Advanced Intercomparison Study with Different Optical Sensing Technologies -- FTIR, UV-DOAS and Conventional Point Sensor Measurements of Atmospheric Gases
Ropertz, A.; T. Lamp; K. Weber; M. Mueller; G. van Haren, Univ. of Applied Sciences, Duesseldorf, Germany.
Air and Waste 92nd Annual Meeting and Exhibition, 20-24 June 1999, St. Louis, MO.
Air and Waste Management Association, Pittsburgh, PA. Paper 99.302, 1999

In summer 1998 a measurement campaign was performed at lake Baldeney See in Germany for the intercomparison of several different remote sensing systems in real field measurements. The project also attempted to determine the ambient air quality level during summer with respect to a complex orographic and climatological situation in an intensively used recreational area. This paper refers to the results of the intercomparison of open-path FTIR and DOAS remote sensing systems. The presentation notes the need for calibration correction for the different systems and includes the results of an open-path FTIR SF6 tracer experiment.

Advanced Laser Diodes for Sensing Applications
Vawter, G.A.; A. Mar; W.W. Chow; A.A. Allerman, Sandia National Labs.
Report No: SAND2000-0112, 38 pp, Jan 2000

The authors have developed diode lasers for short pulse duration and high peak pulse power in the 0.01--100.0 m pulse-width regime. A primary goal of the program was producing up to 10 W while maintaining good far-field beam quality and ease of manufacturability for low cost. High peak power, 17 W, picosecond pulses have been achieved by gain switching of flared geometry waveguide lasers and amplifiers. Such high powers are a world record for this type of diode laser. The light emission pattern from diode lasers is of critical importance for sensing systems such as range finding and chemical detection. The researchers have developed a new integrated optical beam transformer producing rib-waveguide diode lasers with a symmetric, low divergence, output beam and increased upper power limits for irreversible facet damage.

Link: http://www.osti.gov/bridge/product.biblio.jsp?osti_id=752016

Advanced Millimeter Wave Chemical Sensor
Gopalsami, N., Argonne National Lab., IL.
ICAST '99: 15th International Conference on Advanced Science and Technology, 2-3 April 1999, Argonne, IL.
Paper No: ANL/ET/CP-98640. NTIS: DE00012364. 8 pp, Mar 1999

This paper discusses the development of an advanced millimeter-wave (mm-wave) chemical sensor and its applications for environmental monitoring and arms control treaty verification. The purpose of this work is to investigate the use of fingerprint-type molecular rotational signatures in the mm-wave spectrum to sense airborne chemicals. The mm-wave sensor, operating in the frequency range of 220-300 GHz, can work under all weather conditions and in smoky and dusty environments. The basic configuration of the mm-wave sensor is a monostatic swept-frequency radar consisting of a mm-wave sweeper, a hot-electron-bolometer or Schottky barrier detector, and a trihedral reflector. The chemical plume to be detected is situated between the transmitter/detector and the reflector. Millimeter-wave absorption spectra of chemicals in the plume are determined by measuring the swept-frequency radar return signals with and without the plume in the beam path. The problem of pressure broadening, which hampered open-path spectroscopy in the past, has been mitigated in this work by designing a fast sweeping source over a broad frequency range. The heart of the system is a Russian backward-wave oscillator (BWO) tube that can be tuned over 220-350 GHz. Using the Russian BWO tube, a mm-wave radar system was built and field-tested at the DOE Nevada Test Site at a standoff distance of 60 m. The mm-wave system detected chemical plumes very well; the detection sensitivity for polar molecules like methyl chloride was down to a concentration of 12 ppm.

Link: https://www.osti.gov/servlets/purl/12364-Kj8mTg/webviewable/

Air Toxics: Australian Studies
State of Knowledge Report: Air Toxics and Indoor Air Quality in Australia, Chapter 4. Environment Australia, ISBN: 0642547394, 2001

Many different methods are used to monitor concentrations of air toxics in the atmosphere, each targeting a specific group of chemicals. The method used therefore depends on the compound that is to be measured. Continuous (or semicontinuous) monitoring refers to in-field analysis by optical remote measurement systems or online gas chromatography, and it is feasible only for gaseous compounds. Differential optical absorption spectroscopy (DOAS) is an example of a continuous sampling method. A system based on DOAS (Opsis system) is used in a number of Australian States and Territories. DOAS is used to measure gases in both ambient and emission monitoring applications. A portion of this chapter describes a 1995 study conducted by EPA Victoria to evaluate the performance of the DOAS (Opsis) open-path monitoring system and to provide a preliminary assessment of a range of air pollutants at two sites, one at a major industrial chemical site in Altona and the second at a heavily trafficked roadside location in Essendon. Monitoring was conducted from January to May 1995 at the Altona site, and from June to July 1995 at the Essendon site. However, instrumental problems in the first two to three months at the Altona site resulted in significant data loss; therefore the results presented here are for the period from March to May 1995.

Link: http://www.ea.gov.au/atmosphere/airtoxics/sok/chapter4.html

Airborne UV and Visible Spectrometer for DOAS and Radiometric Measurements
Petritoli, Andrea; G. Giovanelli; U. Bonafe; D. Bortoli; I. Kostadinov (ISAO/CNR (Italy) and Solar Terrestrial Influences Lab./Bulgarian Academy of Sciences); F. Ravegnani (ISAO/CNR).
Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research III.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3756, p 544-554, 1999

A UV/Vis spectrometer (GASCOD) for differentiated optical absorption spectroscopy (DOAS) has been developed at ISAO Institute and deployed for ground-based measurements of stratospheric trace gases. An airborne version (GASCOD/A) has been installed on board a M55-Geophysica airplane, a stratospheric research platform capable of flying at an altitude of up to 20 Km. The mechanical and optical layout of the instrument are presented and discussed, as well as laboratory tests and preliminary results obtained during flights onboard the M55- Geophysica.

The ALOMAR Rayleigh/Mie/Raman Lidar: Objectives, Configuration, and Performance
von Zahn, U.; G. von Cossart; J. Fiedler; K.H. Fricke; G. Nelke; G. Baumgarten; D. Rees; A. Hauchecorne; K. Adolfsen.
Annales Geophysicae, Vol 18 No 7, p 815-833, 14 Jul 2000

The authors report on the development and current capabilities of the ALOMAR Rayleigh/Mie/Raman lidar, one of the core instruments of the international ALOMAR facility in Norway. The major task of the instrument is to perform advanced studies of the Arctic middle atmosphere over altitudes between about 15 to 90 km on a climatological basis. The lidar is meant to work together with other remote sensing instruments, both ground- and satellite-based, and with balloon- and rocket-borne instruments performing in situ observations. The instrument is basically a twin lidar, using two independent power lasers and two tiltable receiving telescopes. The power lasers are Nd:YAG lasers emitting at wavelengths 1064, 532, and 355 nm and producing 30 pulses per second each. The power lasers are highly stabilized in both their wavelengths and the directions of their laser beams. The laser beams are emitted into the atmosphere fully coaxial with the line-of-sight of the receiving telescopes. The latter use primary mirrors of 1.8 m diameter and are tiltable within 30° off zenith. Their fields-of-view have 180 mrad angular diameter. Spectral separation, filtering, and detection of the received photons are made on an optical bench which carries, among a multitude of other optical components, three double Fabry-Perot interferometers (two for 532 and one for 355 nm) and one single Fabry-Perot interferometer (for 1064 nm). A number of separate detector channels also allow registration of photons which are produced by rotational-vibrational and rotational Raman scatter on N2 and N2+O2 molecules, respectively. Currently the lidar is heavily used for measurements of temperature profiles, of cloud particle properties such as their altitude, particle densities and size distributions, and of stratospheric winds.

Ambient Gaseous Leak Detection Using Radial Scanning Computed Tomography and Optical Remote Sensing
Hashmonay, Ram A. (Univ. of Washington, Seattle, WA); M.G. Yost; C.-F. Wu.
Proceedings of the 1998 Environmental Monitoring and Remediation Technologies Conference, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 126-132, 1999

The researchers conducted an experiment in a controlled ventilation chamber where a single source of nitrous oxide was released. A scanning open-path Fourier transform infrared (OP-FTIR) system acquired path-integrated concentration (PIC) data of 19 beams scanned in a radial non-overlapping beam geometry. The system was calibrated by creating a homogeneous atmosphere inside the ventilation chamber and using the smooth basis function minimization (SBFM) algorithm, which fits parametric distributions rather than fitting individual pixel concentrations, to reconstruct two-dimensional concentration maps from this beam geometry. The preliminary results show that good reconstructions are possible with this approach. The calibration procedure could be suitable for any open-path optical remote-sensing instruments. In contrast to the complex beam geometries proposed in the past for CT, this radial scanning technique could be applied directly to air monitoring data from diverse instruments, which could greatly broaden the application of CT to obtain rapid reconstructions of ambient air pollution data.

Analysis of an In-Situ Fiber Optic Backscatter Probe
Gross, Barry; Fred Moshary; Yiping Zhang; Samir A. Ahmed, CUNY/City College, New York, NY.
Lidar Remote Sensing for Industry and Environment Monitoring II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4484, p 224-233, 2001

The authors examine the use of an in situ multimode fiber optic backscatter probe to collect multi-spectral backscatter data supplemented by multi-spectral extinction data. To perform particle sizing, efficiency kernels must be constructed that determines the absolute backscatter signal as a function of the particle size parameter (q) for unit concentration. These efficiency kernels can then be used to invert calibrated multi-spectral data. The extinction measurements serve as an empirical correction factor to the backscatter measurement kernels.

Analysis of Field Data from the Duke Forest and Project OPTEX Studies
Lew, Frances; R.J. Paine; J.O. Zwicker; H. Feldman, ENSR Corp., Acton, MA.
Proceedings of the 1998 Environmental Monitoring and Remediation Technologies Conference, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 620-630, 1999

Two field studies were undertaken to evaluate the feasibility of using optical remote sensing technology to determine fugitive emission rates from point, area, and volume sources when the source locations are known. Two different dispersion models were used to estimate the path-average concentration based on a unit emission rate along various beam paths associated with the field studies conducted in Duke Forest, North Carolina, and in Texas. Actual emission rate was estimated via the ratio of the open-path Fourier transform infrared (OP-FTIR)-measured PAC to the modeled PAC.

Analysis of Quasi-Distributed Optical Sensors Combining rf Modulation with the FMCW Method
Zavrsnik, Miha; G. Stewart, Univ. of Maribor, Maribor, Slovenia.
Optical Engineering, Vol 39 No 11, p 3053-3059, Nov 2000

The authors offer a theoretical analysis of a quasi-distributed sensor system for absorption measurements based on the frequency-modulated continuous wave (FMCW) technique combined with frequency modulation spectroscopy (FMS). The method is highly sensitive and applicable to a variety of chemical species with narrow absorption lines, such as in trace gas analysis. Methane is used in this example. The laser diode injection current is sawtooth-modulated to provide a linear scan of the output over a certain frequency/wavelength range and the output is also externally modulated at radio frequencies. The sensor units consist of a series of open-path micro-optic cells constructed from graded index (GRIN) lenses, each with a unique beat frequency. By arranging for only one sideband of the modulation to be attenuated by the absorption feature, a new signal, proportional to the absorbance, appears in the output spectrum at a frequency corresponding to the difference between the rf-modulation frequency and the beat frequency of a cell.

Analysis of Volatile Organic Compounds over Octopus Spring, Yellowstone National Park Using Open-Path Fourier Transform Infra-Red Spectroscopy
Stoner, Daphne L.; John G. Jolley; Karen S. Miller; Dee Jay Fife; W.F. Bauer, Chemical and
Biological Sciences, Idaho National Engineering and Environmental Lab., Idaho Falls, ID.
Ninth Annual V.M. Goldschmidt Conference, 22-27 August 1999, Cambridge, Massachusetts [7264]

Open-path Fourier transform infrared spectroscopy (OP-FTIR) is a remote, non-destructive, optical sensing technique that continuously collects infrared spectral data along a linear path in the open air. The system was deployed in the area of Octopus Spring, Yellowstone National Park, Wyoming, for three days in October 1997. IR spectra were collected for one day over the microbial mats in the effluent channel area and for one day over the source pool. The OP-FTIR data indicated higher concentrations of some volatile and semi-volatile organic compounds--methyl acetate, acetate, and methanol--in the atmosphere over the mats than over the open spring. Dimethyl sulfide concentrations were slightly higher over the source pool than over the areas with microbial mats. The higher concentrations of organic acids and alcohols that were observed indicated a net flux of volatile organic acids out of the mats. Methane was at ambient concentration over the pool and the microbial mat areas. On a few occasions the concentration of methyl mercaptan over the mats increased dramatically simultaneously with decreases in methane concentration. No discernible trends attributable to light-dark periods were noted. This study demonstrated the use of a non-destructive optical-sensing technique for monitoring net flux of volatile organic compounds out of an ecosystem.

Anti-Personnel Landmine (APL) Detection Technology Survey and Assessment: Wide-Area Detection in Support of Arms Control
Kerner, David (DynMeridian, Alexandria, VA), et al., for the Defense Threat Reduction Agency.
Report No: DTR-TR-98-3. 123 pp, Mar 1999

This report documents the execution and results of a survey and assessment of technologies in open source literature and from government and industry that might be applicable for anti-personnel landmine (APL) detection and de-mining operations. These technologies were rated as to their desirable and undesirable features. Initial findings indicated that fully funded RDT&E programs were already being performed by many organizations, both government and private, to address ground-based, point-target APL detection and de-mining. One area, however, in which significant work remains to be accomplished is in developing technical solutions to address the task of wide-area detection (WAD). The term "wide-area detection" is used to signify a capability to detect an APL minefield from a standoff distance and ultimately from an airborne platform. The majority of this report consequently focuses on assessing, based on available information, technologies and their related systems that offer the potential to fully or partially fulfill wide-area detection requirements. In addition, information on the point-target detection and de-mining technologies uncovered during the initial research phase of the survey, while not pertinent to wide-area applications, is included in Appendix A. No single technology or system presently provides a comprehensive solution to the challenge of detecting APL on a wide-area basis. The survey identified seven significant technology areas that may be applicable to WAD, including magnetometry, radar, infrared, millimeter wavelengths, visible wavelengths, light detection and ranging (LIDAR), and electromagnetic induction. Each of these technologies, however, has individual shortcomings based upon factors such as lighting or weather conditions, soil types, vegetation, or APL metal content. A synopsis of their wide-area detection potential is presented.

Link: http://www.uxocoe.brtrc.com/TechnicalReps/apl_report.pdf

Application of a Lidar System to the Estimation of the Ambient Aerosol Source
Molero-Menendez, F.; L. Nunez; P. Salvador; M. Pujadas; B. Artinano, Ctr. de Investigaciones Energeticas, Medioambientales y Tecnologicas/DIAE, Madrid, Spain.
Lidar Remote Sensing for Industry and Environment Monitoring II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4484, p 207-215, 2001

This work presents the aerosol vertical profiles obtained by means of an elastic backscatter ground-based LIDAR, using the 532-nm radiation from a Nd:YAG laser.

The Application of Open-Path Fourier Transform Infrared Spectrometry Using Resolution Enhancement to Gaseous Emissions Monitoring
Davies, N.M., Ph.D. dissertation, Reading Univ., UK, Jun 2000.
Available from British Library Document Supply Centre-DSC:DXN033832

During the quantitative analysis of open-path Fourier transform infrared (FTIR) spectra, gas concentrations were retrieved from the spectra using linear and non-linear techniques and a gas monitoring system capable of open-path measurements in either an active or passive mode over a range of 100 m. A Mattson FTIR spectrometer forms an integral part of the system. Infrared spectra were recorded at urban, industrial, and agricultural sites possessing unique and identifiable emission sources. Linear and non-linear least squares algorithms were used to retrieve gas concentrations from the infrared spectra. The non-linear algorithm demonstrated more flexible and more robust determination than the linear algorithm and allowed synthetic reference spectra to be used more effectively. The instrument line shape (ILS) function of the FTIR spectrometer was measured using a He:Ne laser test rig and a low pressure gas cell. Both methods showed equivalence and the resultant ILS function was used in the non-linear retrieval algorithm. Experiments showed that the retrieved gas concentrations were within 0.3% of the actual gas concentrations.

Application of Raman Lidar to Air Quality Measurements
Philbrick, C.R.; K.R. Mulik, Penn State Univ., Dept. of Electrical Engineering, University Park, PA.
Conference on Laser Radar Technology and Applications V.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4035, p 22-33, 2000

An operational prototype Raman lidar instrument was prepared and demonstrated for the U.S. Navy and is now used for scientific investigations. It makes use of 2nd and 4th harmonic generated laser beams of a Nd:YAG laser to provide both daytime and nighttime measurements. The examples presented in this paper have been selected to show the new level of understanding of air pollution events that is being gained from applications of lidar techniques.

Application of Resonance Raman LIDAR for Chemical Species Identification
Chen, C.L. (Brookhaven National Lab.); D.L. Heglund; M.D. Ray; D. Harder; R. Dobert; K.P. Leung; M. Wu; A. Sedlacek.
Laser Radar Technology and Applications II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3065, p 279-285, 1997.
Paper No: BNL-64388, 8 pp, Jul 1997

DOE's Brookhaven National Laboratory has been developing a remote sensing technique for the detection of atmospheric pollutants based on the phenomenon of resonance Raman LIDAR that has also incorporated a number of new techniques/technologies designed to extend it`s performance envelope. When the excitation frequency approaches an allowed electronic transition of the molecule, an enormous enhancement of the inelastic scattering cross-section can occur, often up to 2 to 4 orders of magnitude, and is referred to as resonance Raman (RR), since the excitation frequency is in resonance with an allowed electronic transition. Exploitation of this enhancement along with new techniques such as pattern recognition algorithms to take advantage of the spectral fingerprint and a new laser frequency modulation technique designed to suppress broadband fluorescence, referred to as Frequency modulated Excitation Raman Spectroscopy (FreMERS), plus recent developments in liquid edge filter technology for suppression of the elastic channel, all help increase the overall performance of Raman LIDAR.

Link: http://www.osti.gov/bridge/product.biblio.jsp?osti_id=495732

Application of SpectraScan Tunable Diode Laser Instruments to Fugitive Emissions
Frish, M.B.; L.J. Edwards; P.N. McDonnell; J.M. Melnyk, Physical Sciences, Inc.
Sensor Review, Vol 19 No 4, p 278-284, 1999

Spectrum Diagnostix has developed a family of tunable diode laser-based instruments used in such applications as fugitive release detection of HF and H//2S in the refining and petrochemical industries and in stack monitoring. The instruments obtain their high sensitivity and chemical selectivity from a technique known as wavelength modulated spectroscopy, in which a near infra-red diode laser's wavelength is scanned rapidly and repeatedly through a molecular absorption line. A photo-detector senses the instantaneous fraction of emitted laser power that is transmitted through the chemical bearing gas. Measurement of the relative amplitudes of offline to online transmission yields a precise value of the quantity of chemical along the laser beam's path. The amplitude-modulated signals are detected via established radio receiver and signal processing techniques. SpectraScan's monitors are designed for permanent installation in harsh industrial and petrochemical sites. This paper describes the SpectraScan instruments and their field applications, and reviews operating data compiled from open-path measurements of HF in refineries.

Application of the Shifting Method as a Technique to Correct for the Background in Quantitative Analysis by Open-Path FTIR
Giese-Bogdan, Stefanie (Univ. of Michigan, Ann Arbor, MI); S.P. Levine; K. Molt.
Journal of the Air & Waste Management Association, Vol 49 No 2, p 114-124, Feb 1999

The generation of a suitable background single-beam spectrum is of major concern in open-path Fourier transform infrared spectroscopy. The Shifting Method can be used to correct for the background without the need to actually measure a background spectrum using the sample single-beam spectrum. This paper describes a thorough study of the Shifting Method.

Augmenting Classical DIAL with Raman-DIAL
Sedlacek, A.J., III; M.D. Ray; M.T. Wu, Brookhaven National Lab.
Application of Lidar to Current Atmospheric Topics III.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3757, p 126-139, 1999

The authors describe a novel method of performing DIAL (Differential Absorption Lidar) measurements of airborne chemicals. The RaDIAL technique utilizes the Raman returns from atmospheric nitrogen and oxygen as the `on' and `off' wavelengths for a particular chemical species. The advantages of RaDIAL for range-resolved chemical species detection/monitoring include insensitivity of the measurement to laser pulse-to-pulse energy fluctuations and variations in aerosol burden. The technique offers the desired high sensitivity associated with DIAL while keeping the data reduction simple and free of complex approximations.

