Diode-laser-based sensor for ultraviolet absorption measurements of atomic mercury

Anderson, Thomas N.; Magnuson, Jesse K.; Lucht, Robert P.

doi:10.1007/s00340-007-2604-z

Cited by 35 publications

(40 citation statements)

References 27 publications

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“…Such commercial instruments use highly stabilised light sources and electronics, which our instrument does not. Nevertheless, our detection limit is significantly better than the 0.1 ppbv (800 ng m −3 ) detection limit reported by Anderson et al 23 , using sum-frequency generation and two diode laser systems, or the 200 ng m −3 estimated by Thiebaud et al 24 with a Hg vapour lamp combined with a UV LED. Both of these systems were designed for the high Hg levels of continuous emission monitoring and made use of additional spectral information to discriminate the absorption of Hg from background absorption.…”

Section: Resultscontrasting

confidence: 58%

Cavity-enhanced absorption using an atomic line source: application to deep-UV measurements

Darby

Smith

Venables

2012

Analyst

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Optical cavities are commonly used to increase the sensitivity of absorption measurements, but have not been extensively used below 300 nm, mainly owing to the limited light sources at these wavelengths. While some progress has been made using cavity ring-down spectroscopy, these systems rely on complex and expensive lasers. Here we investigate an approach combining Cavity-Enhanced Absorption Spectroscopy (CEAS) with an inexpensive low vapour pressure mercury lamp for sensitive absorption measurements at 253.7 nm. We demonstrate that the CEAS absorption in our system is 50 times greater than the absorption found in a single-pass configuration; using this approach, we obtained limits of detection of 8.1 pptv (66 ng m(-3)) for gaseous elemental mercury and 8.4 ppbv for ozone. We evaluate the performance of the system and discuss potential improvements and applications of this approach

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Section: Resultscontrasting

confidence: 58%

Cavity-enhanced absorption using an atomic line source: application to deep-UV measurements

Darby

Smith

Venables

2012

Analyst

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“…The three cells include an Hg cell filled with metallic Hg at ambient pressure (∼ 80 kPa within cell; green line); an Hg cell filled with metallic Hg under low pressure (1.33 × 10 −5 Pa within cell; blue line); and the spectrum of an Hg cell filled with an isotopically enriched, metallic 200 Hg (94 % + isotopic purity) under low pressure (1.33 × 10 −5 Pa within cell; red line). In the lowpressure GEM spectrum (blue line), five of seven known stable Hg isotopes (Schroeder and Munthe, 1998;Spuler et al, 2000) can be seen as individual hyperfine structures, which are commonly observed when atmospheric pressure broadening is eliminated (Anderson et al, 2007;Spuler et al, 2000;Schweitzer, 1963). Differences between the external Hg cell at ambient pressure (green line) and low pressure (blue line) result from collisions of Hg atoms with air molecules, shortening their radiative lifetime or resulting in a phase shift and causing collision-induced/pressure broadening of the absorption line (Demtröder, 2003).…”

Section: Wavelength Locking and Stabilization Using An External Hg Cellmentioning

confidence: 99%

Cavity ring-down spectroscopy sensor development for high-time-resolution measurements of gaseous elemental mercury in ambient air

et al. 2013

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We describe further development of a previous laboratory prototype pulsed cavity ring-down spectroscopy (CRDS) sensor into a field-deployable system for high-time-resolution, continuous, and automated measurement of gaseous elemental mercury (GEM) concentrations in ambient air. We employed an external, isotopically enriched Hg cell for automated locking and stabilization of the laser wavelength on the GEM peak absorption during measurements. Further, we describe implementation of differential absorption measurements via a piezoelectric tuning element for pulse-by-pulse tuning of the laser wavelength onto and off of the GEM absorption line. This allowed us to continuously correct (at 25 Hz) for system baseline extinction losses unrelated to GEM absorption.

Extensive measurement and calibration data obtained with the system were based on spike addition in both GEM-free air and ambient air. Challenges and interferences that occurred during measurements (particularly in ambient air) are discussed including temperature and ozone (O₃) concentration fluctuations, and steps taken to reduce these. CRDS data were highly linear (r² ≥ 0.98) with data from a commercial Tekran 2537 Hg analyzer across a wide range of GEM concentrations (0 to 127 ng m⁻³) in Hg-free and ambient air. Measurements during periods of stable background GEM concentrations provided a conservative instrument sensitivity estimate of 0.35 ng m⁻³ for the CRDS system when time averaged for 5 min. This sensitivity, along with concentration patterns observed in ambient air (with the CRDS system and verified with the Tekran analyzer), showed that the sensor was capable of characterizing GEM fluctuations in ambient air. The value of fast-response GEM measurements was shown by a series of GEM spike additions – highlighting that high-temporal-resolution measurement allowed for detailed characterization of fast concentration fluctuations not possible with traditional analyzers

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“…For the TDLAS technique, at least 80-GHz (three times the absorption linewidth of mercury vapor) of mode-hop-free tuning range is required to extract the whole absorption feature of mercury out of the broadband attenuation due to absorption of other species or particulate scattering [10,12]. However, for the MDL-COSPEC method, there is no special request on mode-hop-free tuning range; instead, the mode hop is used to increase the wavelength coverage and thus obtain an off-resonant baseline.…”

Section: Selectivitymentioning

confidence: 99%

“…An alternative technique for elemental mercury detection is the employment of laser absorption spectroscopy. Various techniques have been developed to generate laser radiation at 253.7 nm, including sum-frequency generation (SFG) by two diode lasers (DLs) [10][11][12], frequency doubling pulsed dye lasers or optical-parametric-oscillator lasers [13][14][15] and frequency quadrupling diode lasers or solid-state lasers [16,17]. By comparison, SFG-DL based systems possess the merits of agile tunability, simplicity and low-cost.…”

Section: Introductionmentioning

confidence: 99%

“…By comparison, SFG-DL based systems possess the merits of agile tunability, simplicity and low-cost. Diode-laser-based systems with mode-hop-free tuning in the range of 35-100 GHz have previously been developed [10][11][12]. For mercury sensing by tunable diode laser absorption spectroscopy (TDLAS) two requirements should be fulfilled: extremely accurate wavelength control and wide mode-hop free tuning range (> 80 GHz).…”

Section: Introductionmentioning

confidence: 99%

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Detection of elemental mercury by multimode diode laser correlation spectroscopy

et al. 2012

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Abstract:We demonstrate a method for elemental mercury detection based on correlation spectroscopy employing UV laser radiation generated by sum-frequency mixing of two visible multimode diode lasers. Resonance matching of the multimode UV laser is achieved in a wide wavelength range and with good tolerance for various operating conditions. Large mode-hops provide an off-resonance baseline, eliminating interferences from other gas species with broadband absorption. A sensitivity of 1 μg/m 3 is obtained for a 1-m path length and 30-s integration time. The performance of the system shows promise for mercury monitoring in industrial applications.

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Diode-laser-based sensor for ultraviolet absorption measurements of atomic mercury

Cited by 35 publications

References 27 publications

Cavity-enhanced absorption using an atomic line source: application to deep-UV measurements

Cavity-enhanced absorption using an atomic line source: application to deep-UV measurements

Cavity ring-down spectroscopy sensor development for high-time-resolution measurements of gaseous elemental mercury in ambient air

Detection of elemental mercury by multimode diode laser correlation spectroscopy

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