate the usefulness of this approach in alerting first responders to potential downwind vapor hazards from an accidental release.

Investigation of the effects of resolution on the performance of classical least-squares (CLS) spectral interpretation programs when applied to volatile organic compounds (VOCs) of interest in remote sensing using open-air long-path Fourier transform infrared (FT-IR) spectrometry

Abstract In the last 10 to 15 years, many investigations into the usefulness of multivariate data analysis techniques have been made using various algorithms to both qualify and quantify data obtained using Fourier transform (FT-IR) spectrometry. In the last 5 to 7 years, many investigations into remote sensing of volatile organic compounds (VOCs) in the atmosphere using open-air long-path FT-IR spectrometry have been made. This paper is a progress report of the attempt of our two laboratories to combine the two fields.

Generating well-characterized chemical plumes for remote sensing research

In the interest of remote sensing research, equipment and techniques have been developed to generate heated plumes with controlled and well-characterized temperature and composition profiles. This report describes the construction of a plume generating device as well as the field operations involved in creating and monitoring heated plumes for research purposes. Performance specifications for the plume generator and its components are provided and typical FTIR validation data are included that illustrate the devices capabilities.

Estimation of VOC emission rates from FTIR measurements and whole-air canister data

Methods of estimating VOC emission rates from a point source are being field tested by the University of Kansas, in cooperation with Region VII of the U.S. EPA and Kansas State University. The methods use path-integrated VOC concentrations, meteorological data, and a form of the Gaussian dispersion equation. VOC concentrations were derived both from a whole-air canister sampling method, with subsequent GC analysis, and from open-path FTIR measurements; estimated emission rates produced from the two analytical methods were compared. Canister-derived concentrations provided higher mean estimation accuracies than did FTIR measurements for both 1, 1, 1-Trichloroethane and toluene; however, for a third data set consisting of all other compounds released, FTIR measurements provided higher values. Estimation accuracy also was evaluated as a function of atmospheric stability and downwind distance; accuracy generally increased and variability decreased as stability increased; accuracy was better at longer than at 50 meters.

Using a gas cell to characterize FT-IR air sensor performance

A gas cell is used to characterize the analytical performance of an FTIR sensor collecting air monitoring data in an active sampling configuration. Hardware and data collection techniques are described and example data are presented. Instrument performance is characterized and discussed in terms of accuracy, precision, linearity, drift, and reproducibility.

Hadamard- and Fourier-transform Infrared Imaging and Spectrometry

A moving (mechanical) two-dimensional Hadamard encoding mask has been employed with a Fourier-transform infrared (FT-IR) spectrometer to combine imaging in two spatial dimensions with the spectral dimension as a form of three-dimensional spectrometry in the mid-infrared and near-infrared spectral regions. Chemical images at chosen wavenumbers and mid-infrared spectra of individual pixel positions in the image have been obtained with acceptable signal-to-noise ratios and reasonable data-acquisition times.

Passive Fourier transform infrared (FTIR) monitoring of SO2 in smokestack plumes: a comparison of remote passive spectra of an actual hot plume with emission spectra collected with a heatable cell

In the interest of developing practical methodologies for remote passive FT-IR analysis of sulfur dioxide in heated smoke stack plumes, IR spectra have been collected in a number of relevant experiments. Field data includes passive remote FT-IR spectra collected at a coal-burning power plant for which plume conditions were characterized by in-stack continuous emission monitors (CEMs), spectra collected of a controlled plume from a model spectrometer, into which controlled levels of sulfur dioxide could be introduced while the spectrometer viewed sky backgrounds similar to those behind the actual power plant plume. An extensive spectral data set has also been collected in the laboratory under controlled target and background conditions using a heated cell. Typical spectra are presented and the potential for characterizing many of the important factors involved in remote passive FT-IR analyses through controlled- condition experiments such as these is discussed.

MONITORING INDOOR AIR QUALITY BY EXTRACTIVE FT-IR SPECTROMETRY

Extractive Fourier-transform infrared (FT-IR) spectrometry has been employed to monitor the indoor air quality of a commercial print shop and a commercial dry cleaning establishment. Monitoring over extended time periods demonstrates that trends in contaminant concentration may be obtained and related to activities taking place at the facility.

Assessment of indoor air quality using extractive Fourier transform infrared (FTIR) measurements

Characterizing indoor air quality requires instrumentation with certain capabilities. Most importantly, indoor air analyzers must be capable of measuring low concentrations of airborne pollutants in complex environments. This capability and many others important to indoor air monitoring applications have been realized in a transportable extractive FT-IR gas analyzer that has recently become commercially available. Feasibility studies have been performed at a variety of sites to evaluate the potential of this new cell-based analyzer for indoor air quality analysis. This paper describes the instrumentation and methodology used to perform these studies and then presents the results of the studies. Through these results, certain conclusions become apparent concerning the instrumental performance features that are required to produce truly useful indoor air quality information.