Better Explosion Prevention with Open Path Gas Detection
Journal of Offshore Technology, Vol 7 No 3, p 14-15, 1999

Commercially available flammable gas detection equipment currently deployed on offshore platforms and onshore hydrocarbon processing plants employs different detection techniques and comes in a variety of physical configurations. Two types of devices are used for hydrocarbon gases: point detectors and open path gas detectors (OPGD).

Bragg Waveguide Sensor with Curved Edge for Fibre Butt-Coupling
Butler, Thomas (Oxford Univ.), Eishi Igata, S.J. Sheard; Neil Blackie (GEC-Marconi), Noori
Nourshargh; Peter Payne (AromaScan Ltd.).
U.K. Patent, 6 pp.

The invention solves the problem of detection of small amounts (such as a few ppm) of volatile hydrocarbon using an optical waveguide sensor. One of the novel features of this invention is the use of a curved waveguide section for the optical fibre input, which in combination with the grating allows high sensitivity and ease of device fabrication. The total device size is typically a few square centimeters in area, with the wave-guiding and polymer layers of thickness around one micron. The main benefit of such a sensor derives from exploiting an optical means of detection, offering superior sensitivity, immunity to electrical interference, distribution of remote signals via optical fiber links, and the possibility of introducing spectroscopic analysis for identification of the hydrocarbon type. Evanescent field sensors have been demonstrated previously, but the novelty of this variant lies in the introduction of both the curved waveguide input and Bragg scattering grating combined with the other features identified above. The effects of the grating can also be exploited by using an index modulation grating or other periodic perturbation, which can occur in any of the waveguide regions. The light source can be derived from a laser, light emitting diode, or incandescent source, and is sufficiently defined by any form of electromagnetic radiation.

Link: http://www.eng.ox.ac.uk/~holsjs/research/files/VOCpatent.pdf

Breathing Easier Through Air Monitoring (BEAM): OPSIS DOAS UV Long-Path Air Monitoring in Portland, Maine
Kahn, Peter R. (U.S. EPA New England Regional Lab.); Catherine Clayton-Richardson (Maine DEP).
U.S. EPA National Environmental Monitoring Technology Conference, 19-20 September 2000, Boston, Massachusetts

To pilot a new approach for providing real-time air quality data to the public, the Maine Department of Environmental Protection has installed an OPSIS DOAS (Differential Optical Absorption Spectroscopy) UV open path system in Portland, Maine. The system measures ozone, nitrogen dioxide, sulfur dioxide, benzene, toluene, m,p,o-xylene, formaldehyde, and phenol over an open path of 627 meters in length. The minimal level of detection for the system ranges from 0.5 ppb to 3 ppb up to 500 ppb to 1000 ppb. The data are presented as hourly averages, updated within 15 minutes after the hour in which the data were collected. The data are downloaded hourly from the monitoring site to a remote computer and quickly uploaded to an Internet website. Each person accessing the website is able to relate current ambient pollutant values to pollutant-specific health guidelines and obtain general information about each pollutant. This presentation describes how the OPSIS system operates, shows the type of data that have been collected, and discusses how stakeholders and a citizen advisory committee helped to develop the means to present real-time data to the public in a useable format. [This same paper was presented at the Air & Waste Management Association's 93rd Annual Conference & Exhibition, 18-22 June 2000, Salt Lake City, UT.]

Calibration and Field Measurement of an UV-Differential Absorption Spectrometer (UV-DOAS)
Weber, K.; S. Adorf; A. Ropertz; T. Lamp; C. Fischer; L. Mamoly, Univ. of Duesseldorf, Germany.
Proceedings of the MicroCAD 2001 - International Scientific Conference, Miskolc, Hungary

No abstract available.

Calibration of Two Open-Path FTIR-Spectrometers
Ropertz, A.; T. Lamp; M. Douard; K. Weber; A. Gaertner; C. Elbers; R. Nitz, Lab. of Environmental Measurement Techniques, Fachhochschule Duesseldorf, Duesseldorf, Germany.
Proceedings of the 1998 91st Annual Meeting & Exposition of the Air & Waste Management Association, San Diego, CA, 14-18 June 1998. Paper 98-TPC.07P

A validation program was undertaken at Fachhochschule Duesseldorf (FHD) to address the substantiation of the characteristics that make the open-path FTIR technique attractive for monitoring ambient air quality. Calibration measurements for ethylene and methane were carried out at the Laboratory for Environmental Measurement Techniques at the FHD. Measurements were made using a high resolution bistatic open-path FTIR Spectrometer and a mid-resolution monostatic system. The calculated calibration functions for the calibrated compounds were non-linear at high absorbances.

Classification and Recognition of Compounds in Low-Resolution Open-Path FT-IR Spectrometry by Kohonen Self-Organizing Maps
Yang, Husheng; J.D. Jegla; P.R. Griffiths.
Fresenius' Journal of Analytical Chemistry, Vol 362 No 1, p 25-33, 4 Sep 1998

This paper describes an investigation of the possibility of using one- and two-dimensional Kohonen self-organizing maps to recognize similarities in low-resolution vapor-phase infrared spectra in an unsupervised mode. Full-range vapor-phase FTIR reference spectra were first used to train the networks, and the trained networks then were used to classify the reference spectra into groups. The researchers also examined the feasibility of reducing the spectral range to be consistent with the atmospheric windows used in open-path FTIR spectrometry. Kohonen networks were found to be relatively immune to the presence of noise. The paper contains an example of using a trained Kohonen map to recognize the presence of selected compounds in field-measured open-path FTIR spectra.

Coherence Addressing of Quasi-Distributed Absorption Sensors by the FMCW Method
Zavrsnik, Mira; George Stewart, Univ. of Maribor, Maribor, Slovenia.
Journal of Lightwave Technology, Vol 18 No 1, p 57-65, Jan 2000

The authors discuss a new addressing mechanism for quasi-distributed absorption sensors based on the frequency modulated continuous wave (FMCW) method. The sensor units consist of open-path microoptic cells constructed from gradient index (GRIN) lenses, each of differing lengths. The interferometric mixing of two signals originating from each cell (from the glass/air interfaces) yields coherence addressing of the cells using FMCW. The time delay between the two reflections, along with the linear frequency ramp of the source, gives rise to beat frequencies in the mixed output that are different for each cell. The connecting fiber length between two successive sensor cells is chosen to be much greater than the coherence length of the source so that the reflections from different cells do not interfere. The interference patterns of all sensor cells add up at the detector whereby each individual sensing cell is identified by its power spectrum in the frequency domain.

Compact CH4 Sensor Based on Difference Frequency Mixing of Diode Lasers in Quasi-Phasematched LiNbO3
Lancaster, D.G.; R. Weidner; D. Richter; F.K. Tittel; J. Limpert, Rice Univ., Houston, TX.
Optics Communications, Vol 175 No 4, p 461-468, 2000

This paper describes a compact, portable, and robust room-temperature CH₄ sensor. A 500 mW alpha-DFB diode laser at 1066 nm and an erbium-doped fiber amplified 1574 nm DFB diode laser in periodically-poled lithium niobate up to 7 µW of narrowband radiation at 3.3 µm is generated by difference frequency mixing. Real-time monitoring of CH₄ using direct absorption in an open-path multipass cell yielded a detection precision of plus or minus 14 ppb.

Compact Diode Laser Based Sensor for Detection of Atmospheric Methane
Zhao, Haishan (Tianjin Jinghang Technical Physics Inst., Tianjin, China); R. Kanders; R.F. Curl; F.K. Tittel.
Proceedings of the 1998 Conference on Optical Remote Sensing for Industry and Environmental Monitoring, 15-17 September 1998, Beijing, China.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3504, p 99-107, 1998

A portable room-temperature diode laser based on mid-infrared gas sensor was developed for open path measurements of methane in ambient air. When in situ and open path detection of methane in atmosphere with sensitivity of 18 ppbm/Hz½ was performed, detection sensitivity was limited by intensity noise.

Compact Mid-Infrared Trace Gas Sensor Based on Difference Frequency Mixing
Tittel, Frank K.; D.G. Lancaster; D. Richter; L. Goldberg; J.P. Koplow, Rice Univ., Houston, TX.
Proceedings of the 1999 Application of Tunable Diode and Other Infrared Sources for Atmospheric Studies and Industrial Processing Monitoring II, 19-20 July 1999, Denver, CO.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3758, p 2-10, 1999

Infrared laser sources have been refined and improved through such technological advances as semiconductor diode lasers and solid state lasers, new nonlinear optical materials, optical fiber, and novel data acquisition techniques. Newer sensors are able to detect molecules at the parts-per-billion (ppb) level in ambient air using infrared absorption spectroscopy. This paper describes real-world applications ranging from urban, industrial, and rural emission studies to spacecraft habitat monitoring.

Comparison of an Open Path Differential Optical Absorption Spectroscopy System and a Conventional in Situ Monitoring System on the Basis of Long-Term Measurements of SO2, NO2, and O3
Kim, Ki-Hyun, (Sejong Univ., Seoul, South Korea); Kim, Min-Young, (Seoul Metropolitan Inst. of Public Health and Environment, South Korea).
Atmospheric Environment, Vol 35 No 24, p 4059-4072, Aug 2001

Atmospheric concentrations of sulfur dioxide, nitrogen dioxide, and ozone within the Ban Po district of Seoul, South Korea, were measured for 14 months using an open-path differential optical absorption spectroscopy (DOAS) system and a conventional point monitoring system. The results of the two systems were compared as part of an instrumental calibration test. The modes for the two systems agreed reasonably well for the different species, especially for SO₂. Changes in meteorological conditions were reflected sensitively in the DOAS performance, which varied greatly among species and seasons.

Comparison of DOAS and Standard Monitoring Measurements in Urban Areas
Sturm, Peter J.; Johannes Rodler, Technische Univ. Graz, Graz, Austria.
Spectroscopic Atmospheric Environmental Monitoring Techniques Conference, 21-22 September 1998, Barcelona, Spain.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 114-122, 1998

Measurements of air pollutant concentrations made using open-path equipment allow comparisons to be made between monitoring measurements and path-averaged measurements. This was carried out in two city areas, one with no direct pollutant sources where the emissions arhomogeneously distributed in the air, and the second an inner-city zone with the measurement path covering two roads of varying traffic loads. Although a good comparison between a UV-DOAS system and monitoring stations was established in the first area, this was not the case in the second test set-up because of the different emissions levels.

Comparison of Line- and Point-Source Releases of Tracer Gases
Eklund, Bart, Radian International LLC, Austin, TX.
Atmospheric Environment, Vol 33 No 7, p 1065-1071, Mar 1999

Field measurements were made of gas emissions from a wastewater treatment system using open path monitoring with detection by FTIR spectroscopy. Emission rates were determined by the ratio technique using a sulfur hexafluoride tracer gas released from a line source, with release of a second tracer gas (ethylene) from various single-point locations as a quality control check. This paper presents a comparison of the line-source and point-source tracer releases for approximating emissions from the area source.

Compendium of Sensing Technologies to Detect and Measure VOCs and HAPs in the Air
ICF, Inc., Fairfax, VA, for U.S. EPA, Common Sense Initiative (CSI) Petroleum Refining Sector
Equipment Leaks Project, 95 pp, Jun 1999

Petroleum refineries have been subject to leak detection and repair (LDAR) programs to reduce emissions of VOCs and other hazardous air pollutants from certain refinery equipment since the late 1970s. ICF was tasked by the Equipment Leaks Project Team of EPA's Common Sense Initiative Petroleum Refining Sub-Committee to investigate and evaluate the new and emerging sensing technologies that might form the basis for alternative work practices under the LDAR regulations at U.S. refineries. The report contains much of the available information on technologies that may be candidates for an alternative work practices program in refineries. There is also a section on leak prevention technologies. The last section of the report contains cost information on the existing LDAR programs and on these newer sensing technologies. Some of the technologies were not yet commercially available at the time this report was written, so capital costs are estimates, and operating and maintenance costs are not available. The capital cost estimates for non-commercial systems tend to be prototype costs. Technology costs come down over time, particularly if there are economies of scale in production. This report also contains an appendix that describes the basic operations of lasers, spectroscopy, and spectral imaging, as well as a bibliography of additional resources.

Link: http://www.epa.gov/csi/petroone.pdf

Confirmation of a Multilayer Arrangement of Aerosols in the Barcelona Air Basin Using Two Independent Lidar Systems
Soriano, C. (Univ. Politecnica de Catalunya, Barcelona, Spain); F. Rocadenbosch; C. Puente; A. Rodriguez; J.M. Baldasano; A. Comeron.
Spectroscopic Atmospheric Environmental Monitoring Techniques.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 212-222, 1998

A study of a temporal series of lidar vertical scans in Barcelona in 1992 revealed a multilayer arrangement of aerosols above the city. A few years after that experiment, the University Politecnica de Catalunya (UPC) in Barcelona, Spain, developed its own lidar system, beginning with the construction of an elastic backscatter lidar. In 1997, the UPC lidar acquired vertical profiles of elastic backscatter in Barcelona's atmosphere. The experiment seems to confirm the results of a 1992 air pollution monitoring campaign as to the aerosol layers being a seasonal effect.

Continuous HAP Monitoring Technologies: How They Work and Where to Buy Them
Air Pollution Consultant, Vol 8 No 6, p 4.1-4.18, Nov-Dec 1998

This paper explains how extractive, open-path, and in situ measurement techniques are incorporated into hazardous air pollutant (HAP) continuous emissions monitoring via sample analyses facilitated by infrared absorption, UV absorption, molecular fluorescence, and ionization detection methods. The text identifies vendors and specifications for different commercially available HAP continuous emissions monitoring systems.

Detection of Aromatic Pollutants in the Environment by Using UV-Laser-Induced Fluorescence
Karlitschek, P.; F. Lewitzka; U. Bünting; M. Niederkrüger; G. Marowsky, Laser Laboratorium Göttingen, Göttingen, Germany.
Applied Physics B Lasers and Optics, Vol 67 No 4, p 497-504, 1998

The authors describe a compact and mobile battery-operated laser induced fluorescence (LIF) system based on a diode-pumped solid-state laser with UV frequency conversion and a 7-ns pulse duration. The third (355 nm) and fourth (266 nm) harmonics of the laser can be used alternately. The detection system consists of a polychromator, a gated image intensifier, and a CCD camera, which can acquire time-resolved spectra with nanosecond time resolution. The detector was tested on 16 polycyclic aromatic hydrocarbons (PAHs), as well as natural water samples contaminated with gasoline and tar.
Fluorescence spectra, decay times, and detection limits were measured, and the results, potentials, and limits of the LIF technique are discussed.

Development and Evaluation of a Modular FT-IR Monitor for Industrial Use
Spellicy, R.L. (Unisearch Associates, Austin, TX); R.J. Brewer; J.R. Morphew; H.R. Woodard.
Proceedings of the 1998 Electro-Optic, Integrated Optic, and Electronic Technologies for Online Chemical Process Monitoring Conference, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3537, p 42-53, 1999

IMx, a modular Fourier transform infrared industrial monitor, was developed for open-path and extractive measurements. These rugged, adaptable, relatively inexpensive systems are being used by environmental services companies for effective stack and open-path monitoring.

Development of a Compact Light Source at 1.67 Um for Methane Leak Detection Using DIAL
Vasa, Nilesh J. (Kyushu Univ., Fukuoka, Japan), Kouji Saito, Kouki Ikuta, Yuji Oki; Mitsuo Maeda (Kyushu Univ., Higashi-ku Fukuoka, Japan).
Lidar Remote Sensing for Industry and Environment Monitoring.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4153, p 471-479, 2001

A sensing system for methane gas leakage monitoring is based on a differential absorption lidar with a high temporal resolution with a spectrally narrowed light surface. An injection seeded optical parametric oscillator (OPO) combined with two-stage optical parametric amplifiers (OPAs) provides a compact light source. The device can satisfactorily detect methane leakage at short range.

Development of DOAS System Based on a Cross-Dispersion Echelle Spectrograph
Schinca, D.C.; J.O. Tocho, Ctr. de Investigaciones Opticas and Univ. de La Plata, Argentina.
Water, Ground, and Air Pollution Monitoring and Remediation, 6-7 November 2000.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4199, p 77-85, 2001

Differential optical absorption spectroscopy (DOAS) typically consists of a collimated broadband radiation source that shines a beam of light through an open atmospheric path several hundred meters long; at the other end, a receiving telescope is located which focus the beam on a medium resolution spectrometer-photodetector system that analyzes the wavelength spectrum of the incoming light within a certain range; hence, the absorption bands of a specific gas component failing in this range are detected. For multicomponent analysis, the spectrometer must be scanned across different wavelength ranges, which can introduce sources of error.

Development of a Probe for in Situ Measurements of Major Species in a Pool Fire Using Multiplexed Near-IR TDLAS
Santangelo, P.J. (Sandia Natl. Lab., Livermore, CA); Ludowise, P.D.; Shaddix, C.R.; Allendorf, S.W.; Ottesen, D.K.; Ross, J.R.; Johnsen, H.A.; G.L. Hubbard.
Proceedings of the 1999 Application of Tunable Diode and Other Infrared Sources for Atmospheric Studies and Industrial Processing Monitoring II, 19-20 July 1999, Denver, CO.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3758, p 202-211, 1999

A tunable diode laser absorption spectroscopy probe has been developed to simultaneously measure in situ concentrations of four gases--CO, C2H2, CH4, and H2O--and the gas-phase temperature in a pool fire. Fiber optic cables transport laser radiation into the fire via a water-cooled probe. Design issues include the optimization of open path, multipass optics for a turbulent, particulate-laden flow, and the application of high-frequency wavelength modulation spectroscopy to frequency-domain multiplexing of diode lasers.

Different Methods of Evaluating Sharp-Peaked Compounds in FT-IR-Spectra Using Benzene as an Example
Lechner, B.; P. Sturm, Technical Univ. Graz, Graz, Austria.
Proceedings of the 1998 Conference on Spectroscopic Atmospheric Environmental Monitoring Techniques Conference, 21-22 September 1998, Barcelona, Spain.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 88-93, 1998

The quantification of benzene in FTIR spectra is restricted by the interference of benzene with carbon dioxide. The authors suggest different methods to overcome the problem with a detector of medium resolution of 0.5 cm^-1 based on the results of experiments performed either in a 10 m gas cell or as open-path experiments.

Differential Absorption Lidar (DIAL) Measurements of the Mechanisms of Volatile Organic Compound Loss from External Floating Roofed Tanks
O'Connor, Simon J. (Shell Research and Technology Centre Thornton, Chester, UK), Harold L. Walmsley; Humphrey Pasley (Brunel Univ., Uxbridge, UK).
Spectroscopic Atmospheric Environmental Monitoring Techniques.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 255-266, 1998

This paper describes how an IR DIAL system has been used both to measure the emission rates of volatile organic compounds (VOCs) from external floating roof tanks and to map the concentration of VOCs over the roofs of tanks. The data presented show concentration iso-surfaces resolved at 0.2 ppm intervals over an operating 50 m diameter tank, and these data are used to validate subsequent models of tank emissions.

Differential Optical Absorption Spectroscopy for Air Pollution Measurement: DOAS
Balin, Ioan, Swiss Federal Inst. of Technology, Lausanne, Switzerland. [project summary] Mar 1999

Based on the UV-VIS-NIR high-frequency structure of the molecular absorption spectra, differential optical absorption spectroscopy (DOAS) is a relatively new spectroscopic technique for measuring trace gas atmospheric concentrations. The advantages of the DOAS technique include simultaneous determination of multiple trace gases (compound simultaneous determination), in situ monitoring, long-path averaged concentrations, adaptation for the validation of 3D Eulerian models, and relatively low cost. The aim of this work is to contribute to the improvement and optimization of a new commercial DOAS system, DOAS 2000, which is being characterized and improved by the LPA-LIDAR Group.

