Determination of elemental mercury by cavity ringdown spectrometry

Tao, Shiquan; Mazzotti, Fabio; Winstead, Chris; Miller, George P.

doi:10.1039/b001879l

Cited by 28 publications

(32 citation statements)

References 10 publications

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“…In addition, nearby absorption lines were identified as the forbidden oxygen (O 2 ) A←X(7, 0) transition (N"=19; Q multiplet). A similar laser system was used later by Tao et al (2000) and by Spuler et al (2000). Tao et al (2000) reported a noise-equivalent (3σ ) 3 Instrument description and laboratory and ambient air testing…”

Section: Performance Of Previous Cavity Ring-down Spectrometers For Hmentioning

confidence: 99%

Toward real-time measurement of atmospheric mercury concentrations using cavity ring-down spectroscopy

2010

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Abstract. Cavity ring-down spectroscopy (CRDS) is a direct absorption technique that utilizes path lengths up to multiple kilometers in a compact absorption cell and has a significantly higher sensitivity than conventional absorption spectroscopy. This tool opens new prospects for study of gaseous elemental mercury (Hg 0 ) because of its high temporal resolution and reduced sample volume requirements (<0.5 l of sample air). We developed a new sensor based on CRDS for measurement of (Hg 0 ) mass concentration. Sensor characteristics include sub-ng m −3 detection limit and high temporal resolution using a frequency-doubled, tuneable dye laser emitting pulses at ∼253.65 nm with a pulse repetition frequency of 50 Hz. The dye laser incorporates a unique piezo element attached to its tuning grating allowing it to tune the laser on and off the Hg 0 absorption line on a pulse-to-pulse basis to facilitate differential absorption measurements. Hg 0 absorption measurements with this CRDS laboratory prototype are highly linearly related to Hg 0 concentrations determined by a Tekran 2537B analyzer over an Hg 0 concentration range from 0.2 ng m −3 to 573 ng m −3 , implying excellent linearity of both instruments. The current CRDS instrument has a sensitivity of 0.10 ng Hg 0 m −3 at 10-s time resolution. Ambient-air tests showed that background Hg 0 levels can be detected at low temporal resolution (i.e., 1 s), but also highlight a need for high-frequency (i.e., pulse-to-pulse) differential on/off-line tuning of the laser wavelength to account for instabilities of the CRDS system and variable background absorption interferences. Future applications may include ambient Hg 0 flux measurements with eddy covariance techniques, which require measurements of Hg 0 concentrations with sub-ng m −3 sensitivity and sub-second time resolution.

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Section: Performance Of Previous Cavity Ring-down Spectrometers For Hmentioning

confidence: 99%

Toward real-time measurement of atmospheric mercury concentrations using cavity ring-down spectroscopy

2010

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“…The laser pulse energy introduced into the cavity decays exponentially with time due to extinction and reflection losses within the cavity. CRDS is used to measure total extinction in the cavity, which is the sum of mirror losses as well as scattering and absorption losses due to particles and gases (Tao et al, 2000;Moosmüller et al, 2005;Atkinson, 2003). The power in the cavity can be quantified by the current signal S t of a photomultiplier tube exposed to the light leaking out of the cavity through the second mirror.…”

Section: Cavity Ring-down Spectroscopy -Overview Of Theorymentioning

confidence: 99%

“…A sequential two-photon laser-induced fluorescence (LIF) spectrometer with a 10 Hz laser system and sensitivity of 0.15 ng m −3 (3σ ) for 10 s also has been employed for laboratory air and ambient air measurements (Bauer et al, 2002(Bauer et al, , 2003. Other CRDS systems, with sensitivities ranging from 2.19 to 27 ng m −3 , operating at 10-50 Hz have been used to measure GEM in the laboratory, inert gas, and flue gas with high GEM levels (Carter, 2004;Faïn et al, 2010;Jongman et al, 1995;Spuler et al, 2000;Tao et al, 2000). Microwave-induced plasmas (MIP)-CRDS with 20 Hz repetition rate and sensitivities that ranged from 400 to 1841 ng m −3 for 2 to 5 s were used for measurements of GEM in argon gas Wang et al, 2005); and cavity-enhanced absorption spectroscopy (CEAS) with a sensitivity of 66 ng m −3 for 10 s (3σ ) was used for measurements of GEM in a static cell .…”

Section: Other Gem Measurement Techniquesmentioning

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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“…The objective of this research project was the writing, implementation and testing of the Labview software to be used in Cavity Ring-down experiments for duel channel monitoring. Our overall conclusion, from both this work and our previous studies, [4][5][6][7][8][9][10][11] is that mercury CRDS remains the most promising technique to provide real-time monitoring of elemental mercury in exhaust gas streams. However, the UV linewidth of tunable light source must be sufficiently narrow to allow the differentiation of the mercury from the SO 2 background and the repetition rate must be sufficiently high (~50 Hz) to provide real-time measurements.…”

Section: Executive Summarymentioning

confidence: 88%

An Optical Offgas Sensor Network Incorporating a HG Cavity Ringdown Spectrometer and IR Diode Lasers

Miller¹

2007

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Determination of elemental mercury by cavity ringdown spectrometry

Cited by 28 publications

References 10 publications

Toward real-time measurement of atmospheric mercury concentrations using cavity ring-down spectroscopy

Toward real-time measurement of atmospheric mercury concentrations using cavity ring-down spectroscopy

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

An Optical Offgas Sensor Network Incorporating a HG Cavity Ringdown Spectrometer and IR Diode Lasers

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