Link: http://gecos.epfl.ch/CPSE/recherches/mars99/doas.html

Diffusive Sampling of VOCs as an Aid to Monitoring Urban Air Quality
Wright, M.D. (Health and Safety Lab, Sheffield, UK); N.T. Plant; T.H. Brown.
Environmental Monitoring and Assessment, Vol 52 No 1-2, p 57-64, Aug 1998

Diffusive sampling of volatile organic compounds (VOCs) onto thermal desorption tubes, followed by gas chromatography, is an established technique for area or personal monitoring of typical workplace concentrations. There is commercial interest in extending the application to environmental levels, particularly for benzene, toluene, and xylene (BTX). Diffusive sampling rates for BTX were measured over periods of one to four weeks in field validation experiments using ambient air and parallel pumped sampling (the reference method). The reference method was also used to investigate the possible bias of the OPSIS open-path spectrophotometer. A bias for BTX was suspected from results of a two-week initial exercise in which several diffusive samplers were placed close to the light path. In a full field validation of the diffusive samplers, the significant bias of BTX concentrations reported by OPSIS were confirmed when compared with concurrent results from the reference method. OPSIS gave benzene and toluene values up to eight times higher than expected from the GC measurements. Xylene discrepancies were smaller, but in one three-day peak episode, OPSIS demonstrated a negative correlation with GC.

DOAS as an Analytical Tool for Effective Air Pollution Management
Jiménez, Rodrigo (Air Pollution Laboratory (LPAS), Swiss Federal Institute of Technology (EPFL),
Lausanne, Switzerland), Hubert van den Bergh, Bertrand Calpini.
Proceedings of the Third Specialty Conference on Environmental Progress in the Petroleum & Petrochemical Industries, 1-3 May 2000, Bahrain, 17 pp, 2000

The DOAS (differential optical absorption spectroscopy) technique has developed into one of practical high performance. Based on the UV-visible molecular absorption of atmospheric gases, DOAS is a spectroscopic technique well suited for a simultaneous detection of many atmospheric trace gases including the criteria compounds NO2, SO2, and O3. The technique is based on the optical absorption of gases over long path lengths ranging from some hundreds of meters up to several kilometers long. DOAS values give pollutant concentrations averaged over relatively large distances, thus avoiding large local perturbations that can be observed in point measurements. This paper summarizes the significance of the DOAS technique in air pollution management.

Link: http://lpas.epfl.ch/lidar/publi/SAS-A&WMA_DOAS.pdf

DOAS Measurements of Atmospheric Ammonia Emissions at a Dairy
Rumburg, B.P. (Washington State Univ., Pullman); G.H. Mount; J.R. Havig; B.K Lamb; H.H. Westberg; R.L. Kincaid; K.A. Johnson.
Eos Trans. AGU, Vol 81 No 48, Fall Meeting Supplement, Abstract B12B-12, 2000

The authors have begun a detailed study of ammonia (NH³) gas at the WSU dairy farm, an operational dairy near Pullman, Washington, to determine an emission inventory. Measurements were made by open short-path spectroscopic absorption in the UV near 200 nm with a time resolution of a few seconds and a limiting sensitivity of a few ppb. This open path method is advantageous over other methods in that it is fast, self-calibrating, and does not have errors associated with NH³ adherence to inlet walls. Ammonia concentrations and fluxes showed a strong seasonal trend correlating with ambient air temperatures.

Doppler Spectral Scanning Differential Absorption Lidar
Jost, B.M. (Air Force Research Lab., NM), D.C. Senft ; D.F. Pierrottet (Univ. of New Mexico/Air Force Research Lab., NM); J. Cardani (Textron Systems Corp.).
Lidar Remote Sensing for Industry and Environment Monitoring II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4484, p 120-127, 2001

In separate tests to examine the effectiveness of Doppler spectral scanning differential absorption lidar (DSS DIAL), CO₂ laser pulses were reflected from either a ground-based retroreflector (36-km round-trip distance) or a retroreflector on the GEOS-3 satellite (approximately 2000-km round-trip distance), with returns split into a reference channel and an absorptive gas-cell channel. Results from the ground-based system produced data that matched expected values in one case, but the repeatability of results was not determined.

Effect of Resolution on Quantification in Open-Path Fourier Transform Infrared Spectrometry under Conditions of Low Detector Noise. 1. Classical Least Squares Regression
Hart, Brian K.; P.R. Griffiths, Univ. of Idaho, Moscow, ID.
Environmental Science & Technology, Vol 34 No 7, p 1337-1345, 2000

Tests of the effects of resolution, spectral window, and background type on the predictive ability of classical least squares regression (CLS) on spectra measured by an open-path Fourier transform infrared (OP-FTIR) spectrometer showed the most accurate quantitative results were obtained by using equidistant backgrounds, reduced spectral windows, and low resolution. The effect of interfering compounds was particularly serious when CLS regression was used to process OP- FTIR spectra.

Effects of Resolution on Quantification in Open-Path Fourier Transform Infrared Spectrometry under Conditions of Low Detector Noise. 2. Partial Least Squares Regression
Hart, Brian K.; J.R. Berry; P.R. Griffiths, Univ. of Idaho, Moscow, ID.
Environmental Science & Technology, Vol 34 No 7, p 1346-1351, 2000

The effects of resolution, spectral window, and background type on the predictive capability of partial least squares regression (PLS) on spectra measured by an open-path Fourier transform infrared (OP-FTIR) spectrometer were tested with spectra of mixtures of alkanes and chlorinated hydrocarbons, and the results were compared with the results obtained with the identical data sets using classical least squares regression (CLS). The most accurate predictions were obtained using the same conditions that were optimal for CLS: equidistant backgrounds, reduced spectral windows, and low resolution. However, good predictions could be achieved with background spectra measured over a very short path. At worst, the relative error of predictions made by PLS was usually less than 5%, and on average, the predicted concentrations of the components of mixtures containing up to five chemically similar analytes made using the PLS algorithm were 120 times more accurate than the predicted concentrations of the components of the identical data sets made using CLS.

Element-Selective Trace Detection of Toxic Species in Environmental Samples Using Chromatographic Techniques and Derivative Diode Laser Absorption Spectrometry
Koch, J.; A. Zybin; K. Niemax, Inst. of Spectrochemistry and Applied Spectroscopy (ISAS), Dortmund, Germany.
Applied Physics B Lasers and Optics, Vol 67 No 4, p 475-479, 1998

This paper presents very sensitive laser absorption techniques based on a double-beam scheme with logarithmic processing of the detector signals and wavelength modulation of laser diodes. Analytical versatility was demonstrated by quantitative analysis of low concentrations of Cr(VI) species in tap water and chlorophenols in plant extracts, both after chromatographic separation.

Emission Rate Apportionment from Fugitive Sources Using Open-Path FTIR and Mathematical Inversion
Hashmonay, Ram A. (Univ. of Washington, Seattle, WA); M.G. Yost; Y. Mamane; Y. Benayahu.
Atmospheric Environment, Vol 33 No 5, p 735-743, Feb 1999

This paper presents a detailed new methodology to address emissions from non-homogeneous fugitive gaseous air pollution sources using an open-path FTIR system in a new field configuration, in which the main measurement path is located downwind from the source and segmented into several secondary paths. The segmentation can be performed by retroreflectors or black bodies situated along the main measurement path, for a unistatic system or bistatic system respectively. An inversion technique used in conjunction with plume dispersion modeling techniques allows reconstruction of the emission rates distribution from different strips of the fugitive source. In a validation field study, large and relatively cold black bodies (approximately 100 C) were successfully used as the sources of infrared radiation. Emission rates from three controlled emission point sources of SF6 were reconstructed by applying the suggested methodology, and agreed well in most runs.

Emission Rates of Benzene and Ammonia Area Sources Determined by Spectroscopic Remote Measurements and Inverse Dispersion Modeling
Schaefer, Klaus; S. Emeis; M. Stockhause; A. Sedlmaier; H. Hoffmann; G. Depta; A. Gronauer, Fraunhofer Inst, for Atmospheric Environmental Research (IFU), Garmisch-Partenkirchen, Germany.
Proceedings of the 1998 Environmental Monitoring and Remediation Technologies Conference, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 212-219, 1999

To determine gaseous emission rates by measurements of path-integrated mixing ratios with open-path spectroscopic systems in an exhaust plume, inverse dispersion modeling was used to quantify the emission rates afterwards with these data based on measurements obtained by Fourier transform infrared (FTIR) spectroscopy and differential optical absorption spectroscopy (DOAS) at 50 to 500 m optical path lengths about 1 to 20 m above ground level. The method was validated at a livestock building with a single exhaust chimney and showed the measurement accuracy for greenhouse gases and ammonia to be about plus or minus 10%.

Emission Source Strengths of Gasoline Filling Processes Determined by Open-Path Spectroscopic Techniques and Inverse Modelling
Schafer, K. (Fraunhofer-Inst. fur Atmospharische Umweltforschung (IFU), Garmisch-Partenkirchen, Germany); M. Stockhause; H. Hoffmann; A. Sedlmaier; S. Emeis.
Proceedings of the 1998 Conference on Spectroscopic Atmospheric Environmental Monitoring Techniques Conference, 21-22 September 1998, Barcelona, Spain.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 223-230, 1998

To estimate the total emissions from gas stations and gasoline tank farms, non-intrusive measurements were performed by a differential optical absorption spectroscopy (DOAS) system to determine the path-integrated concentrations of exhaust compounds (mainly benzene) downwind of the source through the whole exhaust plume. Measurement campaigns were performed during different weather conditions and at different sources. The determined total emissions of gas stations with gasoline vapor recovery system were about 20 mg benzene per kg refueled gasoline, and the emissions from refueling activities vary between 1 and 9 mg benzene per kg refueled gasoline, depending on the behavior of the gasoline vapor recovery system. The emission rates from a gasoline tank farm were measured on an open path through the middle of the area and showed a maximum of 8 µg/m².

Estimating Maximum Concentrations for Open Path Monitoring Along a Fixed Beam Path
Yost, M.G.; R.A. Hashmonay; Yi Zhou; R. Spear; D.Y. Park; S. Levine, School of Public Health and Community Medicine, Univ. of Washington, Seattle.
Journal of the Air & Waste Management Association, Vol 49 No 4, p 424-433, 1999

Open-path optical sensing techniques can be applied to a variety of workplace and environmental monitoring problems. Usually these data are reported in terms of a path-average or path-integrated concentration. The path-average value is not always informative, since concentrations along the path can vary substantially from the beam average. The researchers have developed a statistical model to estimate an upper-bound concentration based on a combination of the path-average and a measure of the spatial variability computed from point samples along the beam path.

Evaluation of an Open-path Fourier Transform Infrared (OP-FTIR) Spectrophotometer Using an Exposure Chamber
Todd, L.A.
Applied Occupational and Environmental Hygiene, Vol 11 No 11, p 1327-1334, 1996

This study investigated the use of a controlled outdoor exposure chamber to evaluate the accuracy of an open-path Fourier transform infrared (OP-FTIR) spectrometer for measuring toluene and cyclohexane. Multiple backgrounds were taken throughout each sampling day, and open-path measurements were compared with point samples taken in the chamber and analyzed by GC-FID. For toluene, the OP-FTIR spectrometer either over-estimated or underestimated concentrations by up to 36% depending upon the spectral library used for quantification. The classical least squares (CLS) and subtraction analysis methods gave similar and lower results than the integration method. For cyclohexane, the OP-FTIR spectrometer overestimated concentrations by an average of 29%. The apparent overestimation, when compared with the point samples taken from the chamber, may have been due to chemical losses on the walls of the sampling lines and Tedlar bags, systematic calibration errors, or the spectral libraries. When backgrounds were used from different times during a sampling day, toluene results were significantly affected if the partial pressure of water vapor varied by more than 10%. Cyclohexane results were essentially unaffected by the use of backgrounds from any time during the sampling day or the sampling week, regardless of changes in the environmental conditions.

Evaluation of CO2, Water Vapour, and Their Turbulent Exchange Rates with an Airborne Open-Path Infrared Gas Analyzer
Graber, Werner K.; Markus Furger, Paul Scherrer Inst., Villigen, Switzerland.
Proceedings of the 1999 Environmental Sensing and Applications Conference, 14-17 June 1999, Munich, Germany.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3821, p 155-161, 1999

Measurements taken over Monte Bondone near Trento, Italy, a plateau in the Alps, were used to examine a methodology of evaluating the exchange rates of CO₂ and water vapor between vegetation and the atmosphere. The gases were measured with a short open-path, fast-responding infrared absorption gas analyzer. To determine the turbulent fluxes due to large-scale eddies, high resolution wind measurements were obtained with a five-hole pressure sonde and a fast Global Positioning System (GPS) receiver.

Evaluation of Open-Path FTIR Spectrometers for Monitoring Multiple Chemicals in Air
Farhat, S.K.; L.A. Todd.
Applied Occupational and Environmental Hygiene, Vol 15 No 12, p 911-923, 01 Dec 2000

The authors investigated the use of a specially designed external calibration cell as a tool for laboratory and field evaluation of the accuracy of open-path FTIR spectrometers. Commonly used instrument performance parameters were measured to see if they could be used to predict whether an instrument is operating correctly. Six instruments from one manufacturer were evaluated with a prototype calibration cell using NIST-traceable sulfur hexafluoride, n-hexane, and cyclohexane. The instrument performance measures could not be used to predict accuracy, but the external calibration cell shows promise as a method of validating the operation of an OP-FTIR spectrometer for quality assurance and quality control.

Evaluation of Virtual Source Beam Configurations for Rapid Tomographic Reconstruction of Gas and Vapor Concentrations in Workplaces
Park, Doo Y.; Michael G. Yost; Steven P. Levine, Univ. of Michigan, Ann Arbor, MI.
Journal of the Air & Waste Management Association, Vol 47 No 5, p 582-591, May 1997

Beam path average data from an open-path Fourier transform infrared (OP-FTIR) spectrometer can be used to reconstruct two-dimensional concentration maps of the gas and vapor contaminants in workplaces and the environment using computed tomographic (CT) techniques. In the past, multiple-source and detector units were required to produce a sufficient number of intersecting beam paths to reconstruct concentration maps, which rendered it impractical for actual field monitoring because of the great expense of multiple pieces of equipment and the difficulty of achieving and maintaining proper alignment. A single monostatic OP-FTIR system capable of rapid beam movement and set up with multiple flat mirrors and retroreflectors to obtain intersecting folded beam paths can be set up and operated much more economically. This paper describes the performance results of such a system in a test room.

Evaluation Procedure for Nonintrusive Exhaust Gas Analysis of Jet Engines Using FTIR Spectroscopy
Lindermeir, Erwin (DLR Institute for Optoelectronics, Wessling, Germany), P. Haschberger; R.M. Geatches (British Aerospace, Bristol, UK)
Spectroscopic Atmospheric Environmental Monitoring Techniques
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 44-55, 1998

The authors present a method for the non-intrusive determination of temperature and concentrations of aeroengine exhaust gases. A MIROR-type FTIR spectrometer measures spectra of the IR radiation emitted by the hot gases in the exhaust. New evaluation software, specially developed for this application, permits line-by-line radiative transfer modeling of the radiance emitted by the exhaust of these engines. Least squares fitting routines are then used to match the measured with the modeled spectrum, thereby determining temperature and species concentrations.

Evolution of Air Pollution Events Determined from Raman Lidar
Mulik, K.R.; C. Li; G.S; Chadha; C.R Philbrick; S. Mathur, Penn State Univ., University Park, PA.
Proceedings of PM2000: Particulate Matter and Health Conference, Air & Waste Management Association, p W11-13, Jan 2000

Measurements of ozone, water vapor, temperature, and extinction were obtained during the EPA-sponsored NARSTO-NE-OPS project using the Lidar Atmospheric Profile Sensor (LAPS) instrument, which was developed as a prototype for the U.S. Navy. The authors present results from the August 1998 pilot study. The LAPS lidar instrument uses multi-channel photon counting detection to measure several wavelengths of Raman scattered signals that provide vertical profiles of atmospheric properties. Measurements were made in the Philadelphia urban environment, where there is a combination of local sources, as well as contributions from long-range transport of distant source regions. Water vapor profiles provided a tracer of the boundary layer dynamics important in describing the distribution of ozone and particulate matter in the lower atmosphere. Species distribution and local mixing rate were found to be of major importance in determining the surface layer concentrations of air pollution components.

Experimental Evaluation of a Radial Beam Geometry for Mapping Air Pollutants Using Optical Remote Sensing and Computed Tomography
Wu, Chang-Fu; M.G. Yost; R.A. Hashmonay; D.Y. Park, Univ. of Washington, Seattle, WA.
Atmospheric Environment, Vol 33 No 28, p 4709-4716, Dec 1999

The authors describe the first experimental evaluation of a non-overlapping radial beam geometry to map air pollutants using computed tomography (CT) and optical remote sensing (ORS) instruments. An open path Fourier transform infrared (OP-FTIR) spectrometer gathered path-integrated concentration data concerning nitrous oxide released from a point source inside a ventilation chamber. The smooth basis function minimization (SBMF) CT algorithm was applied to a radial geometry with 19 rays. Two-dimensional maps were reconstructed from the OP-FTIR measurements and compared with kriged maps calculated from 13-point samples collected simultaneously during the experiments. The CT reconstructions showed good agreement compared to the kriged maps obtained from point samples and also located the peak concentration within 1.2 m, compared to the point samplers.

Experimental Evaluation of an Environmental CAT Scanning System for Mapping Chemicals in Air in Real-Time
Todd, L.A.; S.K. Farhat; K.M. Mottus; G.J. Mihlan.
Applied Occupational and Environmental Hygiene, Vol 16 No 1, p 45-55, 2001

An innovative method called environmental CAT scanning creates real-time, two-dimensional maps of chemical concentrations in air for environmental and occupational applications. The method combines the real-time measuring technique of open-path Fourier transform infrared spectroscopy with the mapping capabilities of computed tomography to produce accurate spatial and temporal information about contaminant concentrations and dispersion patterns. After open-path measurements are obtained over an area, they are processed using a tomographic algorithm to reconstruct the concentrations. This paper describes an experimental evaluation of an environmental CAT scanning system using a field-ready prototype system deployed in a room-size exposure chamber. Twenty-eight experiments were performed using single or multiple plumes of a tracer gas in the chamber.

Field Evaluation of a Method for Estimating Gaseous Fluxes from Area Sources Using Open-Path Fourier Transform Infrared
Hashmonay, R.A.; D.F. Natschke; K. Wagoner; D.B. Harris; E.L. Thompson; M.G. Yost, ARCADIS Geraghty and Miller, Inc., Research Triangle Park, NC.
Environmental Science & Technology, Vol 35 No 11, p 2309-2313, 1 Jun 2001

This paper describes results from the first field experiment designed to evaluate a new approach for quantifying gaseous fugitive emissions of area air pollution sources by combining path-integrated concentration data acquired with open-path Fourier transform infrared (OP-FTIR) and computed tomography (CT). The approach is applicable to many types of industrial areas or volume sources, given the usof an adequate path-integrated optical remote sensing system.

Field Measurement of Air Pollutants near Swine Confined-Animal Feeding Operations Using UV DOAS and FTIR
Secrest, Cary D., U.S. EPA.
Water, Ground, and Air Pollution Monitoring and Remediation, 6-7 November 2000.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4199, p 98-104, 2001

This paper reports the results of ammonia measurements near two confined-animal feeding operations (CAFOs) in September 1999 and March 2000. Measurements at the first site were conducted for 48 hours downwind using two open-path monitors: an ultra-violet differential optical absorption spectrometer (UV-DOAS), and a Fourier transform interferometer (FTIR). Measurements at the second CAFO were taken using only UV-DOAS. This paper describes the calibration of a UV-DOAS, compares UV-DOAS and FTIR measurements, describes the effects of wind and atmospheric stability on ambient ammonia concentration, and suggests potential applications for open-path monitors for assessing risks to public health.

Field Measurement of Greenhouse Gas Emission Rates and Development of Emission Factors for Wastewater Treatment. Final Report, September 1994-March 1997
Eklund, B.; J. LaCosse, Radian Corp., Austin, TX.
Report No: EPA/600/R-97/094, NTIS: PB98-117898. 484 pp, Sep 1997

The report gives results of field testing to develop more reliable greenhouse gas (GHG) emission estimates for wastewater treatment (WWT) lagoons. Field tests of emissions were conducted for WWT lagoons that use anaerobic processes to treat large volumes of wastewater with large biological oxygen demand (BOD) loadings. Air emissions and wastewater were measured at anaerobic lagoons at three meat processing plants and two publicly owned treatment works. The overall emission rates of CH₄, carbon dioxide, carbon monoxide, nitrous oxide, ammonia (NH₃), and chlorofluorocarbons were measured from each source using an open-path monitoring approach. The emitted compounds were identified and quantified by Fourier transform infrared spectroscopy. Emission factors were developed for CH₄ and NH₃ as a function of the plant production rate, wastewater parameters (e.g., influent BOD and chemical oxygen demand (COD) loadings), and WWT system performance (e.g., BOD and COD removal rates).

Report summary (5 pp) online at http://www.epa.gov/ORD/WebPubs/projsum/600sr97094.pdf

Field Measurements of Chemical Emission Sources by Open Path Fourier Transform Infrared Spectroscopes with a Two-Dimensional Searching Model
Yang, J.C.; Y.A. Jihn; J.P. Yu; R.T. Wu, Industrial Technology Research Inst., Chutung Hsinchu, Taiwan.
Air and Waste 92nd Annual Meeting and Exhibition, 20-24 June 1999, St. Louis, MO.
Air and Waste Management Association, Pittsburgh, PA. Paper 99.95, 1999

Open-path Fourier transform infrared (OP-FTIR) spectroscopy can promptly measure numerous chemicals, which makes this system more competitive and efficient than conventional analytical methods. However, spatial variations of airborne concentrations along the beam path are difficult to estimate, which hinders identification of emission sources. A two-dimensional searching model was developed to counter this difficulty. Two sets of OP-FTIR spectrometers were used to measure several horizontal and vertical beam paths to thoroughly cover a plant site. Scans of each beam path were taken continuously for at least 15 minutes to collect representative data for continuous emission sources. The major emission sources were evaluated via point-source monitoring methods. The model has been applied in a petrochemical plant, and the hit of searching within the acceptable variation range of emission sources was 100%. The average time required to locate the major emission sources in a 105,000 square meter plant site was approximately 3.25 hours.

A Field Study Using Open-Path FTIR Spectroscopy to Measure and Map Air Emissions from Volume Sources
Piper, A.R.; L.A. Todd; K. Mottus.
Field Analytical Chemistry and Technology, Vol 3 No 2, p 69-79, 1999

In this study, open-path Fourier transform infrared (OP-FTIR) spectrometer measurements and point samplers were used to evaluate two short-term refined Gaussian dispersion models for predicting the fate of volume source emissions. These data also were used for a pilot Environmental CAT scanning system using two scanning OP-FTIR spectrometers and eight retroreflectors. An environmental CAT scanning system processes a network of intersection OP-FTIR spectrometers using a tomographic reconstruction algorithm that converts real-time measurements to two-dimensional chemical concentration maps of an area. As described in this paper, the authors evaluated the Industrial Source Complex-Short Term (version 3) (ISCST) model and the American Meteorological Society/Environmental Protection Agency Regulatory Model Improvement Committee (AERMOD) model.

Field Test of an UV-DOAS System for Remote Sensing of Hazardous Air Pollutants
Wadden, R.A. (Univ. of Illinois at Chicago School of Public Health), L.L. Lardizabal, P.A. Scheff; D.K. Kenski, (formerly U.S. EPA, Region 5).
U.S. EPA National Environmental Monitoring Technology Conference, 19-20 September 2000, Boston, Massachusetts

The purpose of this project was to demonstrate and evaluate the use of the UV-DOAS (ultra-violet differential optical absorption spectrometer) for remote detection of benzene, toluene, and m-xylene. Monitoring was carried out on 11 days in the Spring of 2000 at the Paxton landfill in southeast Chicago during capping and slope stabilization activities. Ozone and nitrogen dioxide were also measured with the system. The UV projector and receiver, 232 meters apart, were located along the fenceline of the landfill. The system was operated to detect air pollutant concentrations every three minutes. As a check on the measurements, 71 hour-long samples of ambient air were collected in electro-polished stainless steel canisters. Generally, three canisters were filled simultaneously, each located along the beam at different distances from the UV projector. Samples were analyzed for organics using Method TO-14 (gas chromatography / flame ionization detection). In addition, data from continuous monitors for ozone and nitrogen oxides located at the site were compared with the UV-DOAS measurements. Hourly NO₂ concentrations from the UV-DOAS were strongly associated with the reference method measurements (TECO 42). The slope of the least square fit of the data was 1.01 and r2 = 0.69 for 225 observations. Ozone concentrations were also strongly associated with r2 = 0.67 for 233 points; but the slope of the least squares line was only 0.69. On average the UV-DOAS system reported lower values for O₃. Based on 70 hourly canister samples, the UV-DOAS measurements for benzene, toluene, and m-xylene were not associated with ambient concentrations determined by gas chromatography. The lack of association could not be ascribed to any obvious cause, such as lack of calibration, or variation in the three simultaneously collected canister samples. In addition, the average values reported by the system were consistently a factor of 10 higher than the canister concentrations. The UV-DOAS system also proved difficult to maintain consistently because of its extreme sensitivity to vibration. The temporary nature of the project prevented the installation of a permanent, fixed platform. Instead, the projector was bolted to a wooden pallet, secured to the roof of a trailer, and the receiver was located near an open window inside a second trailer. High winds at the landfill often disturbed the alignment of the projector. Consequently, frequent site visits were required to realign the projector and the receiver. Other maintenance problems involved the replacement of the projector's power supply, mirror, and xenon lamp, and eliminating corrosion on the anode and cathode connectors to the lamp. Experience suggests that the UV-DOAS is reliable for NO₂ and O₃, but is not useful for measurements of BETX compounds. Maintenance of the system required much more time than was originally anticipated. The system also requires a permanent, stable platform for optimum performance and reliability, which may be difficult to provide in typical remediation situations.

First Results of Ambient Air Measurements with Different Remote Sensing Systems over a Lake in Germany
Lamp, T.; A. Ropertz; K. Weber; G. van Haren; A. Fischer, Univ of Applied Sciences Duesseldorf, Duesseldorf, Germany.
Proceedings of the 1998 Environmental Monitoring and Remediation Technologies Conference. 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 162-173, 1999

In the summer of 1998 a measurement campaign was performed at the lake Baldeney See in the south of the city of Essen in Germany for the intercomparison of several different remote sensing systems in real field measurements and the determination of the ozone levels during summer. This paper presents early results comparing data from the following remote sensing systems: open-path FTIR, DOAS, and TDL.

A Frequency Agile Bandpass Filter for Direct Detection Lidar Receivers
Gittins, C.M.; W.G. Lawrence; W.J. Marinelli, Physical Sciences, Inc., Andover, MA.
Applied Optics, Vol 37 No 36, p 8327-8335, 1998

This paper discusses the development of a frequency agile receiver for CO₂ laser-based differential absorption lidar (DIAL) systems. The receiver is based on the insertion of a low-order tunable etalon into the detector field of view. The incorporation of the etalon into the receiver reduces system noise by decreasing the instantaneous spectral bandwidth of the IR detector to a narrow wavelength range centered on the transmitted CO₂ laser line, thereby improving the overall D* of the detection system. A consideration of overall lidar system performance results in a projected factor of 2 to 7 reduction in detector system noise, depending on the characteristics of the environment being probed. These improvements can help extend the ability of DIAL to monitor chemical releases from long stand-off distances.

Link: http://www.psicorp.com/html/pubs/PDF/sr-0919.pdf

FTIS Measurements of Hydrocarbon Emissions Due to Natural Gas Production
Haus, R. (DLR Inst. of Planetary Exploration, Berlin, Germany); J. Heland (Franhofer Inst. for Atmospheric Environmental Research, FRG), K. Schafer.
Proceedings of the 1998 Conference on Spectroscopic Atmospheric Environmental Monitoring Techniques Conference, 21-22 September 1998, Barcelona, Spain.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 56-63, 1998

Fourier-transform infrared spectroscopic (FTIS) measurements were performed at natural gas production facilities to study facility potential to release hydrocarbons into the atmosphere. The measurements were taken with a commercial, moderate-resolution, mobile Fourier spectrometer. Gas concentrations in the post-combustion zone above a flare were determined applying a multicomponent air pollution software based on radiative transfer line-by-line calculations and least-squares fit procedures. Emission rates were calculated on the basis of measured concentrations and known fuel flow rates to the flare. Diffuse emissions of the processing area were examined via open-path absorption measurements and Gaussian dispersion modeling. The flare combustion efficiencies were generally above 99% and indicate only a small local environmental impact of methane emissions due to natural gas flaring. Comparatively high diffuse emissions due to site leakages were found to exceed the flare emissions by a factor of about 25.

Fugitive Emission Monitoring with Open-Path FTIR at Times Beach, Missouri, City Park
Taylor, Richard; James Brunnert, Missouri Dept. of Natural Resources.
Environmental Monitoring and Remediation Technologies, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 2-8, 1999

During the cleanup of dioxin-contaminated soils from the Times Beach, Missouri, Superfund site, investigations found that approximately 12,000 square feet of soil was contaminated by toluene, ethylbenzene, and xylenes. This paper outlines the open-path FTIR air monitoring procedures used to monitor the perimeter of the excavation and stockpile areas for the protection of off-site workers and the public during the project and the difficulties encountered while sampling at the site.

General-Purpose Lidar System Computer Model with Experimental Verification with Fog/Oil/Smoke Conditions
Giles, J.W. ( Johns Hopkins Univ., Baltimore, MD), I.N. Bankman, R.M. Sova, W.J. Green, Jr., T.F. King, J.F. Marcotte, D.D. Duncan; John A. Millard (Raytheon Electronic Systems, Tucson, AZ).
Lidar Remote Sensing for Industry and Environment Monitoring II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4484, p 178-185, 2001

This paper describes a general-purpose remote sensing lidar system model developed for use with aerosol targets as well as hard targets in various atmospheric conditions and battlefield aerosol smoke conditions. A description of the model with equations, some of the aerosol parameters, and the results of experimental validation of the model for a hard target in military fog oil smoke are presented.

Generation of Front-Surface Low-Mass Epoxy-Composite Mirrors by Spin-Casting
Richardson, R.L.; P.R. Griffiths, Command Technologies Inc., Satellite Beach, FL.
Optical Engineering, Vol 40 No 2, p 252-258, Feb 2001

A project was undertaken to make spin-cast mirrors for use as reflectors, telescopes, and cat's-eyretroreflectors in open path Fourier transform infrared (OP/FT-IR) spectrometry. The mirrors were designed for portable outdoor use and optimized for minimal mass and maximum ruggedness and mechanical strength. After spin-casting, the only preparation prior to silvering was a thermal post-cure. The authors discuss the materials, hardware, and procedures used to spin-cast paraboloidal mirrors.

Generation of Synthetic Background Spectra by Filtering the Sample Interferogram in FT-IR
Espinoza, Luis H.; Thomas M. Niemczyk (Dept. of Chemistry, Univ. of New Mexico, Albuquerque); Brian R. Stallard.
Applied Spectroscopy, Vol 52 No 3, p 375-379, Mar 1998

The authors present a method of generating a background spectrum based on filtering the analyte features from the sample spectrum. When the filtering method is used, the accuracy of the results obtained is found to be dependent upon the analyte peak width, peak height, and type of filter employed. This paper offers guidelines for the use of this background generation technique for quantitative determinations.

Industrial Applications of Optical Sensing
Tate, J.D.; P. Chauvel; M. Walsh; K. Taylor, Dow Chemical Co., La Porte, TX.
Air and Waste 90th Annual Meeting and Exhibition, 8-13 June 1997, Toronto, Canada.
Air and Waste Management Association, Pittsburgh, PA. Paper 97.RA141.06, 1997

As an alternative to point sampling, optical sensing technology allows the user to monitor a large region of space in a short period of time, often less than a few minutes. The data available from this technology can be used to detect fugitive emissions, emissions during maintenance procedures and emissions which could lead to process outages. One example is the use of open-path FTIR to monitor ambient air. Optical sensing is a valuable tool for determining the origin, identity and amounts of fugitive emissions in a plant environment. One of the conclusions of the evaluations is that optical sensing (e.g., OP-FTIR) allows for real-time monitoring of gaseous emissions over a large region of space and so can provide a cost-effective means to meet ambient air monitoring objectives. The authors describe benefits derived from using optical sensing over more traditional methods, such as the lower long-term cost-of-ownership over electrochemical or GC monitoring.

Industrial Site Particulate Pollution Monitoring with an Eye-Safe and Scanning Industrial Fiber Lidar
Belanger, B.; A. Fougeres; M. Talbot; J. Cormier, Institut National d'Optique, Canada.
Water, Ground, and Air Pollution Monitoring and Remediation, 6-7 November 2000.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4199, p 67-76, 2001

The Institut National d'Optique of Canada has developed an eye-safe, portable, industrial fiber lidar (IFL) for particulate pollution monitoring on industrial sites. At the port facility of an aluminum plant during boat unloading, materials like bauxite, alumina, spathfluor, and calcined coke having mass extinction coefficients ranging from 0.53 to 2.7 m2/g can be detected. The lidar measurements have been compared to high volume samplers. Based on these comparisons, it has been demonstrated that the IFL is able to monitor the relative fluctuations of dust concentrations and can be integrated to the process control of the industrial site for alarm generation when concentrations are above threshold.

Innovative Approach for Estimating Fugitive Gaseous Fluxes Using Computed Tomography and Remote Optical Sensing Techniques
Hashmonay, R.A.; M.G. Yost.
Journal of the Air and Waste Management Association, Vol 49 No 8, p 966-972, 01 Aug 1999

The authors have combined computed tomography (CT) with path-integrated optical remote sensing (PI-ORS) concentration data in a new field beam geometry. This paper presents a new approach to quantify emissions from fugitive gaseous air pollution sources.

Instrumentation for Multiplex Spectroscopic Sensing. Appendix A: Spectroscopic Diagnosis of Chemical Processes: Applications of Optical Parametric Oscillators. Appendix B: Optical Heterodyne Signal Generation and Detection in Cavity Ringdown Spectroscopy Based on a Rapidly Swept Cavity
Orr, Brian J., Macquarie Univ North Ryde (Australia).
DTIC Order No: ADA386165. 42 pp, Jan 2001

This report discusses an effort to develop novel radiation techniques for remote spectroscopic sensing applications of interest to the USAF. The project applies tunable lasers and nonlinear-optical devices to spectroscopic sensing of gases in the atmosphere or elsewhere via remote sensing methods such as long-path absorption or DIAL/ Lidar (ground-based, airborne, or satellite-based). Another useful approach comprises probe-based sensing, in which a central control unit is connected optoelectronically to one or more optical probe modules that can sample traces of specific gases in industrial or environmental settings. Attainment of objectives in these areas met with mixed success. Progress on a proposed novel approach to multiple-wavelength remote sensing has been disappointingly slow, with many technical problems still to be solved. Offsetting this negative outcome is highly satisfactory progress in developing another innovative laser-spectroscopic technique that is amendable to probe- based sensing.

The full text of this report is available in PDF through the DTIC search engine at http://stinet.dtic.mil/str/tr_fields.html

Instrumentation for Optical Remote Sensing
Kagann, Robert H., AIL Systems Inc, Deer Park, NY.
Proceedings of the 1997 Air & Waste Management Association's 90th Annual Meeting & Exhibition, 8-13 June 1997, Toronto, Canada. Paper 97-RA141.03

The analytical techniques for spectroscopic air-quality measurements made either in the infrared (IR) or the ultraviolet (UV) regions of the spectrum are almost identical. The instrumentation for IR and UV share some commonality in the optical design, but the optical components, the sources, and the detectors are very different, with dispersive (grating) spectrometers typically used in the UV systems and Michaelson interferometers (FTIR) in the IR systems. Three basic configurations--open-path, extractive, and open-cell--are used for environmental measurements. Both UV and FTIR can be open-path systems, the extractive systems are mainly FTIR, and the open-cell systems are mainly UV. This paper describes the different designs and design trade-offs for these systems, along with brief descriptions of tuneable diode laser (TDL) and non-dispersive optical sensors.

Intercomparison of Different Remote Sensing Systems: FTIR, DOAS and TDL
Lamp, T.; A. Ropertz; M. Mueller; G. van Haren; K. Weber; A. Fischer, Fachhochschule Duesseldorf, Duesseldorf, Germany.
Proceedings of the 1999 Environmental Sensing and Applications Conference, 14-17 June 1999, Munich, Germany.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3821, p 384-394, 1999

In the summer of 1998 a measurement campaign was performed at the lake Baldeney See to the south of the city of Essen in Germany to compare several different remote sensing systems in real field measurements and to determine ozone levels during summer. This paper examines the results of the intercomparison of open-path FTIR, DOAS, and TDL for remote sensing and presents a new automatic background generation routine for analyzing the FTIR spectra.

Investigation of the Emission of Monocyclic Aromatic Hydrocarbons from a Wastewater Treatment Plant at Lausanne (Switzerland) by Differential Optical Absorption Spectroscopy (DOAS)
Jiménez, R. (Air Pollution Laboratory (LPAS), Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland), T. Iannone, H. van den Bergh, B. Calpini; D. Kita (Thermo Environmental Instruments Inc., Franklin, MA).
Proceedings of A&WMA 93rd Annual Conference & Exhibition, 18-22 June 2000, Salt Lake City, Utah. Paper #830, 17 pp, 2000

A measurement campaign was carried out during September 1999 in the Lausanne area to measure the contribution of wastewater treatment plants to the emission of volatile organic compounds in the area. The concentrations of monocyclic aromatic hydrocarbons over a wastewater treatment plant were monitored by differential optical absorption spectroscopy (DOAS) and gas chromatography (GC-FID). A flame ionization detector (FID) was used for monitoring the overall concentration of non-methane hydrocarbons (NMHC). A comparison is presented of the concentrations of benzene, toluene, ethylbenzene, xylenes, 1,2,4-trimethylbenzene, and phenol over the wastewater treatment plant as measured by DOAS and GC-FID.

Link: http://lpas.epfl.ch/lidar/publi/A&WMA_2000_MAH.pdf

Investigation on Infrared Laser Absorption Spectroscopy Measurement of Acetylene Trace Quantities
Chen, Weidong; J. Burie; D. Boucher, Univ. du Littoral, Dunkerque, France.
Infrared Physics and Technology, Vol 41 No 6, p 339-348, Dec 2000

A laser-based infrared spectrometer was developed for use in high-resolution spectroscopic analysis of trace gases in the atmosphere and tested on trace levels of acetylene to investigate optimal detection conditions: a trade-off choice between higher line absorption strength for sensitive detection and better spectral discrimination from lines overlapping for open path trace-gas monitoring applications. Continuous wave, broadly tunable coherent infrared radiation was generated from 8 to 19 µm in a gallium selenide crystal by laser difference-frequency mixing.

Investigations of Hot Exhaust Gases with Passive FTIR Emission Spectroscopy
Heland, J. (Fraunhofer Inst. for Atmospheric Environmental Research, FRG), K. Schaefer; R. Haus (DLR Inst. of Planetary Exploration, Berlin, FRG).
Spectroscopic Atmospheric Environmental Monitoring Techniques.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 2-10, 1998

Passive FTIR emission spectroscopy using a commercial medium resolution instrument with a telescope has been applied to analyze the hot exhaust gases of various combustion sources, such as industrial and building smoke stacks, aircraft engines, flares, and forest fires. To interpret the remotely measured spectra a multi-layer, line-by-line spectra retrieval software using the molecular spectral databases HITRAN and HITEMP has been developed, validated, and successfully used to determine the exhaust gas temperatures and the concentrations of various exhaust gases for different combustion conditions of the sources. This paper addresses the feasibility and the setup of passive IR measurements, the basic theory of radiative transfer, special features of the commercially available spectra analysis code, and the results of different measurement applications.

Localizing Gaseous Fugitive Emission Sources by Combining Real-Time Optical Remote Sensing and Wind Data
Hashmonay, R.A.; M.G. Yost, Dept. of Environmental Health, Univ. of Washington, Seattle.
Journal of the Air & Waste Management Association, Vol 49 No 11, p 1374-1379, 1999

This paper presents a new approach to localize point emissions from ground-level fugitive gaseous air pollution sources by combining smooth basis functions minimization (SBFM) with path-integrated optical remote sensing concentration data acquired along the crosswind direction in alternating beam path lengths to estimate the crosswind plume's ground-level peak location downwind from the source.

Long-Path Monitoring of NO₂ with a 635 nm Diode Laser Using Frequency Modulation Spectroscopy
Somesfalean, G.; J. Alnis; U. Gustafsson; H. Edner; S. Svanberg, Dept. of Physics, Lund Inst. of Technology, Lund, Sweden.
Applied Optics [manuscript still in draft as of 12/01]

The authors conducted an situ long-path absorption spectroscopy monitoring study of traffic-generated nitrogen dioxide emissions over a road intersection at peak traffic hours. High sensitivity was achieved by employing two-tone frequency modulation spectroscopy at a visible absorption band of NO₂ using a tunable high-power diode laser operated around 635 nm. A real-time laser absorption spectrometer was achieved by repetitively applying a rectangular current pulse to the diode laser DC drive current, allowing detection of isolated NO₂ absorption lines. A detection limit of 10 mg/cubic meter for NO₂ at atmospheric pressure with a 160 m absorption path was demonstrated.

Link: http://www.members.tripod.com/~Alnis/raksts8.pdf

Mapping Air Contaminants Indoors using a Prototype Computed Tomography System
Samanta, A.; L.A. Todd.
Annals of Occupational Hygiene, Vol 40 No 6, p 675-691, 1996

Single and multiple plumes of sulphur hexafluoride were measured and mapped using a prototype open-path Fourier transform infrared spectrometer (OP-FTIR)-computed tomography (CT) system in an indoor exposure chamber. The OP-FTIR-CT system accurately mapped the position of concentration peaks at different locations in the chamber, and estimated concentrations within a range of 4-50% when compared with point samples measured by gas chromatography with an electron capture detector. Two OP-FTIR spectrometer configurations, one with 100 rays and the other with 136 rays, were used to scan the chamber and reconstruct the concentration maps. Ray configuration and time to scan the entire chamber were found to have a profound effect on the quality of the reconstructed maps. The ability to obtain real-time, non-invasive measurements, and to generate spatially and temporally resolved maps of multiple chemicals, makes the OP-FTIR-CT system a promising technique for monitoring source emissions and evaluating exposures to air contaminants in a workplace.

Mapping Air in Real-Time to Visualize the Flow of Gases and Vapors: Occupational and Environmental Applications
Todd, L.A., Univ. of North Carolina at Chapel Hill.
Applied Occupational and Environmental Hygiene, Vol 15 No 1, p 106-113, 2000

This paper describes an open-path method for measuring and mapping pollutants in air in real time that can be used for visualizing the flow of gases and vapors in both indoor industrial and outdoor environmental applications. This method uses open-path Fourier transform infrared (OP-FTIR) spectrometry and computed tomography for real-time mapping of concentrations of chemicals in air. These maps provide near real-time visualization of contaminant generation, movement, concentrations, and emission rates for multiple chemicals simultaneously at low limits of detection. In a field study, field-generated tomographic maps were compared with concentrations estimated using the Industrial Source Complex-Short Term (ISCST) model, with fairly good correlations (R2 =0.67) found between the five-minute overall-average cell concentrations in the tomographic and ISCST model maps. Overall, the tomographic map concentrations over-predicted the ISCST model concentrations by 24%.

Mapping Air Pollutants at Hanford's Tank Farms Using Optical Remote Sensing
Hashmonay, Ram A.; Michael G. Yost; Robert S. Crampton, Dept. of Environmental Health, Univ. of Washington, Seattle.
Responsive Science: Forging Regulatory Resolution at DOE Sites Workshop, Washington, DC, 2000: Consortium for Risk Evaluation with Stakeholder Participation

The researchers have developed a novel method for mapping air-pollution with a path-integrated optical remote sensing (ORS) systems. In preliminary studies, tank farm emissions in the 200 east area were monitored using open-path Fourier transform infrared (OP-FTIR) spectroscopy. The AW farm primary tank ventilation stack and the C farm stacks measurements provided baseline concentration and emission data when no waste transfer or removal activities were taking place. Ammonia concentrations were low from the human exposure perspective, except for the immediate area of tank C-103 where concentrations could have exceeded the TLV-STEL. Another monitoring event occurred during a sluicing process test in tank C-106. This test aimed to drive hydrocarbon emissions to high levels (up to 400 ppm) which were detected in the stack during sluicing with an organic vapor analyzer (OVA). During the 8-hour test process, the OP-FTIR real-time total hydrocarbon measurement through the stack outlet correlated very well with the OVA data. Further, nitrous oxide concentrations were highly correlated to the total hydrocarbon concentrations over the same time period, which suggests that nitrous oxide might be a suitable tracer gas for mapping the hydrocarbons to assess worker exposure to hydrocarbons in the vicinity of the tank farm. OP-FTIR has the capability of identifying and detecting a wide range of gases, but it is limited in range and sampling time. When measurements are desired only for one or two gases (like nitrous oxide), a simpler and more cost-effective ORS system like a tunable diode laser (TDL) could be devised. A TDL system when coupled with our novel mapping techniques could provide real-time maps of the gas distribution over the entire 200 East or West areas.

Link: http://www.cresp.org/dcwrkshp/posters/pst_han7/pst_han7.html

Mapping Chemicals in Air Using an Environmental CAT Scanning System: Evaluation of Algorithms
Samanta, A.; L.A. Todd, University of North Carolina, Chapel Hill.
Atmospheric Environment, Vol 34 No 5, p 699-709, 2000

A technique called Environmental CAT Scanning combines the real-time measuring technique of open-path Fourier transform infrared spectroscopy with the mapping capabilities of computed tomography to produce two-dimensional concentration maps. A network of open-path measurements is obtained over an area, and measurements are then processed using a tomographic algorithm to reconstruct the concentrations. Recent research has focused on the process of evaluating and selecting appropriatreconstruction algorithms for use in the field by using test concentration data from both computer simulation and laboratory chamber studies.

Mapping the Air in Real-Time to Visualize the Flow of Gases and Vapors: Occupational and Environmental Applications
Todd, Lori A., Univ. of North Carolina School of Public Health, Chapel Hill
Applied Occupational & Environmental Hygiene, Vol 15 No 1, p106-113, Jan 2000

A method for determining chemical concentrations in an area in near real time combines open-path Fourier transform infrared spectroscopy to scan an area and measure average concentrations with the mapping capability of computed tomography. A tomographic reconstruction algorithm applied to the average concentration measurements to reconstruct two-dimensional chemical concentration maps of the study area allows a map to be generated in a matter of minutes on a personal computer. Concentrations of multiple chemicals can be resolved in near real-time for an entire area with far fewer measurements than would be required using conventional point samplers, as has been indicated by results from chamber and field studies conducted to evaluate the system.

Maximizing the Use of Open-Path FTIR for 24 -Hour Monitoring Around the Process Area of an Industrial Chemical Facility
Perry, Stephen H.; Patrick L. McKane; Douglas E. Pescatore; Amy E. DuBois. Presented at the Air & Waste Management Association Annual Meeting, San Francisco, CA, September 1995.

Abstract not available.

Measurement and Speciation of Fluoride Emissions at a Phosphate Fertilizer Manufacturing Plant Using Open-Path FTIR and TDL
Ball, Mike (Terra Air Services/Petris Technology, Houston, TX); Darin Howe (SF Phosphates Limited Co., Rock Springs, WY); Jim Bauer (Boreal Laser, Inc., Spruce Grove, Alberta).
The 92nd Annual Air & Waste Management Association Meeting & Exhibition, June 1999, St. Louis, MO, 10 pp.

As part of a plant expansion permitting strategy, SF Phosphates Co. (SFP) decided to perform a series of open-path Fourier transform infrared (FTIR) measurements. The measurements were undertaken to speciate the fluoride emissions from the phosphogypsum storage area at SFP's Wyoming phosphate fertilizer complex and thereby determine the relative percentages of hydrogen fluoride (HF) and silicon tetrafluoride (SiF4) present in the total fluoride emissions from this area source. This paper discusses the findings of the fluoride speciation project and compares results and strengths of the measurement techniques.

Measurement of Ambient Air Quality in Urban Settings Using Open-Path FTIR
Kagann, R.H.; W.L. Woturski; W.T. Walter; D. Robert; M. Robert, AIL Systems, Inc., Deer Park, NY.
Air and Waste 92nd Annual Meeting and Exhibition, 20-24 June 1999, St. Louis, MO.
Air and Waste Management Association, Pittsburgh, PA. Paper 99.435, 1999

Recent improvements in signal processing techniques for open-path FTIR (OP-FTIR) have resulted in a dramatic reduction of detection limits for infrared-active chemicals, including ambient species. A RAM2000 system was deployed over a seven-day period to measure ambient air quality in an urban-industrial environment at worst-case hot and humid conditions to test the application of OP-FTIR technology to urban air monitoring.

Measurement of Aromatic Hydrocarbons with the DOAS Technique
Axelsson, Hakan; Hans Edner; Anders Eilard; Annika Emanuelsson; Bo Galle; Kenrik Kloo; Par Ragnarson, Swedish Environmental Research Inst., Goteborg, Sweden.
Applied Spectroscopy, Vol 49 No 9, Sep 1995

This project includes a study of the differential absorption characteristics, between 250 and 280 nm, of twelve light aromatic hydrocarbons representing major constituents in technical solvents used in the automobile industry. Spectral overlapping between the different species, including oxygen, ozone, and sulfur dioxide, has been investigated and related to the chemical structure of the different aromatics. Due to spectral overlapping, interference effects in the long-path DOAS (differential optical absorption spectroscopy) application have been investigated both in quantitative and qualitative terms using data from a field campaign at a major automobile manufacturing plant.

Measurement of Atmospheric Trace-Gases with UV-DOAS Systems
Bacher, Michael [Thesis], Technical University Graz, Institut für Verbrennungskraftmasch. und Thermodynamik, 1998

Some of the most important polluted gases from road traffic are the non-methane volatile organic compounds (NMVOCs). Benzene, toluene, and the xylenes also fall under NMVOCs. These compounds can be detected by UV-DOAS. With a UV-DOAS measurement system developed by the company OPSIS, it is possible to measure atmospheric trace-gases by open path equipment. The results can be verified by comparison measurements. At the ambient air quality measurement there are cross-sensitivities between ozone and benzene, and benzene and toluene. These cross-sensitivities can be minimized by a mathematical correction. The cross-sensitivity correction is independent of the length of the measurement path.

Measurement of Formaldehyde (HCHO) by DOAS: Intercomparison to DNPH Measurements and Interpretation from Eulerian Model Calculations
Jiménez, R. (Air Pollution Laboratory (LPAS), Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland), A. Martilli, I. Balin, H. van den Bergh, B. Calpini; B.R. Larsen (Environment Institute (EI), European Commission Joint Research Center (JRC), Ispra, Italy); G. Favaro (Inst. of Env. Protection and Agriculture (IUL), Bern, Switzerland); D. Kita (Thermo Environmental Instruments Inc., Franklin, MA).
Proceedings of A&WMA 93rd Annual Conference & Exhibition, Salt Lake City (UT), June 18-22. Paper #829, 15 pp, 2000

The researchers present and compare formaldehyde measurements obtained in spring 1998 in the Milan area by two different techniques, a long-path UV visible absorption spectroscopic system (DOAS) and a sampling technique (DNPH). Despite having different spatial and time resolution, DOAS and DNPH measurements of formaldehyde compared fairly well. The formaldehyde concentration time series retrieved from DOAS were analyzed with respect to meteorological conditions, particularly regarding heterogeneous removal processes, and the concentration of other air pollutants associated with formaldehyde emission and production. Pollutant dynamics calculations, made with a 3D photochemical grid (Eulerian) model over a wide spatial domain, were compared to the measurements and provided a basis for the interpretation of the formaldehyde measurements performed during an intensive observation period.

Link: http://lpas.epfl.ch/lidar/publi/A&WMA_2000_HCHO.pdf

Measurement of Municipal Waste Site Emissions with the Open-Path FTIR Measurement Technique
Lamp, Torsten (Fachhochschule Duesseldorf, Duesseldorf, Germany); M. Douard; J. Kaizik; G. van Haren; K. Weber.
Proceedings of the 1998 91st Annual Meeting & Exposition of the Air & Waste Management Association, 14-18 June 1998, San Diego, CA.
Air & Waste Management Assoc, Pittsburgh, PA. Paper 98-TA19B.06, 15pp, 1998

The German standard 'TA Siedlungsabfall' dictates that the emissions of municipal waste sites be measured at regular intervals. Measurements at a waste site in Germany confirmed the performance of the open-path FTIR (OP-FTIR) measurement method for this application.

Measurements of Sulfur Dioxide and Formaldehyde in Taipei Using a Differential Optical Absorption Spectrometer
Mathew, Lizamma; Wu R. Tai; Jiunn-Guang Lo, Dept. of Atomic Sciences, National Tsing Hua Univ.,
Hsinchu, Taiwan, Republic of China.
Journal of the Air & Waste Management Association, Vol 51 No 1, p 94-101, Jan 2001

This paper details the results of a 1999 air quality study in Taipei, Taiwan, an area of stagnant air due to its location in a basin. Measurements were made using a differential optical absorption spectrometer (DOAS). The researchers conclude from the results that DOAS can replace conventional measurement techniques and, in some cases, give better representative results.

Measurements of Water Vapor, Surface Ozone, and Ethylene Using Differential Absorption Lidar
Jain, Sohan L.; B.C. Arya; Arun Kumar, National Physical Lab., New Delhi, India.
Lidar Remote Sensing for Industry and Environment Monitoring.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4153, p 305-313, 2001

A differential absorption lidar system using a tunable CO$-2$/ laser has been designed and developed at National Physical Laboratory, New Delhi, to monitor minor gas constituents in the atmosphere. This paper describes the experimental setup and the results obtained.

Measuring Chemical Emissions Using Open-path Fourier Transform Infrared (OP-FTIR) Spectroscopy and Computer-Assisted Tomography
Todd, L.A.; M. Ramanathan; K. Mottus; R. Katz; A. Dodson; G. Mihlan, Dept. of Environmental Sciences and Engineering, Univ. of North Carolina at Chapel Hill.
Atmospheric Environment, Vol 35 No 11, p 1937-1947, 2001

This paper reports on a large-scale, multi-seasonal field study to measure nitrogen emissions from an extensive swine confinement facility. The study measured emission rates using tracer gases and a horizontal network of open-path Fourier transform infrared (FTIR) optical rays placed less than a meter above the surface of an approximately 6-acre swine waste lagoon in Eastern North Carolina to simultaneously monitor ammonia and tracer gases every two minutes. The open-path measurements were combined with the mathematical mapping techniques of computer-assisted tomography (CAT) to create two-dimensional concentration maps of the gases for the entire lagoon surface. The study not only provided nitrogen emission rate measurements using a new technology able to measure concentrations over large areas in real time, it was the first large-scale outdoor field study to use this technique.

Measurements with UV-DOAS in a Street Tunnel for Validation of Emission Factors for Road Vehicles
Rodler, Johannes; P.J. Sturm; B. Lechner, Technical Univ. of Graz, Graz, Austria.
Sensors, Systems, and Next-Generation Satellites IV, Barcelona, Spain.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4169, p 422-431, 2001

Tunnel experiments to measure automobile emissions were carried out in the 10-km-long Plabutschtunnel near Graz, Austria, in 1998 and 1999. A UV-DOAS system operated in open-path mode ~4 km inside the tunnel with pathlengths of 220 m to 430 m. A comparison of NO₂ measurements was performed with a standard chemiluminescent analyzer (point measurement) and the DOAS system (open-path measurement). A standard air quality monitoring system (AQM) in a container was installed in a niche inside the tunnel on one end of the DOAS path. The analysis of data showed good agreement of emissions derived from the measurements with the existing PC and HDV emission factors for CO, however, this was not the case for benzene and NOx emissions obtained from heavy-duty vehicles.

Millimeter-Wave Radar Sensing of Airborne Chemicals
Gopalsami, N.; A.C. Raptis, Energy Technology Division, Argonne National Laboratory, Argonne, IL.
IEEE Transactions on Microwave Theory and Techniques, Vol 49 No 4I, p 646-653, Apr 2001

This paper discusses the development of a millimeter-wave radar chemical sensor for applications in environmental monitoring. The authors investigated the use of fingerprint-type molecular rotational signatures in the millimeter-wave spectrum to sense airbornchemicals. The millimeter-wave sensor, operating in the frequency range of 225-315 Ghz, can work under all weather conditions and in smoky and dusty environments. The basic configuration of the sensor is a monostatic swept-frequency radar that consists of a millimeter-wave sweeper, a hot-electron bolometer or Schottky barrier detector, and a corner-cube reflector. Chemicals situated between the transmitter/detector and reflector are scanned, and the millimeter-wave absorption spectra of the chemicals are determined by measuring the swept-frequency radar return signals with and without the plume in the beam path. The problem of pressure broadening has been mitigated by designing a fast-sweeping source over a broad frequency range. Thheart of the system is a backward-wave oscillator (BWO) tube that can be tuned over 220-350 Ghz. Using the BWO tube, the researchers built a millimeter-wave radar system and field-tested it at DOE's Nevada Test Site in Nevada at a standoff distance of 60 m. The millimeter-wave system detected chemical plumes very well; detection sensitivity for polar molecules such as methyl chloride was down to 12 ppm for a 4-m two-way path length.

Mini-Raman Lidar System for Stand-Off In-Situ Interrogation of Surface Contaminants
Ray, Mark D.; J. Sedlacek; J. Arthur, Brookhaven National Lab.
Application of Lidar to Current Atmospheric Topics III.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3757, p 50-59, 1999

The Mini-Raman Lidar System (MRLS) is a `proof-of-principle' chemical sensor that combines the spectral fingerprinting of solar-blind UV Raman spectroscopy with the principles of lidar for short-range (meters to tens of meters), non-contact detection and identification of unknown substances on surfaces. The MRLS is portable and has been used both in the lab and in the field. Theoretical estimates and actual laboratory data suggest the possibility of detecting contaminants with a surface coverage of <1 g/m² at a distance of three meters for one second of signal integration. The researchers outline their plans for the development of a prototype system.

A Miniature, High-Resolution Laser Radar Operating at Video Rates
Smithpeter, C.L.; R.O. Nellums; S.M. Lebien; G. Studor, Sandia National Labs.
SPIE Aerosense 2000 Proceedings, 24-28 April 2000, Orlando, FL.
Report No: SAND2000-1548C, 8 pp, Jun 2000

The authors are developing a laser radar to meet the needs of NASA for a 5-lb, 150-cubic-inch image sensor with a pixel range accuracy of 0.1-inch. NASA applications include structural dynamics measurements, navigation guidance in rendezvous and proximity operations, and space vehicle inspection. The sensor is based on the scannerless range imager architecture developed at Sandia. This architecture modulates laser floodlight illumination and a focal plane receiver to phase encode the laser time of flight (TOF) for each pixel. The researchers believe this approach has significant advantages over architectures directly measuring TOF including high data rate, reduced detector bandwidth, and conventional FPA detection. A limitation of the phase detection technique is its periodic nature, which provides relative range information over a finite ambiguity interval. To extend the operating interval while maintaining a given range resolution, a LADAR sensor using dual modulation frequencies has been developed. This sensor also extends the relative range information to absolute range by calibrating a gating function on the receiver to the TOF. The modulation frequency values can be scaled to meet the resolution and range interval requirements of different applications. Results from the miniature NASA sensor illustrate the advantages of the dual-frequency operation and the ability to provide the range images of 640 by 480 pixels at 30 frames per second.

Link: http://www.osti.gov/bridge/product.biblio.jsp?osti_id=761044

Mobile System for Open-Path Trace Gas Detection in the Mid-Infrared Using a Raman-Shifted Cr:LiSAF Source
Wamsley, P.R.; C.S. Weimer; J.T. Applegate; S.P. Beaton; B.S. Beyer, OPHIR Corp, Littleton, CO.
Application of Lidar to Current Atmospheric Topics III, 22 July 1999, Denver, CO.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3757, p 142-150, 1999

The authors have used stimulated Raman scattering in hydrogen to shift pulsed, Cr:LiSAF laser emission from the near infrared to the mid-infrared band, as well as injection seeding the oscillator with a spectrally narrow, low-power diode laser to produce a tunable, spectroscopic grade source. Combining this laser source with transmitting and receiving optics enables double-ended, long-path DIAL measurements.

Molecular Line Absorption in a Scattering Atmosphere. Part II: Application to Remote Sensing in the O₂ A Band
Heidinger, Andrew K.; Graeme L. Stephens.
Journal of the Atmospheric Sciences, Vol 57 No 10, p 1615-1634, 15 May 2000

This paper explores the feasibility of using O₂ A-band reflectance spectra in the retrieval of cloud optical and physical properties. Analyses demonstrate that these reflection spectra are sensitive to optical properties of clouds such as optical depth tc and phase function, vertical profile information including cloud-top pressure, pressure thickness, and the surface albedo. The advantage of additional information provided by active profilers (radar and lidar) is explored. The additional profile information improves not only the retrieval of vertical profiles of extinction but also the optical properties of individual cloud layers.

Monitor Ambient Air with Optical Sensing Systems
Tate, J.D (Dow Chemical Company); P. Chauvel; K. Taylor.
Chemical Engineering (New York), Vol 104 No 6, p 110-114, 30 Jun 1997

OP-FTIR spectroscopy is gaining popularity for ambient air monitoring because of its versatility and commercial availability. Real-time monitoring of gaseous emissions over a large process area (e.g., distances of 50 meters or more) provides more data than conventional point monitoring systems that monitor smaller areas and require a recovery time between sensing events. This paper discusses how OP-FTIR works, gives cost comparisons, and reports results of an evaluation of the method.

Monitoring of Volcanic Sulphur Dioxide Emissions Using Differential Absorption Lidar (DIAL), Differential Optical Absorption Spectroscopy (DOAS), and Correlation Spectroscopy (COSPEC)
Weibring, P.; H. Edner; S. Svanberg; G. Cecchi; L. Pantani; R. Ferrara; T. Caltabiano.
Applied Physics B Lasers and Optics, Vol 67 No 4, p 419-426, Oct 1998

The total fluxes of sulphur dioxide from the Italian volcanoes Etna, Stromboli, and Vulcano were studied using optical remote sensing techniques to compare active (laser) techniques with passive monitoring. Differential absorption lidar (DIAL) measurements were implemented by placing the Swedish mobile lidar system on board the Italian research vessel Urania and sailing under the volcanic plumes. Simultaneously, the passive differential optical absorption spectroscopy (DOAS) technique was used for assessing the total overhead gas burden. Correlation spectroscopy (COSPEC) was also implemented in one of the campaigns.

Motor Vehicle Fleet Emissions by OP-FTIR
Bradley, Kimberly S.; K.B. Brooks; L.K. Hubbard; P.J. Popp; D.H. Stedman, Univ. of Denver, Denver, CO.
Environmental Science & Technology, Vol 34 No 5, p 897-899, 2000

The researchers deployed open-path Fourier transform infrared (OP-FTIR) spectroscopy to measure the variations in ambient concentrations of carbon monoxide, carbon dioxide, and nitrous oxide caused by emissions from motor vehicles at a high traffic site in the Denver metropolitan area. Comparison of the OP-FTIR data to average emissions results obtained from on-road exhaust analysis using individual vehicle remote sensing showed reasonable agreement.

Multi-Pollutant Concentration Measurements Around a Concentrated Swine Production Facility Using Open-Path FTIR Spectrometry
Childers, J.W. (ManTech Environ Technology Inc., Research Triangle Park, NC); E.L. Thompson Jr.; D.B. Harris; D.A. Kirchgessner; M. Clayton; D.F. Natschke; W.J. Phillips.
Atmospheric Environment, Vol 35 No 11, p 1923-1936, 2001

Concentration ranges of ammonia and methane were determined at a swine production facility in eastern North Carolina. Open-path Fourier transform infrared (FTIR) spectrometry was used to measure the concentrations of multiple gases in real time over relatively long paths, each of which described. Ammonia concentrations were similar to those observed at other agricultural or industrial operations, and methane concentrations were highest along the eastern berm of the waste lagoon during periods of light to minimal winds.

Multispectral Thermal Imager Mission Overview
Weber, P.G. (Los Alamos National Lab., Los Alamos, NM); B.C. Brock (Sandia National Labs., Albuquerque, NM); A.J. Garrett (Savannah River Technology Center, Aiken, SC); B.W. Smith (Los Alamos National Lab., Los Alamos, NM), C.C. Borel, W.B. Clodius, S.C. Bender; R.R. Kay (Sandia National Labs., Albuquerque, NM), M.L. Decker.
Imaging Spectrometry V.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3753, p 340-346, 1999

The Multispectral Thermal Imager (MTI) is a research and development project sponsored by DOE and executed by Sandia and Los Alamos National Laboratories and the Savannah River Technology Center and partners. The MTI mission is to demonstrate the efficacy of highly accurate multispectral imaging for passive characterization of industrial facilities and related environmental impacts from space. MTI provides simultaneous data for atmospheric characterization at high spatial resolution for environmental monitoring and other civilian applications. This paper describes the MTI mission, development of desired system attributes, some trade studies, the schedule, and overall plans for data acquisition and analysis. This effort drives the sophisticated payload and advanced calibration systems, as well as the data processing and some of the analysis tools.

Link: http://nis-www.lanl.gov/~borel/weber_spie799a.pdf

Near-Infrared Diode Laser Air Monitoring
Holdsworth, Robert J.(Univ. of Huddersfield, W. Yorkshire, UK); Philip A. Martin.
Environmental Monitoring and Assessment, Vol 52 No 1-2, p 141-148, Aug 1998

Inexpensive near-infrared diode lasers are being used to enable high sensitivity, real-time monitoring of gases both in open-path measurements of urban air quality and in industrial environments for stack emission monitoring. Individual species can be detected in a highly selective manner via overtone and combination bands of their vibrational spectra. Operating at room temperature and with simple optical components, they can be made into portable instruments, ideal for field measurements. When combined with optical fibers, they can be used for monitoring remote and possibly dangerous locations. This paper presents current progress on the development of a near-infrared diode laser system with the results of detection tests on ammonia and acetylene. Sensitivities of the order of parts per million and below have been attained.

New Approaches of Aromatic Hydrocarbon Measurements by DOAS
Platt, Ulrich, Inst. für Umweltphysik, Univ. Heidelberg, Heidelberg, Germany.
Workshop: Chemical Behaviour of Aromatic Hydrocarbons in the Troposphere, 27-29 February 2000, Valencia

It is possible to detect the strong, structured UV-absorption features of aromatic hydrocarbons by DOAS (differential optical absorption spectroscopy), for which computer-readable high-precision reference spectra are now available. Interference due to the oxygen Herzberg I system has prevented the absolute determination of aromatic-hydrocarbon concentrations in the past, but solutions to the problems are described here that now allowing the detection of a large variety of monocyclic aromatic hydrocarbons at sensitivities broadly comparable to the traditional gas chromatographic (GC) analysis. In comparison to GC, the DOAS technique offers better specificity (e.g., allowing separation of p- and m- xylene) and much higher sensitivity for phenols (including cresols) and aromatic aldehydes.

Link: http://www.physchem.uni-wuppertal.de/PC-WWW_Site/pub/valencia2000/proceedings/Platt.pdf

A New DOAS Parameterization for Retrieval of Trace Gases with Highly-Structured Absorption Spectra
Maurellis, A.N.; R. Lang; W.J. van der Zande.
Geophysical Research Letters, Vol 27, p 4069-4072, 2000

Differential optical absorption spectroscopy (DOAS) has proven to be an extremely useful technique for retrieving trace gas columns from atmospheric measurements of reflected solar irradiance. DOAS is strongly constrained by the complexity of the absorption spectral structure that may be sampled by individual pixels in a detector array (for example, in the vibration-rotation bands of many species in the visible and infrared). A spectral structure parameterization (SSP) modification to DOAS depends primarily on structure in the absorption cross-section of the atmospheric species intended for retrieval.

DOAS-SSP can be used to determine which absorption spectra are suitable for use in DOAS retrievals, as well as how to extend DOAS trace gas retrieval to those species with highly-structured absorption spectra.

New DOAS Technique Based on Acousto-Optic Spectrometer
Pozhar, Vitold E.; Vladislav I. Pustovoit, Scientific Technological Ctr. of Unique Instrumentation.
Ultraviolet Atmospheric and Space Remote Sensing: Methods and Instrumentation II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3818, p 69-76, 1999

Finding the optimum measurement algorithm formulated for acousto-optical spectrometers (AOS) exhibiting random spectral access is a problem that the authors address using the example of the measurements of substance abundance in a two-species mixture.

New Method of Elaboration of the Lidar Signal
Stelmaszczyk, K.; A. Czyzewski; A. Szymanski; A. Pietruczuk; S. Chudzynski; K. Ernst; T. Stacewicz.
Applied Physics B Lasers and Optics, Vol 70 No 2, p 295-299, Feb 2000

In lidar measurements noise and fluctuations strongly affect the results because of the rapid decrease of the signal-to-noise ratio with an increase of distance. The differential absorption lidar (DIAL) is particularly sensitive to the signal instabilities. The authors present both a method of signal acquisition that is suitable for registration of both large light fluxes and single photons, and a new method of solution of the DIAL equations. The new procedures are more stable than the traditional algorithm used for signal elaboration, and they increase the effective range of lidar measurements.

The NIST Quantitative Infrared Database
Chu, P.M; F.R. Guenther; G.C. Rhoderick; W.J. Lafferty.
Journal of Research of the National Institute of Standards and Technology, Vol 104 No 1, p 59-81, 31 Jan 1999

The U.S. EPA has developed protocol methods for emissions monitoring using both extractive and open-path FTIR measurements. Depending upon the analyte, the experimental conditions, and the analyte matrix, approximately 100 of the hazardous air pollutants (HAPs) listed in the 1990 Clean Air Act amendment can be measured. The National Institute of Standards and Technology (NIST) has initiated a program to provide quality-assured infrared absorption coefficient data based on NIST-prepared primary gas standards. For each compound, the absorption coefficient spectrum was calculated using nine transmittance spectra at 0.12 cm^-1 resolution and the Beer's law relationship. The uncertainties in the absorption coefficient data were estimated from the linear regressions of the transmittance data and considerations of other error sources such as the nonlinear detector response. For absorption coefficient values greater than 1 x 10^-4µmol/mol^-1m^-1, the average relative expanded uncertainty is 2.2%. This quantitative infrared database is currently an ongoing project at NIST, and additional spectra will be added to the database as they are acquired.

The Nonlinearity and Related Band Strength of Carbon Monoxide When Applied in Ambient Air Measurement Using Open Long-Path Fourier Transform Infrared Spectrometry
Chang, Shih-Yi; Tai-Ly Tso; Jiunn-Guang Lo, Dept. of Nuclear Science, National Tsing Hua Univ.,
Taiwan, Republic of China.
Journal of the Air & Waste Management Association, Vol 51 No 9, p 1332-1338, Sep 2001

The accuracy of CO concentration determination by open-path Fourier transform infrared (FTIR) spectrometry has been re-evaluated in detail. The working principle of the FTIR gas analyzer relies mainly on spectroscopic technique. Some of the applications use the open-path FTIR system, a fully nonsampling method. The user may sometimes find it difficult to evaluate the results of the concentration output; nevertheless, an approach can be applied to estimate the origin of errors and make some further corrections, especially for small molecules.

Novel Approach For Tomographic Reconstruction of Gas Concentration Distributions in Air: Use of Smooth Basis Functions and Simulated Annealing
Drescher, A.C.; A.J. Gadgil; P.N. Price; W.W. Nazaroff.
Atmospheric Environment, Vol 30 No 6, p 929-940, 1996

Transport and dispersion of pollutants in indoor air can be studied by controlled release and monitoring of tracer gases. This paper describes an air species measurement method based on remote optical sensing coupled with computed tomographic reconstruction. The method provides good spatial and temporal resolution of tracer gas concentrations in a sampling plane. A set of experiments is described along with a greatly improved algorithm for reconstructing concentrations.

Novel Industrial Application: Flammable and Toxic Gas Monitoring in the Printing Industry
Jacobson, Esther; Yechiel Spector, Spectrex Inc., Cedar Grove, NJ.
Proceedings of the 1999 Optical Online Industrial Process Monitoring Conference Location, 22 September 1999, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3859, p 113-118, 1999

This paper describes an open path electro-optical gas monitoring system specifically designed for in situ online monitoring of flammable and toxic atmospheres in the printing industry in general and for air-duct applications in particular. A light source and a detector located at a predetermined distance provide the basis for using different band pass filters at the absorbing channel and the non-absorbing channel to enable accurate gas detection under extreme environmental conditions, plus offering immunity to sources of heat and background light.

On Camera-Based Smoke and Gas Leakage Detection
Nyboe, Hans Olav, Ph.D. dissertation, Norges Teknisk-Naturvitenskapelige Univ., Trondheim, Norway.
Report No: NEI-NO-1102, OSTI: DE99751240. ISBN: 82-471-0259-5. 134 pp, 1999

This thesis describes the development of a passive volume gas detector able to detect leakage anywhere in the area monitored. The detector relies on an ordinary monochrome camera as sensor. Because a gas leakage may perturb the index of refraction, parts of the background appear to be displaced from their true positions, and it is necessary to develop algorithms that can deal with small differences between images. The thesis develops two such algorithms. Many image regions can be defined and several feature values can be computed for each region. The value of the features depends on the pattern in the image regions. Testing showed that observations of reference materials, gas, smoke, and human activity can be classified with fairly high accuracy. The detector measures the magnitude of pixel differences, size of detected phenomena, and image distortion. Experiments show that apparent motion caused by a gas leakage or heat convection can be detected by means of a monochrome camera. Small leakages of methane can be detected at a range of about four meters. Other gases, such as butane, where the densities differ more from the density of air than the density of methane does, can be detected further from the camera. Gas leakages large enough to cause condensation have been detected at a camera distance of 20 meters.

On the Application of Open-Path Fourier Transform Infra-Red Spectroscopy to Measure Aerosols: Observations of Water Droplets
Hashmonay, R.A; Yost, M.G.
Environmental Science & Technology, Vol 33 No 7, p 1141-1144, 01 Apr 1999

An experiment applying open-path Fourier transform infrared (OP-FTIR) spectroscopy to measure aerosols was conducted in a standard shower chamber that generated a condensed water aerosol cloud. The OP-FTIR beam acquired spectra through the cloud of water droplets. The authors matched calculated extinction spectra to measured extinction in the spectral range between 500 and 5,000 wavenumbers by using Mie theory for spherical particles. Size distribution parameters can be retrieved from OP-FTIR spectra acquired over a 1 km optical path with reasonable detection limits for aerosols with optical properties equivalent to water.

1 Kilometer Open Path Multiple Reflection System Applied in Atmospheric FTIR Trace Gas Analysis
Galle, Bo; Johan Mellqvist, Swedish Environmental Research Inst (IVL), Goteborg, Sweden.
Doktorsavhandlingar vid Chalmers Tekniska Hogskola, No 1522, 16 pp, 1999

An open path multiple reflection system with a 1 km optical path over a physical path of 25 m was constructed and adapted to a medium resolution FTIR spectrometer. The system can detect mixing ratios down to 10^-9 for specific atmospheric constituents for trace gas emission monitoring. The system has been applied in field experiments to studies of biogenic trace gas emissions, industrial fugitive emission monitoring, and industrial hygiene measurements. The system is easy to set up and align and operates effectively under severe environmental conditions.

OP-FTIR Monitoring for Ammonia Emissions in the San Joaquin Valley
Zwicker, Judith O. (Remote Sensing Air, Inc, St. Louis, MO); E. Ringler; T. Waldron; D. Coe.
Proceedings of the 1998 Environmental Monitoring and Remediation Technologies Conference, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 150-161, 1999

A pilot study was undertaken in 1997 to evaluate the use of open-path Fourier transform infrared (OP-FTIR) technology for the determination of emission factors for ammonia at a dairy farm, alfalfa field, and waste water treatment plant in the San Joaquin Valley. Point sampling using active and passive denuder samplers were also carried out. This paper describes the OP-FTIR monitoring, tracer releases, meteorological monitoring, and the resulting data.

Open-Path FTIR Data Reduction Algorithm with Atmospheric Absorption Corrections: the NONLIN Code
Phillips, W. (SpectraSoft Technology, Tullahoma, TN); G.M. Russwurm (ManTech Environmental Technology, Inc.).
Environmental Monitoring and Remediation Technologies, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 194-203, 1999

Problems that affect FTIR open-path data quality include the inability to obtain a true I degree or background, spectral interferences of atmospheric gases such as water vapor and carbon dioxide, and matching the spectral resolution and shift of the reference spectra to a particular field instrument. The NONLIN algorithm is based on a non-linear fitting scheme and is not constrained by many of the assumptions required for the application of linear methods such as classical least squares (CLS). Although applications of the algorithm have proven successful in circumventing open path data reduction problems, there exist temperature and water partial-pressure effects that should be incorporated into the NONLIN algorithm for accurate quantification of gas concentrations.

Open-Path FTIR Measurement of Criteria Pollutants and Other Ambient Species in an Industrial City
Kagann, Robert H. (AIL Systems Inc., Deer Park, NY); C.D. Wang; K.L. Chang (Le and Der Co. Ltd.); C.H. Lu.
Environmental Monitoring and Remediation Technologies, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 140-149, 1999

A RAM2000™ system was deployed over a seven-day period to measure ambient air-quality in an urban-industrial environment while testing applications of open-path FTIR (OP-FTIR) technology to urban areas. Several of the ambient ozone-precursor species have poor OP-FTIR detection limits because of overlap of their infrared absorption by very strong water vapor lines. The test indicated improvements over earlier results in the detection limits of the criteria pollutants, ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Open-Path FT-IR Spectrometry: Is Completely Unattended Operation Feasible?
Griffiths, Peter R.; B.K. Hart; H. Yang; R.J. Berry, Univ. of Idaho, Moscow.
Talanta, Vol 53 No 1, p 223-231, Oct 2000

Most protocols used for open-path Fourier transform infrared spectrometry (OP/FTIR) require that spectra be measured at a resolution of 1 cm^-1 and that the concentrations of the analytes be calculated by classical least squares regression (CLS). For most volatile organic compounds in air, the rotational fine structure is not resolvable and better accuracy can be obtained when the spectrum is measured at lower resolution (typically 8 cm^-1), provided that the algorithm used for quantification is partial least squares regression (PLS). By measuring the spectrum at low resolution, the need for a liquid nitrogen-cooled mercury cadmium telluride detector is reduced and a pyroelectric detector operating at ambient temperature can be used instead. Applying PLS instead of CLS means that spectral features due to water vapor do not have to be compensated and a short-path background spectrum can be used, greatly simplifying field measurements.

Open-Path UV Fourier-Transform Gas Monitor with No Moving Parts
Lenney, J.P. (Siemens Environmental Systems Ltd, Dorset, UK); W. Hirst; M.J. Padgett; B.A. Patterson; N.K. Hedges; D. Strachan; W. Sibbett.
Pure and Applied Optics: Journal of the European Optical Society, Part A, Vol 7 No 4, p 875-887, Jul 1998

The authors report on the development of a UV Fourier transform spectrometer-based system for open-path monitoring of both hazardous and environmental gases. The device has no moving parts and is designed for unattended operation. The real-time response of the system allows for the use of maximum entropy modeling to predict the size and location of a gas leak, as has been verified by initial field tests with open-air gas releases of SO₂ and H₂S.

Open-Path UV Fourier Transform Gas Monitor with No Moving Parts
Lenney, James P. (Siemens Environmental Systems Ltd., Dorset, UK); W. Hirst (Shell Research Ltd.); M.J. Padgett (Univ. of St. Andrews); B.A. Patterson (Siemens Environmental Systems Ltd.); N.K. Hedges (Shell Research Ltd.); D. Strachan; W. Sibbett (Univ. of St. Andrews).
Spectroscopic Atmospheric Monitoring Techniques Conference.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3106, p 23-32, 1997

The authors report on the development of a UV Fourier transform spectrometer-based system for open-path monitoring of both hazardous and environmental gases. The device has no moving parts and is designed for unattended operation. Lab tests have successfully detected the present of and differentiated between SO₂ and H₂S present in a 1-meter test cell down to 1.0 ppm levels. The multiple gas feature of the instrument allows for other possible applications with regards to environmental monitoring.

Open Verdict on Air Quality
Radojevic, Miroslav, Univ. of Brunei Darussalam, SE Asia.
Chemistry in Britain, No 8, Aug 2000

During the 1990s, a novel approach to air quality monitoring using spectroscopy--known as open-path methods--gained ground. Instead of measuring pollution at a specific location, open-path methods record the average pollutant concentration along the path length of a light beam. Measurements are made in situ and there is no disturbance in the air flow due to pump sampling as with point analyzers. Open-path methods are used for the remote sensing of the atmosphere and provide better estimates of average pollutant concentrations over a given area. A single instrument can measure several components, both organic and inorganic. Different types of open-path systems include differential optical absorption spectroscopy (DOAS), Fourier transform infrared (FTIR) spectroscopy, light detection and ranging (Lidar), differential absorption lidar (Dial), and tunable diode laser spectroscopy (TDLAS). DOAS is the most widely applied open-path method used for air quality monitoring. FTIR is another commonly used open-path method. This paper discusses the different techniques.

Link: http://www.chemsoc.org/chembytes/ezine/2000/radojevic_aug00.htm

Optical Designs for Improving Performances of Aerosol Sensing Micropulse Lidars
Rubio, M. (Optical Sciences Ctr./Univ. of Arizona); J.A. Reagan (Univ. of Arizona).
Lidar Remote Sensing for Industry and Environment Monitoring II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4484, p 25-35, 2001

Micro-pulse lidars (MPLs) are designed to adhere to eye-safety restrictions while achieving acceptable signal-to-noise ratios. Accurate MPL measurements are typically only possible beyond the full overlap distance, which is usually 4 km or more. The fraction of laser beam energy that is within the receiver field of view versus range is called the overlap function. Current MPL designs have an overlap-related problem in that the majority of the atmospheric aerosols are located below an altitude of 4 km to 5 km, within the partial overlap region, nor is the overlap function thermally constant, which introduces errors in the experimentally derived overlap function and system constant factor and leads to errors in the retrieved lidar signal.

Optimal Detection and Concentration Estimation of Vapor Materials Using Range-Resolved Lidar with Frequency-Agile Lasers
Warren, R.E. (SRI International); R.G. Vanderbeek (U.S. Army Edgewood Research, Development, and Engineering Ctr.), F.M. D'Amico.
Application of Lidar to Current Atmospheric Topics III, 22 July 1999, Denver, CO.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3757, p 167-177, 1999

This paper considers range-resolved lidar with short (delta function) transmitter pulses for estimating range-dependent vapor concentration for arbitrary pulse shapes. The detection and estimation approaches are illustrated on a combination of synthetic and field test data collected at the Idaho National Engineering and Environmental Laboratory test site.

Overview of Raman Lidar Techniques for Air Pollution Measurements
Philbrick, C.R., Pennsylvania State Univ.
Lidar Remote Sensing for Industry and Environment Monitoring II.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 4484, p 136-150, 2001

Vibrational and rotational Raman lidar signals provide simultaneous profiles of meteorological data, ozone and measurements of airborne particulate matter. An operational prototype Raman lidar instrument makes use of a Nd:YAG laser to provide both daytime and nighttime measurements. This paper illustrates the utility of Raman lidar to describe the evolution of air pollution events with examples from several data sets that have been selected to show the new level of understanding of air pollution events that is being gained from applications of lidar techniques.

Practical Issues in Applying Ultra-Broadband (UB) Radiation to the Monitoring of Hazardous Air
Pollutants (HAPs) at Extended Distances
Ting, A. (Naval Research Lab., Washington, DC), J. Qiu; C. Manka (RSI, Inc., Lanham, MD).
Report No: NRL/MR/6795-00-8481, DTIC Order No: ADA385009. 13 pp, Nov 2000

The ultra-broadband (UB) radiation source being developed at the Naval Research Laboratory has the potential to become a versatile source of radiation for active remote sensing of chemical hazardous air pollutants (HAPs) at extended distances. However, before the realization of this important application of the radiation source, some practical issues involved in the research and development of the technique of UB generation and HAP detection have to be examined. These issues include the list of possible candidate HAPs for the present wavelength range of the UB radiation and the various background noise level and the related signal-to-noise ratios. This report offers a semiquantitative analysis of these issues and provide discussions on some of the complexities to be resolved.

The full text of this report is available in PDF through the DTIC search engine at http://stinet.dtic.mil/str/tr_fields.html

Project OPTEX: Field Study at a Petrochemical Facility to Assess Optical Remote Sensing and Dispersion Modeling Techniques
Paine, Robert J.; J.O. Zwicker; H. Feldman, ENSR Corp., Acton, MA.
Proceedings of the 1997 Air & Waste Management Association's 90th Annual Meeting & Exhibition, 8-13 June 1997, Toronto, Canada. Paper 97-TA33.02

The American Petroleum Institute conducted a field study at a Texas petrochemical facility in October 1996 to test the ability of optical remote sensing (ORS) techniques to characterize fugitive emissions and to assemble ambient and tracer sampler data for evaluating air dispersion models. This paper reports on the design of the OPTEX (Operational Petrochemical Tracer Experiment) field study and summarizes the measurements obtained in the field.

QA/QC Issues in OP/FTIR Monitoring
Childers, Jeffrey W.; G.M. Russwurm; E.L. Thompson Jr., Man Tech Environmental Technology, Inc., Research Triangle Park, NC.
Proceedings of the 1997 Air & Waste Management Association's 90th Annual Meeting & Exhibition, 8-13 June 1997, Toronto, Canada. Paper 97-RA141.07

Despite efforts to develop QA/QC procedures in OP/FTIR monitoring, there are still no universally accepted procedures for determining the accuracy and precision of OP/FTIR data. When the concentrations of atmospheric species are measured over a long open path, several factors can influence accuracy and precision. This paper presents a discussion of factors that influence the accuracy and precision of OP/FTIR data, and ways to recognize potential sources of errors.

Quantitative Analysis of Flue Gas FTIR-Spectra Employing a New Mathematical Method to Determine the Instrumental Line Shape
Windpassinger, R., Lehrstuhl fur Elektrische Messtechnik, Munchen, Germany.
Proceedings of the 1998 Conference on Spectroscopic Atmospheric Environmental Monitoring Techniques Conference, 21-22 September 1998, Barcelona, Spain.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 64-70, 1998

Multivariate quantitative analysis of FTIR-spectra requires that the spectral line shapes of sample spectrum and spectral reference match as closely as possible. In open-path measurements, the instrumental line shapes (ILS) generally differ because of the differences in the optical geometry of the setups, or in the case of synthetic reference spectra, because the ILS cannot exactly be determined from the measuring parameters. This article gives an overview over the parametrical model of the ILS approximation and its integration in the spectral evaluation algorithm, and presents results of their application to transmission spectra of extractive and open-path exhaust gas measurements.

Rapid Measurements and Mapping of Tracer Gas Concentrations in a Large Indoor Space
Fischer, Marc L.;, P.N. Price; T.L. Thatcher; C.A. Schwalbe; M.J. Craig; E.E. Wood, R.G. Sextro; A.J.
Gadgil, Lawrence Berkeley National Laboratory, Berkeley, CA.
LBNL-45542, 17 pp, 2000

Rapid mapping of gas concentrations in air benefits studies of atmospheric phenomena ranging from pollutant dispersion to surface layer meteorology. The researchers demonstrated a technique that combines multiple open-path tunable diode laser (TDL) spectroscopy and computed tomography to map tracer gas concentrations with approximately 0.5 m spatial and 7 second temporal resolution. Releasing CH4 in a large ventilated chamber, path-integrated CH4 concentrations were measured over a planar array of 28 "long" (2-10 m) optical paths, recording a complete sequence of measurements every 7 seconds during the course of hour-long experiments. Maps of CH4 concentration were reconstructed from the long-path data and compared with simultaneous measurements from 28 "short" (0.5 m) optical paths. On average, the reconstructed maps capture ~74% of the variance in the short path measurements. The accuracy of the reconstructed maps is limited, in large part, by the number of optical paths and the time required for the measurement. Straightforward enhancements to the instrumentation will allow rapid mapping of three-dimensional gas concentrations in indoor and outdoor air, with sub-second temporal resolution.

Link: http://eetd.lbl.gov/env/mlf/pubs/LBNL45542.pdf

Real Time Air Monitoring Using Open-Path FTIR
Gamiles, D.S., Oak Ridge Y-12 Plant, Oak Ridge, TN/Univ. of North Carolina at Chapel Hill.
Report No: Y/AMT-616. NTIS: DE00001351. 1 pp, Sep 1998

Over the last several years there has been renewed interest in the use of open-path Fourier Transform Infrared (FTIR) spectroscopy for a variety of air monitoring applications. The intersect has been motivated by the need for new technology to address the regulator requirements of the Clean Air Act Amendment of 1990. Interest has been expressed in exploring the applications of this technology to locate fugitive-source emissions and measuring total emissions from industrial facilities. No technical conclusions have been published as a result of this CRADA project.

Reduction of Stray Light in Monostatic Open-Path FT-IR Spectrometers with a Plane Correction Mirror
Richardson, R.L.; P.R. Griffiths, Univ. of Idaho, Moscow, ID.
Applied Spectroscopy, Vol 51 No 8, p 1254-1256, Aug 1997

The use of an inexpensive mirror in the beam splitter of an open-path Fourier transform infrared systems minimizes the quantitative errors due to stray light because the inserted mirror prevents radiation from reaching the wall of the beam-splitter housing. Stray radiation striking the off-axis paraboloidal detector mirror is at an angle with respect to the principal axis and is not focused onto the detector.

Remote Detection of Chemicals by Millimeter-Wave Spectroscopy
Gopalsami, N. (Argonne Natl. Lab., Argonne, IL); A.C. Raptis.
Proceedings of the 1998 Conference on Millimeter and Submillimeter Waves IV, 20-23 July 1998, San Diego, CA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3465, p 254-265, 1998

This paper discusses the development and field testing of a remote chemical detection system based on millimeter-wave (mm-wave) spectroscopy. The monostatic, swept-frequency radar consists of a mm-wave sweeper, a hot-electron-bolometer detector, and a trihedral reflector. The chemical plume to be detected is situated between the transmitter/detector and the reflector. Millimeter-wave absorption spectra of chemicals in the plume are determined by measuring the swept-frequency radar return signals with and without the plume in the beam path. The problem of pressure broadening, which hampered open-path spectroscopy in the past, has been mitigated here by designing a fast sweeping source over a broad frequency range. The heart of the system is a Russian backward-wave oscillator (BWO) tube that can be tuned over 225-315 GHz. A mm-wave sweeper that includes the BWO tube was built to sweep the entire frequency range within 10 ms. The radar system was field-tested on methyl chloride at the DOE Nevada Test Site at a standoff distance of 60 m. The system detected methyl chloride plumes down to a concentration of 12 ppm.

Link: http://www.osti.gov/servlets/purl/290799-ZlOteV/webviewable/290799.pdf

Remote Sensing of Atmospheric Pollution by Passive FTIR Spectrometry
Beil, A.; R. Daum; G. Matz; R. Harig, Technische Univ. Hamburg-Harburg, Hamburg, Germany.
EUROPTO '98 (Barcelona): Spectroscopic Atmospheric Environmental Monitoring Techniques.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 32-43, 1998

This paper describes recent experimental results obtained with a new, highly sensitive FTIR remote sensor and a data analysis method that does not require a previously measured background spectrum.

The influence of environmental and instrumental parameters on the sensitivity of the method is discussed. The authors present experimental results to illustrate the enhancement of the signal to noise ratio that can be achieved by the alignment of the spectrometer to backgrounds with a high temperature difference to the environment.

Link:http://www.tu-harburg.de/et1/Emt/Publications/europto.pdf

Remote Sensing of Organics and Other Air Pollutants Using a UV-DOAS System
Wadden, R. (Univ. of Illinois, Chicago), L. Lardizabal, P. Scheff; D. Kenski (Lake Michigan Air Directors Consortium, Des Plaines, IL).
American Industrial Hygiene Conference & Exposition, 2-7 June 2001, New Orleans, Louisiana

The purpose of this project was to demonstrate and evaluate the use of the UV-DOAS (ultra-violet differential optical absorption spectrometer) for remote detection of benzene, toluene, and m-xylene. Ozone and nitrogen dioxide were also measured with the system. Monitoring was carried out on 11 days in the Spring of 2000 at the Paxton landfill in southeast Chicago during capping and slope stabilization activities. The UV projector and receiver, 232 meters apart, were located along the fence line of the landfill. The system was operated to detect air pollutant concentrations every three minutes. As a check on the measurements, 71 hour-long samples of ambient air were collected in stainless steel canisters. Based on 70 hourly canister samples, the UV-DOAS measurements for benzene, toluene, and m-xylene were not associated with ambient concentrations determined by gas chromatography. The lack of association could not be ascribed to any obvious cause, such as lack of calibration or variation in the three simultaneously collected canister samples. In addition, the average values reported by the system were consistently a factor of 10 higher than the canister concentrations.

Sandia Multispectral Airborne Lidar for UAV Deployment
Daniels, J.W.; P.J. Hargis, Jr.; T.D. Henson; J.D. Jordan; A.R. Lang; R.L. Schmitt.
4th Joint Workshop on Standoff Detection for Chemical and Biological Defense26-30 October 1998, Williamsburg, VA.
SAND98-2386C, 11 pp, 1998

Sandia National Laboratories has initiated the development of an airborne system for W laser remote sensing measurements. System applications include the detection of effluents associated with the proliferation of weapons of mass destruction and the detection of biological weapon aerosols. This paper discusses the status of the conceptual design development and plans for both the airborne payload (pointing and tracking, laser transmitter, and telescope receiver) and the Altus unmanned aerospace vehicle platform. Hardware design constraints necessary to maintain system weight, power, and volume limitations of the flight platform are identified.

Link: http://www.osti.gov/bridge/product.biblio.jsp?osti_id=1069

Scanning Infrared Remote Sensing System for Identification, Visualization, and Quantification of Airborne Pollutants
Harig, Roland; Gerhard Matz; Peter Rusch, Technische Univ. Hamburg-Harburg, Hamburg, Germany.
Instrumentation for Air Pollution and Global Atmospheric Monitoring.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 4574, Paper No 11, 2001

For the localization of a leak and a complete assessment of the situation in the case of the release of a hazardous cloud, information about the position and the size of a cloud is essential. To this end, an imaging passive remote sensing system comprised of an interferometer (Bruker OPAG 22), a data acquisition, processing, and control system with a digital signal processor (FTIR DSP), an azimuth elevation scanning mirror, a video system with a DSP, and a personal computer has been developed. The system has a high selectivity, low noise equivalent spectral radiance, and it allows identification, visualization, and quantification of pollutant clouds.

Link: http://www.tu-harburg.de/et1/ftir/lib/scanningftir_quant.pdf

Sensor Takes Chemicals' "Fingerprints"
Mouché, Carol.
Pollution Engineering Online, Apr 1998

A chemical sensor developed by the DOE's Brookhaven National Laboratory (BNL) to detect the use of chemical weapons in terrorist attacks has the potential to be a useful tool for assessing unknown chemicals in the field. The Mini-Raman Lidar (light detection and ranging) System (MRLS) can be used to monitor industrial emissions, investigate environmental crimes, determine the effectiveness of environmental cleanups and assess the hazards of chemical fires. The mini-sensor is a 2-foot-square cube that works at short distances of a few feet to tens of feet. The device combines the latest laser and detector technology with a phenomenon known as Raman scattering. Laser light is aimed at a target and scatters off its molecules. A spectrometer analyzes the scattered light to reveal a chemical fingerprint, which is compared with other fingerprints in a computerized library. Every molecule possesses a unique spectral fingerprint that can be exploited for chemical identification. Raman spectroscopy can be used for chemicals in the gaseous, liquid, solid, or aerosol states. The system is being developed for ground/surface contamination evaluation, but it also can be used to monitor airborne emissions at short ranges. The MRLS works at ranges of three feet to tens of feet--a significantly shorter distance than the several mile ranges typically associated with lidar. The system is completely mobile. It uses an ultraviolet laser for sample illumination, a 5-inch receiver telescope outfitted with a spectrometer, and an intensified-CCD detector for signal acquisition and analysis. The entire system is controlled by a laptop and consumes less than 1000 watts of power at line voltage, with all hardware residing on a small cart. Co-inventors Dr. Art Sedlacek and Dr. Mark D. Ray have applied for a patent. The MRLS has not yet been commercialized, but the team is working on an end-user version. Contact: Art Sedlacek, BNL Dept. of Advanced Technology, 516-344-2404, sedlacek@bnl.gov.

Link: http://www.pollutionengineering.com/archives/1998/pol0401.98/suppl/technws.htm#sensor

Signal Optimization, Noise Reduction, and Systematic Error Compensation Methods in Long-Path DOAS Measurements
Simeone, Emilio (Kayser Italia S.r.l., Livorno, Italy); Alessandro Donati.
Spectroscopic Atmospheric Environmental Monitoring Techniques.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 139-147, 1998

The methods that allow long-path measurements in the UV region are presented and discussed in this paper. These methods have been assessed using SPOT, the new Italian DOAS instrument developed and manufactured by Kayser Italia. The system is equipped with a tele-controlled optical shuttle on the light source unit, allowing background radiation measurement. Wavelength absolute calibration of spectra by means of a collimated UV beam from a mercury lamp integrated in the telescope has been exploited. Also, possible thermal effects on the dispersion coefficients of the holographic grating have been automatically compensated by means of a general non-linear fit during the spectral analysis session. The DOAS technique can be used in field for very fast measurements in the 245-275 nm spectral range, on path lengths up to about 2500 m.

Simultaneous Detection of Methane, Oxygen and Water Vapour Utilising Near-Infrared Diode Lasers in Conjunction with Difference-Frequency Generation
Gustafsson, U.; J. Sandsten; S. Svanberg.
Applied Physics B Lasers and Optics, Vol 71 No 6, p 853-857, Dec 2000

An all-diode-laser-based spectrometer simultaneously detects methane, oxygen, and water vapor via a 760-nm diode laser and a 980-nm diode laser in conjunction with difference-frequency generation to 3.4 mm in a periodically poled lithium niobate crystal. Each of the output wavelengths resonates with one of the molecular species. Simultaneous recordings over a 15-meter open path of laboratory air show the wide applicability of a diode-laser-based difference-frequency spectrometer for the detection of molecular species in different wavelength ranges. By increasing the frequency of the 760-nm diode laser and decreasing the frequency of the 980-nm diode laser, a maximum continuous tuning range in the mid infrared of 3.6 cm^-1 is achieved, which enables the recording of several methane lines at atmospheric pressure. The signal-to-noise ratio in the recorded methane spectra indicates that sub-ppm detection of methane at atmospheric pressure is feasible.

Spatial and Temporal Visualization of Gases and Vapors in Air Using Computed Tomography: Numerical Studies
Bhattacharyya, R.; L.A. Todd.
Annals of Occupational Hygiene, Vol 41 No 1, p 105-122, 1997

With an optical remote sensing (ORS) and computed tomography (CT) system, two-dimensional maps of chemical concentrations in the air can be created over a confined space such as a workplace room. An ORS-CT system was evaluated using 15 simulated test maps that model the generation and dispersion of contaminant plumes over time. For this study, scanning an entire room in 10 minutes was sufficient for exposure evaluation, source monitoring, and leak detection.

Stable Gas Plume Composition Measured by OP-FTIR spectroscopy at Masaya Volcano, Nicaragua, 1998-1999
Horrocks, Lisa; M. Burton; P. Francis; C. Oppenheimer, Open Univ., Milton Keynes, UK.
Geophysical Research Letters, Vol 26 No 23, p 3497-3500, 1999

Non-eruptive plume gas composition data were collected by open-path Fourier transform infrared (OP-FTIR) spectroscopy at the summit of Masaya Volcano, Nicaragua, in 1998 and 1999. This paper reports on the collection process and technology and the results of the data analysis.

Static Fourier-Transform Ultraviolet Spectrometer for Gas Detection
Courtial, J. (Univ. of St. Andrews, Fife, Scotland); B.A. Patterson; W. Hirst; A.R. Harvey; A.J. Duncan; W. Sibbett; M.J. Padgett.
Applied Optics, Vol 36 No 13, p 2813-2817, 1 May 1997

This paper reports on the design, construction, and initial evaluation of a FTUV spectrometer based on Wollaston prisms to be used as part of an optical, open-path, gas-detection system. This type of system can satisfy accepted industry safety requirements for the detection of hazardous gases at eye-safe illumination levels.

Stationary and Time-Dependent Indoor Tracer-Gas Concentration Profiles Measured by OP-FTIR Remote Sensing and SBFM-Computed Tomography
Drescher, A.C. (Univ. of California, Berkeley, CA); D.Y. Park; M.G. Yost; A.J. Gadgil; S.P. Levine; W.W. Nazaroff.
Atmospheric Environment, Vol 31 No 5, p 727-740, Mar 1997

Measurement of gas concentrations in indoor air using optical remote sensing (ORS) and computed tomography (CT) has been suggested but not thoroughly investigated. In experiments, one time-varying and 11 different steady-state tracer-gas concentration profiles were generated in a ventilated chamber and sampled in a horizontal plane by an open-path Fourier transform infrared (OP-FTIR) spectrometer for subsequent CT inversion. CT reconstructions were performed using the recently developed smooth basis function minimization (SBFM) technique. The CT reconstructions were compared with simultaneously gathered point-sample concentration measurements. Agreement between the two sampling methods was qualitatively very good, with concentration profiles generated by both methods showing the same features of peak location and shape. Quantitative agreement was generally good to within 50%.

Theoretical Analysis of a Quasi-Distributed Optical Sensor System Using FMCW for Application to Trace Gas Measurement
Zavrsnik, Miha; George Stewart, Univ. of Maribor, Maribor, Slovenia.
Sensors and Actuators, B: Chemical, Vol 71 No 1-2, p 31-35, Nov 2000

The authors evaluated the performance of a quasi-distributed sensor system for narrow band absorbers that use the frequency-modulated continuous wave (FMCW) method, including signal-to-noise analysis. The sensor units consist of open-path micro-optic cells constructed from GRIN lenses, each of differing lengths. Interferometric mixing of two signals originating from each cell (from the glass/air interfaces) is employed to address the cells. Due to the linear frequency ramping of the source, different beat frequencies arise in the output for each cell. The interference patterns of all sensor cells add up at the detector, whereby each individual sensing cell is identified by its power spectrum in the frequency domain.

Three Dimensional, Integrated Characterization and Archival System for Remote Facility Contaminant Characterization
Barry, R.E.; P. Gallman; G. Jarvis; P. Griffiths, Oak Ridge National Lab.
8th International Topical Meeting on Robotics and Remote Systems, 25-29 April 1999, Pittsburgh, PA.
ORNL/CP-102025, 8 pp, Apr 1999

The three-dimensional integrated characterization and archival system (3D-ICAS) was developed for the purpose of rapid, field-level identification, mapping, and archiving of contaminant data. The system consists of three subsystems, an integrated work and operating station, a 3-D coherent laser radar, and a contaminant analysis unit. Target contaminants that can be identified include chemical (currently organic only), radiological, and base materials (asbestos). In operation, two steps are required. First, the remotely operable 3-D laser radar maps an area of interest in the spatial domain. Second, the remotely operable contaminant analysis unit maps the area of interest in the chemical, radiological, and base material domains. The resultant information is formatted for display and archived using an integrated workstation. A 3-D model of the merged spatial and contaminant domains cart be displayed along with a color-coded contaminant tag at each analysis point. In addition, all of the supporting detailed data are archived for subsequent QC checks. The 3D-ICAS system is capable of performing all contaminant characterization in a dwell time of 6 seconds. The radiological and chemical sensors operate at EPA regulatory levels. Base materials identification is accomplished using a molecular vibrational spectroscopy, which can identify materials such as asbestos, concrete, wood, or transite. The multipurpose sensor head is positioned robotically using a small CRS Robotics A465 arm, which is registered to the environment map by the 3-D laser radar.

Link: http://www.osti.gov/servlets/purl/4617-GF2pfB/webviewable/

Three-Wavelength UV Ozone DIAL Based on a Raman Cell Filled with Two Raman Active Gases
Simeonov, V. (Air Pollution Laboratory, Swiss Federal Inst. of Technology, Lausanne, Switzerland); B. Lazzarotto; P. Quaglia; H. van den Bergh; B. Calpini.
ILRC 2000: 20th International Laser Radar Conference, July 2000, Vichy, France

A three-wavelength UV ozone differential absorption lidar (DIAL) with a transmitter based on the use of a single Raman cell filled with two Raman active gases has been developed. The cell is filled with a mixture of hydrogen and deuterium as active gases and argon as a buffer gas, and pumped with the fourth harmonic of a Nd:YAG laser. The beams have identical spatial intensity distribution and identical temporal and power profiles. They can probe the same volume of air at the same time, which contributes to the decrease of systematic errors. With special care, the negative influence of the optical crosstalk among channels in the receiving part and the spatial non-uniformity of the receiving photo-sensors can be diminished. The component blocks of the lidar were tested. A complete test of the whole system and comparison with simultaneous tethered balloon measurements will be performed and reported.

Link: http://lpas.epfl.ch/lidar/publi/ILRC2000valio.pdf

Tomographic Reconstruction of Air Pollutants: Evaluation of Measurement Geometries
Todd, L.A.; Runa Bhattacharyya.
Applied Optics, Vol 36 No 30, p 7678-7688, 20 Oct 1997

Thirteen novel optical remote-sensing geometries for tomographically reconstructing chemical pollutants in air were evaluated in mathematical studies. The researchers examined the reconstructions generated by each geometry for locating chemical leaks, identifying plumes, and evaluating human chemical exposures. Their approach used three numerical image-quality measures for both static and time-varying concentration maps. Visual evaluation proved the most useful method of evaluating the geometries. The study demonstrates the feasibility of using geometries with only a few detectors for tomographic imaging of air pollutants.

Link: http://www.sph.unc.edu/tomography/tomographic-reconstr-1997.pdf

Tomographic Reconstruction of Tracer Gas Concentration Profiles in a Room with the Use of a Single OP-FTIR and Two Iterative Algorithms: ART and PWLS
Park, D.Y.; J.A. Fessler; M.G. Yost; S.P Levine, Hansung University, Seoul, Korea.
Journal of the Air & Waste Management Association, Vol 50 No 3, 2000

Computed tomographic (CT) reconstructions of air contaminant concentration fields were conducted in a room-sized chamber employing a single open-path Fourier transform infrared (OP-FTIR) instrument and a combination of 52 flat mirrors and 4 retroreflectors. A total of 56 beam path data were repeatedly collected for around 1 hr while maintaining a stable concentration gradient. This paper describes the algorithms applied and the results of the experiments, which indicate that this beam geometry and the use of a single OP-FTIR scanning system, in combination with the PWLS algorithm, is a system applicable to both environmental and industrial settings.

Total Emissions Monitoring Using a Multi-Beam Integrated Real-Time Remote Sensing System
Pawloski, J.N.; R.E. Gibbons, Terra Air Services, Houston, TX.
Specialty Conference on Measurement of Toxic and Related Air Pollutants, 29 April-1 May 1997, Research Triangle Park, North Carolina.
Air and Waste Management Association, Pittsburgh, PA. p 575-585, 1997

A large west coast refinery contracted with Terra Air Services to design and install a real-time emissions monitoring system utilizing open-path remote sensing technologies--FTIR, UV, and TDL units--in conjunction with concurrently collected meteorological data. The complete system incorporates two FTIR, two UV, two laser units, and six organic gas detectors. A total of thirty-four toxics are monitored with the possibility of including other species of concern when required. This paper describes system layout implementation and operational functions.

Toxic Cloud Imaging by Infrared Spectrometry: A Scanning FTIR System for Identification and Visualization
Harig, R.; G. Matz, Technische Univ. Hamburg-Harburg, Hamburg, Germany.
Field Analytical Chemistry and Technology, Vol 5 No 1-2, p 75-90, 2001

An imaging passive remote sensing system has been developed that is comprised of an FTIR spectrometer, an azimuth elevation scanning mirror, a data acquisition and control system with a digital signal processor (DSP), and a personal computer. The DSP system controls the scanning mirror, collects the interferograms of the FTIR spectrometer, and performs the Fourier transformation. The spectra are transferred to the personal computer and analyzed by a real-time identification algorithm that does not require background spectra for the analysis, with the results of the identification algorithm visualized in false color images. The system has a high selectivity, low noise equivalent spectral radiance, and it allows localization of clouds and their sources. This paper presents the automatic identification algorithm, the scanner system, the software for real time identification and imaging, and the results of field measurements.

Link: http://www.tu-harburg.de/et1/ftir/lib/scanningftir.pdf

Trends and Future Applications of Optical Remote Sensing and Computed Tomography to Map Air Contaminants
Todd, Lori A.; M.G. Yost; R.A. Hashmonay, Univ. of North Carolina at Chapel Hill, Chapel Hill, NC.
Proceedings of the 1998 Environmental Monitoring and Remediation Technologies Conference, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 399-404, 1999

In the 20 years since their development, there have been no commercial applications of combined computed tomography (CT) and optical remote sensing (ORS) due to hardware limitations and slow acceptance by the occupational and environmental scientific communities. A CT-ORS monitoring system offers the potential for near real-time mapping of multiple gases over large areas. The authors discuss potential applications of CT-ORS, such as using open-path Fourier transform infrared spectroscopy for mapping leaks and evaluating worker exposures and quantifying emission flux from a process facility. Tunable diode laser, differential optical absorption spectroscopy, or differential absorption lidar can be used to provide large-scale (greater than 1km) CT reconstructions to help locate industrial emissions and provide improved estimates of pollutant transport.

Tunable IR Differential Absorption Lidar for Remote Sensing of Chemicals
Prasad, C.R.; P. Kabro, Science & Engineering Services, Inc.
Application of Lidar to Current Atmospheric Topics III.
Proceedings of SPIE--The International Society for Optical Engineering, Vol 3757, p 87-95, 1999

The researchers are developing a differential absorption lidar (DIAL) tunable in the 3 to 5 micrometers range for detecting low concentrations of chemical species with high sensitivity (5 ppb) and accuracy measurements for greater than 5 km range. A diode-pumped ytterbium YAG laser was built for pumping and rapidly tuning an optical parametric oscillator (OPO) over the mid-infra red region. The simulated performance of the topographical IR-DIAL showed that 5 ppb concentration can be measured at 5 km range with a 35 cm telescope.

Ultraviolet Interferometry Applied to Open Path Gas Monitoring
Johnston, Jeffrey E.; E.V. Ivanov, SCI-TEC Instruments Inc, Saskatoon, Sask., Canada.
Proceedings of the 1997 ISA TECH/EXPO Technology Update, 7-9 October 1997, Anaheim, CA.
Safety Systems, Plant Protection, and Environmental Concerns ISA TECH/EXPO Technology Update
Conference Proceedings, Vol 1 No 4, p 233-240, 1997

This paper describes the principle of operation for a prototype instrument constructed to perform open path gas measurements. The instrument consists of an ultraviolet transmitter, a receiver containing four solid state interferometers, and a computer to record the data. This instrument is not sensitive to internal misalignment, vibration, and scintillation effects like conventional dual beam interferometers, due to the solid state nature of the interferometric elements. A novel gas measurement technique, correlation interferometry, enables data to be extracted in real time. The authors contrast this technology with other technologies currently used for open path monitoring. [This paper was also presented at the April 1997 ISA meeting: Ultraviolet Interferometry Applied to Open Path Gas Monitoring, Johnston, Jeffrey E.; Ivanov, Evgeniy V., SCI-TEC Instruments Inc, Saskatoon, Sask., Canada. Proceedings of the 1997 42nd Annual ISA Analysis Division Symposium, 7-9 April 1997, New Orleans, LA. p 17-24, 1997]

A Unique Application of an Extractive FTIR Ambient Air Monitoring System for the Simultaneous Detection of Multiple-ppb-Level VOCs
Cantu, A. (Westinghouse Electric Corp., Carlsbad, NM); G. Pophal (Radian International, LLC, Austin, TX), S. Hall, C.T. Laush.
Applied Physics B Lasers and Optics, Vol 67 No 4, p 493-496, 1998

This paper details the design, implementation, and application of an extractive Fourier transform infrared (FTIR) ambient air monitoring system. The system achieves simultaneous detection and accurate quantification of several volatile organic compounds (VOCs) in the range of sub-parts per million on a continuous, near-real-time basis. The system was deployed at the Waste Isolation Pilot Plant (WIPP) in Carlsbad, New Mexico, to detect 1,1-dichloroethylene, carbon tetrachloride, methylene chloride, chloroform, 1,1,2,2-tetrachloroethane, 1,1,1-trichloroethane, chlorobenzene, 1,2-dichloroethane, and toluene, as well as other ambient air constituents.

A Unique Bistatic FTIR Monitor for Long Path Open-Air Measurements
Spellicy, R.L.; R.J. Brewer, Unisearch Associates, Round Rock, TX.
Air and Waste 92nd Annual Meeting and Exhibition, 20-24 June 1999, St. Louis, MO.
Air and Waste Management Association, Pittsburgh, PA. Paper 99.214, 1999

A unique bistatic open-path FTIR monitor has been developed and deployed at an industrial site. Developed to address long-path open-air monitoring while preserving high signal-to-noise ratio for low level detection, this monitor eliminates the path radiance issues usually associated with bistatic systems. Initial test results showed good accuracy and precision when the systems were tested against an in situ calibration cell in the instrument.

Update of QA/QC Issues for Field Data
Kricks, Robert J.; Robert L. Scotto, RJK Consulting, Cranford, NJ.
Proceedings of the 1997 Air & Waste Management Association's 90th Annual Meeting & Exhibition, 8-13 June 1997, Toronto, Canada. Paper 97-RA141.02

The authors compare and contrast the application of elements of an FTIR QA/QC protocol document during the collection of data to be analyzed off-line to the collection of data reported in real-time. Application of TO-16 QA/QC requirements to optical remote sensing data collection is examined. Data precision, accuracy, completeness, comparability, and repeatability issues are discussed within the context of project specific QA plans. Application of QA/QC procedures to project data provide examples.

Urban Air Pollution Monitoring with DOAS Considering the Local Meteorological Situation
Gobiet, A.; D. Baumgartner; T. Krobath; R. Maderbacher; E. Putz.
Environmental Monitoring and Assessment, Vol 65 No 1/2, p 119-127, Nov 2000

Concentrations of ozone, NO₂ and, SO₂ measured with a DOAS system 70 m above ground level in the city of Graz were compared with data from conventional ground stations. On average, the concentrations 70 m above ground were more than twice the ground-level concentrations.

Use of Dispersion Modeling and a Differential Optical Absorption Spectroscopy (DOAS) Monitor for Improving Pollution Prevention Procedures Around an Industrial Site
Thomas, Dominique (Environnement SA); V. Delmas (Air Normand); M. Bobbia; V. Tatry (INERIS); J. Moussafir (ARIA Technologies); J. Piquard (Environnement SA); D. Buty (ARIA Technologies); A. Coppalle (CORIA); T. Menard (INERIS).
Environmental Monitoring and Remediation Technologies.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 279-289, 1999

Two measurement campaigns have been performed in the lower SEINE Valley in France using a variety of techniques. Dispersion models (both Gaussian and Lagrangian, part of the ADSO software suite from Aria Technologies) were used both as predictive tools and a-posteriori to judge the effect of emission reduction. A long-path integrating monitor, the SANOA UV-DOAS, was used to assess average pollutant concentrations along a line, as opposed to point monitoring. Eleven point monitors for SO₂ comprised another monitoring unit. Several wind sensors, including ultrasonic anemometers and a SOund raDAR (SODAR) were deployed as well. Measurement and model data have been analyzed to determine a better tailoring of emission reduction to real situations.

The Use of Light Detection And Ranging (LIDAR) for Determining Plume Characteristics. Progress Report
Wayson, Roger L.; Gregg G. Fleming; Brian Kim, U.S. DOT, Research and Special Programs Admin.,
John A. Volpe National Transportation Systems Center, Air Quality Facility, Cambridge, MA.
Report Nos: FAA-AEE-01-02, DTS-34-FA12A-LR2, 7 pp, Jun 2001

The first study of the Emission and Dispersion Modeling System (EDMS) multi-year validation effort included gathering data on the initial plume characteristics from airplane exhaust. Input values previously used in the EDMS were primarily based on engineering judgment. With the improvements being made to EDMS Version 4.0 it became apparent that greater detail was needed for these data to continue the improvement in estimating local pollutant concentrations. Although LIDAR had never been used before in this application, it had been used for studies of wing-tip vortices and for other pollutant evaluations. The Volpe Center contacted NOAA, which has several LIDAR units and the flexibility to re-engineer the units and associated software on a project-by-project basis. NOAA supplied two units: one system used ultraviolet light as the scan laser and was called the Ozone

Profiling Atmospheric Lidar (OPAL); the second unit used the infrared spectrum and was named the High Resolution Solid State Doppler Lidar (HRDL). Each unit was contained in a trailer. The OPAL system proved to be the more effective of the two systems in determining the plume parameters.

Use of Open-Path FTIR Monitoring for Emission Rate Assessment of Industrial Area Sources During Winter Conditions
Kricks, Robert J. (RJK Consulting, Cranford, NJ), J.A. Keely; R.L. Spellicy (Unisearch Associates Inc.); S.H. Perry (Kassay Field Services, Inc.).
Environmental Monitoring and Remediation Technologies, 2-5 November 1998, Boston, MA.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3534, p 27-37, 1999

Open-path Fourier transform infrared (OP-FTIR) spectroscopy was used to collect emission data for chemical compounds from several area sources at a northwestern industrial facility in 1997. The data collected were used in conjunction with meteorological measurements to assess the emission rate of specific chemicals. The release of a tracer gas at a known emission rate and its subsequent measurement with the OP-FTIR allowed for correction of emission rates to account for local effects on the site-specific vertical dispersion coefficients used for emission assessments. Emission rate determinations were done for process ponds, and fence-line concentration measurements were also made.

Use of Open-Path FTIR Spectroscopy to Address Air Monitoring Needs During Site Remediations
Minnich, T.R.; R.L. Scotto, Minnich and Scotto, Inc.
Remediation, Vol 9 No 3, p 79-92, 1999

This paper provides an overview of open-path Fourier-transform infrared (FTIR) spectroscopy and its principles of operation, describes the nature of the data generated, discusses the benefits associated with thtechnology's use in site cleanup, presents emission-rate estimation techniques, and examines the reasons why it has not gained more support over the years. A case study in which the technology was used to drive an 11-month emergency removal action under the direction of the U.S. EPA illustrates the usefulness of this monitoring technology.

Use of Quality Assurance Procedures for FTIR Field Measurement Data
Ropertz, Alexander (Fachhochschule Duesseldorf); T. Lamp; M. Mueller; G. van Haren; K. Weber.
Environmental Sensing and Applications.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3821, p 437-448, 1999

To assess the applicability of quality assurance procedures for field measurements, OP-FTIR field measurement data of a three-month continuous measurement campaign were evaluated with regard to the signal strength, the influence of stray light, water vapor concentration, baseline noise, wave number shifts, and the detection limits. The long-time signal stability of OP-FTIR systems and UV-DOAS systems also were intercompared. The results of these assessments are presented in this paper.

Using a Fourier Transform Spectrometer for Tropospheric UV-Visible DOAS Measurements
Carleer, Michel (Univ. Libre de Bruxelles); R. Colin; A.C. Vandaele (Institut d'Aeronomie Spatiale de Belgique).
Spectroscopic Atmospheric Environmental Monitoring Techniques.
Proceedings of SPIE - The International Society for Optical Engineering, Vol 3493, p 11-19, 1998

The authors built a DOAS optical setup based on a Bruker IFS 120M spectrometer to assess the advantages and drawbacks of using a Fourier transform spectrometer (FTS). Comparisons are made between the characteristics and performance of this setup and those of the more conventional grating-based instruments. FTS identifies a reproducible and precise wave-number scale, which greatly simplifies the algorithms used to analyze the atmospheric spectra, and permits the recording of large spectral regions at relatively high resolution, enabling the simultaneous detection of numerous chemical species with better discriminating properties. However, an FTS records high frequency signals and does not have the signal integration capabilities of the CCD-based grating spectrographs and therefore requires fairly large amounts of light, and also is limited to short- to medium-absorption path lengths.